Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Plasma Physics
Volume 67, Number 15
Monday–Friday, October 17–21, 2022; Spokane, Washington
Session KI02: Low Temperature PlasmasLive Streamed
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Chair: Yevgeny Raitses, PPPL Room: Ballroom 100 B |
Tuesday, October 18, 2022 3:00PM - 3:30PM |
KI02.00001: Experimental Insights into Instability-Induced Cross-Field Transport in Hall Effect Thrusters Invited Speaker: Benjamin A Jorns Hall effect thrusters are one of the mostly widely used forms of in space propulsion. Their ability to achieve high exhaust velocities translates to an order of magnitude higher fuel economy when compared to chemical rockets. These devices also are attractive due to their moderate to high thrust density, which stems from the quasi-neutral nature of the acceleration process. Despite a high level of maturity and decades of development efforts, there are aspects of the operation of Hall thruster—most notably the electron dynamics—that remain poorly understood. In particular, there is experimental and numerical evidence that the cross-field electron transport is non-classical, resulting from the onset of drift-driven instabilities. The lack of understanding of this non-classical process has precluded the development of fully predictive models for these thrusters. This work highlights recent experimental efforts to infer the growth and saturation of these instabilities. These measurements in turn are related through the framework of quasilinear theory to an effective electron transport. The experimental insights are leveraged to inspire closure models that represent the non-classical transport in a reduced fidelity fluid model. The predictive capability of this fluid model is assessed against experimental measurements. |
Tuesday, October 18, 2022 3:30PM - 4:00PM |
KI02.00002: Electron Behavior in a Magnetically Expanding Plasma Invited Speaker: Justin Little Plasma expansion along diverging magnetic fields is a fundamental process for a variety of low-temperature plasmas with applications to plasma processing and spacecraft electric propulsion. Expansion coincides with the conversion of plasma thermal energy into directed ion kinetic energy. For plasmas in which the electron temperature greatly exceeds the ion temperature, ion acceleration is driven mainly by the formation of an ambipolar electric field. The gradient in electron pressure provides the source of the ambipolar electric field in addition to transferring the force of the accelerated plasma onto the magnetic circuit via diamagnetic drift currents. This talk will focus on two important topics related to the behavior of electrons in magnetically expanding plasmas that are critical to the thermal-to-kinetic energy conversion efficiency. The first topic, electron cooling, describes how electron energy is transported along the magnetic field lines. Experimental and theoretical results will be presented that highlight the importance of field-aligned electron heat conduction on electron cooling and the resulting energy conversion process. The second topic, electron demagnetization, describes how the electrons detach from the expanding magnetic field. Both experiment and theory will again be used to argue that electron detachment can result from finite Larmor radius effects in regions of low magnetic field and high magnetic field curvature. |
Tuesday, October 18, 2022 4:00PM - 4:30PM |
KI02.00003: Magnetic confinement and instability in E×B Penning source: Discovery of high-magnetic-confinement mode Invited Speaker: June Young Kim Understanding instability is essential to effectively generate high-density plasma and deliver a stable ion beam current in several applications of E×B sources, such as the semiconductor process to electric propulsion. Gradient-drift driven instabilities originating from ambipolar electric fields aligned with density gradients perpendicular to the magnetic-field line have recently received renewed attention in linear instability studies, and comprehensive considerations have been proposed as a part of the theory of the gradient-drift instability. Notably, partially magnetized plasmas have a chamber dimension comparable to the Larmor radius of their ions, implying that boundary effects are important in the formation of instabilities. We focused on the importance of the boundary effect and proposed the breaking of spatially symmetric non-ambipolar flow. By using a positively biased additional electrode, we effectively broke the spatial symmetry of the global flow of electrons and ions. Finally, in the steady-state, the plasma density tends to peak in the plasma core, approaching plasma densities that are four times larger than those observed in the case where the instability is the strongest. We have verified the transition into a strong-magnetic-confinement mode by measuring the edge-to-center density ratio (h-factor) that estimates the degree of plasma loss to the boundary. A high-magnetic-confinement mode with a reduced h-factor of 0.16 is observed, which demonstrates that the saturation of magnetic confinement due to the gradient-drift driven instability can be prevented by an asymmetric nonambipolar flow. |
Tuesday, October 18, 2022 4:30PM - 5:00PM |
KI02.00004: Diagnostics of plasma-liquids systems: challenges and their mitigation Invited Speaker: Shurik Yatom Non-equilibrium, low-temperature plasma is gaining a steady and dedicated following in the bustling inter-disciplinary community interested in plasma science and technology. Small scale, uncomplicated ways of plasma generation in ambient atmosphere and high plasma-induced chemical reactivity make low-temperature plasma very attractive for a wide variety of applications in biomedicine, environmental remediation, and agriculture, prompting new avenues for studying plasma in rich chemical environments and plasma interaction with liquids. Often, these environments pose new challenges for plasma investigation, application of diagnostic methods and interpretation of results. |
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