High current hollow cathode phenomena

Friedly, V. J.; Wilbur, P. J.

doi:10.2514/6.1990-2587

Cited by 8 publications

(6 citation statements)

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“…Without a plasma, the pressure increases linearly with mass flow rate as is expected from a choked orifice. During operation the pressure increases both with mass flow rate and discharge current, a behavior similar to other cathodes [35,68,69].…”

Section: Total Pressure Measurementssupporting

confidence: 61%

“…We also applied the algorithm to Friedly's cathode [35] with an estimated work function of 2 eV for the insert material (as reported in [31], p 91). We found the calculated results to be within 20% of experimental data, but did not have the same agreement as that of the NSTAR.…”

Section: Wall Temperaturementioning

confidence: 99%

“…We found the calculated results to be within 20% of experimental data, but did not have the same agreement as that of the NSTAR. The temperatures reported by Friedly [35] are that of the exterior of the cathode and are Experimental data from [48,74,87]. (c) and (d) NEXIS cathode.…”

Section: Wall Temperaturementioning

confidence: 99%

“…Multiple approaches exist to estimate the total pressure, many of which are used within the context of a zero-dimensional cathode model: empirical relationships, designed for a mercury hollow cathode [30][31][32][33][34][35] or based on the available data from the literature [36], isentropic [37] or isothermal [38,39] flow approaches, Poiseuille flow theory [29,40,41], a modification of Poiseuille flow theory [42,43], and an 'equivalent temperature' or modified specific gas constant taking into account the ionization fraction [38,39,44,45]. We have shown in [36] that the empirical relationships developed in [30][31][32][33][34][35] do not generalize to other cathodes and that the assumptions of isentropic, isothermal, or viscous Poiseuille flow are invalid in the flow regime in which cathodes operate. The empirical relationship we proposed in [36] covers available data from the literature but may not generalize to new designs unless they are similar to cathodes included in the analysis used to derive the relationship.…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Physics of thermionic, orificed hollow cathodes: I. Theory and experimental validation

Taunay¹,

Wordingham²,

Choueiri³

2022

Plasma Sources Sci. Technol.

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A model aimed at illuminating the physics of thermionic, orificed hollow cathodes is developed and validated with experimental data. The model is intended to describe the variation of total (neutrals, ions, and electrons) static pressure with controllable parameters. That pressure must be properly evaluated because it influences important plasma parameters in the cathode such as the attachment length and the electron temperature, which directly impact the lifetime of thermionic inserts. The model, which combines a zero-dimensional approach to the conservation of energy and momentum for the combined plasma-neutral fluid and a charge-exchange-limited ambipolar diffusion model, allows for the computation of all plasma quantities, including the total fluid pressure. The model depends on the operating conditions (discharge current and mass flow rate), cathode geometry, and the gas species, along with two non-controllable parameters: the neutral gas temperature and the sheath potential. Total pressure data at up to 307 A of cathode discharge current were obtained experimentally and were used, along with data from the literature, to validate the model. Good agreement is obtained for all quantities. The model is used in a companion paper to clarify the role of magnetic and gasdynamic pressure in the scaling of total pressure, to derive scaling laws applicable to thermionic, orificed hollow cathodes, and to propose novel cathode design rules.

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Section: Total Pressure Measurementssupporting

confidence: 61%

Section: Wall Temperaturementioning

confidence: 99%

Section: Wall Temperaturementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Physics of thermionic, orificed hollow cathodes: I. Theory and experimental validation

Taunay¹,

Wordingham²,

Choueiri³

2022

Plasma Sources Sci. Technol.

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show abstract

“…High-energy ion presence has been confirmed by several sets of experimental data [18][19][20][21][22][23][24][25]. The proposed mechanisms have included the formation of potential hills [26], charge exchange between ions and neutrals [27], double ionization [28], triple ionization [29], multiple collisions [30], and magnetoplasmadynamic mechanisms [21].…”

Section: Introductionmentioning

confidence: 99%

Assessment of the T5 and T6 Hollow Cathodes as Reaction Control Thrusters

Grubisic

Gabriel

2016

Journal of Propulsion and Power

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Hollow cathodes have been proposed as reaction control thrusters for all-electric and small spacecraft. This paper makes an assessment of modified T5 and T6 hollow cathodes for use as millinewton range thrusters. The influence of terminal parameters such as discharge current, mass flow rate, and cathode/anode geometry on thrust production is discussed. The data indicate that the T5 cathode may be able to develop specific impulses in the range of 150-250 s with argon at reasonable thrust efficiencies of up to 14%. As such, hollow-cathode thrusters may meet some limited applications. However, it is unlikely that this type of thruster could be improved significantly or could compete with similar thrusters in the same operating range. High specific impulse operation is also shown to develop large discharge voltage fluctuations, which may significantly limit the lifetime of such a device.

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Physics of thermionic orificed hollow cathodes: II. Scaling laws and design rules

Taunay¹,

Wordingham²,

Choueiri³

2022

Plasma Sources Sci. Technol.

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Scaling laws for the total pressure, electron temperature, and attachment length within orificed hollow cathodes are derived from a theoretical zero-dimensional model combined with a charge-exchange-limited ambipolar diffusion model. These quantities are critical as they control the operational life of thermionic hollow cathode inserts. The underlying models were delineated and evaluated experimentally in a companion paper (Part 1). In the present paper, scaling laws are derived from first principles for the total pressure, and from a semi-analytical approach for the electron temperature and attachment length. The total pressure is found to scale with the sum of the square of the mass flow rate multiplied by a weak function of discharge current, and with the square of the discharge current. This scaling can be physically interpreted as due to the relative importance of the Lorentz force density and the gasdynamic pressure. Both electron temperature and attachment length are found to vary inversely with the neutral gas pressure-cathode diameter product. The predicted emission length is found to be between 0.6–1.4 times the insert radius for the experimental data considered, to scale weakly with the pressure-diameter product for P d ≥ 2 Torr-cm, and to be nearly independent of the orifice diameter. The analysis suggests that the diffusion-dominated nature of the insert plasma can account for the scaling of the emission length. A general cathode design rule is formulated based on the results of the analysis: insert diameter should be chosen such that the attachment length is similar to the insert length to minimize the emission current density.

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High current hollow cathode phenomena

Cited by 8 publications

References 0 publications

Physics of thermionic, orificed hollow cathodes: I. Theory and experimental validation

Physics of thermionic, orificed hollow cathodes: I. Theory and experimental validation

Assessment of the T5 and T6 Hollow Cathodes as Reaction Control Thrusters

Physics of thermionic orificed hollow cathodes: II. Scaling laws and design rules

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