Motivation Motivation / Objectives Ring cusp discharges provide highly efficient plasma thrusters Development of an efficient microdischarge (~ cm) large delta-v missions using small spacecraft formation flying and control for larger spacecraft Previous Work and Objectives 3 cm 3 cm Mechanism Primary Electron Losses Secondary Electron Losses P ps P pw P piz P px P sw P siz P sx Micro-Ion MiXI (mth).9% 8.%.% 8.8%.6%.%.% NSTAR (TH) 69.%.7% 3.7% 6.6% 9.% 7.%.% Miniature discharge, MiXI (3cm) Overall impressive performance Design bracketed by field strength: Efficiency: requires high field strength Stability: requires low field strength Improved knowledge of near-surface cusp region needed for optimization Microdischarges (~ cm) Increased surface area-to-volume ratio with smaller discharge Efficiency/stability balance Plasma volume is increasingly dominated by the magnetic cusp field at small scale Conversano R., Wirz R., CubeSat Lunar Mission Using a Miniature Ion Thruster, AIAA--683 Wirz R., Computational Modeling of a Miniature Ion Thruster Discharge, AIAA--3887 Mao H. S., et al., Plasma Structure of Miniature Ring-Cusp Ion Thruster Discharges, AIAA-- Objectives ) Investigate the behavior and structure of plasma for a single cusp ) Develop an efficient multi-cusp microdischarge AFOSR Space Propulsion and Power Program Review, http://www.wirz.seas.ucla.edu/ Engineering
Report Documentation Page Form Approved OMB No. 7-88 Public reporting burden for the collection of information is estimated to average hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, Jefferson Davis Highway, Suite, Arlington VA -3. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number.. REPORT DATE SEP. REPORT TYPE 3. DATES COVERED -- to --. TITLE AND SUBTITLE Near-Surface Cusp Confinement of Micro-Scale Plasma a. CONTRACT NUMBER b. GRANT NUMBER c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) d. PROJECT NUMBER e. TASK NUMBER f. WORK UNIT NUMBER 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) University of California Los Angeles (UCLA),Engineering,Los Angeles,CA,99 8. PERFORMING ORGANIZATION REPORT NUMBER 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES). SPONSOR/MONITOR S ACRONYM(S). DISTRIBUTION/AVAILABILITY STATEMENT Approved for public release; distribution unlimited. SPONSOR/MONITOR S REPORT NUMBER(S) 3. SUPPLEMENTARY NOTES Presented at the AFOSR Space Propulsion and Power Program Review held -3 September in Arlington, VA. U.S. Government or Federal Rights License. ABSTRACT. SUBJECT TERMS 6. SECURITY CLASSIFICATION OF: 7. LIMITATION OF ABSTRACT a. REPORT b. ABSTRACT c. THIS PAGE Same as Report (SAR) 8. NUMBER OF PAGES 9a. NAME OF RESPONSIBLE PERSON Standard Form 98 (Rev. 8-98) Prescribed by ANSI Std Z39-8
Approach Complete Single Cusp Experiment Electrons only Model: Electron cusp confinement Underway Wire Probe Cusp Confinement Discharge Experiment - Primary electrons - Neutrals (xenon) - Ions - Secondary electrons Model: Multi-species cusp confinement Electron Gun Preliminary Efforts Microdischarge design model Microdischarge experiment Magnet (behind plate) Microthruster development and testing Cusp Confinement Discharge Experiment Measure particle flux for single cusp Ring cusps upstream for improve primary electron confinement Ring plenum gas injection upstream E-gun supplies μa of ev electrons Wall Probe embedded into sliding downstream plate o Non-invasive planer scans of cusp o μm diameter effective area o Orifice design behaves at RPA e - gun..3. Gas. feed plenum...3...6.7 Aperture plate Simulation Domain..8.6.. Ring-cusp magnets (a) (b) (c) (d).6.6.6.66.68.7.7 Cylindrical magnet Wall Probe Computational Model.D PIC-MCC model Adaptive Cartesian mesh nd order electric potential [] and field calculation Modified Boris particle pushing technique [] Generalized weighting scheme [3] Anisotropic elastic scattering of electrons [] Analytical equations for permanent magnets [,6] [] Fox J. M., Ph.D. Dissertation, Aeronautics and Astronautics Dept., MIT, 7 [] Wirz R., Katz I., AIAA-- [3] Verboncoeur J., J. Comput. Phys., 7 () 7 [] Okhrimovskyy A., Bogaerts A., and Gijbels R., Phys. Rev. E, 6, 37 () [] Engel-Herbert R. and Hesjedal T, J. Appl. Phys., 97, 7 () [6] Babic S. I., Akyel C., Progress In Electromagnetics Research C, (8), 7-8 AFOSR Space Propulsion and Power Program Review, http://www.wirz.seas.ucla.edu/ Engineering
Results: Cusp Confinement Discharge Computational Model Experiment....... Potential (V) 6 8...3. E+ 3E+3 6E+3 9E+3 Primary Electrons (m -3 )...3.......3.. E+3 E+ 3.E+ Secondary Electrons (m -3 ) E+ 3E+ E+ 7E+ Ions (m -3 ) Normalized Current Density.8 Example Ion Trajectories.6...8.6...3.36.38... Primary Electron Ion Secondary Electron 3 Radial Positon (mm) - - - e - (x -8 Torr) - - e - (x -3 Torr) - - - Observations Ionization due to primaries near the cusp causes high local ion density Ions are directed axially toward wall by electrostatic force Near-surface confinement behavior highly dependent on upstream B- field structure Plasma distribution affected by e-gun misalignment x -..... Current Current Density Density (A/m (A m - ) 6 - - -6 x - - ions (x -3 Torr) - Leak radius : r l Hybrid gyroradius: h r l h e i - x - x -3 8 6 mv ei, qb....3. Wirz R., Araki S., Dankongkakul B., Near- Surface Cusp Confinement for Weakly Ionized Plasma, AIAA--398 Units (mm) Primary Electrons Ions Secondary Electrons Leak Radius (Experiment).6.77.9 Leak Radius (Model).8.3.3 Gyroradius b... Hybrid Gyroradius.9.9 /.37.37 AFOSR Space Propulsion and Power Program Review, http://www.wirz.seas.ucla.edu/ Engineering 3
Microdischarge Analysis and Design Miniature Discharge (3 cm) Analysis Plasma properties dominated by magnetic field structure and invariant to discharge power Strong magnets pinches down plasma volume, leading to poor volumetric utilization Confirms computational/theoretical analysis that strong magnets and high discharge currents can lead to the onset of instability Mao H. S., Goebel D., Wirz R., Plasma Structure of Miniature Ring-Cusp Ion Thruster Discharges, AIAA-- Microdischarge Design (preliminary efforts) Objectives: large plasma volume, desirable cusp strength, stability Considering unconventional discharge designs Primary confinement efficiency on order of larger discharges (~%) Two-fluid plasma model (e - and ions) needed Micro cathode design and testing underway Micro cathode Concluding Remarks / Future Work Important insight derived from exp/comp single cusp effort for near-surface and volumetric confinement Future Work Experiment: weakly ionized plasma analysis for single cusp and microdischarge Continue to use semi-analytical tools for microdischarge design exploration Comp Efforts: Detailed design:.-d hybrid PIC model for weakly ionized plasma microdischarge design and analysis Acknowledgements: AFOSR YIP and Dr. Mitat Birkan Grant FA9---9 Students: Sam J. Araki, Ben Dankongkakul, Hann Mao AFOSR Space Propulsion and Power Program Review, http://www.wirz.seas.ucla.edu/ Engineering