Experiments with a coaxial hall current plasma accelerator

Grossmann, W.; Hassan, H. A.; Hess, R. V.

doi:10.2514/3.3050

Cited by 19 publications

(3 citation statements)

References 3 publications

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“…Coaxial Hall discharges have been used as high-specificimpulse plasma accelerators for more than 40 yrs. 1,2 In a typical coaxial Hall plasma accelerator ͑Fig. 1͒, the discharge is sustained in imposed orthogonal magnetic and electric fields.…”

Section: Introductionmentioning

confidence: 99%

Time and space-correlated plasma potential measurements in the near field of a coaxial Hall plasma discharge

Smith

Cappelli

2009

Physics of Plasmas

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Space-and time-correlated measurements of floating and plasma potential are made in the near field, external flow cathode region of a coaxial Hall plasma discharge using an emissive probe synchronized to quasicoherent fluctuations in discharge current. The luminous axial feature frequently observed in the near field of operating plasma accelerators is found to be concomitant with a spike in the plasma potential ͑and electron temperature͒. The structure of the plasma potential allows for multiple avenues for back-streaming ions to accelerate toward the discharge front pole and may pull some classes of ions toward the central axis. The fluctuations in plasma properties exhibit a complex structure at frequencies on the order of the so-called "breathing mode" ionization instability often seen in these types of discharges. Most notably, the plasma potential appears to fluctuate in a helical fashion, resembling tilted drift waves rotating about the central axis. A simple analysis of these waves draws attention to the possible role that they may play in driving anomalous cross-field electron transport in the near field region.

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Section: Introductionmentioning

confidence: 99%

Time and space-correlated plasma potential measurements in the near field of a coaxial Hall plasma discharge

Smith

Cappelli

2009

Physics of Plasmas

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“…Hall-effect thrusters have been used as high-efficiency electric propulsion devices for nearly 50 years. 1,2 Though a variety of geometries have been developed, annular designs are one of the most common. Annular Hall thrusters, such as that schematically illustrated in Fig.…”

Section: Motivation and Backgroundmentioning

confidence: 99%

On the role of fluctuations, cathode placement, and collisions on the transport of electrons in the near-field of Hall thrusters

Smith

Cappelli

2010

Physics of Plasmas

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The performance of Hall thrusters can be highly sensitive to the position and operational parameters of the external cathode, hinting that the electron transport in the near-field is strongly dependent on the emitted electrons' initial properties. In addition, the plasma plumes of Hall discharges often exhibit fluctuations which are expected to alter electron trajectories. By implementing recent near-field plasma potential measurements made on a low-power Hall thruster in 3D electron-trajectory simulations, it is shown that electron transport from the external cathode to the thruster channel is strongly sensitive to cathode parameters including position, orientation, and electron emission divergence. Periodic, low-frequency ͑i.e., 25 kHz͒ plasma potential fluctuations reduce electron transport to the channel of the thruster by more than 65% compared to the transport achieved with static 3D fields and substantially homogenize the electron density distribution. Additional gas-phase collisions are found to have only marginal effects, even when prescribed to occur at exaggerated rates ͑reaching 10 MHz͒. The three-dimensionality of the E and B fields, together with electron-wall collisions, appear to be important drivers of cross-field transport in this region of the discharge, yielding sufficient levels of electron transport to the channel without invoking plasma turbulence.

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“…For the diffuse discharge the azimuthal current density is related to the radial current density by the simple expression 1000-je/jr = UeTe = (jBz/Uee (7) where n e and e are the electron number density and the electron charge, respectively. When co e r e is greater than one, Eq.…”

Section: Importance Of the Hall Parametermentioning

confidence: 99%

Occurrence and behavior of current spokes in MPD arcs

Cochran

Fay

1971

AIAA Journal

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A pulsed MPD arc has been operated to experimentally determine the occurrence of the rotating spoke mode of operation and to investigate voltage characteristics and spoke frequency of the MPD arc. It was found that the single rotating current spoke occurs at intermediate current levels above a critical magnetic field strength. A comparison of the spoke frequency measurements with the actuator-disk theory of Fay and Cochran shows that the actuatordisk model gives a satisfactory prediction of the behavior of the spoke frequency until a limiting frequency is reached after which the spoke approaches a constant rotational speed which is the same for all gases. The variation in the electrode voltage was found to obey the correlation of Patrick and Schneiderman when the arc was operated in the diffuse mode at lowpower levels. In the spoke mode voltages several times this prediction were measured and can be explained in terms of the EMF generated by the rotating spoke. Several criteria are suggested which predict the observed spoke/no-spoke boundaries. Nomenclature a 2 = sound speed of gas at arc exit A = channel cross-sectional area downstream of arc B -magnetic field strength CD = nondimensional drag coefficient d = radial electrode gap D = width of arc e = charge of an electron E = electric field 7 = total current j = current density I = mean electrode radius ra = mass flow rate m = mass of a molecule n e = electron number density n = molecule number flow rate T = gas temperature U = gas speed U c = critical speed V e = electrode voltage VQ = sum of voltage drops in electrode boundary layers /3= constant of order one CD = dissociation energy €i = ionization energy /io = permeability of free space p = density a--electrical conductivity co = angular velocity a)«T e -Hall parameter Subscripts r, z, 9 = radial, axial, and azimuthal components

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Experiments with a coaxial hall current plasma accelerator

Cited by 19 publications

References 3 publications

Time and space-correlated plasma potential measurements in the near field of a coaxial Hall plasma discharge

Time and space-correlated plasma potential measurements in the near field of a coaxial Hall plasma discharge

On the role of fluctuations, cathode placement, and collisions on the transport of electrons in the near-field of Hall thrusters

Occurrence and behavior of current spokes in MPD arcs

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