Langmuir probe measurements in a discharge from a hollow cathode

Csiky, G. A.

doi:10.2514/6.1969-258

Cited by 13 publications

(30 citation statements)

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“…For the plume mode, if the sheath edge is assumed to lie outside the cathode as in the proposed model, it can be shown 4 that only a small portion of the electrons that have been accelerated through the sheath will undergo ionizing collisions. Thus fast electrons are present in the discharge and apparently make enough excitation collisions to give luminousity to the plume.…”

Section: Discussion Of Resultsmentioning

confidence: 99%

Langmuir probe measurements in a discharge from a hollow cathode

Csiky

1970

Journal of Spacecraft and Rockets

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U SE of the vapor-fed hollow cathode both as plasma-bridge neutralizer and as the ion chamber electron source has been advantageous in mercury bombardment ion thrusters. 1^3 A hollow cathode differs from earlier types (e.g., refractory metal ribbon, or oxide magazine) in several important ways. For example, it is-a source of mercury atoms, as well as of electrons. Consequently, a very large pressure gradient exists just outside the hollow-cathode orifice as a result of the mercury vapor expanding into a region of low pressure. Also, electron injection is from a much smaller area than it is with other types of cathodes. The properties of the external discharge plasma obtained also differ, and it was necessary to introduce a baffle in the discharge chamber of the electron bombardment thruster to obtain good performance when the discharge was fed by a hollow cathode. 3 To investigate the nature of the hollow-cathode discharge, Langmuir probe measurements were made in a diode configuration with a plane circular anode placed opposite the hollowcathode. The hollow cathode assembly consisted of a 0.32-cm-outside-diam tantalum tube with a 0.1-cm-thick, 2% thoriated tungsten-alloy disk attached to one end by electronbeam welding. A 0.02-cm-diam orifice was cut in the center of the tungsten disk. A barium carbonate coated tantalum foil insert placed inside the tube facilitated starting the discharge. In operation, the cathode tube was electrically heated by a tungsten-rhenium wire wound around it and embedded in a flame-sprayed coating of alumina.The anode was a 14-cm-diam stainless steel disk. The distance of the cathode could be varied. The experiments were conducted in a 45-cm-diam vacuum bell jar. The typical pressure during the runs was on the order of 10~6 torr.

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Section: Discussion Of Resultsmentioning

confidence: 99%

Langmuir probe measurements in a discharge from a hollow cathode

Csiky

1970

Journal of Spacecraft and Rockets

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“…With this, the energy of ions impinging upon the neutralizer can be calculated. Also, because the transition from spot to plume mode is associated with a significant increase in measured electron temperature, the Langmuir probes were used as a sensitive transition detector [4,5]. Thin-sheath analysis was used to analyze the Langmuir probe current-voltage characteristic.…”

Section: Diagnosticsmentioning

confidence: 99%

“…Ideally, this would be the lowest flow rate at which the neutralizer can still operate in the spot mode. The hollow cathode spot mode is a quiet, low-voltage discharge condition characterized by the visible presence of a luminous spot of intense ionization and excitation in the orifice of the cathode [4,5]. Although the minimization of neutralizer flow can improve the specific impulse, it can also have deleterious effects on the neutralizer assembly lifetime.…”

Section: Introductionmentioning

confidence: 99%

“…Large keeper-tocathode, peak-to-peak voltage oscillations are commonly measured in this mode [4,5]. These large voltages can drive sputter erosion of the neutralizer assembly, giving rise to cathode-orifice-channel enlargement and orifice-plate texturing [5][6][7]. Over time, a neutralizer can transition from the spot to the plume as it undergoes natural erosion of the orifice or through deposition processes within the orifice channel while operating at a fixed flow rate [6].…”

Section: Introductionmentioning

confidence: 99%

“…The plume is produced by electron excitation of neutrals external to the cathode. Large keeper-tocathode, peak-to-peak voltage oscillations are commonly measured in this mode [4,5]. These large voltages can drive sputter erosion of the neutralizer assembly, giving rise to cathode-orifice-channel enlargement and orifice-plate texturing [5][6][7].…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Characterization of an Ion Thruster Neutralizer

Foster

Williams

Patterson

2007

Journal of Propulsion and Power

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The neutralizer of a high-power ion thruster was characterized over a range of flow rates at the nominal thruster operating condition of 3.6 A of ion beam current at a beam voltage of 5500 V. Near-neutralizer Langmuir probes were used to characterize the local plasma and detect the transition from spot to plume mode. Consistent with the Langmuir probe measurements, it was found that neutralizer coupling voltage, rather than the magnitude of neutralizer-keeper-voltage oscillations, was most indicative of the spot to plume mode transition. Additionally, neutralizer-keeper-barrel erosion due to extreme, off-axis ions was investigated. No such energetic ion flux was detected using strategically placed, coated witness plates. Nomenclature Ja= accelerator-grid current Jb = beam current T = time Vg = neutralizer coupling voltage Vnk = neutralizer keeper-to-cathode voltage Vp = plasma potential

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Evidence of the ionization instability and ion acoustic turbulence correlation in sub-ampere hollow cathodes

Potrivitu

2022

J Electr Propuls

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Plasma instabilities in the plume of hollow cathodes have been extensively researched in particular for high-current operation. The rise of plume mode ionization-like instability leads to a degradation of cathode’s performance along with the emergence of highly energetic ions that can produce sputtering of various cathode’s surfaces. Numerical simulations using 2D fluid or hybrid codes brought forward an interesting correlation between the evolution of ion acoustic turbulence (IAT) and emergence of plume mode oscillations. Such numerical findings were proven to be true by experimental measurements of wave dispersion and plume mode-IAT correlation in the plume of cathodes emitting currents >10 A. This study brings forward evidence of the correlation between plume mode oscillations and IAT in the plume of low-current cathodes operating with Kr at sub-ampere current levels. It is shown that at <1 A the plume mode instability is highly correlated with the IAT and the anomalous electron collision drives the electron transport in the cathode plume. The fluctuations in IAT wave energy lead to large temperature oscillations which then drive fluctuations in the density via ionization.

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Langmuir probe measurements in a discharge from a hollow cathode

Cited by 13 publications

References 0 publications

Langmuir probe measurements in a discharge from a hollow cathode

Langmuir probe measurements in a discharge from a hollow cathode

Characterization of an Ion Thruster Neutralizer

Evidence of the ionization instability and ion acoustic turbulence correlation in sub-ampere hollow cathodes

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