Hollow Cathode and Keeper-Region Plasma Measurements Using Ultra-Fast Miniature Scanning Probes

Goebel, Dan M.; Jameson, Kristina K.; Watkins, Ron M.; Katz, Ira

doi:10.2514/6.2004-3430

Cited by 48 publications

(31 citation statements)

References 7 publications

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“…Since the probes reside in the plasma for only a very short time, discharge currents of over 35 A have been used without damaging the probe. 8 Plasma densities in the hollow cathode approaching 10 15 cm −3 at temperatures of 2 -5 eV are observed, depending on the current, flow rate, and cathode orifice size. It is found that the plasma potential on axis in the cathode is on the order of 10-20 V, and decreases as the discharge current increases at a given flow rate.…”

Section: In 1962mentioning

confidence: 97%

Hollow cathode theory and experiment. I. Plasma characterization using fast miniature scanning probes

Goebel

Jameson

Watkins

et al. 2005

Journal of Applied Physics

105

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A detailed study of the spatial variation of plasma density, temperature, and potential in hollow cathodes using miniature fast scanning probes has been undertaken in order to better understand the cathode operation and to provide benchmark data for the modeling of the cathode performance and life described in a companion paper. Profiles are obtained throughout the discharge and in the very high-density orifice region by pneumatically driven Langmuir probes, which are inserted directly into the hollow cathode orifice from either the upstream insert region inside the hollow cathode or from the downstream anode-plasma region. A fast transverse-scanning probe is also used to provide radial profiles of the cathode plume as a function of position from the cathode exit. The probes are extremely small to avoid perturbing the plasma; the ceramic tube insulator is 0.05cm in diameter with a probe tip area of 0.002cm2. A series of current-voltage characteristics are obtained by applying a rapid sawtooth voltage wave form to the probe as it is scanned through the plasma at speeds of up to 2m∕s to produce the profiles with a spatial resolution of about 0.05cm. At discharge currents of 10–25A from the 1.5-cm-diameter hollow cathode, the plasma density inside the cathode is found to exceed 1014cm−3, with the peak density occurring upstream of the orifice. The plasma potentials on axis inside the cathode are found to be in the 10–20V range with electron temperatures of 2–5eV, depending on the discharge current and gas flow rate. A potential discontinuity or double layer of less than 10V is observed in the orifice region, and under certain conditions appears in the bright “plasma ball” in front of the cathode. This structure tends to change location and magnitude with discharge current, gas flow, and orifice size. A potential maximum proposed in the literature to exist in or near the cathode orifice is not observed. Instead, the plasma potential increases from the orifice exit both radially and axially over several centimeters to values of 5–10V above the anode voltage. The potential and temperature profiles inside the cathode are insensitive to anode configuration changes that alter the discharge voltage at a given flow. Application of an axial magnetic-field characteristic of the cathode region found in ring-cusp ion thrusters increases the plasma density in the cathode plume, but does not significantly change the potential or temperature. Measurements of the plasma profiles and the internal cathode parameters for a hollow cathode operating at discharge currents of up to 25A in xenon are shown and discussed.

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Section: In 1962mentioning

confidence: 97%

Hollow cathode theory and experiment. I. Plasma characterization using fast miniature scanning probes

Goebel

Jameson

Watkins

et al. 2005

Journal of Applied Physics

105

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show abstract

“…While the orifice wall temperature is varied, electron temperature equation, Equation (20), and orifice plasma energy balance equation, Equation (21), are solved with bisection method in order to obtain the orifice plasma electron temperature (T eV,orf ) and plasma density (n o ). While the orifice wall temperature is varied, electron temperature equation, Equation (20), and orifice plasma energy balance equation, Equation (21), are solved with bisection method in order to obtain the orifice plasma electron temperature (T eV,orf ) and plasma density (n o ).…”

Section: Solution Of Model Equationsmentioning

confidence: 99%

“…The ionization rate function, as a function of electron temperature, T eV,ins , is calculated according to the expression given in [15]. Even tough, it is speculated by [20] and experimentally observed by [21] that a double layer is formed at the constriction between insert and orifice region plasma, the effect of the double layer is not taken into account in Equation (1). As found in studies [22] and [23], for xenon flow rates higher than 1 sccm, neutral gas flow sweeps the ions from insert to orifice.…”

Section: Emitter Modelmentioning

confidence: 99%

“…The same logic is applied for the orifice region plasma. While the orifice wall temperature is varied, electron temperature equation, Equation (20), and orifice plasma energy balance equation, Equation (21), are solved with bisection method in order to obtain the orifice plasma electron temperature (T eV,orf ) and plasma density (n o ). This time, energy balance equation written for the orifice wall, Equation (23), is used as convergence criterion.…”

Section: Solution Of Model Equationsmentioning

confidence: 99%

See 1 more Smart Citation

Global Numerical Model for the Assessment of the Effect of Geometry and Operation Conditions on Insert and Orifice Region Plasmas of a Thermionic Hollow Cathode Electron Source

Korkmaz

Çelik

2014

Contrib. Plasma Phys.

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Thermionic hollow cathodes have been widely used in wide variety of areas such as spacecraft electric propulsion systems, material processing and lasers for more than half a century as efficient electron sources. Especially in electric propulsion systems, hollow cathodes are being used as electron sources for propellant ionization and ion beam neutralization. Moreover, it is also a promising candidate for utilization as a stand-alone propulsion system in microsatellites or nanosatellites due to its small physical size, low power consumption and ease of operation. On the other hand, the small geometry of the typical orificed hollow cathodes makes the plasma diagnostics difficult which is why numerical studies become important for understanding the driving physical processes behind their operation, and the effects of the geometry and the operation parameters on cathode performance. In this paper, a global numerical model for the insert and orifice plasma of a hollow cathode is presented where volume averaged plasma parameters are considered for both regions. The results of this study show that the developed model can be used for designing and sizing orificed hollow cathodes as comparisons with the results of experimental and other numerical studies are in good agreement with the ones obtained from the developed model.

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“…26 Friedly's cathode, 14 Salhi's xenon and argon cathode, 17 Domonkos's SC012, EK6, and AR3 cathodes, 21 the T6 cathode from the Royal Aerospace Establishment, 25,27 and the NSTAR and NEXIS cathodes from the Jet Propulsion Laboratory. [28][29][30][31][32] The neutral gas temperature is estimated to be either three times the maximum insert wall temperature, 18 or 3000 K if wall temperature data is unavailable. The list of cathodes reviewed is shown in the Appendix.…”

Section: Introductionmentioning

confidence: 99%

Correction: An empirical scaling relationship for the total pressure in hollow cathodes

Taunay

Wordingham

Choueiri

2018

2018 Joint Propulsion Conference

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A non-dimensional scaling relationship for the total pressure inside thermionic, orificed hollow cathodes is derived empirically from a large database of experimental measurements and is analyzed statistically. The relationship allows calculating the total pressure inside hollow cathodes, which is necessary for self-consistent analytical models of the insert region and for insert lifetime calculations. The scaling relationship is a function of cathode operational parameters and is expressed as a non-dimensional power law. It is compared to experimental data for self-consistency and to theoretical modeling efforts. It is found that the empirical correlation agrees with experimental data with an R-squared value of 0.98 and average error of 24.5%, allows calculating the pressure over a range of three orders of magnitude or five orders of magnitude in the non-dimensional space, and is able to capture the dependency of the total pressure on the discharge current where theoretical models can not. For the dataset considered the scaling is shown to be insensitive to variations in the cathode orifice length, propellant ionization energy, and viscosity.

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Hollow Cathode and Keeper-Region Plasma Measurements Using Ultra-Fast Miniature Scanning Probes

Cited by 48 publications

References 7 publications

Hollow cathode theory and experiment. I. Plasma characterization using fast miniature scanning probes

Hollow cathode theory and experiment. I. Plasma characterization using fast miniature scanning probes

Global Numerical Model for the Assessment of the Effect of Geometry and Operation Conditions on Insert and Orifice Region Plasmas of a Thermionic Hollow Cathode Electron Source

Correction: An empirical scaling relationship for the total pressure in hollow cathodes

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