Discharge Chamber Plasma Structure of a 30 cm NSTAR-type Ion Engine

Herman, Daniel A.; Gallimore, Alec D.

doi:10.2514/6.2004-3794

Cited by 20 publications

(20 citation statements)

References 21 publications

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“…High energy neutrals can be produced by charge exchange with ions accelerating through the sheath upstream of the screen grid but with Debye lengths on the order of 0.01 to 0.1 mm [33], sheath thickness on the order of 10 Debye lengths [34], and estimated charge exchange mean free paths on the order of 10 cm for a 25 eV ion; this mechanism is estimated to account for less than 10% of the observed thrust. Ions created in the vicinity of the cathode with energies (relative to the cathode) in excess of the discharge voltage could escape directly or escape as neutrals following charge exchange collisions; however, for cathodes studied in simulated discharge chamber environments, those ions tend not to be axially directed [35][36][37].…”

Section: Discharge-only With Plasmamentioning

confidence: 99%

Thrust Stand Characterization of the NASA Evolutionary Xenon Thruster

Diamant¹,

Pollard²,

Crofton³

et al. 2011

Journal of Propulsion and Power

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Direct thrust measurements have been made on the NASA Evolutionary Xenon Thruster using a standard pendulum-style thrust stand constructed specifically for this application. Values have been obtained for the full 40-level throttle table, as well as for a few offnominal operating conditions. Measurements differ from the nominal NASA throttle table 10 values by 3.1% at most, while at 30 throttle levels, the difference is less than 2.0%. When measurements are compared with throttle table 10 values that have been corrected using recently obtained ion beam current density and charge-state data, they differ by 1.2% at most, and at 37 throttle levels, they differ by 1.0% or less. Thrust correction factors calculated from direct thrust measurements and from recently acquired plume data agree to within measurement error for all but one throttle level. Measurements of thrust due to cold flow, neutralizer, and discharge-only operation are also presented.Nomenclature A e = neutralizer exit aperture area c = neutral mean thermal speed C cf = cold flow thrust correction for offaxis flow= load cell reading F T , F = thrust g = acceleration due to gravity at sea level H = dimension J b = ion beam current k = Boltzmann constant, also ratio of specific heats l = distance from pivot to counterweight center of mass L C = dimension L CG = distance from pivot to thruster center of mass L F = distance from pivot to thruster centerline L S = dimension M e = moments due to gas and electrical connections m CW = counterweight mass _ m d = discharge chamber mass flow rate m n , m = neutral atomic mass _ m n = neutralizer mass flow rate m T = thruster mass p e = pressure at neutralizer exit q = elementary charge R = accelerator grid aperture radius, also specific gas constant t = accelerator grid aperture thickness T n = neutral gas temperature T o = neutralizer gas stagnation temperature u e = neutralizer gas effective exhaust velocity V b = ion beam voltage V bps = beam power supply voltage X C = dimension X S = dimension Y = dimension = angle = thrust correction factor for beam divergence = total thrust correction factor = dimension " = angle relative to aperture centerline = pendulum angle = angle = angle from grid centerline

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Section: Discharge-only With Plasmamentioning

confidence: 99%

Thrust Stand Characterization of the NASA Evolutionary Xenon Thruster

Diamant¹,

Pollard²,

Crofton³

et al. 2011

Journal of Propulsion and Power

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“…Equation (4) predicts T e to vary between 2.0 and 5.3 eV for discharge voltages between 24 and 32 V. Equations (2-4) were used to correct the LIF signal obtained at different discharge voltages for variations in the population of the excited state that might otherwise be interpreted as variations in the overall population of sputtered material. Subsequent probe data taken by Herman and Gallimore [33] in the same FMT showed T e between 2.5 and 5.0 eV across the face of the cathode keeper. Data were collected over a range of discharge currents at a roughly constant discharge voltage of 25 V. All data were collected in the keepered configuration.…”

Section: Erosion Measurementsmentioning

confidence: 86%

“…Over this range, T e was shown to vary by less then 20%. This is of the order of the experimental error [33].…”

Section: Erosion Measurementsmentioning

confidence: 91%

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Measurement of 30-Centimeter Ion Thruster Discharge Cathode Erosion

Williams

Smith

Gallimore

2008

Journal of Propulsion and Power

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Relative erosion rates of the discharge cathode assembly of a 30-cm ion engine are measured using laser-induced fluorescence. Molybdenum and tungsten erosion products are interrogated downstream of the discharge cathode assembly during beam extraction. Erosion of the discharge cathode assembly is characterized for both keepered and unkeepered configurations. The erosion increases with both discharge current and voltage, and spatially resolved measurements agree with observed erosion patterns. Erosion rates are calculated using data from previous wear tests. Magnitudes and trends in the rates are correlated with both previous and subsequent wear tests. Laser-induced fluorescence is demonstrated to be a technique to measure relative internal erosion rates, and a path is identified for measuring absolute rates. Nomenclature= speed of light, 2:998 10 8 m=s E ij = energy of electronic state i with respect to state j, eV h = Plank's constant, 6:626 10 34 Js f oj = oscillator strength G = gaunt factor g i = degeneracy of state i g = Gaussian line shape, s I = intensity, W=m 2 I SAT = saturation intensity, W=m 2 J D = discharge current, A l = power-broadened line shape, s m C = discharge cathode flow rate, sccm m M = main flow rate, sccm n e = plasma density, cm 3 n i;j = density of state i or j, cm 3 n o = ground-state density, cm 3 P = thruster power, kW R oj = collisional population rate, cm 3 =s T e = electron temperature, eV TH = equivalent NSTAR throttle point V D = discharge voltage, V v = velocity, m=s = homogeneous relaxation rate, Hz = wavelength, m = frequency, Hz = cross section, m 2

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“…When hot enough, the probe will float near the true plasma potential. A floating emissive probe provides a direct measure of plasma potential without the requirement of a voltage sweep or data reduction operations, as it is in the case of the standard emissive or the Langmuir probes [27,28].…”

Section: Floating Emissive Probementioning

confidence: 99%