Thermal Plasma Measurements:Laboratory Experiment and In Situ Ionospheric Data

AbstractHemispherical electrostatic analyzers are a commonchoice for particle instrumentation suites in satellite andsounding rocket programs. We use an extension of thisdesign to measure the thermal particle population in theionosphere down to about 0.1eV. This paper will presentour efforts to interpret the thermal data in the presence of apotential sheath around a sounding rocket payload. Thedayside cusp/cleft auroral data used is that from theSERSIO (Svalbard EISCAT Rocket Study of IonOutflows) rocket, which was launched January 22, 2004 at8:57UT from Ny-Alesund, Svalbard, Norway. Theperformance of our thermal ion detectors will be presentedas well as our recent work with density extraction andtemperature measurements. Comparison of our data withEISCAT observations compels us to further investigateour detector response. Fabrication has begun on acalibration/testing facility that will quantify our thermalion analyzer performance. A microwave source will beused to create a low energy neutral plasma (tenths of aneV range). The design and proposed energy/sheath testingwill be outlined. This work will further influence SERSIOdata analysis and thermal particle detection - a keyelement to understanding bulk processes in theionosphere.

Kristen Frederick-Frost, Kristina LynchDartmouth College

Paul Kintner, Marc Lessard, Roger Arnoldy, Eric Klatt, Mark Widholm, Elizabeth MacDonald, NickolayIvchenko, Yasunobu Ogawa

Interpreting Data

Payload Potential

In Situ Data and All Sky Camera

Svalbard EISCAT Rocket Study of Ion Outflows

MISSION: Investigate ion outflows (increased ion velocityabove 500km in conjunction with enhanced electron or ion

temperatures) in dayside cusp/cleft region with in situ particleand wave instrumentation while simultaneously observing event

with incoherent scatter radar.

Unusually broad altitude coverage of thermal particlepopulation

ESR Particle Instrumentation

Hemispherical electrostaticanalyzers designed tomeasure ionospheric thermalions (Range 0.1-20 eV) andprecipitating electrons (5-16000 eV)

Retarding Potential Analyzerdesigned to measureionospheric thermalelectrons. Range 0-3 eV.

42m field-aligned radar located inLongyearbyen used to detect outwardion flow

Given the ACS failure, we havelimited directional information.Efforts have been concentratedon energy information andtemperature extraction.

Temperatures of the suprathermal andprecipitating populations are obtained fromthe hemispherical electron detector data.

In addition to ion coretemperatures, the thermal iondata can also be used to extractpayload potential. The effects ofpayload ram must be includedfor temperature accuracy.

Ram/Flow Effects

V1

V2

Vram

Note the differencein distance betweenthe energy contoursif the collimatingdetector aperture isparallel orperpendicular to theram direction. Theworst case is theperpendicularaperture, giving anion temperature thatis too high.

ESR Line ProfilesCourtesy of Y. Ogawa

TeTi

In Situ Data

Image courtesy of Huigen Yang andZejun Hu, Polar Research Institute ofChina

ViNe

ELEPHANTExperimental Low Energy Plasma for

Hemispherical Analyzer Nominal Testing

Application•Chamber Dimensions dxl - 1.2x1.5 m (24-30 lD )

•Base Pressure ~10E-8 Torr•Operational Pressure ~10E-5 Torr•Neutral lmfp ~ 10m, unn ~ 45 Hz

•Ions unmagnetized•Electrons magnetized

Microwave Plasma SourceBowles, Duncan, Walker, Amatucci, Antoniades, 1996

ElectronsEe ~ 0.5 eVVthe ~ 3E5 m/swce ~ 1E7 Hzre ~ 0.03 m

Nitrogen IonsEi ~ 0.05 eV

Vthi ~ 450 m/swci ~ 370 Hz

ri ~ 1.2 m

Plasma Density 104-106 1/ccB = Earth Field

lD ~ 0.5 cm - 5 cm

ERPA cross-section

Entrance +4V

Selection screen -2.6V to +1.4V

Collimator +4V

Anode +7V

2.2 in

In Situ Data and EISCAT Radar Data

†

eV = -kTe ln

kTe

2pme

kTi

2pmi+

v 2

16+

iph

4ne-

I4pr2ne

Laboratory Experiment

Areas of Investigation

•Quantify thermal particle detector response and identifylowest detectable energy

•Investigate sheath formation variables such as neutral densityand particle energy

•Study the shape and structure of the potential in the boundaryregions between plasma and detectors with and without forcedbias.

• How does this inform the SERSIO thermal particle dataanalysis?

Thermal particlecalibration facilitycurrently underconstruction.

Designed to utilize amicrowave plasmasource for chargingand float studies.

Conclusions•SERSIO sees structured regions of high Ti(1.5 eV) which we interpret as thebeginning of SCIFER-like BBELF TIAevents

•Quantification of in situ measurements ofthe thermal particle population requirescareful measurement of flows andpotentials around spacecraft.

•As part of this continuing effort, we aredeveloping a thermal plasma source andcalibration facility.

•Data indicate ~50km columns ofhigh Ti at high altitude ~700km

•High Ti events are not Tedependent.

•Largest Ti event associated withhole in the electron precipitation

•High Ti events coincident withwave enhancements seen by Cornell

•Background ~2eV ion tail seenthroughout the flight

•Lower altitude signature of BBELFconics seen in SCIEFER mission

•Spacecraft potential was calculated using Te and Ti from thethermal particle data.•Difference between calculated and observed fsc is Te, notdensity dependent.

•Thus we need to include effects of plasma flow in ourcalculation of fsc.

Fahleson, 1967

UiO Camera,Ny-Alesund

Launch

TOF=410s