1 / 22

OPTIMIZING THE PERFORMANCE OF PLASMA BASED MICROTHRUSTERS*

OPTIMIZING THE PERFORMANCE OF PLASMA BASED MICROTHRUSTERS* Ramesh A. Arakoni, a) J. J. Ewing b) and Mark J. Kushner c) a) Dept. Aerospace Engineering University of Illinois, Urbana, IL b) Ewing Technology Associates, Bellevue, WA c) Dept. Electrical and Computer Engineering

gaye
Download Presentation

OPTIMIZING THE PERFORMANCE OF PLASMA BASED MICROTHRUSTERS*

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. OPTIMIZING THE PERFORMANCE OF PLASMA BASED MICROTHRUSTERS* Ramesh A. Arakoni,a) J. J. Ewingb) and Mark J. Kushnerc) a) Dept. Aerospace Engineering University of Illinois, Urbana, IL b) Ewing Technology Associates, Bellevue, WA c) Dept. Electrical and Computer Engineering Iowa State University, Ames, IA mjk@iastate.edu, arakoni@uiuc.edu, jjewingta@aol.com http://uigelz.ece.iastate.edu ICOPS 2006, June 4 - 8, 2006. * Work supported by Ewing Technology Associates, NSF and AFOSR. ICOPS06_MT_00

  2. AGENDA  Microdischarge (MD) devices as thrusters  Description of model  Scaling of thrust  Geometrical effects  Conclusions. Iowa State University Optical and Discharge Physics ICOPS06_MT_01

  3. MICRODISCHARGE PLASMA SOURCES • Microdischarges are plasmas that leverage pd scaling to operate at high pressures (10s-100s Torr) in small reactors (100s m). • Typically operated as a dc discharge using wall stablization.  High E/N in the cathode fall generates energetic electrons producing high ionization. • High power densities (10s kW/cm3) owing to small volume of discharge, producing high neutral gas temperatures. • Increase in gas temperature in flowing gas produces thrust. Iowa State University Optical and Discharge Physics ICOPS06_MT_02

  4. MICRODISCHARGES AS MICROTHRUSTERS • Micro-satellites weighing < few kg or require Ns to mNs of thrust for station keeping. • Thrusters based on MD devices can deliver the required thrust using a only a few Watts of power.  The MD operates as an efficient heat source for the propellant. Expansion of the hot gas provides the required thrust. 300 mm hole diameter Ref: Kimura, Horisawa, AIAA 2001-3791 Ref: J. Slough, J.J. Ewing, AIAA 2005-4074 Iowa State University Optical and Discharge Physics ICOPS06_MT_03

  5. CALCULATION OF THRUST  The force provided by the thruster is calculated by: where dm/dt is the mass flow rate, Ve is the exit. Ref: Robert G. Jahn, Phys. of Electric Propulsion, Mc-Graw Hill, 1989. Iowa State University Optical and Discharge Physics ICOPS06_MT_04

  6. EFFICIENCY OF THRUSTER  The incremental thrust obtained due to the discharge is given by:  Common metric for efficiency is the thrust per unit power input to the system. In this case, we look at incremental thrust per unit power.  Typical values of the efficiency for electro-thermal and arc thrusters are about 0.1 – 0.2 N/kW.  Theoretical limit on efficiency is 2/Ve,where Ve is the exit velocity. Iowa State University Optical and Discharge Physics ICOPS06_MT_05

  7. DESCRIPTION OF MODEL • To investigate microdischarge sources, nonPDPSIM, a 2-dimensional plasma-hydrodynamics code was used. • Finite volume method used on cylindrical unstructured meshes. • Implicit drift-diffusion-advection for charged species • Navier-Stokes for neutral species • Poisson’s equation (volume, surface charge) • Secondary electrons by ion impact. • Electron energy equation coupled with Boltzmann solution • Monte Carlo simulation for beam electrons. Iowa State University Optical and Discharge Physics ICOPS06_MT_06

  8. DESCRIPTION OF MODEL: CHARGED PARTICLE, SOURCES  Continuity (sources from electron and heavy particle collisions, surface chemistry, photo-ionization, secondary emission), fluxes by modified Sharfetter-Gummel with advective flow field.  Poisson’s Equation for Electric Potential:  Secondary electron emission: Iowa State University Optical and Discharge Physics ICOPS06_MT_07

  9. ELECTRON ENERGY, TRANSPORT COEFFICIENTS • Bulk electrons: Electron energy equation with coefficients obtained from Boltzmann’s equation solution for EED. • Beam Electrons: Monte Carlo Simulation • Cartesian MCS mesh superimposed on unstructured fluid mesh. • Greens functions for interpolation between meshes. Iowa State University Optical and Discharge Physics ICOPS06_MT_08

  10. DESCRIPTION OF MODEL: NEUTRAL PARTICLE TRANSPORT • Fluid averaged values of mass density, mass momentum and thermal energy density obtained using unsteady, compressible algorithms. • Individual species are addressed with superimposed diffusive transport. Iowa State University Optical and Discharge Physics ICOPS06_MT_09

  11. EXPERIMENTAL GEOMETRY (BY OTHERS)  Plume characterizes densities of excited states.  Ref: John Slough, J.J. Ewing, AIAA 2005-4074 Iowa State University Optical and Discharge Physics ICOPS06_MT_10

  12. GEOMETRY OF THE MICROTHRUSTED • Plasma channel geometry: • 300 m at inlet, 500 m at cathode. • 130 m thick electrodes, 1.5 mm dielectric gap. • Anode grounded; cathode bias varied based on power deposition (a few W). • 30 Torr (4 kPa) Argon at inlet, expanded to low pressures (5 - 10 Torr) downstream. • Gradation of meshing with a fine mesh near the discharge and coarse mesh near the outlet. Iowa State University Optical and Discharge Physics ICOPS06_MT_11

  13. 15 SCCM: PLASMA CHARACTERISTICS [e] 1011 cm-3 Logscale E field (kV/cm) [Ar+] 1011 cm-3 Logscale Potential (V)  Power deposition occurs in the cathode fall by beam electrons and ion drift. • Electric fields of > 22 kV/cm in cathode fall. • 15 sccm Ar, 30/10 Torr, 0.5 W -270 140 140 22.5 0 1.4 1.4 0 Iowa State University Optical and Discharge Physics ICOPS06_MT_12

  14. 15 SCCM: NEUTRAL FLUID [Ar(4s)] 1011 cm-3 Logscale [Ar(4p)] 1011 cm-3 Logscale Gas temp (K) Expt. plume • Gas heating and consequent expansion is a source of thrust. • More extended plume in experiment due to supersonic status. • 15 sccm Ar, 30/10 Torr, 0.5 W 200 400 675 300 2 4 Iowa State University Optical and Discharge Physics  Ref: John Slough, J.J. Ewing, AIAA 2005-4074 ICOPS06_MT_13

  15. VELOCITY INCREASE WITH DISCHARGE Animation 0 – 0.6 ms Cold flow Power on • Gas heating and subsequent expansion produces increase in velocity. • When turning on discharge, pulsation initially occurs. • Incremental thrust: 0.05 mN, •  thrust/power: 0.1 N/kW Total thrust: 0.12 mN.  15 sccm Ar, 30 – 10 Torr  0.5 W. 0 300 Iowa State University Optical and Discharge Physics Axial velocity (m/s) ICOPS06_MT_14

  16. 30 sccm, 1 W: AXIAL VELOCITY, THRUST Animation 0 – 0.55 ms Cold flow Power on • Increasing power produces increase Mach number near 1. • Incremental thrust: 0.2 mN • Total thrust of  0.5 mN. •  Thrust per unit power: 0.17 N/kW.  30 sccm Ar, 30 – 10 Torr  1.0 W 600 0 Iowa State University Optical and Discharge Physics Axial velocity (m/s) ICOPS06_MT_15

  17. POWER DEPOSITION: PLASMA, GAS HEATING 0.5 W 0.75 W 0.5 W 0.75 W 1.4 x 1013 2.6 x 1013 Max 875 K Max 675 K • Ionization efficiency increases with power due to larger excited state density • At higher temperatures and lower densities decouple power transfer from ions to neutrals. 100 1 Max 300 [e] cm-3 (logscale) (°K) Iowa State University Optical and Discharge Physics ICOPS06_MT_16

  18. POWER DEPOSITION: FLOW VELOCITY Power off 0.5 W 0.75 W Max 160 Max 300 Max 400 Vy in exit plane.  Increase in flow speed and thrust of 250% predicted with 0.75 W Iowa State University Optical and Discharge Physics MAX 0 ICOPS06_MT_17

  19. EFFECT OF GEOMETRY: CATHODE THICKNESS  No significant effect of electrode thickness on velocity profile.  Thicker electrode could lead to longer service life. • 30 sccm Ar, 30 / 10 Torr • 1.0 W Iowa State University Optical and Discharge Physics ICOPS06_MT_18

  20. EFFECT OF GEOMETRY: END CAP  Maximum increment in velocity for end cap thickness of 500 m.  Optimal thickness required to expand (and not cool) the hot gas. Iowa State University Optical and Discharge Physics  1W, 30 sccm Ar, 30/10 Torr ICOPS06_MT_19

  21. OPTIMAL GEOMETRY: DOWNSTREAM PRESSURE  5 Torr  10 Torr  5 Torr  10 Torr Max 1920 Max 1440 Max 6 x 1014 Max 2.5 x 1014 • Lower downstream pressure produces a more confined plasma (a bit counter-intuitive) • Higher power density leads to hotter neutral gas. 100 MAX 1 400 [e] cm-3 logscale Gas temp (°K)  1W, 30 sccm Ar Iowa State University Optical and Discharge Physics ICOPS06_MT_20

  22. CONCLUDING REMARKS • A microdischarge was computationally investigated for potential use in microthrusters. • At flow rates of a few 10s sccm and up to 1 W power, 0.1 – 0.5 mN of thrust were achieved. • Thrust specific power consumption of 0.1-0.2 N/kW is predicted in-line with other arc discharge thrusters. • Placement of electrodes is important with respect to confinement of plasma and possible cooling of gas. • Slightly embedded electrodes resulted in maximum incremental thrust for a given flow rate and power. Iowa State University Optical and Discharge Physics ICOPS06_MT_21

More Related