Plasma & Space Propulsion Lab
The UCLA Plasma & Space Propulsion Lab is investigating the plasma processes in advanced space propulsion systems through a combined experimental, computational, and analytical approach.
The 3 cm Miniature Xenon Ion (MiXI) thruster, developed by Wirz in 2005, was the first miniature ion thruster to demonstrate stable operation and noteworthy total efficiency at these scales. However, the main performance limitation was the high discharge loss of ~450 eV/ion due to poor primary electron confinement from the magnetic cusp design. The current objective of this project is to design a more efficient discharge for the MiXI thruster using discharge EEDFs and plasma parameter analysis.
This project investigates the existence of high energy ions generated in high current hollow cathode plumes using Laser Induced Fluorescence (LIF) and plasma probes. Ion acoustic turbulence is generated from a high electron to ion relative drift velocity, and wave-particle interactions lead to heating of plasma in the plume. Energetic ions can cause erosion of cathode surfaces used for long duration missions using Hall thrusters. We test a 100 A-class hollow cathode at JPL and perform LIF measurements to study the formation of energetic ions and the evolution of the IVDF in the plume.
The Plasma and Space Propulsion Lab is undertaking research into the generation of small DC plasma elements for incorporation into photonic crystals and metamaterial devices. These devices can precisely control EM radiation in the form of waveguides, splitters, multiplexers, bandgap filters, and more. The inclusion of plasma elements gives these devices rapid tunability and modulation, widening their applications and expanding the frontier of ultra-fast electronics.
We investigate the time-dependent sputtering behavior of materials with micro-architectured surfaces for extending the lifetime of devices with similar plasma environments (electric propulsion/fusion). A hollow cathode generated argon or xenon plasma is directed to a biased target via solenoid magnets to provide energetic ion bombardment. Tested materials include refractory metals (molybdenum, rhenium), carbon-based compounds, and dielectric (Al2O3, Macor).
The interaction of charge-exchange collisions ions created in the plume of ion and Hall-effect thrusters interacting with background electric fields contribute to unwanted spacecraft surface sputtering and grid erosion, thereby limiting the thruster and spacecraft operation and lifetime. Improving our understanding of heavy species collisions (e.g. momentum-exchange and charge exchange collisions between ions and neutrals) in intermediately-ionized plasma is necessary for furthering the development and use of electric propulsion devices for deep space missions.
A microplasma source for photonic crystal applications is currently being developed at UCLA. Wirz' hybrid model, DC-Ion, is being used to simulate and diagnose this microdischarge. For validation, a well-characterized ring-cusp discharge is first modeled with the code.
In collaboration with AFRL, we investigate extraction mechanisms in ionic liquid electrospray thrusters for optimizing for the design of multi-emitter arrays. Initial studies will include electrostatic simulation of the emitter-extractor domain to determine particle paths for varying geometries. As this project is ongoing, future efforts may include collaborative experimental investigation of thruster prototypes, electrospray plume characterization, and electrohydrodynamic modeling and simulation.
Degradation of plasma-facing materials is a significant problem in electric propulsion, pulsed power technologies, and fusion energy experiments. To reduce material degradation, new micro-engineered materials are being developed that reduce sputtering and thermal stress through an increased surface volume and area exposed to the heat flux, along with the use of micron-sized dendrites, nodules, or fibers that can deform independently.
The objective of this work is to provide in situ imaging of micron-scale surface structures using a long distance microscope (LDM) to study plasma-material interactions, in particular ion-induced erosion of plasma-facing materials. A CMOS camera and microscope system is used to capture live images of material erosion resulting from exposure to a magnetically confined plasma. Focus stacking images to create composite images and height maps at various time steps yields videos displaying the time-dependent erosion.
Magnetic cusp confinement of plasma at conducting surfaces involves interactions between a highly divergent magnetic field, ions, electrons, neutral particles, and the pre-sheath and sheath conditions that develop along the surface boundary. Large plasma devices have benefitted greatly by using permanent magnet cusps for bulk plasma confinement for both terrestrial and space applications; however, the magnetic cusp confinement mechanisms and the associated plasma dynamics very near the conducting surface are poorly understood.
High power solar electric propulsion capabilities have the potential for significantly decreasing the mass and cost of many future NASA exploration missions. Reducing the spacecraft’s mass and complexity of power processing by utilizing Direct Drive power technology will save mission cost, as suggested by studies of high power systems.
The development of permanent magnet microdischarge on the scale of 1 cm requires an improved understanding of magnetic cusp confinement physics very near the anode. Larger magnetically confined discharges benefit from relatively low surface-to-volume ratios, which can provide favorable electron confinement and high ionization efficiency.
This research aims to demonstrate the applicability of magnetic shielding to low power Hall thrusters as a means to significantly improve operational lifetime. The key life-limiting factors of conventional Hall thrusters, including ion-bombardment sputter erosion of the discharge channel and high-energy electron power deposition to the channel walls, are well understood on all thruster scales.