High Energy Plume Impingement on Spacecraft Systems

AFOSR Telecon

Jarred Alexander YoungMay 13, 2013

Current Events

Beam Analysis Looking into CEX environment for multiple

distances and pressures Hi-definition energy peak scans Ion Reflection testing

Material Experiments Completed all tests with Si coupons (150 &

250 eV) Completed first round of Aluminum sample

testing

CEX Analysis

Objective: Conduct RPA analysis on ion beam at multiple pressures

Small I-V humps observed during testing of beam for axial profiling

RPA scans centered around these regions to examine beam behavior

0 50 100 150 200 250

-5.00E-07

0.00E+00

5.00E-07

1.00E-06

1.50E-06

2.00E-06

2.50E-06

I-V Comparisons as function of Pressure, Distance: 59.97 mm

Voltage (V)

Curr

ent

(A)

CEX Analysis

-5 0 5 10 15 20 25 30 352.35E-06

2.36E-06

2.37E-06

2.38E-06

2.39E-06

2.40E-06

2.41E-06

2.42E-06

I-V Curve, Distance: 59.97 mm, Pressure: 3.6E-4 torr

Collector Voltage (V)

Beam

Curr

ent

(A)

CEX Analysis

-5 0 5 10 15 20 25 30 350.00E+00

2.00E+00

4.00E+00

6.00E+00

8.00E+00

1.00E+01

1.20E+01

Energy Distribution, Distance: 59.97 mm, Pressure: 3.6E-4 torr

Particle Energy (eV)

Curr

ent

Spectr

al D

ensit

y (

A/V

)

RPA Results Summary

Distance (mm)

Beam Energy, Pressure 1(eV)

Current Spectr

al Density

, Pressur

e 1 (A/eV)

Beam Energy CEX,

Pressure 1(eV)

Current Spectr

al Density

CEX, Pressur

e 1 (A/eV)

Beam Energy, Pressure 2(eV)

Current Spectr

al Density

, Pressur

e 2 (A/eV)

Beam Energy CEX,

Pressure 2(eV)

Current Spectr

al Density

CEX, Pressur

e 2 (A/eV)

19.28 mm

147.48 1.06E-8 12.238.17E-

10151.44 1.08E-8 2.04 1.52E-9

40.66 mm

149.67 1.07E-85.21(5.5

2)

5.38E-10

(4.52E-10)

152.39 6.98E-92.11(2.4

1)

1.85E-9(1.18E-

9)

59.97 mm

147.48 1.08E-8 8.198.65E-

10151.80 6.93E-9 2.27 3.54E-9

80.71 mm

149.49 1.09E-8 ? ? 153.38 6.09E-9 ? ?

CEX Analysis

Third pressure scan reveals interesting beam current structure

Larger CEX energies observed at 14 mtorr than previous pressures ~25 eV More likely than “main

energy” ions to occur

0 20 40 60 80 100 120 140 160 180 200

-5.00E-07

0.00E+00

5.00E-07

1.00E-06

1.50E-06

2.00E-06

2.50E-06

I-V Comparison at multiple pressures

0.40 mtorr4.1 mtorr14 mtorr

Collector Voltage (V)

Beam

Curr

ent(

A)

CEX Analysis

0 5 10 15 20 25 30 35 40 45 500.00E+00

1.00E-07

2.00E-07

3.00E-07

4.00E-07

5.00E-07

6.00E-07

7.00E-07

I-V Curve, Distance: 57.09 mm, Pressure: 13.9 mtorr

Collector Voltage (V)

Beam

Curr

ent

(A)

CEX Analysis

0 5 10 15 20 25 30 35 40 45 50

-1.00E-09

-5.00E-10

0.00E+00

5.00E-10

1.00E-09

1.50E-09

2.00E-09

2.50E-09

3.00E-09

3.50E-09

Energy Distribution, Distance: 57.09 mm, Pressure: 13.9 mtorr

Particle Energy (eV)

Curr

ent

Spectr

al D

ensit

y (

A/V

)

RPA Results Summary 2

Pressure(mtorr)

Beam Energy

(eV)

Current Spectral Density, (A/eV)

Beam Energy

CEX, (eV)

Current Spectral Density

CEX, (A/eV)

0.40 147.15 8.47E-9 10.38 4.11E-10

4.1 150.3 6.66E-8 2.92 3.72E-10

14 144.29 5.83E-9 27.65 (15.53)

3.12E-9(1.04E-9)

Ion Reflection Testing

RPA pointed at right wall of chamber, about 70 mm away from beam exit

Preliminary Results Lower pressure: electron

current dominated Higher pressure: 5 nA of

ion current reported over small voltage step▪ Could be mechanical noise▪ Energy around 10 eV

0 20 40 60 80 100 120 140 160 180 200

-1.00E-08

-9.00E-09

-8.00E-09

-7.00E-09

-6.00E-09

-5.00E-09

-4.00E-09

-3.00E-09

-2.00E-09

-1.00E-09

0.00E+00

I-V Curve, Pressure: .38 mtorr

Voltage (V)

Curr

ent

(A)

Ion Reflection Testing

RPA pointed at chamber door

Preliminary Results Lower pressure: ~0.55

nA of electron current Higher pressure: ~0.86

nA of electron current

Conclusion: Ion reflection not a factor

0 20 40 60 80 100 120 140 160 180 200

-1.00E-09

-9.00E-10

-8.00E-10

-7.00E-10

-6.00E-10

-5.00E-10

-4.00E-10

-3.00E-10

-2.00E-10

-1.00E-10

0.00E+00

I-V Curve, Pres-sure: .42mtorr

Voltage (V)

Curr

ent

(A)

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

Si Material Testing

Tested all 150 eV and 250 eV samples

Sample 3 had multiple broken tips on top row, but majority of tips were undamaged

Broken tips doped with Aluminum according to EDS

All samples showed elevated levels of Argon Can’t confirm because no

before scans were taken

All samples returned to ISU for APT testing

Al Material Testing

Objective: Expose Al samples to ion beam at: Energy levels: 150 eV, 250

eV Exposure durations: 1, 2, &

3 hours

Aluminum 1350-O used for samples

Three types of observation Photographic/Visual SEM Imaging & EDS Contact Profilometry

Al Material Sample Results

Surface modifications Pitting and slight polishing

effects for low duration exposure

Polishing effect for higher exposure times with minor pitting

EDS scans showed evidence of Chromium Al 1350-O has low

concentration of Cr (.01%) Could be sputtered material

from RPA grids Average Concentration: 0.4%

(Error: 0.1%)

Al Sample “After” Photos

Sample 1: 150 eV, 1 hour

Sample 2: 150 eV, 2 hour

Sample 3: 150 eV, 3 hour

Sample 4: 250 eV, 1 hour

Sample 5: 250 eV, 2 hour

Sample 6: 250 eV, 3 hour

Future Work

Adapt experimental procedure for second batch of sample experiments

Work on joint abstract for Winter AIAA conference