Ion extraction from a plasma

Aston, G.; Wilbur, P. J.

doi:10.1063/1.329071

Cited by 44 publications

(22 citation statements)

References 18 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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“…The SEM photos are digitized and analyzed to extract feature angles. [28][29][30] Such steering will cause a skewed distribution of ion incident angles at the sample, which can explain varying deviations from verticality evident in sidewall profiles at different locations in the beam pattern. This leads to average deviations of 1°-1.4°per sidewall and a corresponding maximum feature aspect ratio of 21-29:1.…”

Section: Etching Characteristicsmentioning

confidence: 99%

Ultrahigh vacuum chemically assisted ion beam etching system with a three grid ion source

Hryniewicz¹,

Chen²,

Hsu³

et al. 1997

Journal of Vacuum Science &Amp; Technology A: Vacuum, Surfaces, and Films

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Articles you may be interested inInvestigation of electrochemical etch differences in AlGaAs heterostructures using Cl2 ion beam assisted etching J. Vac. Sci. Technol. A 33, 021304 (2015); 10.1116/1.4904211High-aspect-ratio chemically assisted ion-beam etching for photonic crystals using a high beam voltage-current ratio J.Dry etching and consequent burring regrowth of nanosize quantum wells stripes using an in situ ultrahigh vacuum multichamber system A chemically assisted ion beam etching system has been developed which performs high quality, highly anisotropic etching of AlGaAs/GaAs at relatively low ion energies ͑200 eV͒. The use of three grid ion optics in a Kaufman ion source allows etching at low energies with reasonable rates without loss of profile verticality. All ultrahigh vacuum etching chamber construction with a high throughput turbomolecular pump and high vacuum loadlock provide routine high quality etching of AlGaAs without the use of etch chamber cryo panels or cryo pumps. Low ion energy and a clean vacuum environment permit the use of a single level, non hard baked photoresist mask. Benefits include high pattern resolution and fidelity, low mask erosion rate, good dimensional control, and easy, complete mask stripping as well as reduced substrate damage.

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“…This assumption is justified by the experimental results. 12 Electron density is determined by Boltzmann equation, so it decreases as potential drops. As a result, ambipolar flow at flat upstream boundary gradually changes into unipolar flow on the way to intragrid region.…”

Section: R T E V I £2 £mentioning

confidence: 99%

Three-dimensional numerical model of ion optics system

Hayakawa¹

1992

Journal of Propulsion and Power

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A numerical model, that can be used to compute the trajectories of ions extracted through ion optics systems composed of two or three grids which have their centerline translated with respect to each other, is described. This model can be applied to predict not only thrust, beamlet current and beamlet divergence angle, but also beamlet deflection angle in any given ion extraction system. In this model, periodic boundary conditions are assumed, that is, sets of holes exist side by side to infinity. This assumption remarkably reduces computing power required. The aspects of deflected ion beamlets are revealed. Computed results are compared with experimental results. f(fi, J J JAB R T e V i, £2, £ 3

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Ion extraction from a plasma

Cited by 44 publications

References 18 publications

Thrust Stand Characterization of the NASA Evolutionary Xenon Thruster

Thrust Stand Characterization of the NASA Evolutionary Xenon Thruster

Ultrahigh vacuum chemically assisted ion beam etching system with a three grid ion source

Three-dimensional numerical model of ion optics system

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