WEBVTT

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Mark Kushner: Okay.

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Mark Kushner: It's, my pleasure to introduce Dr. Janos Feliges from the Jet Propulsion Laboratory.

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Mark Kushner: Dr. Falidi tolls the rank of Senior Research Scientist and Principal Engineer

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Mark Kushner: Achieve there as a quant scientist, if I'll try.

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Mark Kushner: Dr. Meredith Khalidis comes to us with his PhD from the

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Mark Kushner: His research over the past number of years has encompassed quite a few occupational plasma and fluid dynamics problems. Planes of name include supporting the MR sample for a short mission.

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Mark Kushner: And of course, most of his work, I'd say, has fallen under the camp recently in electric propulsion. He has developed two of the most widely used propulsion codes. Again, and has been used to do flight qualification efforts for supporting both psychic camp.

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Mark Kushner: Dr. McLeese is an affiliate and a fellow of the…

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Mark Kushner: received some of the highest assumptions awarded by NASA, including just Alan.

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Mark Kushner: So, it's a great pleasure to have you join us today for your lecture. Looking forward to, seeing it, and then on our part, we're going to bestow upon you one of the highest honors that we have. Oh, great. Perfect. Oh, thank you so much. I appreciate it.

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Mark Kushner: Thank you. Understood.

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Mark Kushner: Thank you. Oh, okay.

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Mark Kushner: Thank you.

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Mark Kushner: Okay, everybody can hear me okay?

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Mark Kushner: All right. Well, thank you. Thank you, Ben, for, for the kind introduction, and,

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Mark Kushner: Thank you to the Institute for the invitation, and thank you to all of you for taking the time, faculty and students for taking the time to attend the talk today. Yeah, so I,

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Mark Kushner: joined JPL about 22 years ago now, and I was…

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Mark Kushner: Asked to come in to develop a modeling and simulation program at the laboratory.

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Mark Kushner: That at the time, had capabilities that really didn't… either didn't exist for certain thrusters.

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Mark Kushner: or were just too basic to have a meaningful impact on our missions. And reasons for that, were, largely associated with computational resources.

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Mark Kushner: Funding fluctuations…

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Mark Kushner: But also, the complexity of these plasmas, as I will try to share with you today.

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Mark Kushner: is quite significant, and therefore, the larger EP community, had to deal with, the inadequacies of the modeling, of that time.

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Mark Kushner: In fact, at the time, so we're talking here about, you know, 20 or 30 years ago.

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Mark Kushner: At the time, some of the more rigorous scientific codes existed at a few universities only, and none of them had ever reached the level of maturity that we need

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Mark Kushner: for practical impact through our robotic missions, things like assessing life and performance and things of that nature. So that was one of the reasons I was brought in.

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Mark Kushner: And, my hope…

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Mark Kushner: you know, certainly we've made significant progress in the last two decades, for the better, and I'd like to think, I'd like to believe that our work at JPL played a role in that, perhaps an important role.

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Mark Kushner: So, which brings me to the topic of the presentation today.

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Mark Kushner: Which is, through a few examples, I will try and share with you the impact that, modeling and simulations of electrical parcel plasmas has had, not only to our missions, but also to the EP community in general.

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Mark Kushner: So, I am assuming here that some of you

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Mark Kushner: have not or are not working in electrical pollution, so I'm going to go through some of the mandatory basics of EP.

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Mark Kushner: Starting with a fundamental principle of electropulsion, which is actually pretty simple. We utilize electrical energy to break down the propellant.

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Mark Kushner: And then use electromagnetic fields to accelerate the heavy part of the propellant, the ions, to produce a propulsive force that does, in turn, work on the operating gas.

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Mark Kushner: And depending on the, type for the nature of the acceleration mechanism, we have

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Mark Kushner: Placed various thrusters in loosely defined categories, namely electromal, electrostatic, and electromagnetic thrusters.

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Mark Kushner: Club.

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Mark Kushner: Magnrido plasmody dynamic and plastic plasma thrusters, for example, are in the class of electromagnetic thrusters.

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Mark Kushner: Some of the thrusters I'll be talking mostly about today, hole thrusters, mostly inline engines, are, electrostatic. Some argue that hole thrusters are also electromagnetic. I am on that for now.

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Mark Kushner: I should mention that,

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Mark Kushner: One of the differences, unique differences between electropulsion and some of the other forms of propulsion, like chemical.

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Mark Kushner: is that because the energy, the electrical energy, is not… is only limited by the power supply we can carry on the spacecraft, in principle, we can achieve much higher exhaust speeds.

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Mark Kushner: Than chemical propulsion, which is limited by the

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Mark Kushner: energy that can be released in chemical reactions, and that means, as the rocket equation tells us, that I am sure all of you have learned about, tells us that with these higher exhaust speeds, we can deliver a higher mass fraction to our final destination, and that's sort of the unique aspect of elective propulsion.

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Mark Kushner: I know also that the Institute here,

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Mark Kushner: involves work, plasmas that is outside electric propulsion, so I thought, as I was looking through some of the interviews and some of the previous speakers that have,

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Mark Kushner: given talks at this institute, a wide range of plasma applications, so I thought it might be useful.

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Mark Kushner: To put things in context as far as the kinds of plasma environments we deal with in electrical pulsion, and show things in this general graph that plots typical plasma conditions with plasma density, electrical temperature on the vertical axis, plasma frequency in the bilength.

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Mark Kushner: To show you where the kinds of environments we're dealing with.

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Mark Kushner: Reside relative to some of the… some other, typical plasma applications.

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Mark Kushner: We are in this relatively benign region of plasmas, so I'm talking about temperatures that are in the order of a few to tens of electron volts.

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Mark Kushner: Plasma densities in this region of 10 to 11, 10 to the 12th cubic centimeter, and certainly nowhere near some of these other plasma beasts that exist in this region of this plot, like, for example, conditions that are

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Mark Kushner: generated in the Z machine. Some of you may recognize it. This is, I believe, still the largest X-ray generator in the world, in the Z machine, which is a plasma generator at Sandia National Labs.

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Mark Kushner: And they create conditions that are truly

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Mark Kushner: mind bending. For example, we're talking about 100 terawatts in a single pulse.

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Mark Kushner: with plasma temperatures that reach somewhere in the order of 100 keV, and tens of megauss of magnetic fields during the implosion of the liners.

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Mark Kushner: We get excited if you exceed… if we exceed a few hundred cows in multiple clusters. So, very different environments.

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Mark Kushner: Not only in terms of plasma conditions, but also in terms of spatial scales that we're dealing with. These are, you know, typical laboratory discharge devices.

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Mark Kushner: Nothing too, too fancy about them, and certainly a little bit smaller than some of these astrophysical plasmas that sometimes, we work on. I was fortunate enough many years ago to do plasma simulations. In fact, these are some of my simulations that I used with an idea… that I

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Mark Kushner: developed with a… an ideal MHD code, a Magrido Hydrodynamics code.

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Mark Kushner: of turbulence in galaxy clusters. These are clusters of galaxies, not one galaxy.

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Mark Kushner: And these are regions in space that exist

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Mark Kushner: And they're a bit large, so the unit here for spatial size is in the order of megaparsecs, so just to give you an idea of what that is, 10 megaparsecs is about, a little over.

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Mark Kushner: 10 to the 16 Earth diameters. So a little bit bigger than the devices that we're dealing with here, just to give you a sort of a context of

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Mark Kushner: Both special, scales and conditions.

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Mark Kushner: So, some of these,

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Mark Kushner: electric propulsion devices that I just showed to the lower left, actually reached a flight, flight-qualified maturity very early on, as I show you here some of the different thrusters that have been used.

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Mark Kushner: Both by government and the industry.

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Mark Kushner: And last time I presented this chart, which was back in 2020, I deliberately wanted to include, you know, the old data. At that time, there were about a little over 1,200 satellites with electric propulsion in space.

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Mark Kushner: And now, in 2025, that number exceeds several thousands, and that's a number that's largely been driven by the frequent launches of SpaceX's Starlink, which is a spacecraft that has all thrusters.

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Mark Kushner: So, certainly, a, a…

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Mark Kushner: significant increase in the presence of electrical propulsion in space. And,

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Mark Kushner: The investment in the commercial sector in electropulsion satellites is only expected to increase, on average, in the next decade.

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Mark Kushner: So, all these thrusters that I mentioned, all these missions that I mentioned, include also international missions, as I list here some of the more

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Mark Kushner: You know, well-known, international missions.

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Mark Kushner: From various agencies worldwide.

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Mark Kushner: Pepe Colombo here is mission to Mercury, and it was originally on a 7-year journey to the planet.

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Mark Kushner: was supposed to, enter orbit, next month, on the 5th of December. It has been delayed somewhat, but it's still on its way there.

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Mark Kushner: And it's a first… it's a mission that we contributed to. We're fortunate at JPL to contribute to with our modeling work.

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Mark Kushner: using our hollow cathode simulations to support their qualification of the neutralizer cathodes. These are… this is a spacecraft that employs Kauffman-type ion thrusters, so we supported their qualification of the neutralizer cathodes.

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Mark Kushner: So, it seems, then, that the presence of electric propulsion in space is quite prevalent.

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Mark Kushner: But what I failed to point out is that almost all of these thousands of spacecraft that I mentioned

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Mark Kushner: almost all of them are in near-Earth orbits.

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Mark Kushner: In fact, indeed, there's only a handful of missions that have flown with EP in deep space.

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Mark Kushner: And the reason for that is because these missions require operation by these thrusters for very long periods of time, whereas

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Mark Kushner: In near-Earth orbit, the electropulsion is typically used intermittently, and therefore doesn't require as much… as much lifetime as some of these deeper space missions. So, for example.

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Mark Kushner: our Dawn mission.

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Mark Kushner: which was a mission to the most massive bodies in the asteroid belt, Vesta and Sirius, launched back in 2007.

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Mark Kushner: And it had 3 30 centimeter ion engines on it.

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Mark Kushner: accumulated by the end of its extended mission in 2018, about 6 years of operation of this iron engines.

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Mark Kushner: So then, the challenge becomes… it's starting to become quite evident. That is, when you're dealing with such long operations, the question is, how do you demonstrate that these thrusters will last for as long as we want them to last?

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Mark Kushner: In a facility. Do you test them for the total amount of time? 6 years in this case, or 9 engine, or do you…

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Mark Kushner: Test them.

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Mark Kushner: only for a fraction of that time? And if yes, is that good enough? What about failure modes that may present themselves, reveal themselves, at some point later in the mission, after the termination of a test?

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Mark Kushner: That did not test them for the entire period.

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Mark Kushner: What about operating conditions? Do you test them for all the operating conditions, or just a fraction of them? And if the latter, is that sufficient? So that is then, as you are beginning to realize, the main challenge that has also

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Mark Kushner: led to this much fewer number of deep space missions, with electric launches.

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Mark Kushner: So, clearly then, The answer to how you do this must.

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Mark Kushner: Come in the way of a combination between Carefully designed wear tests.

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Mark Kushner: and rigorous physics-based modeling, because that is the only way that we can achieve a very cost-effective and timely, qualification… strategy for qualification of EP for our missions, or our deep space missions.

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Mark Kushner: And the reason for that is that

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Mark Kushner: On the side of wear tests, These tests provide to us.

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Mark Kushner: Are an invaluable source of information.

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Mark Kushner: About failure modes, when they occur. But they also, for example, when they occur, and what is their nature.

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Mark Kushner: But, as you can imagine, these tests can be quite cumbersome.

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Mark Kushner: And time-consuming, and costly.

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Mark Kushner: And only provide us a small sample of all the processes that led to the failure.

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Mark Kushner: On the other side, models, if done accurately, rigorously.

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Mark Kushner: Can provide us an unprecedented insight, an insight at a level of detail that is unmatched by most of these wear tests.

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Mark Kushner: But they're very complex, and they require, as I will try to share with you in the rest of the presentation, they're very complex, and they require rigorous validation from some of these tests and additional experiments that are, you know, dedicated to

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Mark Kushner: specifically to provide plasma measurements for model validation. So the main takeaway is that we need a combination of these things as the only way to, you know, achieve

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Mark Kushner: Truly a cost-efficient and timely qualification process for deep space missions.

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Mark Kushner: So, which brings me to the point that I made a little bit earlier about why it is that the complexity of these plasmas in electric propulsion was one of the reasons that we found ourselves in this, long, protracted path, in supporting,

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Mark Kushner: our missions, for deep space.

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Mark Kushner: And so, in addition to some of the extensive mathematical governing laws, some of which I will share with you today.

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Mark Kushner: That can also be computationally intensive, in terms of solving them numerically.

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Mark Kushner: We also have to deal with a wide range of spatial temporal scales.

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Mark Kushner: That include… that must include very important interactions between the plasma and the walls.

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Mark Kushner: And all of these things, of course, require, as I mentioned in the previous chart, rigorous model validation by diagnostics, plasma diagnostics that themselves are not very trivial. They're also quite complicated, costly, and can sometimes be difficult to interpret, just like

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Mark Kushner: Numerical simulation results can sometimes be difficult to interpret.

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Mark Kushner: So… I appreciate that by sharing these next couple charts, I might be running the risk of

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Mark Kushner: scaring everybody with this petrifying prospect that the rest of the presentation is going to be some kind of a deep dive into very difficult equations and mathematical terms. I promise you it is not. I'm only going to use these next charts… that's two charts to make a point.

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Mark Kushner: And that is… let us begin with…

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Mark Kushner: The typical, government equations for viscous hydrodynamics.

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Mark Kushner: with a continuity, momentum, and energy equation in a typical form that they're expressed with a stress tensor at the bottom. And when you try to update these equations

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Mark Kushner: with…

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Mark Kushner: plasmas and Max's equations, they become a bit more complicated. This is a particular type of approximation we call the resistive magnetohydrodynamics, which is typically more applicable to electric propulsion that produces higher density plasmas and high ionization fractions.

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Mark Kushner: And we've certainly applied these kinds of models before, but they're also, to electric propulsion, but they're also quite appropriate in other plasma applications that, produce very density… very high density plasmas, like in pulse power, fusion, and other areas.

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Mark Kushner: The point is that this becomes… this system becomes much more complicated, and notice here that I've actually also added an additional energy equation for the radiation field, because there are certain plasma

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Mark Kushner: situations, not particularly in electrical polio, but in other applications where the radiation field is non-equilibrium, and therefore you actually have to solve for an additional energy equation that can be,

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Mark Kushner: Modeled as a, as a, as a radiation temperature.

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Mark Kushner: So I also mentioned that,

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Mark Kushner: We are dealing… we have to deal with a very different

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Mark Kushner: wide-ranging spatial scales, and that's because we have to understand how these… the plumes from these electric propulsion devices interact with spacecraft. So we are worried about things like erosion of the solar arrays, interaction, collective currents, etc, by the various surfaces of the spacecraft.

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Mark Kushner: So we're talking… we're talking here about relatively lower plasma densities, because we're dealing with an expanded plume, but also scale sizes in the order of meters, which is what this spacecraft look like today. Then, of course, at the… at the next level, we have to…

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Mark Kushner: we have to deal with the, engine itself, so we're talking about modeling the plasma inside discharge chambers. So this is, this is a typical 30 centimeter ion engine that I'm showing there, so we're talking about tens of centimeters.

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Mark Kushner: higher plasma densities. Then these types of engines

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Mark Kushner: require operation of hollow cathodes. I will talk about cathodes a little bit later in more detail, but that means that now we're getting into even smaller scales of the order of the

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Mark Kushner: of the path of tube, which is in the order of centimeters, and also now we are also increasing the plasma density. And then, of course, we also need to deal with

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Mark Kushner: how the plasma behaves in that little small hole, which is the orifice of the cathode, and I will show you why it is that that orifice is very, very important.

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Mark Kushner: regarding the operation and the life of the devices, which can be as small as a few hundred micros. So we're dealing with widely varying spatial scales, and that's important because, compared to the size of the particular device that we're dealing with, it determines

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Mark Kushner: the mean free path for collisions relative to the… to the size of the device, as you have learned in your introductory courses in fluid mechanics or plasma physics, that will determine

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Mark Kushner: what range of the Knudsen number we're operating, and therefore will dictate to us what is an appropriate numerical approach to model these plasmas, which can vary between anywhere from one extreme, which is using continuum fluid mechanics.

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Mark Kushner: To another… to the other extreme, where we follow, essentially, the particles individually.

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Mark Kushner: Or, statistically, in some way, through the distribution function, all falling under this category of kinetic methods.

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Mark Kushner: So, I'm… I appreciate that this is a bit late in the afternoon, and that this talk will be…

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Mark Kushner: may get a little bit long, so I thought you might break down the monotony if I shared with you.

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Mark Kushner: along the way, as I go from one topic to another, some relevant quotes from

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Mark Kushner: some true pioneers in science and engineering, like the few of them that I show here in this rare photo, when they actually got together in the late 1940s, to discuss so-called, at the time, electric spaceship propulsion. So, the point is that

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Mark Kushner: Electrical pulsion is actually never… not a very old… it's a very old idea. In fact, sometimes when I speak with the older generation, my academic advisor and others before him, they sometimes tell me that electrical pulsion is like

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Mark Kushner: Old wine in Newport's names.

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Mark Kushner: So… Let me then talk about…

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Mark Kushner: electric spaceship propulsion, and go through some of the… get into a bit more detail about the operational principles of some of the thrusters I will be discussing today.

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Mark Kushner: Iron engines, as I show 3 of them here that are, you know, quite famous, because they're either flown on missions or are supposed to fly on missions.

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Mark Kushner: And they, accelerate the ions electrostatically through, through, two grids that are… are at different potentials, so they create, because of the different potential, plus potential, they create an electric field that accelerates these ions to small holes.

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Mark Kushner: That are… that are on these… on these two grids.

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Mark Kushner: And they operate with two hollow cathodes.

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Mark Kushner: The purpose of the cathodes are to provide electrons.

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Mark Kushner: In the case of the neutralizer, it provides electrons to neutralize the beam so that we don't charge up the spacecraft. In the case of this cathode inside the chamber, which we call the discharge hollow cathode, it is to provide electrons to ionize the propellant inside the chamber, which is then accelerated through this

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Mark Kushner: for the streets that I mentioned.

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Mark Kushner: For Hawk Rusters, the operational principle is a little bit different.

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Mark Kushner: So here, what we have is an annular channel, where there is an applied radial… largely radial applied magnetic field, and the cathode that can be either on the outside, as shown here, or in the middle, provides electrons that are… that then are attracted towards the anode, and have

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Mark Kushner: Have to cross magnetic field lines, as they make it into the anode, and they are, as we call them, strongly magnetized, and therefore they see the magnetic field and are

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Mark Kushner: changed by the presence of the magnetic field, their paths, that is, whereas the ions have a gyro radius that's much, much larger than the size of the device, and therefore are magnetized, and as these… these electrons are forced by the presence of the magnetic field to undergo an eco-speed drift, as we call it.

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Mark Kushner: It generates a whole current that interacts in turn with the applied magnetic field to produce the JCOSB, or Lorentz force, and that's the force that accelerates the ions.

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Mark Kushner: Holocathode is itself another very, very important device, because iron engines and hoh thrusters, as I have shown you, do not… cannot operate without it, without them.

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Mark Kushner: And it is a device that involves some very, very intriguing and complicated physics. Physics that span a very wide range of spatial scales.

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Mark Kushner: First of all, essentially, what we have is that we have the propellant. So it's a geometrically simple device, it's just a tube that has some special material here we call the emitter, that when you hit it, it emits electrons.

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Mark Kushner: And you heat it using this heater coil outside, typically.

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Mark Kushner: And what happens is that you provide… we provide the propellant from the back, and then these emitted electrons from the heated insert.

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Mark Kushner: Interact with the neutrals, ionize them, so you create a partially ionized… partially ionized gas.

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Mark Kushner: But there are some… as this, as this plasma evolves inside this chamber, inside this tube, there are very important sheaths, very complicated, important sheaths, regions near the surfaces that develop, that make the simulation, the modeling of them quite complicated. There are highly non-linear boundary conditions that are coupled to the system.

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Mark Kushner: Governing laws in the chamber.

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Mark Kushner: And to complicate things further, as the neutral gas gets ionized, it is still dense enough and hot enough such that the viscous effects cannot be ignored. So we, in fact, in the neutral gas part, the governing laws that have to be solved are, in fact, the Navier-Stokes equations. So we have to solve, in addition to the Navier-Stokes, we have to solve the plasma equations, and we'll show you how they look.

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Mark Kushner: look like, but not get into too much detail, as I promised.

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Mark Kushner: And then, as the… as the gas, the neutral gas expands to the orifice,

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Mark Kushner: we begin to lose collisionality because it expands and the density is… is decreasing, and we are achieving conditions of higher Knudsen number when the fluid

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Mark Kushner: Approaches that we used to model the interior evolution of the gas are no longer applicable, so it involves also, therefore, transition.

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Mark Kushner: or transitional models that can capture the transition between the collisional and the collisionless part of the neutral gas. And then add to that the fact that we extract electrons at high enough speeds that, as I will show you a little bit later, are enough

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Mark Kushner: to produce waves that can become unstable, that generate some turbulence in the plume, and then we also, in some cases, for discharge holocathodes, we also have an applied magnetic field that attempts to confine some of these electrons. So, very, very complicated system.

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Mark Kushner: very intriguing physics, and very challenging to model. In fact, I have argued with many colleagues and some of the students, even in fact today, that, in fact, the problem of the whole cathode is actually much more complicated than any of the other thrusters that we're examining today, including the whole thruster.

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Mark Kushner: Okay.

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Mark Kushner: So, Let me now get into, sort of the main…

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Mark Kushner: subject of today's presentation, which is about the physics models and their impact, and I couldn't think of a more

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Mark Kushner: Fitting segue… Than this very eloquent characterization of a model.

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Mark Kushner: By one of the truly, if not the most brilliant mathematicians of all time.

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Mark Kushner: In fact, one of his, high school…

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Mark Kushner: childhood friends, and also a colleague later, when they worked together on the Manhattan Project.

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Mark Kushner: His name is Eugene Wigner, also a physicist and a Nobel laureate, said about him that there are only two people, kinds of people, in this world.

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Mark Kushner: Johnny von Neumann and the rest of us.

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Mark Kushner: Sure.

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Mark Kushner: With that in mind, My first task when I joined JPL,

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Mark Kushner: Remember, my group supervisor at the time asked me that we need to build a holo cathode code in a week.

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Mark Kushner: So at the time, no such morals existed, and if they did, they were quite rudimentary.

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Mark Kushner: Of course, it took about a year to develop.

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Mark Kushner: Very long hours, and many years after that, to advance the models, validate them with additional measurements, etc, etc.

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Mark Kushner: But at the end, we produced the 2D orifice cathode code that we call ORCA2D today, that allowed us to, sort of, for the first time, to see how the plasma inside these cathodes really evolves, because by that time, we…

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Mark Kushner: really only had plasma measurements inside the cathode along the center line of the cathode, so we really didn't have a very accurate idea, at least not a comprehensive idea. There had been attempts before to model the cathode in 2D, but the models were quite rudimentary.

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Mark Kushner: So this was the first time where a truly comprehensive system of equations was developed, solved, with the appropriate sheath boundary conditions that captured the emission of the electrons from this thermionic boundary, thermionic emitter.

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Mark Kushner: It gave us a picture of what this plasma looked like, how it evolved, what it looked like in two dimensions.

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Mark Kushner: And then, of course, we extended this model from the interior to also include the exterior, so we can capture some of the plume properties and try to assess how the plasma responds to changes in things like the emission temperature, the diameter of the orifice.

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Mark Kushner: How these things affect the operation of the cathode and its life.

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Mark Kushner: And here, I just show a representative comparison between our simulation results for the plasma density and some of the measurements that were done, both inside and the outside.

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Mark Kushner: So,

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Mark Kushner: Several years later, in fact, about a decade later, we also saw other similar, computational tools and approaches like ORCA2D be developed in Europe.

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Mark Kushner: So, the… the ORCA2D, enabled Okay, us two…

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Mark Kushner: be able to model processes and phenomena that we couldn't model before. I give you a few examples here. For example, we were able, with ORCA2D, after we started, you know, the validation, the advancement of the code.

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Mark Kushner: To incorporate self-induced magnetic field effects that allowed us to model the plasma when you operate the cathode with much higher currents that we were used to

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Mark Kushner: at the time, so typically, ion engines that I showed earlier, like in the order of the 30 centimeter Deep Space 1 ion engine.

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Mark Kushner: operate with currents in the order of 10, 20 amps or so. Here, we want it to go up to 100 amps and 500 amps, where the self-induced magnetic field

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Mark Kushner: can no longer be ignored relative to the applied field, so we updated the code to be able to capture those things, and for the first time, we were able to do also plasma simulations of very high current cathodes.

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Mark Kushner: We also, incorporated cross-sections, that allowed us to model Argonne.

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Mark Kushner: cathodes like this. Another big effort that was very, very complicated was to couple the

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Mark Kushner: Plasma cathode code with a thermal model that allowed us, for the first time, to self-consistently compute the temperature of the emitter

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Mark Kushner: versus having to supply it by direct measurement, and that was a very complicated and cumbersome effort. And also, we were also able to capture the transport of barium, which is an important pregnant of these emitter materials.

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Mark Kushner: That facilitates the emission of electrons, and it was important for us at the time to know how this barium evolves after it gets released from the emitter inside the discharge.

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Mark Kushner: The…

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Mark Kushner: The benefits of ORCA Today were even more far-reaching than some of the examples that I showed you earlier, because it also served as the framework for the development of a new code.

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Mark Kushner: that started, back in around 2008, that we called All2DE, which, is… so the ORCA2DE are essentially the same equations, but updated to include, applied magnetic fields.

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Mark Kushner: more appropriate sheath boundary conditions for the electrics versus conductors, and a number of other things.

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Mark Kushner: And it was the first code at the time that solved the governing equations for this type of discharge.

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Mark Kushner: on a mesh that was aligned with the magnetic field. And what that did was it allowed us to model hole thrusters with much more complicated magnetic field topologies, and I will show you a little bit later what the implications of that are.

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Mark Kushner: capability, were. So these codes, as, as Ben mentioned in the introduction, especially Ho Tuli, has been licensed to other institutions of academia,

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Mark Kushner: And the government and the private sector. I gave you a few examples here. And we're continuing to use it and, and,

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Mark Kushner: develop it and advance it further, and similar codes, again, like ORCA2D, started appearing in Europe several years later, where the governing equations were solved on magnetic field line measures.

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Mark Kushner: So, hold to the also, led to several firsts.

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Mark Kushner: allowed us to…

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Mark Kushner: do things that we couldn't do before with whole thruster simulations. One of them I mentioned already, the ability to do… to simulate the plasma and magnetic field line meshes. It allowed us not only to,

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Mark Kushner: Be able to model magnetic fields with complex topologies, but also, for the first time, because now the region can be extended much further downstream than previous codes could.

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Mark Kushner: I give sort of the typical domain that previous codes before Hall2D were able to simulate.

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Mark Kushner: also allowed us to, self-consistently incorporate the whole of Taffet boundary, but in turn.

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Mark Kushner: Showed us, quite clearly, because now we were solving the electrons in

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Mark Kushner: purely in… truly in two dimensions, identified itself consistently what regions of the plasma deviate from some of the assumptions that were quite typical in Hofester simulations, one of them being the isothermality of the magnetic field lines. You can see here.

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Mark Kushner: The overlay of the electron temperature contours with the applied magnetic field, how they do not align, they don't match, which was expected, but it was rewarding to see that we're able to capture itself consistently.

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Mark Kushner: was also…

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Mark Kushner: we're able to do multi-channel both faster simulations. I… Ben was kind enough to show me that beast in their facility earlier on. I have not appreciated the… how big this is, even though I actually put the geometry in to simulate it, but it's one thing to see it,

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Mark Kushner: in front of you versus simulating. But nevertheless, this was the first time that we're able to, perform simulations of a nested hole thruster with hole 3D.

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Mark Kushner: By the time I arrived at JPL in the early 2000s.

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Mark Kushner: My colleagues had already advanced some of our existing codes intended to capture erosion of the grids in iron engines. These are the charge exchange 2D and 3D codes. And charge exchange, the name comes from the process that actually leads to the

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Mark Kushner: major cause of erosion in this grid. So remember that the ion engines accelerate ions by applying a different voltage between two grids, and then the ions

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Mark Kushner: pass through these small holes. I'll show a schematic of them here, and the electric field is designed, due to the geometry and the way the voltage is applied, is designed to

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Mark Kushner: Guide the ions, the high-energy ions, away from the grids, but what happens is because the gas is only partially ionized, it's not fully ionized, you always have some neutrals around.

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Mark Kushner: And these neutrals

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Mark Kushner: There is a so… what we call a charge exchange collision that occurs between fast ions and these slow neutrals that is large enough to occur here at high enough rates to produce slow ions that in turn go back

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Mark Kushner: Are attracted back through the sheath, to the grids and erode and lead to these

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Mark Kushner: what we call typical pits and grooves, erosion patterns, these holes over here that you see, that ultimately, as they grow larger, they lead to the failure of the engine.

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Mark Kushner: So, in fact, So we're talking about physics models and impact of these models.

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Mark Kushner: These models were used to design a new ion engine we call the Nuclear Electric Xenon Iron System, or Nexus, that was developed

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Mark Kushner: back in the early 2000s, for the JIMO mission. This was the Jupiter IC Moon's orbiter.

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Mark Kushner: Which was part of Project Prometheus back then, so we are old enough to remember. And this was an engine that was designed exclusively using these tools.

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Mark Kushner: And this was not… I should point out, this engine was not until about just a small

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Mark Kushner: incremental change from previous engines that I showed before that have already flown, like the 30 centimeter iron engine I showed in previous charts. This was a significant advancement of iron engines. This was a much larger engine, twice as large.

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Mark Kushner: And it also processed 10 times the flow rate as in previous engines. It was 10 times the power as in the 30 centimeter ion engine I showed before. And it was designed using these codes.

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Mark Kushner: So I'll show some of these examples here of predicted performance, and it was designed in a way that the grids did not erode.

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Mark Kushner: Unfortunately, the mission was canceled before we were able to fly it, but this engine exists at our laboratory, and it's a 60 centimeter iron engine that was designed and developed

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Mark Kushner: Solely based on the guidance of these models.

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Mark Kushner: So, talking then about, as we get into the final stretch of the presentation.

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Mark Kushner: I wanted to give a few more examples to illustrate the relevance and the impact of these models, and I'm gonna… I have selected a few representative examples from some of the work that we did… done over the last two decades to sort of show you

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Mark Kushner: What we're able to do with these models, and how cool they have been.

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Mark Kushner: So…

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Mark Kushner: One puzzling problem that remained elusive for some time was, revealed by a long-duration test that NASA performed

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Mark Kushner: Back in the… in there, also in the early 2000s, of one of the, Deep Space One, spare ion engines. This is, again, a 30 centimeter ion engine.

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Mark Kushner: And this was a test that was,

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Mark Kushner: funded by NASA, and it lasted over 30,000 hours, and it was voluntarily ended, around, was it 2000…

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Mark Kushner: 2004.

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Mark Kushner: And what we found there was something that was very puzzling, and we didn't know how to explain it.

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Mark Kushner: That was… I mentioned that these engines operate with two cathodes. One of them is what we call the neutralizer cathode that provides electrons to neutralize the beam.

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Mark Kushner: And what happened is that, at the beginning, this is a cross…

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Mark Kushner: cutaway of the orifice of the neutralizer cathode that I show here, and you can see here its original shape at the start of the test.

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Mark Kushner: And what happened is that as the test evolved.

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Mark Kushner: After about 8,000 hours, we saw that there was enough erosion to open up this channel, this orifice here.

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Mark Kushner: To this kind of shape.

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Mark Kushner: But then, after the test continued.

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Mark Kushner: After 30,000 hours, that never really changed. It stayed at that shape.

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Mark Kushner: And we didn't really know why that was occurring, and obviously there were important implications about not knowing the answer to this problem, because an obvious question will be, well.

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Mark Kushner: If you don't know what caused the erosion and why it stopped, how do you know that if you put this cathode on the ion engine on the spacecraft, that if you change the operating condition somewhat, the behavior is not going to be different?

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Mark Kushner: How do you know that after 30,000 hours, it will not

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Mark Kushner: continue to erode again for some other reason. So there are many questions that brought up… that generated a high risk.

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Mark Kushner: That we had to… a problem that we had to understand.

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Mark Kushner: Let me also point out a very important point.

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Mark Kushner: Which is, this size, this diameter here, is about 250 microns.

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Mark Kushner: So, there is no probe that can enter that region and tell us what the conditions are that may hopefully inform the process that erodes. So, numerical simulation was the only way to answer, to try and investigate what happened.

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Mark Kushner: So we used our aquatic node.

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Mark Kushner: I should mention, to make things even more complicated, the discharge holo cathode, which was also

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Mark Kushner: Operated in this test.

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Mark Kushner: that had an orifice, I show the discharge collocathode here, that had an orifice that was a few times larger than the orifice of the neutralizer cathode.

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Mark Kushner: Never erode it.

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Mark Kushner: Did not change shape at all.

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Mark Kushner: So, we didn't know the answer to that either.

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Mark Kushner: And to make the long story short, then, is what the ORCA2D simulations showed us, is that because of the smaller orifice, the current density through the orifice was so much higher that it

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Mark Kushner: Forced plasma to sort of concentrate in this region, generating enough ions, much more ions than in this case.

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Mark Kushner: That when accelerated through the sheath that was created by the potential rise due to the resistive drop.

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Mark Kushner: Or enough to erode the orifice. But as the orifice kept getting bigger and bigger, at some point, the current density was reduced to such a level where the erosion stopped.

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Mark Kushner: And that is the reason why the erosion stopped, because it reached that current density, limiting current density, where it was no longer providing enough ions and enough energy to erode further the surface. And this is the comparison that we showed from

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Mark Kushner: Predictions of what simulations showed the erosion should be with the actual profile that was measured after the end of the test.

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Mark Kushner: So that was one example.

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Mark Kushner: Contributions and impact.

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Mark Kushner: of these models. Another one…

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Mark Kushner: is, shown here, where another long-standing problem that had, you know, remained elusive for a long time was what happens in the plume of these cathodes. And what we observed was that when we made measurements of the plasma conditions along the center line of this device.

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Mark Kushner: What we found was that our models Grossly underpredicted.

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Mark Kushner: the properties, I show one of them here, which is the electron… electron temperature.

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Mark Kushner: And, I'm sorry, there's a plasma potential.

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Mark Kushner: Grossly underpredicted that.

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Mark Kushner: as I show here, comparison between the prediction in our original simulations with the measurements.

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Mark Kushner: And what we found after, a lot of investigation is that, we realized

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Mark Kushner: That precisely because of this disagreement, we looked into the details of the conditions that are generated near this

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Mark Kushner: In this neoprene region, and found that these conditions are

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Mark Kushner: Appropriate for generating, growing, a particular type of wave.

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Mark Kushner: called the ion acoustic wave that can become unstable under these conditions, generating some turbulence that effectively increased the anomalous resistivity. And when we incorporated a model in our code.

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Mark Kushner: That, sort of represented

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Mark Kushner: the… how the collision frequency increases in the presence of this turbulence, we got a much, much better agreement. This was the first time

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Mark Kushner: After many years of experimental investigations of these devices.

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Mark Kushner: That, what proposed the presence of iron acoustic turbulence in these devices, and it was a, it was a new finding.

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Mark Kushner: So, what came a few years later.

315
00:50:17.690 --> 00:50:21.360
Mark Kushner: Was, we were lucky enough to have with us

316
00:50:21.700 --> 00:50:25.440
Mark Kushner: A very talented and young engineer at the time.

317
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Mark Kushner: The, at the time, refers to the young, not the talented, who, was able to, apply some

318
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Mark Kushner: very, cool diagnostics to… and some of these… some of your students today are enjoying the benefits of

319
00:50:43.740 --> 00:50:50.399
Mark Kushner: Of all of this, diagnostics that capture directly, measure directly the dispersion of these waves.

320
00:50:51.560 --> 00:51:00.730
Mark Kushner: Confirming, for the first time, the presence of… very clearly the presence of this… of this, an acoustic turbulence in the plume.

321
00:51:01.630 --> 00:51:14.470
Mark Kushner: And it was… it was a… it was a very rewarding effort, because it was first a theoretical prediction that these waves exist, and then, of course, came the experimental verification. So it was a… it was an excellent

322
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Mark Kushner: Excellent work. And then, of course, now, today, as I look at some of the papers and the work that others are doing as well, most of the CAFET models nowadays

323
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Mark Kushner: and sort of pursue a method and strategy similar to work at today, incorporate some kind of an anomalies resistivity model based on ionacoustic waves.

324
00:51:42.870 --> 00:51:45.940
Mark Kushner: So, continuing on the theme of…

325
00:51:47.950 --> 00:51:57.199
Mark Kushner: discharge dynamics in these cathodes. Another long-standing problem was the so-called spot-to-plum mode transition.

326
00:51:57.740 --> 00:52:10.029
Mark Kushner: That is, this is a very, very old problem, so what happened is that in the 1960s, when they were evaluating these cathodes for employment in iron engines and ultimately in spacecraft.

327
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Mark Kushner: They found that if they operated the cathode at high enough flow rates, the discharge evolved in the plume

328
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Mark Kushner: In a very confined, region, almost looked like a spot, that's why they called it the spot mode.

329
00:52:26.670 --> 00:52:37.890
Mark Kushner: But then what they found is that as they started reducing the flow rate, they found that the spatial extent of the plume changed

330
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Mark Kushner: very clearly.

331
00:52:40.530 --> 00:52:49.300
Mark Kushner: But more importantly, is that they found that the level of fluctuations The level of fluctuations

332
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Mark Kushner: measured in the keeper, in this case, of the cathode, also increased. And that was very important because this increase of fluctuations led to significant increases in the erosion of the tube of the whole cathode.

333
00:53:08.850 --> 00:53:11.660
Mark Kushner: And therefore, it was a failure mode.

334
00:53:12.030 --> 00:53:15.429
Mark Kushner: That limited the application of these devices.

335
00:53:16.110 --> 00:53:28.969
Mark Kushner: And we didn't really have a good understanding of what leads to the change, what are the conditions and why one transitions from the spot to blue mode.

336
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Mark Kushner: And this was a problem that had remained elusive, unresolved since the 1960s and 70s, as I said.

337
00:53:37.950 --> 00:53:40.350
Mark Kushner: And, of course, she mentioned that

338
00:53:40.610 --> 00:53:51.280
Mark Kushner: The approach then, because we didn't have a very… we didn't have any good understanding of why these modes occur, the approach then was to test and test again.

339
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Mark Kushner: So it was essentially, Testing these devices.

340
00:53:56.880 --> 00:54:03.970
Mark Kushner: In a wide range of operating conditions, changing the current, changing the… changing the mass flow rate, and sort of create an envelope

341
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Mark Kushner: Where, empirically, the, The limits of stability were defined.

342
00:54:12.000 --> 00:54:17.399
Mark Kushner: And that gave us the guidance of where not to operate these cafes.

343
00:54:18.420 --> 00:54:21.070
Mark Kushner: It was a very… a truly empirical approach.

344
00:54:22.350 --> 00:54:26.450
Mark Kushner: So, what happened then?

345
00:54:29.430 --> 00:54:30.970
Mark Kushner: So what happened then.

346
00:54:31.510 --> 00:54:37.789
Mark Kushner: We managed to secure some funding to go after this problem and used our OCA2D code.

347
00:54:38.430 --> 00:54:44.400
Mark Kushner: to, simulate this device and try to understand

348
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Mark Kushner: remote, and for the first time, we were able to actually capture some of these dynamics in a manner that also agreed, as I show here, between comparisons between the fluctuations of the keeper voltage

349
00:54:59.730 --> 00:55:14.419
Mark Kushner: And the fluctuations we're calculating in the simulation code sort of capture the trend of increasing fluctuations according to the measurements as we reduce the flow rate in this particular cathode, which is about a 25 ampoly cathode.

350
00:55:14.600 --> 00:55:33.080
Mark Kushner: And we found that these are waves that are frequency much slower than the ionacoustic waves, but at a higher phase velocity, and they are related, without getting into too much detail, they're related to how the gas is ionized and some of the

351
00:55:33.080 --> 00:55:36.379
Mark Kushner: The… the dynamics associated with the ionization.

352
00:55:37.050 --> 00:55:42.399
Mark Kushner: But that was the first time that we were also able to capture some of these dynamics.

353
00:55:42.840 --> 00:55:48.099
Mark Kushner: For this very long-standing problem of spot plume mode transitions.

354
00:55:49.640 --> 00:56:06.300
Mark Kushner: So, let me switch now to… switch gears to hole thrusters as we get into the final stretch. So, hole thrusters, the main failure mode, used to be the erosion of the channel. I show here some measurements of,

355
00:56:06.460 --> 00:56:11.120
Mark Kushner: I think these were from an SPT100 measurements that were done in Russia.

356
00:56:11.200 --> 00:56:19.409
Mark Kushner: A test, a long test, where you can see how the ions that are… that are accelerated from the channel

357
00:56:19.410 --> 00:56:32.290
Mark Kushner: not controlled properly, they have enough energy to bombard the surfaces, the surface of the chamber, surfaces here, and start eroding it away. So you can see here how the channel opens up.

358
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Mark Kushner: And ultimately, if it continues to open up, even though the erosion rates begin to decrease, they are never… they never reach a zero level, and therefore, as they continue to… as the channel continues to open up.

359
00:56:48.400 --> 00:57:03.149
Mark Kushner: ultimately, the ions, the magnets are exposed to the ion beam, and when they start to get bombarded, then we get failure of the engine, because the magnetic field is no longer. So.

360
00:57:03.480 --> 00:57:04.900
Mark Kushner: That's sort of the main…

361
00:57:05.360 --> 00:57:19.739
Mark Kushner: used to be the main failure mode for whole thrusters, and I show here one picture of what happens to the thruster. This particular thruster that was developed by collaboration between a French company and

362
00:57:20.090 --> 00:57:31.879
Mark Kushner: Russian company, the PPS1350, how thrust it looked like, but all this erosion after 10… a little over 10,000 hours of… of testing.

363
00:57:36.750 --> 00:57:38.769
Mark Kushner: So, she pointed out that this was…

364
00:57:38.960 --> 00:57:49.490
Mark Kushner: This lack of understanding of how and why the channel roads was a main reason why hull thrusters, for five decades.

365
00:57:49.640 --> 00:57:52.229
Mark Kushner: But never been flown on a deep space mission.

366
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Mark Kushner: So…

367
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Mark Kushner: One of the problems that remains elusive today that is directly related with our ability to, predict erosion

368
00:58:09.270 --> 00:58:24.070
Mark Kushner: is this so-called anomalous transport problem, where we do not fully understand how electrons that come from the cathode, that I showed you earlier, get into the anode.

369
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Mark Kushner: traverse the applied magnetic field and reach the anode. It appears from measurements that the transport of the electrons occurs at a rate that's much different than classical collisions.

370
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Mark Kushner: predict.

371
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Mark Kushner: And this is very important. Our lack of understanding for this process is quite important, because, as you can see here.

372
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Mark Kushner: from measurements of the ion velocity that are shown here in symbols along the center line Of the channel.

373
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Mark Kushner: You can see here that, if you…

374
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Mark Kushner: Simulate, capture the ion velocity profile to be close to the measurements, but

375
00:59:11.410 --> 00:59:26.220
Mark Kushner: not exactly the measurements. So you have… I show here, two different solutions that are quite close to the measurements, and one, if we didn't know any better, if we didn't have erosion measurements, one could claim that both of these solutions are accurate enough.

376
00:59:26.280 --> 00:59:39.799
Mark Kushner: But it turns out that even these small differences in the ion velocity can cause a significantly different result in our prediction erosion. So what I show here is data

377
00:59:39.800 --> 00:59:55.359
Mark Kushner: Of the wear rate of this part of the channel… of the channel here of this particular whole thruster, and how it is that the erosion prediction is significantly different if you use one velocity profile, which is still close to the measurements, compared to the other.

378
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Mark Kushner: So it's a very, very challenging problem.

379
00:59:58.200 --> 01:00:06.480
Mark Kushner: Not only from the fact that we don't understand the mechanism that leads to this enhanced transport, but also how sensitive it is, how the erosion results are sensitive to it.

380
01:00:09.110 --> 01:00:17.549
Mark Kushner: So, what we're looking for, then, is… because we want to do… we want to perform… be able to perform these simulations fast enough.

381
01:00:17.790 --> 01:00:21.720
Mark Kushner: We cannot afford… particle codes.

382
01:00:21.740 --> 01:00:37.529
Mark Kushner: that, resolve the electron dynamics, because that would be prohibitively, costly from a computational point of view. So what we're looking for is we're looking for analytical models that are physics-based, we call them closure models.

383
01:00:37.530 --> 01:00:52.040
Mark Kushner: that can, we can use in 2DX isometric simulations, that can be performed fast enough to have a meaningful impact on our assessment of electrical partial devices, like OFASTOS. That's sort of the quest

384
01:00:52.080 --> 01:01:09.520
Mark Kushner: the big drive behind the problem that you sometimes hear called the anomalous transport problem in all factors. So we're looking for a transport coefficient that accurately represents the physics of whatever mechanism it is that drives anomalous transport of these electrodes.

385
01:01:11.110 --> 01:01:26.979
Mark Kushner: So I mentioned earlier the value of having a lot of measurements. I've discussed with students at lunch today how important that is. Here's one example of why that has been a significant and invaluable source of information for us.

386
01:01:27.010 --> 01:01:46.789
Mark Kushner: the range of different measurements that we have been able to accumulate through the last 10 or 15 years of testing different horses has provided us with the ability to test different theoretical models, different theories. In this particular case.

387
01:01:46.890 --> 01:01:55.250
Mark Kushner: Recently, we were able to use this data to guide the theoretical derivations of a new model that we produced.

388
01:01:55.510 --> 01:02:08.170
Mark Kushner: an analytical expression of which is shown here on the top, that seemed to yield very good agreement, given the velocity of the electron. So what I show here are comparisons

389
01:02:08.170 --> 01:02:19.580
Mark Kushner: Different operating conditions and different hull thrusters, showing comparisons between the ion velocity and the data, that when you use them in numerical simulations.

390
01:02:19.580 --> 01:02:38.990
Mark Kushner: they produce an anomalous collision frequency profile that I show here in the symbols, that essentially serve as our empirical model of the collision frequency, which is therefore what we're trying to match. And you can see here the

391
01:02:39.020 --> 01:02:55.690
Mark Kushner: The blue, which is the predictions from the theoretical model, how well they match different operating conditions and different thrusters. So thrusters that I mentioned here vary in size significantly, so we have a thruster here that is as big as a Sora can.

392
01:02:56.170 --> 01:02:58.010
Mark Kushner: All the way up to,

393
01:02:58.130 --> 01:03:14.270
Mark Kushner: a much higher power, 12-kilowatt level hole thruster that's about 80 centimeters in diameter. So a wide range of not only operating conditions, but also size. So this was very promising. The physics behind this are described in some of my papers.

394
01:03:14.340 --> 01:03:29.619
Mark Kushner: We argue that is some combination of electrostatic instabilities in the electron cyclotron range and the lower hybrid range that sort of combine to saturate and lead to this anomorous transport. That is what we argue.

395
01:03:29.950 --> 01:03:44.620
Mark Kushner: And the challenge, however, is to now implement it in 2D axis metric simulations, and that is very challenging, because of the… especially in frameworks that solve generalized Ohm's law.

396
01:03:44.960 --> 01:03:58.009
Mark Kushner: But what we, what we found recently was, a, company from, from Europe that is developing, fully kinetic codes.

397
01:03:58.400 --> 01:04:07.719
Mark Kushner: wanted to try out our model. Again, our whole2D code is not a fully kinetic code, that is, it doesn't

398
01:04:08.110 --> 01:04:11.760
Mark Kushner: Capture directly the dynamics of the electrons.

399
01:04:12.110 --> 01:04:13.360
Mark Kushner: But they do.

400
01:04:13.570 --> 01:04:24.400
Mark Kushner: And they tried our model, and what I'm about to show you here is an animation of how the plasma evolved in the numerical simulations, but what I wanted to point out

401
01:04:24.450 --> 01:04:39.350
Mark Kushner: is, look at these profiles over here and how they will evolve. In particular, this red line over here, which is the anomalous collision frequency, which is what we're looking for, starting from a cold start.

402
01:04:39.350 --> 01:04:50.579
Mark Kushner: So you can see here that they didn't start from a state that was already close to the steady state, and how it evolves and remains in steady state.

403
01:04:58.550 --> 01:05:02.440
Mark Kushner: So, you can see here that, that the,

404
01:05:02.490 --> 01:05:18.149
Mark Kushner: Anomalous collision frequency evolves to achieve a shape as we expect it to be, and the ion velocity also achieves the same kind of qualitative profile as we expect.

405
01:05:18.150 --> 01:05:27.110
Mark Kushner: And it remains in steady state, it doesn't break up, it doesn't… doesn't destabilize, and these are sort of the… the traces of the…

406
01:05:27.110 --> 01:05:46.180
Mark Kushner: the currents that the code computes. There's still a lot to learn about the code. We try to understand how exactly the simulations will perform to make sure that these results are real, but I wanted to share with you these first attempts from 2D… 2.5D kinetic codes

407
01:05:46.180 --> 01:06:02.510
Mark Kushner: seem to be incorporating our theoretical model using a Monte Carlo collision operator, and seem to be getting some very promising results. So on our part, at the laboratory, we're trying to reproduce some of these results.

408
01:06:02.510 --> 01:06:07.889
Mark Kushner: But using our own code, by adding some terms in our governing equations that we think

409
01:06:07.890 --> 01:06:11.269
Mark Kushner: might be representative of what they're able to capture, and we can at the moment.

410
01:06:15.890 --> 01:06:33.649
Mark Kushner: But even in the absence of fully predictive anomalous transport models, I wanted to emphasize that these codes are still invaluable for our mission. So, even if we take, measurements of the

411
01:06:34.200 --> 01:06:50.909
Mark Kushner: effective measurements of the anomalous transport model that we are missing, and incorporate it in our codes, so essentially using the measurements as our closure model, you can still get, have an invaluable impact from these codes. And what I show here are

412
01:06:50.960 --> 01:06:55.520
Mark Kushner: Is… is how the code was used to inform

413
01:06:55.660 --> 01:07:02.450
Mark Kushner: our Psyche mission, which is the mission that was launched to the,

414
01:07:02.740 --> 01:07:10.689
Mark Kushner: to the dwarf planet of Psyche, which is a metal, metal, small body.

415
01:07:10.890 --> 01:07:20.649
Mark Kushner: And it was launched in 2023, and it was the first mission that employed all thrusters beyond lunar orbit.

416
01:07:21.210 --> 01:07:30.689
Mark Kushner: And it was important for us to know, even though the live test that they run prior to the launch of the mission, extended

417
01:07:31.640 --> 01:07:35.079
Mark Kushner: Longer than the required lifetime of the thruster.

418
01:07:35.490 --> 01:07:50.799
Mark Kushner: The mission still needed to understand whether the life of the thruster would still be sufficient if, for example, we're in the position to change slightly operating conditions, or to change the thrusting profile.

419
01:07:51.310 --> 01:08:05.370
Mark Kushner: So, what we did here is that we used our code and validated it with live test measurements of the erosion of the channel. This is the channel of this particular thruster we call the SPT140.

420
01:08:05.540 --> 01:08:22.619
Mark Kushner: And then used our models to predict what the erosion would look like, given certain, thrusting profiles that were slightly different than the original mission I envisioned. And we found that… we predicted that there were no,

421
01:08:22.700 --> 01:08:41.550
Mark Kushner: No, there was really no risk, and that the mission could operate, with these, different profiles, and that was an important… an important finding for, decision makers for these missions, and allowed for the launch of this mission back in 2023.

422
01:08:44.979 --> 01:08:46.369
Mark Kushner: So,

423
01:08:47.040 --> 01:08:56.940
Mark Kushner: The final three charts here, is, one of our, another major breakthrough that we were fortunate enough to

424
01:08:57.510 --> 01:09:11.370
Mark Kushner: to get to, and it was associated with the erosion of the… of these whole thrusters. I mentioned that not understanding… I mentioned earlier that not understanding how the erosion of this particular thruster evolves was a

425
01:09:11.819 --> 01:09:14.629
Mark Kushner: It was the main reason why these thrusters didn't fly.

426
01:09:14.819 --> 01:09:17.130
Mark Kushner: For 5 decades since their inception.

427
01:09:17.250 --> 01:09:20.670
Mark Kushner: And one of the things that, we found

428
01:09:20.760 --> 01:09:38.250
Mark Kushner: from testing simulations was the following. So there was a test that was run over a particular commercial hole thruster called, like, the BPT4000, where they found that after running the test for about

429
01:09:38.800 --> 01:09:46.979
Mark Kushner: 5,000 hours, Until that point, the channel eroded as… People had expected.

430
01:09:47.160 --> 01:09:54.369
Mark Kushner: But, like in that neutralizing cathode that I shared with you earlier, the erosion after 5,000 hours essentially stopped.

431
01:09:54.970 --> 01:10:00.890
Mark Kushner: This had never… had never been seen before, and the reasons for it was not… were not known.

432
01:10:01.680 --> 01:10:09.139
Mark Kushner: The implications of not knowing was, in fact, or in fact, as you can imagine, Quite serious, because…

433
01:10:09.260 --> 01:10:11.049
Mark Kushner: If this was a real effect.

434
01:10:11.530 --> 01:10:15.889
Mark Kushner: And there was something happening in the thruster that allowed us

435
01:10:16.000 --> 01:10:26.119
Mark Kushner: To, have a much longer life, that would have incredible Incredibly favorable implications for us.

436
01:10:26.310 --> 01:10:28.740
Mark Kushner: But we didn't know whether this was…

437
01:10:29.390 --> 01:10:34.899
Mark Kushner: Not really a true effect, and it was… Either a facility effect.

438
01:10:35.040 --> 01:10:39.789
Mark Kushner: Or some kind of an anomaly, since we have never seen behavior like this before.

439
01:10:39.990 --> 01:10:42.660
Mark Kushner: An anomaly that would not happen again.

440
01:10:42.920 --> 01:10:48.080
Mark Kushner: So it was very important for us, then, to look into this in much more detail.

441
01:10:48.940 --> 01:10:51.789
Mark Kushner: And Hall 2D at the time was, in fact.

442
01:10:52.190 --> 01:11:11.290
Mark Kushner: Built on a magnetic field aligned mesh precisely to allow us to simulate magnetic field topologies of this level of complexity, because as the channel eroded, it exposed features of the magnetic field that could not be modeled by previous codes.

443
01:11:11.360 --> 01:11:19.900
Mark Kushner: So that is… that was essentially the motivation for us building the whole thruster code that I described earlier with a magnetic field of light mesh.

444
01:11:21.210 --> 01:11:22.720
Mark Kushner: So what we found…

445
01:11:25.600 --> 01:11:35.750
Mark Kushner: was what we call today the magnetic shielding first principles, which is essentially that the magnetic field topology that was exposed

446
01:11:35.950 --> 01:11:49.440
Mark Kushner: was of a particular shape that, when combined… I'm going to keep it at a high level here. There, as you can imagine, for the last 10 years, there have been several general publications explaining these physics, but essentially what happened is that the

447
01:11:49.440 --> 01:11:57.440
Mark Kushner: The physics of the ions as they pass by the channel, and the particular topology of the magnetic field.

448
01:11:58.110 --> 01:12:16.370
Mark Kushner: essentially protected the walls from bombardment of the ions. As I show here, the… what the plasma properties that are relevant to ion erosion looked like in the beginning of the test, and what they look like when this magnetic field is exposed.

449
01:12:16.930 --> 01:12:28.030
Mark Kushner: Where you get much lower… much lower plasma potentials, much lower sheath drops, and therefore the ions just simply pass by and are not attracted, or do not bombard

450
01:12:28.110 --> 01:12:42.080
Mark Kushner: the channel with the kinetic energy they had in the previous configuration. That, of course, allowed us then to develop a strategy where you can actually build the magnetic field

451
01:12:42.090 --> 01:12:49.750
Mark Kushner: Initially, to behave in this way, in this magnetic shielding way, and therefore have the channel never erode.

452
01:12:50.060 --> 01:12:58.859
Mark Kushner: And that's what we did in an effort back in 2012, where we were funded internally at the laboratory.

453
01:12:59.570 --> 01:13:03.150
Mark Kushner: To prove our findings.

454
01:13:03.350 --> 01:13:13.960
Mark Kushner: So we took a thruster that some of you may be familiar with, the H6 thruster, which was built in collaboration between this university

455
01:13:14.100 --> 01:13:30.840
Mark Kushner: JPL and the Air Force, UH6 thrust faster. We modified it, we did numerical simulations with our whole thruster code, and showed how it is that the magnetic field should be designed in a manner to achieve magnetic shielding of these walls over here.

456
01:13:31.680 --> 01:13:37.040
Mark Kushner: We did that, we modified the thruster, and then we did,

457
01:13:37.380 --> 01:13:54.569
Mark Kushner: Several measurements, including direct erosion measurements, and showed unambiguously that the plasma properties that we expected by putting probes here, the plasma properties were as predicted by the models, much lower plasma potentials and electron temperatures.

458
01:13:55.180 --> 01:13:57.849
Mark Kushner: And also, the erosion rates.

459
01:13:58.020 --> 01:14:14.320
Mark Kushner: that were measured in the original configuration, the one that did not have magnetic shielding were high, whereas when we implemented magnetic shielding, they were essentially within the noise of the instrument, so there was really no erosion.

460
01:14:16.390 --> 01:14:23.369
Mark Kushner: So that was a, as you can imagine, a significant breakthrough that sort of made news, and a lot of, a lot of folks,

461
01:14:24.400 --> 01:14:43.559
Mark Kushner: advertised it worldwide and had important implications, and what's more important to us was that many programs evolved after that, trying to incorporate magnetic shielding in the thrusters, and I'll list some of them, here.

462
01:14:43.680 --> 01:14:52.159
Mark Kushner: Including incorporating magnetic shielding in a wide range of different thrusters and operating conditions and sizes.

463
01:14:52.720 --> 01:15:04.760
Mark Kushner: And, including our latest thruster, the qualifact rocket with Magnetic Shielding, is built right now by Aerojet as the APS system to go on gateway.

464
01:15:07.000 --> 01:15:17.180
Mark Kushner: Well, that was the last chart. I wanted to thank you. I know it was a long talk. I appreciate your time. I would open it up for questions, but as you are

465
01:15:18.460 --> 01:15:33.009
Mark Kushner: sort of formulating your questions, I'm going to put some personal photos here from a trip I took back in 2014, in the beautiful city of Budapest, where I was lucky enough to visit.

466
01:15:33.190 --> 01:15:39.699
Mark Kushner: this very famous gymnasium called the Fasori Evangelicos Gymnasium, where…

467
01:15:40.630 --> 01:15:48.359
Mark Kushner: Many of the Martians, these are the Hungarian scientists that contributed to the Manhattan Project, attended.

468
01:15:48.610 --> 01:15:53.770
Mark Kushner: We're talking about folks like Edward Teller, Eugene Wigner, who is…

469
01:15:54.800 --> 01:16:10.410
Mark Kushner: Whose name is here on this plaque, who's also a Nobel laureate, and of course, John van Neumann. Janos Harsani, also a Nobel laureate, but in economics. So you can imagine the waves that are emanating from this high school.

470
01:16:10.490 --> 01:16:15.370
Mark Kushner: That produced so many brilliant scientists. And over here to the left.

471
01:16:16.260 --> 01:16:23.549
Mark Kushner: That's me, under the plaque, on a building that Johnny von Neumann grew up.

472
01:16:23.630 --> 01:16:39.730
Mark Kushner: Until the age of 18, and where he was rumored, to, see his mother one day, who was a heavy smoker, gazing out the window, smoking a cigarette, and he, he asked her

473
01:16:39.870 --> 01:16:42.930
Mark Kushner: Mother, what are you calculating?

474
01:16:43.230 --> 01:16:46.610
Mark Kushner: And that is not the punchline. The punchline is that he was 5 years old.

475
01:16:47.380 --> 01:16:50.820
Mark Kushner: So, I'll open it up for questions. Thank you, everybody, for your time.

476
01:16:55.640 --> 01:16:58.589
Mark Kushner: Thank you very much for that excellent seminar.

477
01:16:58.590 --> 01:17:21.479
Mark Kushner: We unfortunately need to end now, because there's a class that's here at 4.30. So, perhaps we could, reconvene for questions, just in the atrium, and we can, continue at that point.

478
01:17:21.480 --> 01:17:23.259
Mark Kushner: You're living with your 5-year-old?