High Energy Plume Impingement on Spacecraft Systems

AFOSR Telecon

Jarred Alexander YoungOctober 2, 2013

Current Events Langmuir Probe testing

Probes completed and setting up for electron temperature scanning

Power Supply High voltage supply for ion source currently being

designed▪ Based on COTS parts

Plasma Environment Looking into surface potentials of spacecraft in near-LEO

and GEO orbits Researching surface charging effects

Langmuir Probe Test Arrangment

TOP VIEW SIDE VIEWz z

x y

i+ i+

Probe Mount

Probe

RPA Configurations for Beam Testing

Configuration A

Configuration BCEX testing from beam scattering

Near-Earth Plasma Environment

Plasma environment on orbit mostly consists of atomic hydrogen and oxygen

Densities of plasma lower as altitude increases Temperature increases with altitude

Source: Spacecraft Charging and Hazards to Electronics in Space (Mikaelian, 2001)

Near Earth Plasma Environment

The Plasmasphere, which extends to 4 earth radii from the equator, is made up of a dense plasma with an electron temperature of roughly 1 eV

GEO usually lies outside of the Plasmapause, where the density of the plasma environment drops, but subsequently has a higher electron temperature Plasmapause location varies based on time of day Plasmapause environment has non-collisional plasma, but causes electrically coupled

charging on spacecraft

Source: The Near-Earth Plasma Environment Plaff (2012)

Near-Earth Plasma Environment

Extrapolated data points from Denton, et al. (1999)

Electron temperature varies from daytime to night time and magnetic latitude

Data was only taken up to ~8500 km

Data used to calculate sheath potentials on spacecraft

Electron Temperature Data

0 1000 2000 3000 4000 5000 6000 7000 8000 90000

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

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Electron Temperature vs. Altitude, 15ᵒ Magnetic Lat-itude, Daytime

Low Solar ActivityHigh Solar Activity

Altitude (km)

Elec

tron

Tem

pera

ture

(eV

)

Old Wall Potential Data

0 1000 2000 3000 4000 5000 6000 7000 8000 90000

0.5

1

1.5

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Wall Potential of Spacecraft vs. Orbital Altitude, 15ᵒ Magnetic Altitude, Daytime

Low Solar ActivityHigh Solar Activity

Altitude (km)

Wal

l Pot

entia

l, Ab

solu

te V

alue

(V)

Investigation into Al Sample Results

Recent Al sample experiments showed no material removed, yet evidence of smaller, lighter elements reaching surface of samples

Gregov and Lawson (1971) showed that significant damage was not caused to W samples until around 400 eV with Ar+

Large number of vacancy clusters were created where atoms were missing or misplaced due to ionic impact.

Results also showed misplaced atomic material being diffused to the surface during the annealing process

Investigation into Al Sample Results

Shin (2002) showed that Ar+ could cause sputtering in Si samples at energy ranges of 500 eV and more through MEIS testing At 500 eV, a sputter depth of 5.1 nm was

achieved

Takeaway Ion beam needs to be more energetic to

actually cause material damage

Investigation into Al Sample Results

NASA Handbook on Surface Charging References penetration

depth of Aluminum according to Mass Stopping Power (concept used in radiation therapy)

Based on graph and projected calculations, our ion beams have only penetrated the samples by 5 Å▪ Can we confirm this using a

ReaxFF simulation?

Future Work Work on electron temperature gathering for PSU group

Data will be included into plasma simulation

Work on next phase of material testing Develop power supply solution for high energy beam testing Determine energies for low energy testing▪ Go through SCATHA and ATS-6 mission data for plasma parameters

in GEO

Work on SciTech paper More Si samples to be tested? More data from ISU group from APT?