Laser-induced fluorescence characterization of ions emitted from hollow cathodes

Williams, George; Smith, Timothy B.; Domonkos, Matthew T.; Gallimore, Alec D.; Drake, R. P.

doi:10.1109/27.901252

Cited by 45 publications

(30 citation statements)

References 10 publications

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“…The cathode pressure increased from about 5 to 130 hPa (namely, from about 3.8 to 97.5 torr), when the mass flow rate was increased from 0.1 to 1 mg/s. The theoretical pressure at the highest mass flow rate (i.e., 1 mg/s) is in reasonably good agreement with the measured one for a ratio of the plasma heavy particles temperature and the wall temperature between 2 and 3, which is in agreement with the experimental findings by Williams [15]. On the contrary, the model slightly over-predicted the pressure value recorded at the lowest mass flow rate (i.e., 0.1 mg/s), even when considering the heavy particles in a thermal equilibrium condition with the cathode walls.…”

Section: Cathode Performancesupporting

confidence: 89%

“…The parameter Th/Tw represents the ratio of the heavy particles temperature, Th, to the cathode wall temperature, Tw. As expected [15], a value of Th/Tw comprised between 1 and 4 gives a good estimate of the cathode internal pressure. In the heaterless configuration, the cathode was ignited by flowing 1 mg/s Xe, applying 700 V to the keeper, and regulating the keeper power supply to 1 A.…”

Section: Cathode Performancesupporting

confidence: 80%

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Development of Hollow Cathodes for Space Electric Propulsion at Sitael

et al. 2017

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Hollow cathodes are electron sources used for the gas ionization and the beam neutralization in both ion and Hall effect thrusters (HETs). A reduction of power and propellant consumption from the cathode is particularly needed in small satellite applications, where power and mass budgets are inherently limited. Concurrently, the interest in high-power HETs is increasingly fostered for a number of space applications, including final positioning and station-keeping of Geostationary Earth Orbit (GEO) satellites, spacecraft transfers from Low Earth Orbit (LEO) to GEO, and deep-space exploration missions. As such, several hollow cathodes have been developed and tested at Sitael, each conceived for a specific power class of thrusters. A numerical model was used during the cathode design to define the geometry, in accordance with the thruster unit specifications in terms of discharge current, mass flow rate, and lifetime. Lanthanum hexaboride (LaB6) hollow cathodes were successfully developed for HETs with discharge power ranging from 100 W to 20 kW. Experimental campaigns were carried out in both stand-alone and coupled configurations, to verify the operation of the cathodes and validate the numerical model. The comparison between experimental and theoretical results are presented, offering a sound framework to drive the design of future hollow cathodes.

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Section: Cathode Performancesupporting

confidence: 89%

Section: Cathode Performancesupporting

confidence: 80%

Development of Hollow Cathodes for Space Electric Propulsion at Sitael

et al. 2017

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“…No large potential hills near the cathode exit have been found in these experiments that could produce high-energy primaries or ions sometimes reported in the literature. [16][17][18][19] It is likely that dc or low-frequency probe measurements miss plasma instabilities or turbulence that might be responsible for these particles, and that any moderate-energy primary population from the cathode is rapidly thermalized by collisional processes in the high plasma density and neutral pressure cathode plume region.…”

Section: Resultsmentioning

confidence: 99%

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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“…The optimization of the discharge conditions however requires a detailed knowledge of the plasma properties itself. The small geometric dimensions in MHCD's have limited detailed quantitative experimental diagnostic studies of their properties, although some examples of such studies have been reported [2][3][4][5][6][7]. Probe and microwave diagnostics are very challenging due to the reduced dimensions of the discharge and thus, spectroscopy is the technique most commonly used to study MHCD discharges [8][9][10][11][12][13][14][15][16][17], Modeling and simulation have also been carried out to understand the basic physics of microdischarges.…”

Section: Introductionmentioning

confidence: 99%

Predicted Properties of Cylindrical Microhollow Cathode Discharges in Helium Using a Two‐Dimensional, Self‐Consistent Fluid Model

Meng

Yan

et al. 2009

Contrib. Plasma Phys.

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In this paper, a numerical simulation model was developed to simulate the helium plasma in a cylindrical Microhollow cathode based on a two-dimensional, time-dependent and self-consistent fluid model. The aim of our work is to provide estimates of the main discharge and plasma parameters and to help understand the basic mechanisms governing the MHCD devices. Accurate solutions of the continuity equations, electron energy balance equation and possion's equation with realistic boundary conditions are obtained. Realistic discharge characteristics are simulated, which are very important to understand the phenomena of microhollow cathode discharge (MHCD). The results show that there exists a hollow cathode effect in the discharge process. He electric field is mainly a radial field close to the cathode in the discharge area. The influences of gas pressure and cathode dimension on discharge characteristics were also investigated.

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Laser-induced fluorescence characterization of ions emitted from hollow cathodes

Cited by 45 publications

References 10 publications

Development of Hollow Cathodes for Space Electric Propulsion at Sitael

Development of Hollow Cathodes for Space Electric Propulsion at Sitael

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

Predicted Properties of Cylindrical Microhollow Cathode Discharges in Helium Using a Two‐Dimensional, Self‐Consistent Fluid Model

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