High Energy Plume Impingement on Spacecraft Systems

AFOSR Telecon

Jarred Alexander YoungFebruary 26, 2013

Current Events Beam Analysis

Looked at energy peaks for varying anode voltages Looked at current extraction capabilities as function of▪ Discharge Voltage▪ Accel Grid Voltage

Examined beam current as function of radial position

Performed sample testing at two different energy levels for 8 samples

Fixed all remaining ion engine glitches

Beam Testing

0 50 100 150 200 250 300 350

-5.00E-07

0.00E+00

5.00E-07

1.00E-06

1.50E-06

2.00E-06

2.50E-06

3.00E-06

3.50E-06

4.00E-06

I-V Curves at varying Anode Voltages

100 V120 V140 V160 V180 V200 V220 V240 V260 V

Discriminator Voltage (V)

Beam

Cur

rent

(A)

Beam Testing

0 50 100 150 200 250 300 350

-5.00E-07

0.00E+00

5.00E-07

1.00E-06

1.50E-06

2.00E-06

Beam Energy Distributions as a function of Anode Voltage

100 V120 V140 V160 V180 V200 V220 V240 V260 V

Particle Energy (eV)

Curr

ent

Spec

tral

Den

sity

(A/

eV)

Beam Testing

0 50 100 150 200 250 300 350

-5.00E-07

0.00E+00

5.00E-07

1.00E-06

1.50E-06

2.00E-06

2.50E-06

Comparison of I-V Curve vs. Collector Voltage, with respect to Discharge Voltage

30 V Discharge40 V Discharge50 V Discharge60 V Discharge70 V Discharge80 V Discharge

Discriminator Voltage (V)

Beam

Cur

rent

(A)

Beam Testing

0 50 100 150 200 250 300 350

-5.00E-07

0.00E+00

5.00E-07

1.00E-06

1.50E-06

2.00E-06

2.50E-06

I-V Curves with Respect to Accelerator Voltages at Constant Discharge Current

-100 V-200 V-300 V-400 V-500 V-600 V

Discriminator Voltage (V)

Beam

Cur

rent

(A)

Beam Testing

130 135 140 145 150 155 160 165 170 175

-5.00E-07

0.00E+00

5.00E-07

1.00E-06

1.50E-06

2.00E-06

2.50E-06

3.00E-06

Beam Current vs. Collector Voltage, 130-170 V

Closeup

Collector Voltage (V)

Beam

Cur

rent

(A)

130 135 140 145 150 155 160 165 170 175

-3.00E-07

-2.00E-07

-1.00E-07

0.00E+00

1.00E-07

2.00E-07

3.00E-07

4.00E-07

Ion Energy Distribution, 130-170 V Closeup

Ion Energy (eV)

Curr

ent

Spec

tral

Den

sity

(A/

eV)

Picoammeter switching

Picoammeter switching

Beam Testing Results Energy Range: 95-259 eV

Beam Current Max recorded: 3.5 μA (RPA)▪ Current should scale as ~(90mm/5mm)2

▪ Calculated total beam current: 1.134 mA▪ Calculated Current Density: 0.18 μA/mm2

▪ Calculated Flux Level: 1.11E18 #/m2-s Accel bias has strong effect on beam current

extraction Discharge bias has moderate effect on current

extraction, but may help improve beam focus

Material Testing Performed plume exposure

tests on Si coupons

Test Parameters Energy levels: 150 & 250 eV Exposure times comparable

to deposition of 50, 100, or 150 monolayers

Distance from Beam Exit: ~2 cm

Scanned samples for Argon and Tungsten atoms

Material Testing

Scanned coupons with Hitachi SU-70 Field SEM machine w/EDS

All 150 eV samples didn’t show any notable damage

Material Testing Results

Showed that samples may be doped with Argon Data not conclusive until EDS scan of

control sample is performed

Surface is relative undamaged from 150 eV for those exposure times

Future Work

Finish sample SEM scans and ship samples to ISU

Perform axial beam data collection Looking at distance from engine vs.

energy distribution

Compile data for PSU ion engine simulation