Experimental studies of anode sheath phenomena in a Hall thruster discharge

Dorf, L.; Raitses, Yevgeny; Fisch, Nathaniel J.

doi:10.1063/1.1915516

Cited by 44 publications

(20 citation statements)

References 23 publications

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“…For example, a sharp increase in the near-wall potential associated with self trapping of fast electrons in plasma volume was reported by Demidov et al [57]. The jump can also be related to a change in the current closure to the anode as reported by Dorf et al in [15]. Experiments with conducting walls performed by Stangeby and Allen [58] revealed the current amplifier effect when changing the wall potential, a situation that is different from the present one where the target plasma has a diameter larger than its length.…”

Section: Resultsmentioning

confidence: 73%

“…Positive ion sheath formed when applying a negative bias with respect to plasma potential, V pl , has been extensively investigated starting with the pioneering work of Langmuir. Recently, there is also a growing interest in electron sheath [15] and its transition to anodic glow [16][17][18]. However, there is very limited understanding of the negative charge sheath formed by both electron and negative ion.…”

Section: Introductionmentioning

confidence: 99%

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Properties of highly electronegative plasmas produced in a multipolar magnetic-confined device with a transversal magnetic filter

Draghici¹,

Stamate²

2010

J. Phys. D: Appl. Phys.

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Highly electronegative plasmas were produced in Ar/SF 6 gas mixtures in a DC discharge with multipolar magnetic confinement and transversal magnetic filter.Langmuir probe and mass spectroscopy were used for plasma diagnostics. Plasma potential drift, the influence of small or large area biased electrodes on plasma parameters, the formation of the negative ion sheath, and etching rates by positive and negative ions have been investigated for different experimental conditions.Reducing the electron temperature below 1 eV the density ratio of negative ion to electron exceeded 100 even for very low amounts of SF 6 gas. The plasma potential drift could be controlled by proper wall conditioning. A large-electrode biased positively had no effect on plasma potential for density ratios of negative ion to electrons larger than 50. For similar electronegativities or higher a negative ion sheath could be formed by applying a positive bias of a few hundred volts.

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Section: Resultsmentioning

confidence: 73%

Section: Introductionmentioning

confidence: 99%

Properties of highly electronegative plasmas produced in a multipolar magnetic-confined device with a transversal magnetic filter

Draghici¹,

Stamate²

2010

J. Phys. D: Appl. Phys.

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“…A positive anode sheath will tend to form for a large enough transverse magnetic field due to the small crossfield electron mobility. More generally, a positive anode sheath can be due to any mechanism that impedes electron flow to the anode (geometry, small anode or anode partially covered with dielectric as reported by Dorf et al 55,56 ).…”

Section: The Near-anode Regionmentioning

confidence: 99%

Micro instabilities and rotating spokes in the near-anode region of partially magnetized plasmas

Boeuf

2019

Physics of Plasmas

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Electron and ion transport in the near-anode region of a partially magnetized plasma under conditions typical of Hall thrusters or magnetron discharges is studied with fully kinetic, Particle-In-Cell Monte Carlo Collision (PIC-MCC) simulations assuming a uniform magnetic field and no ionization. We derive a simple relation that defines the magnetic field at the transition point between negative and positive sheath. For magnetic fields around or above this transition point, PIC-MCC simulations show the development of short wavelength azimuthal instabilities that cascade to longer wavelengths ("rotating spokes") as the magnetic field is increased. Both short-wavelength and large-wavelength fluctuations can coexist under some conditions. A detailed study of the fluid dispersion relation is used to analyze the PIC-MCC results. Small coherent structures can be associated with the destabilization of ion sound waves by density gradient and collisions. Longer wavelengths or rotating spokes are characteristic of the collisionless Simon-Hoh instability. The small structures are dominant for larger plasma density gradients while the larger structures correspond to smaller density gradients and larger magnetic fields. Anomalous transport associated with these instabilities can be significant, with effective collision frequencies larger than 2 × 10 7 s −1 in xenon for magnetic fields above the transition point.

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“…This situation is present in cases of electrodes with surface areas too small for sufficient flux. 22,23 Between the two sheath types is a nosheath regime where the flux equals the electron current draw by the discharge.…”

Section: Discussionmentioning

confidence: 99%

Potential contour shaping and sheath behavior with wall electrodes and near-wall magnetic fields in Hall thrusters

Dao

Walker

2012

Physics of Plasmas

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Graphite electrodes are embedded within the discharge channel of a Hall effect thruster to focus ions for improved performance. Cusp-shaped magnetic fields are added around the electrodes to shield the electrodes from high electron current. Internal plasma potential measurements inside the discharge channel show that the presence of floating graphite does not significantly affect the potential contours at 150 V anode potential. Creation of closed contour pockets are observed with the electrodes biased 10 and 30 V above the anode potential. The electrodes also cause a compression of the acceleration region in the thruster. The cause of the changes in the potential contours is attributed to a shifting of discharge electrode from the anode to the electrodes and an expansion of the near-wall plasma sheath. The presence of the cusp magnetic fields is shown to affect the current collected by the electrodes, a behavior associated with modification of the plasma sheath properties due to magnetization of electrons. V C 2012 American Institute of Physics. [http://dx.

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Experimental studies of anode sheath phenomena in a Hall thruster discharge

Cited by 44 publications

References 23 publications

Properties of highly electronegative plasmas produced in a multipolar magnetic-confined device with a transversal magnetic filter

Properties of highly electronegative plasmas produced in a multipolar magnetic-confined device with a transversal magnetic filter

Micro instabilities and rotating spokes in the near-anode region of partially magnetized plasmas

Potential contour shaping and sheath behavior with wall electrodes and near-wall magnetic fields in Hall thrusters

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