[american institute of aeronautics and astronautics 37th joint propulsion conference and exhibit -...

(c)2001 American Institute of Aeronautics & Astronautics or Published with Permission of Author(s) and/or Author(s)' Sponsoring Organization.

At A A A01-34126

AIAA 2001-3351

Ion Flux, Energy, and Charge-StateMeasurements for the BPT-4000 HallThruster

James E. Pollard and Kevin D. DiamantThe Aerospace Corporation, El Segundo, CA

Vadim Khayms and Lance WerthmanLockheed Martin Space Systems, Sunnyvale, CA

David Q. King and Kristi H. de GrysGeneral Dynamics, Redmond, WA

37th AIAA/ASME/SAE/ASEEJoint Propulsion Conference & Exhibit

8-11 July 2001Salt Lake City, Utah

For permission to copy or to republish, contact the copyright owner named on the first page.For AIAA-heid copyright, write to AIAA Permissions Department,

1801 Alexander Bell Drive, Suite 500, Reston, VA, 20191-4344.


AIAA 2001-3351

ION FLUX, ENERGY, AND CHARGE-STATE MEASUREMENTS FOR THE BPT-4000 HALLTHRUSTER

James E. Pollard and Kevin D. DiamantThe Aerospace Corporation, P.O. 92957 - M5/754, Los Angeles, CA 90009

Vadim Khayms and Lance WerthmanLockheed Martin Space Systems, 1111 Lockheed Martin Way, Sunnyvale, CA 94086

David Q. King and Kristi H. de GrysGeneral Dynamics Ordnance and Tactical Systems, P.O. Box 97009, Redmond, WA 98073

ABSTRACTThe BPT-4000 Hall current thruster was characterizedwith respect to the angle-dependent ion flux, ionenergy, and charge-state distributions at 1.0 m from theexit plane with discharge powers of 2.0-4.5 kW anddischarge potentials of 200-500 V. At 3.0 kW and 300V the half-angles containing 95% and 99% of theplume current were 55° and 83° for ions having anenergy-to-charge ratio of E/q > 20 V, and the ratio oftotal plume current to discharge current was 63%. Theprimary ion peak at E/q = 284 V was detected out to80° from centerline. An intermediate energy peakshifted from 200 V to 50 V with increasing angle andwas assigned to elastically scattered primary ions. Athigher angles this feature merged with the low energyion population (< 50 V) produced by charge-exchangereactions. The flux was dominated by low-energy ionsat angles beyond 50° from centerline. Peaks in the E/qdistribution above 350 V were due to fast multiply-charged ions undergoing charge-decreasing collisions.The charge-state distribution was not stronglydependent on angle or energy between 30° and 75°,with Xe+2 contributing 19%-26% of the current andXe+3 contributing 5%-9%. Langmuir probe current vs.voltage curves at 0.56 m from the exit plane yielded theelectron density, temperature, and plasma potentialfrom least-squares fitting with the assumption of aMaxwellian speed distribution.

INTRODUCTIONXenon Hall current thrusters (HCTs) have beenselected as an alternative to the hydrazine arcjetpropulsion systems now offered on Lockheed Martingeosynchronous satellites, in line with the industry-wide trend toward higher specific impulse technologyfor stationkeeping, repositioning, and partial orbitinsertion. The ionized plume of an HCT is aremarkably complex environment that must be wellunderstood to predict and mitigate possible effects onthe host spacecraft such as erosion of solar panels andrefraction of communication beams. Although the fluxof energetic ions drops rapidly with increasing anglerelative to thruster centerline, the periphery of theplume is sufficiently erosive to remove measurableamounts of material from solar panels over long

duration burns. Sputtering rates depend on the ionkinetic energy and charge-state distribution.Communication signal propagation is influenced by theelectron number density, which depends on angle anddistance from the thruster. Charge buildup andneutralization on the spacecraft are greatly affected bythruster operation, because ion and electron densities inthe plume are far higher than the ambient plasmadensity at geosynchronous altitude. The choice of HCTplacement and orientation on the spacecraft is driven bythe predicted magnitudes of these effects. To addressthese issues, plume effects for 2-5 kW HCT's havebeen evaluated at several facilities.1 '2 '3-4 '5

This paper describes measurements of the angle-dependent ion flux, ion energy, charge-statedistributions, and Langmuir probe characteristics in theplume of a 4.5-kW class HCT. Data were recordedwith discharge powers of 2.0-4.5 kW and dischargepotentials of 200-500 V, with the most comprehensivemeasurements at 3.0 kW and 300 V. Two productsderiving from this work are (1) a ground-test databasethat enables a prediction of on-orbit plumecharacteristics by means of mathematical modeling, and(2) a spacecraft material erosion model validated withsputtering rate measurements for collimated materialsamples. Modeling of the plume/spacecraft interactionsis being done by Lockheed Martin, SAIC, and theUniversity of Texas.6'7 Exposures of spacecraftmaterial samples and solar cells were performedconcurrently with the present measurements, and thetest results are reported separately.8'9

TEST FACILITYA laboratory model BPT-4000 HCT from GeneralDynamics10 was tested at the Aerospace Corporation ina 2.4-m diameter x 9.8-m long vacuum chamber havingfour re-entrant cryopumps plus one 4-ft diametercryotub. Two re-entrant pumps were suspended behindthe thruster, and two others were in the downstreamsection of the chamber which was lined with carboncomposite sheets and flexible graphite to minimize theyield of sputtered material. The base pressure with nogas load was l.OxlO"7 torr after 24 hours of pumping,with 90% of the residual gas being water vapor, and theremainder being air and hydrocarbons.

Copyright © 2001 by The AerospaceCorporation. Published by theAmerican Institute of Aeronautics andAstronautics, Inc., with permission.

1

American Institute of Aeronautics and Astronautics


A model EMHP 600-50 discharge supply andadditional laboratory supplies were used to operate theBPT-4000, while an automated data acquisition systemrecorded thruster telemetry and provided interlockprotection if specified process limits were exceeded.The discharge filter circuit was located outside thevacuum chamber and was connected to the thrusterusing cables with a total length of 3 m. Current wasmeasured by a Hall-effect sensor having a 150-kHzbandwidth so that discharge oscillations could bedisplayed on an oscilloscope. Flow rates were set bythermal mass-flow controllers and were calibratedbased on the pressure rise into a 1-liter volume.Diagnostic probes were mounted on a rotating arm forsampling the plume over a ± 140° angular rangerelative to centerline. A three-axis motorized translatorwas used to position the thruster as needed for each ofthe plume measurements.

Telemetry values at three operating points are listed inTable 1. Throughout this test the telemetry remained ingood agreement with previous measurements byGeneral Dynamics. During each initial firing afterexposure to atmosphere it was necessary to run for 3-4hours to degas the thruster while the operatingparameters converged on their nominal values.Degassing was characterized by a decreasing dischargecurrent at constant xenon flow rate, a higher amplitudeof discharge current oscillations, and increased plumedivergence relative to the fully warmed up thruster. Aslong as the chamber was not vented, subsequent cold-starts required about 1.5 hours to achieve steady-stateoperation.

Table 1. BPT-4000 telemetry at three operating points.

Discharge power (kW)Discharge potential (V)Discharge current (A)Cathode potential(V)Anode flow rate (mg/s)Cathode flow rate (mg/s)Corrected pressure (10~5 torr)

3.030010.0

-12.210.71.080.96

4.530015.0-9.814.81.511.33

3.04007.5

-11.48.4

0.840.71

lonization gauges at each end of the chamber displayedidentical pressure readings with a cold flow of xenon,while during thruster operation the downstream gaugeread higher than the upstream gauge by a factor of 1.7because of the directed flow of propellant. Anassessment of facility effects was needed forextrapolating the ground-test results to on-orbitconditions, for which purpose a supplementary flow ofxenon was admitted through a side port to raise thebackground pressure by a factor or 2x or 5x duringsome of the measurements.

Residual gas analysis of the vacuum chamber showedthat only the mass peaks at 2, 18, and 28 amu wereenhanced significantly by thruster operation. Based onthe relative amounts of daughter ions at 12, 14, and 16amu, the enhanced signal at 28 amu was predominantlyCO rather than N2. Hydrogen (2 amu) and CO (28amu) showed a prompt response during dischargestartup and shutdown that indicated a plasma-assistedchemical reaction between adsorbed water and thecarbon-covered surfaces. Water vapor (18 amu)changed on a slow time scale that suggested productionby heating the internal surfaces of the vacuum chamber.

ION FLUXIon flux was measured by a probe having a positively-biased collector inside a negatively-biased enclosurewith a grid-covered entrance aperture, as shown in Fig.1. To prevent electrons from reaching the ion collector,the grid and enclosure were at -20 V, while thecollector potential ranged from 0 V to +100 V. Theoptical transparency of the grid was measured as 43%at normal incidence, and this value was assumed toequal the transmission for ions.

Initially we surveyed the angle-dependent flux andenergy distributions for a range of operating pointsusing an uncollimated flux detector and a deflectionanalyzer mounted on the rotating arm at 1.0 m from theexit plane. A few measurements were made with anuncollimated probe facing away from the HCT to assessthe non-directional ion flux, and this gave a signal thatwas at least 100 times less than with the forward facingprobe at all angles. Subsequently we placed the twoflux probes on the arm at 1.0 m from the exit plane, onefully exposed to the plume and the other inside agraphite collimator, as shown in Fig. 1. The collimatorwas identical to those holding the material samples inplume exposure tests,9 and it had no vent ports otherthan the entrance aperture. During the exposure tests,two additional flux probes were placed in graphitecollimators on the sample rakes at ± 55° from thrustercenterline. This arrangement provided an accuratemeasurement of the ion flux incident on the samplesand an assessment of the flux attenuation factor due tothe collimators.

Probe currents of 0.1 iiA to 5.0 mA were recorded bydigital multi-meters, using 1.25° steps for the flux vs.angle scans. Dividing the measured current by thecollector area (3.88 cm2) and by the grid transmission atnormal incidence (43%) converted the raw data to ionflux. Values obtained in this way were directlyapplicable to the fast ion flux that originated near theexit plane. For slow ions that originated from a largersource volume, one must consider the angularacceptance of the probes. Mesh transparency decreaseswith increasing off-normal incidence, effectively



reaching zero at 70° and resulting in a solid-angle viewfactor of 0.16 for the uncollimated probe. Thecollimated probe had an 8° acceptance half-angle and asolid-angle view factor of 0.0021. These view factorsare the fraction of the total flux that probes woulddetect if exposed to a random, omni-directional source.

Figure 2 shows the angle-dependent flux measured bythe rotating probes with a collector bias potential of 0V. A dip in the ion flux within ± 4° of centerline was aconsequence of the annular source geometry of theHCT. Comparing data sets from the two rotatingprobes, the collimator excluded 30% to 90% of the totalion flux depending on the angle. The ratio ofcollimated to uncollimated flux is shown in Fig. 2.Close to centerline the dynamic pressure of neutralxenon inside the graphite tube enhanced the probabilityof ion-neutral collisions. For this reason, theattenuation scaled with incident ion current within 25°from centerline, leading to a double-humped minimumin the ratio of collimated to uncollimated flux. Atangles beyond 40° an increasing fraction of the totalflux was at low energy as a result of ion-neutralcollisions in the plume, and the source volume extendedwell beyond the exit plane. Hence the collimatorattenuated the ion flux at high angles because of thenarrow field of view rather than because of the dynamicpressure. Increasing the collector bias potential of theuncollimated probe demonstrated that the flux wasdominated by low-energy ions at angles beyond 50°from centerline, as seen in Fig. 3. For example, 87% ofthe total flux near centerline was at energies above 100eV, while at 70° only 1% of the flux was above 100 eV.A shoulder in the flux distribution between 60° and 80°was composed of ions having E/q < 50 V.

A high degree of flux symmetry about the centerlinewas seen throughout the test. Under the assumption ofan axisymmetric plume, the angle-dependent ion fluxj(6) can be integrated to yield the total plume ioncurrent J at 1.0 m from the exit plane,

140°

J = R (1)<9=0°

where R= 1.0 m and A0 = 1.25°. Table 2 shows theuncollimated probe results with a collector potential of+20 V for all of the operating points studied here. Thismeasurement excludes ions with E/q < 20 V. The ratioof plume ion current to discharge current variedbetween 53% and 67% depending on the operatingpoint. A general trait of Hall thrusters is that about one-third of the electron current emitted by the cathode willflow into the discharge channel and be collected by theanode, while the remaining two-thirds will flow awayfrom the thruster to neutralize the ion beam. The ion

current in the plume would then be about two-thirds ofthe discharge current, as is seen in our results.

Facility background pressure causes the fraction of totalcurrent carried by low-energy charge-exchange ions toincrease with distance. The flux probe signal willdecrease with distance because the solid-angle viewfactor discriminates against low-energy ions. Toevaluate the loss of fast ions from charge-exchangecollisions, the angle-dependent ion flux was recorded asa function of xenon background pressure at 3 kW and300 V, and the results are listed in Table 3.Extrapolating the plume ion current to zero backgroundpressure yielded 6.3 A, compared with the value of 5.4A measured at minimum background pressure(0.96x10"5 torr). Xe+1 at 300 eV has a charge-exchangecross section of 55 A2 which leads to a reactionprobability of 16% for a 1.0 m path length at 0.96x10~5

torr.11 This would decrease the fast ion current from6.3 A at the exit plane to 5.3 A at 1.0 m. Hence theextrapolation of the measurements to zero backgroundpressure is consistent with the cross section data. Theratio of plume ion current to discharge current was 63%at zero background pressure, which was also thefraction of the electron current emitted by the cathodethat was needed for ion beam neutralization.

Integrating the angle-dependent ion flux yields theplume current contained within a given half-angle, asshown in Fig. 4 at 4.5 kW with a range of dischargepotentials. The uncollimated flux probe was used witha collector potential of +20 V. The results arerepresented in Tables 2 and 3 by listing the half-anglescontaining 95% and 99% of the ion current. Figure 4illustrates how plume divergence varies with dischargepotential when the collector is set to exclude most ofthe low-energy ions that predominate at angles beyond50°. (For an HCT at a given power level, higherdischarge potential generally means higher specificimpulse.) Among the operating points shown in Fig. 4at constant discharge power, those with lower dischargepotential gave lower divergence. At 250 V and 300 Vthe ion flux at angles beyond 40° was actually less thanthe flux measured at 350 V, 450 V, and 500 V, eventhough the propellant flow rate and discharge currentincreased as discharge potential was lowered.

At 3 kW, 300 V and minimum background pressure,the 95% and 99% current half-angles were 50° and 79°for ions having an energy-to-charge ratio of E/q > 20 V.From Table 3, the extrapolation to zero backgroundpressure shifted the half-angle outward by 4°-5° relativeto the measurements at minimum background pressure.Table 3 also lists the integrated ion current and half-angles for collector potentials of 0, +20, +50, and +100V with a 3.0 kW, 300 V discharge. We made anarbitrary choice of +20 V collector potential for



computing the plume ion current and half-angles asfunctions of operating point. For a 3.0 kW, 300 Vdischarge, increasing the collector potential to +50 Vdecreased the plume ion current from 5.4 A to 5.0 Aand narrowed the 95% current half-angle from 50° to39°.

ION ENERGYSeveral recent investigations of ion energy distributionsin HCT plumes have been reported.5'12'13'14 In thepresent experiment two kinds of probes were used tospan the full range of energies. The retarding potentialanalyzer (RPA) and deflection analyzer shown in Fig. 1were used with an angular step size of 5°, although theangular data in this paper are plotted in 10° incrementsfor clarity. A picoammeter/voltage source scanned thevoltage and recorded the ion current for each analyzer.With a sufficiently high potential on the RPA collector,a large negative current was observed because electronspenetrated the mesh, and this limited the maximumenergy that could be measured. Subsequent tests in ourlaboratory have used a modified RPA design thatallows an energy scan from 0 V to 500 V to be recordedwith a single detector.

The collimated RPA measured the absolute differentialflux (j.tA/cm2/V) vs. energy-to-charge ratio with goodsensitivity to intermediate energies (E/q = 50 to 330 V),as shown in Fig. 5. The primary ion peak at 284 V wasdetected out to 80° from centerline. A feature between50 V and 200 V that moved to lower voltage withincreasing angle was assigned to elastically scatteredprimary ions.6 Beyond 80° the spectrum wasdominated by charge-exchange ions with E/q < 50 Vthat arose from neutral atoms losing an electron to apassing ion and being accelerated by the potential dropbetween the plasma and the grounded probe. Figure 5represents the energy distribution impinging on thecollimated material samples in erosion testing. We alsomeasured the distribution with the uncollimated RPA.The latter displays elastically scattered primary ions at alevel similar to the collimated probe, but low-energycharge-exchange ions are increased by a factor of 10-100 compared with the collimated RPA.

An electrostatic deflection analyzer5 mounted on therotating arm gave the relative differential flux vs. E/qwith good sensitivity to the higher energy portion of thedistribution (50 V to 900 V), as shown in Fig. 6. Thedeflection analyzer had a large enough angular aperture(4° half-angle) to view the entire exit plane area of thethruster at a distance of 1.0 m. In addition to theprimary ion peak, the E/q distribution included peaksabove 350 V that arose from fast multiply-charged ionsundergoing charge-decreasing collisions.5'12 Theirintensities here were 100-200 times less than that of theprimary ion peak. In a previous study in this facility

using a different Hall thruster, the high-energy peakswere 200-1000 times less than the primary ion peak.5Charge-exchange reactions leading to the observed E/qvalues must occur downstream of the acceleration zoneand must involve relatively little momentum transfer toyield the observed widths.

Relative differential flux data from the deflectionanalyzer (Fig. 6) can be put on an absolute scale bycomparing the signal level with the corresponding datafrom the collimated RPA (Fig. 5). Figure 7 shows thecomposite energy distribution from the two data setsplotted on axes having the same span as the deflectionanalyzer data in Fig. 6. The voltage where the spliceoccurred was different for every angle, but the databelow 290 V are all from the RPA, and the data above310 V are all from the deflection analyzer. Except forthe low-energy cut-off in the deflection analyzertransmission, the relative differential flux curves (Fig.6) have shapes that are remarkably similar to theabsolute differential flux curves measured with thecollimated RPA (Fig. 7). The favorable comparison ofmeasurements using different probe designs impliesthat Fig. 7 is an accurate representation of the flux andenergy distribution seen by the material samples inplume exposure tests.

CHARGE STATESAngle-dependent charge-state distributions weremeasured using a compact time-of-flight (TOF)spectrometer (Fig. 1) that was derived from an earlierhigh-resolution TOF developed for gridded ionthrusters.15 The entrance aperture was 77 cm from theexit plane. A pulsed electric field produced a packet ofions with a duration of 2-4 jis that passed through afield-free drift region to be detected by an electrostaticdeflector (AE/E ~ 0.06) and an ion multiplier.Amplified signals were recorded by a digitaloscilloscope that averaged the waveform for 2000sweeps at each angle.

Ions at a given E/q had velocities proportional to q]/2,and hence the charge states were dispersed in time. Theamplitude and duration of the pulsed electric field weretuned to control the sensitivity and resolution of thespectrometer. Settings were chosen to produce flat-topped peaks with intensities proportional to thefractional current of each charge state. The deflectorwas normally set to transmit the primary peak in the E/qdistribution, but reducing the repeller voltage allowed ameasurement of the charge-state distribution for lowerenergy ions.

Unlike the other plume diagnostics described here, theTOF spectrometer had a field of view that includedonly a fraction of the HCT exit plane. The viewingdirection could be moved across the exit plane by



tuning the pulsed electric field, and we attempted tomaximize the signal for each spectrum by centering onthe discharge annulus on the side nearest the detector.Subsequent tests in our laboratory have used a charge-state analyzer with a wider field of view to eliminatethis step.

The TOP spectrum in Fig. 8 was measured at 40° fromcenterline and showed significant amounts of doubly-and triply-charged xenon that must be taken intoaccount in the erosion model. A low-amplitude signalduring the first 4 JLIS was caused by capacitive pickup ofthe pulsed electric field. The relatively short driftdistance allowed a complete separation of Xe+I fromthe multiply-charged ions, but the TOP signals for Xe+2,Xe+J, and Xe+4 were partially overlapped. Figure 9shows the charge-state fractional currents measuredbetween 10° and 75° relative to thruster centerline,mostly for primary ions at E/q ~ 300 V with additionaldata points for 200 V and 100 V measured at a fewangles. The charge-state distribution was not stronglydependent on angle or E/q between 30° and 75°: Xe+2

contributed 19%-26% of the current and Xe+3

contributed 5%-9%. Fractional currents will vary as afunction of distance, because the cross section forresonant charge exchange with neutral Xe is higher forXe+1 (55 A2) than for Xe+2 (25 A2).11 The distributionat the exit plane was not measured, but we expect ahigher fraction of Xe+1 at the exit plane than wasobserved at 1.0 m.

LANGMUIR PROBEA limited set of measurements was performed with aheated Langmuir probe to evaluate this technique inpreparation for future studies with HCT's. Thecollecting area of the probe was a 1.1-mm diameter, 21-mm long stainless steel tube that was held at 350°C bymeans of an internal tungsten heater and thermocouple.Amatucci et al.16 found that surface contaminants on aLangmuir probe wire adversely affected the accuracy ofelectron temperature and plasma potentialmeasurements, but heating the wire above 300°Cremedied the problem. Our probe was mounted on arotating arm at a radius of 0.56 m from the center of theexit plane, and current vs. voltage curves were recordedin 10° angular steps.

For a Maxwellian electron speed distribution, the initialrise of the J-V curve has an exponential dependence,17

- l .602xl0-'2

'« y (2)

-F/7 for V<Vp

where D and L are the probe diameter and length, «e isthe electron density, Tc is the electron temperature, andVp is the plasma potential. Semilog plots of the electroncurrent and its first derivative as functions of probepotential show satisfactory agreement with the linearbehavior predicted by Eq. (2) at intermediate voltages.Identification of Vp was based on the departure fromnon-linearity of the first derivative dJ/dV. Least-squares fitting to the exponential portion of each J-Vcurve yielded the plasma parameters listed in Table 4.Electron density decreased from 6.7xl09 cm""3 at 20°from centerline to 0.16xl09 cm"3 at 160°, while theplasma potential decreased from 9.2 V to 2.9 V. A mapof plasma potential as a function of position is neededfor predicting the energy of charge-exchange ions thatimpinge on spacecraft surfaces. The electrontemperature was between 1.9 eV and 2.5 eV andshowed no systematic dependence on plume angle.

CONCLUSIONPlume characteristics for the BPT-4000 Hall currentthruster were measured to support mathematicalmodeling of plume/spacecraft interactions, includingerosion of spacecraft materials, surface charging, andcommunication signal propagation. Timed exposuresof collimated material samples were performed inconjunction with the experiments reported here, and aneffort was made to determine the flux, energy, andcharge-state distributions of the ions impinging on thesamples. Flux values that apply to the collimatederosion tests differ significantly from the uncollimatedflux values because of attenuation by the dynamicpressure inside the collimator. Extrapolation of the datato zero background pressure shifted the plumedivergence half-angle outward by 4°-5° relative tomeasurements at the minimum background pressure of0.96xlO~5 torr. Four distinct xenon ion populationswere observed: (1) primaries with an E/q distributioncentered at 20-25 V below the discharge potential, (2)elastically scattered ions at intermediate E/q values thatshifted to lower energy with increasing angle fromcenterline, (3) charge-exchange ions with E/q < 50 V,and (4) high-energy ions that resulted from charge-decreasing collisions by Xe+2 or Xe+3. Multiply-charged xenon ions contributed 25%-35% of the currentat angles where the plume can impinge on solar arrays,but the fraction measured in this test is believed to behigher than what would pertain on-orbit.

ACKNOWLEDGEMENTThis project was performed in support of the LockheedMartin Space Systems commercial satellite programunder Contract CY01M8601K. Michael Glogowskiwas the Lockheed Martin program manager and madekey contributions to the planning and execution of theHall thruster test.



Table 2. Total plume ion current and half-angles as functions of operating point using +20 V collector potential.Discharge power

(kW)

2.0

3.0

4.5

Discharge Dischargepotential (V) current (A)

200 10.0300 6.7300 10.0350 8.6400 7.5450 6.7500 6.0250 18.0300 15.0 .350 12.8450 10.0500 9.0

Plume current Plume/discharge 95% current(A) current ratio half-angle5.9 59%4.4 66%5.4 54%5.3 61%4.9 65%4.1 62%4.0 67%9.6 53%7.9 53%7.1 55%5.9 59%5.9 65%

Table 3. Total plume ion current and half-angles at 3.

Collector Corrected pressure Plume current Plume/dischargepotential (V) ( 1 0~5 torr) (A) current ratio

+20+20+20+20

0+20+50+ 100

0 (extrapolated)0.961.824.560.960.960.960.96

Table 4. Electron properties

Angle Density (109

20° 6.730° 3.840° 2.450° 1.560° 1.070° 0.7380° 0.5790° 0.49100° 0.36120° 0.27140° 0.20160° 0.16

6.3 63%5.4 54%4.7 47%3.4 34%

6.3 63%5.4 54%5.0 50%4.7 47%

at 0.56 m from the exit plane

69°70°50°64°69°70°64°

39°41°58°65°66°

0 kW and 300 V.

95% currenthalf-angle

55°50°46°38°75°50°39°35°

at 3.0 kW and 300V


91°96°79°90°96°96°88°60°69°86°95°95°


83°79°75°64°111°79°60°46°

cm""3) Temperature (eV) Plasma potential (V)2.12.01.92.12.01.92.22.42.52.32.42.4

9.28.17.36.86.15.05.44.74.84.03.62.9



136 mm

22mmdiam

43% graphitetransmitting collimator

mesh

37 mmdiam

repellerplate

slit repellerP|ate plate

Fig. 1. Probes for measuring ion flux, ion energy, and charge-state distributions.



1.0E+01

1.0E-03

1.0E-04-150 -100 -50 0

Degrees

50 100 150

Fig. 2. Angle-dependent ion flux measured by two rotatable probes with a collector bias of 0 V for a 3-kW, 300-V discharge.The ratio of collimated to uncollimated flux gives the attenuation factor due to the collimator.

1.0E+01

-150 100 150

Fig. 3. Angle-dependent ion flux as a function of collector potential measured with an uncollimated probe for a 3-kW, 300-Vdischarge. Low-energy charge-exchange ions are excluded when the collector potential is increased.



100%

90%30 40 100 110

Fig. 4. Fraction of total plume current within a given half-angle for a range of discharge potentials at 4.5 kW. An uncollimatedprobe was used with a collector potential of+20 V.

1.0E+01 :

300 350

Fig. 5. Energy-per-charge distributions measured with the collimated retarding potential analyzer for a 3-kW, 300-V discharge.



1.0E-06

1.0E-07 :-..-.--

100 200 300 400 500 600 700 800 901.0E-12

Fig. 6. Energy-per-charge distributions measured with the deflection analyzer for a 3-kW, 300-V discharge.

1.0E+01

1.0E+00

1.0E-01

1.0E-02

1.0E-04

1.0E-05

elastically primary ionsscattered

0 100 200 300 400 500 600 700 800 900

Fig. 7. Composite energy-per-charge distributions measured with the collimated RPA and deflection analyzer for a 3-kW, 300-Vdischarge.

10



2.50

2.00

lonization potentialXe+1 12eVXe+2 33 eVXe+3 65 eVXe+4 104eV

-0.50

O.OE+00 2.0E-06 4.0E-06 6.0E-06 8.0E-06 1.0E-05 1.2E-05 1.4E-05 1.6E-05 1.8E-05 2.0E-05

Time (s)

Fig. 8. Time-of-flight spectrum of plume ions at 40° from thruster centerline for a 3-kW, 300-V discharge. Peaks intensities areproportional to the charge-state fractional currents.

90% -

80%

70%

60%

50% -

300V200V

@ 100V

20%

10%

+2

20 30 40 50 60

Degrees

80 90

Fig. 9. Charge state distribution vs. angle and energy for a 3-kW, 300-V discharge.

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REFERENCES

I K.H. de Grys, D.L. Tilley, and R.S. Aadland, UBPTHall thruster plume characteristics," Paper AIAA-99-2283, 35th Joint Propulsion Conference, 20-24 June1999, Los Angeles, California.2 F.S. Gulczinski, R.R. Hofer, and A.D. Gallimore,"Near-fie Id ion energy and species measurements of a 5kW laboratory Hall thruster," Paper AIAA-99-2430,35th Joint Propulsion Conference, 20-24 June 1999,Los Angeles, California.3 K. Kozubsky, S. Kudriavtzev, and S. Pridannikov,"Plume study of a multimode thruster SPT-140," PaperIEPC-99-073, 26th International Electric PropulsionConference, 17-21 Oct 1999, Kitakyushu, Japan.4 J.M. Fife, W.A. Hargus, D.A. Jaworske, R.Jankovsky, L. Mason, C. Sarmiento, J.S. Snyder, S.Malone, J. Haas, and A.D. Gallimore, "Spacecraftinteraction test results of the high performance Hallsystem SPT-140," Paper AIAA-2000-3521, 36th JointPropulsion Conference, 17-19 July 2000, Huntsville,Alabama.5 J.E. Pollard and E.J. Beiting, "Ion energy, ionvelocity, and thrust vector measurements with the SPT-140 Hall thruster," 3rd International Conference onSpacecraft Propulsion, 10-13 Oct 2000, Cannes, France.6 I. Katz, G. Jongeward, V. Davis, M. Mandell, I.Mikellides, R. Dressier, I. Boyd, K. Kannenberg, J.Pollard, and D. King, "A Hall effect thruster plumemodel including large angle elastic scattering," PaperAIAA-2001-3355, 37th Joint Propulsion Conference, 8-I I July 2001, Salt Lake City, Utah.7 G. Hallock, J. Wiley, E. Spencer, B. Meyer, and J.Loane, "Development and application of theBeamServer code for plume impact analysis on satellitecommunications," Paper AIAA-2001-33 54, 37th JointPropulsion Conference, 8-11 July 2001, Salt Lake City,Utah.8 S. Hu, J. Anne, B. Emgushov, V. Khayms, K.Kannenberg, L. Werthman, and V. Smentkowski,"Development of a sputter database for Hall thrusterplume effects evaluation," Paper AIAA-2001-3356,37th Joint Propulsion Conference, 8-11 July 2001, SaltLake City, Utah.9 K. Kannenberg, V. Khayms, S. Hu, B. Emgushov, L.Werthman, and J. Pollard "Validation of a Hall thrusterplume sputter model," Paper AIAA-2001-3986, 37thJoint Propulsion Conference, 8-11 July 2001, Salt LakeCity, Utah.

F.Wilson, D. King, M. Willey, R. Aadland, D. Tilley,and K. de Grys, "Development status of the BPT familyof Hall thrusters," Paper AIAA-99-2573, 35th JointPropulsion Conference, 20-24 June 1999, Los Angeles,California.11 S. Pullins, R.A. Dressier, Y.-H. Chiu, and D.J.Levandier, "Ion dynamics in Hall effect and ionthrusters: Xe+ + Xe symmetric charge transfer," PaperAIAA-2000-0603, 38th Aerospace Sciences Meeting,10-13 Jan 2000, Reno, Nevada.12 L.B. King and A.D. Gallimore, "Ion energydiagnostics in the plume of an SPT-100 from thrust axisto backflow region," Paper AIAA-98-3641, 34th JointPropulsion Conference, 13-15 July 1998, Cleveland,Ohio.13 S. Roche, N. Gascon, L. Magne, S. Bechu, A.Bouchoule, P. Lasgorceix, D. Pagnon, C. Perot, L.Albarede, M. Touseau, M. Dudeck, and M. Lyszyk,"Operating conditions and plasma study of an ATON-class Hall thruster," 3rd International Conference onSpacecraft Propulsion, 10-13 Oct 2000, Cannes, France,ESASP-465, p. 351.14 V. Garkusha, A. Kochergin, A. Rusakov, A.Semenkin, E. Evlanov, Yu. Lebedev, and S. Podkolzin,"Ion energy measurement of a D-55 Hall thruster," 3rd

International Conference on Spacecraft Propulsion, 10-13 Oct 2000, Cannes, France, ESA SP-465, p. 359.15 J.E. Pollard, "Plume angular, energy, and massspectral measurements with the T5 ion engine," PaperAIAA-95-2920, 31st Joint Propulsion Conference, 10-12 July 1995, San Diego.16 W.E. Amatucci, M.E. Koepke, T.E. Sheridan, M.J.Alport, and J.J. Carroll III, "Self-cleaning Langmuirprobe," Rev. Sci. Instrum., 64, 1253 (1993).17 F.F. Chen, "Electric probes," in Plasma DiagnosticTechniques, edited by R.H. Huddlestone and S.L.Leonard, (Academic Press, New York, 1966), p. 135.

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