John Michael Fife and Matt Gibbons

1
Initial Use of a 3-D Plasma Simulation System for
Predicting Surface Sputtering and Contamination
by Hall Thrusters20 May 2002

• John Michael Fife and Matt Gibbons
• Air Force Research Laboratory
• Edwards AFB, CA
• Doug VanGilder and David Kirtley
• ERC, Inc
• Edwards AFB, CA

2
Outline

• Introduction Electric Propulsion
• Motivation
• Approach
• Preliminary Results
• Summary

3
IntroductionTypical Parameters of Small Thrusters
Ion Engine (NASA 30-cm NSTAR)
Hall Thruster (SPT-140 DM3)
Electric Propulsion Thrusters
4
MotivationEmission of High-Energy Particles
Electric Propulsion is ENABLING for New Missions.
However, High-Energy Particles are Emitted
Hall Thruster 300eV Xenon Ions (20 km/s)
5
MotivationRequired Air Force Capability
Need to Predict

• Contamination and Sputtering of Spacecraft
  Surfaces
• Solar Arrays
• Radiators
• Sensors
• Optics
• Cross-Contamination (S/C Clusters)
• Electromagnetic Interference
• Spacecraft Charging
• Observability

Sputtering
Hall Thruster Plume
Contamination
GEO Spacecraft
Hall Thruster Plume (SPT-140 DM3)
6
MotivationRequired Air Force Capability
A single FLEXIBLE, USABLE 3-D code which can be
used to model thruster plumes in ALL of the
following situations
FLEXIBLE

• 1. A spacecraft in LEO or GEO
• Most common application
• Greatest immediate need

• 2. Multiple nearby spacecraft in LEO or GEO
• Supports new AF thrusts
• Never-before modeled

• 3. Inside a vacuum test facility
• Necessary for strong code validation
• Independent utility Design of vacuum test
  facilities

Cryopanels
Thruster
Sensor
Sputtering
Contamination
Hall Thruster Plume
Beam Dump
Formation Flying S/C Constellation
Pumps
7
MotivationRequired AF Capability

• USABLE
• Typical simulation can be set up in lt 1 day by a
  user with lt 3 days training (no physics expertise
  necessary)
• Runs take lt 3 hours, but can be increased for
  higher fidelity
• Most input selections have a reasonable default,
  but complete user specification is allowed.

8
MotivationExisting Codes
Known 3-D Thruster-S/C Interaction Codes
1. Oh and Hastings -- MIT 2. Samanta Roy and
Hastings -- MIT 3. Wang -- JPL 4. Environment
Work Bench (EWB) -- SAIC 5. NASCAP 2K -- SAIC
None of these codes, in their current states,
have the functionality and/or flexibility to meet
AF requirements.
9
Thruster-S/C Interaction MS Approach
Approach Build a STANDARD FRAMEWORK into which
various types of 3D plasma simulations can be
easily developed and INTERCHANGED.
10
StatusModules Currently Functioning
COLISEUM Interpreter
LEVEL 0
GUI Front End
Hybrid-PIC-MCC
Prescribed Plume
PIC-PIC
LEVEL 1
Etc...
Ray Tracing
Hybrid-PIC-DSMC
Source
Space Env.
Surface
Etc
LEVEL 2
Volume
Detector
Material
ARROWS INDICATE DIRECTION OF MODULE DATA AND
FUNCTION ACCESS
Black Complete Grey Partially
Complete Light Grey Incomplete
11
Thruster-S/C Interaction MS Approach (Cont.)
surface.c

• Stores and manipulates surface data
• Triangular elements
• Automatic zone decomposition. Zone defined as
• Contiguous
• Radius of curvature gt x
• Calculated values
• Centroid
• Normal vector
• Storage and tagging of surface properties

12
Thruster-S/C Interaction MS Approach (Cont.)
ONE Model for Surface Sputtering
material.c

• User-definable
• Currently implemented Gardner et al.,2000

• Stores and manipulates material properties
• Material property database (material.txt)
• Contains all materials (surface and propellant
• Assumes default values for missing fields
• Material interaction database (mat-mat.dat)
• Contains all potential material interactions
• Supports multiple sputtering models

Y sputter yield (atoms/ion) E particle
energy q incidence angle (off-normal, radians)
Sputter yield for singly ionized xenon at E300eV
13
Thruster-S/C Interaction MS Approach (Cont.)
source.c

• Provides source boundary conditions at
  user-specified source elements
• Source velocity distribution

• Projected flux at point p

• Functions which are built into each source
  element record
• project() -- Returns the ray projection of the
  source velocity distribution function from the
  centroid of S to point p
• sample() -- Returns a random sampling from the
  source velocity distribution

14
ApproachCollaboration
15
Preliminary ResultsExecution Sequence
Define 3D Geometry SolidWorks
SolidWorks .geo Format
Mesh Surface COSMOS
ANSYS Format
COLISEUM
Tecplot Format
Output Visualization Tecplot
GEO spacecraft solid object generated using
SolidWorks
16
Preliminary ResultsGEO Spacecraft Case
COLISEUM results for generalized geosynchronous
spacecraft using prescribed_plume() with 200W
Hall thruster plume model by SAIC
coliseum.in Load GEO Satellite geometry and
apply 200W Hall thruster plume material_load
material.txt mat_mat.txt surface_load ANSYS
GEO_Sat.ANS prescribed_plume_load 2DCIRC
plume_SAIC_200W.dat 0.7 1.5 2.1 0 1
0 prescribed_plume SPUTTER surface_save TECPLOT2
GEO_Sat.dat FLUXNORMAL.XE DENSITY.XE
SPUTTER_RATE
17
Preliminary ResultsGEO Spacecraft Case (Cont.)
Roussel et al.
Constant Sputter Yield (Roussel mean)

• Roussel sputter model vs. constant sputter yield
  -- very different results
• Sputtering and deposition results show potential
  issues in using EP on spacecraft

18
Preliminary ResultsLaboratory Test Case
COLISEUM results for generalized laboratory
experiment using prescribed_plume() with 200W
Hall thruster plume model by SAIC
coliseum.in Load laboratory vacuum chamber
and apply 200W Hall thruster plume material_load
material.txt mat_mat.txt surface_load ANSYS
GEO_Sat.ANS prescribed_plume_load 2DCIRC
plume_SAIC_200W.dat 0.08 0.0 0.0 1 0
0 prescribed_plume SPUTTER surface_save TECPLOT2
GEO_Sat.dat FLUXNORMAL.XE DENSITY.XE
SPUTTER_RATE

19
Preliminary ResultsRay Tracing Module
COLISEUM results for test case geometry using
ray() with Faraday cup measurements of a 4.5 kW
Hall thruster plume.
coliseum.in Load test case and apply 4.5 kW
Hall thruster plume source material_load
material.txt mat_mat.txt surface_load ANSYS
EngineConfig_Test_Low.ANS source_specify 18
FLUX_PHI 0007 spt_140_flux.dat 12.0e-6 16000.0
1.0 ray sputter surface_save TECPLOT2
EngineConfig_Test_Low.dat FLUXNORMAL.XE
DENSITY.XE SPUTTERRATE

20
Summary

• MOTIVATION Air Force has specific requirements
  which cannot be fully met with a single unified
  software package
• APPROACH A new 3D plasma simulation system
  (COLISEUM) is being developed in-house
• Allows easy implementation of various plasma
  simulation modules
• Using object-oriented, supportable coding
  techniques
• National effort (Govt., Academia, Industry)
• Using COTS extensively
• STATUS
• Three Level 2 modules, and two Level 1 modules
  are complete and tested
• Current capabilities include
• Superposition of existing plumes onto surfaces
• Ray tracing of sources onto surfaces
• FUTURE WORK
• Improvement of Level 2 modules (including
  addition of new source types)
• Development of more advanced Level 1 modules
  (PIC, DSMC)