Recommended Practice for Use of Emissive Probes in Electric Propulsion Testing

Sheehan, J. P.; Raitses, Yevgeny; Hershkowitz, N.; McDonald, Michael

doi:10.2514/1.b35697

Cited by 47 publications

(27 citation statements)

References 125 publications

(259 reference statements)

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“…The probe is operated in the regime of strong thermionic electron emission, manifested itself as the saturation of the hot-probe floating potential with respect to the ground. 45 For the correct interpretation of this floating potential reading, the contribution from the heating voltage (V h ), typically V h ∼ 4 V, ought to be taken into consideration. Indeed, 1 /2V h is subtracted from the measured voltage value.…”

Section: Plasma Potential (Vp) -Floating Emissive Probementioning

confidence: 99%

Boundary-induced effect on the spoke-like activity in E × B plasma

et al. 2019

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The spoke instability in an E × B Penning discharge is shown to be strongly affected by the boundary that is perpendicular to B field lines. The instability is the strongest when bounded by dielectric walls. With a conducting wall, biased to collect electron current from the plasma, the spoke becomes faster, less coherent and localised closer to the axis. The corresponding anomalous cross-field transport is assessed via simultaneous time-resolved measurements of plasma potential and density. This shows a dominant large-scale E×B anomalous character of the electron cross-field current for dielectric walls reaching 40-100% of the discharge current, with an effective Hall parameter β eff ∼ 10. The anomalous current is greatly reduced with the conducting boundary (characterised by β eff ∼ 10 2 ). These experimental measurements are shown to be qualitatively consistent with the decrease of the E field that triggers the collisionless Simon-Hoh instability.

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Section: Plasma Potential (Vp) -Floating Emissive Probementioning

confidence: 99%

Boundary-induced effect on the spoke-like activity in E × B plasma

et al. 2019

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“…A principal signature of electron discharges in plasma thrusters is the low primary electron energies expected in the outer sheath, on the order of 100 eV, and only occasionally in the several hundred eV regime. Accurate experimental measurements are exceedingly difficult in this energy range due to the limited thickness of the sheath layer, which is often outside the resolution of experimental probes [31][32][33]. Modeling then suggests itself as a complementary tool to experiments to increase our qualitative and quantitative understanding of SEE processes.…”

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confidence: 99%

Calculation of secondary electron emission yields from low-energy electron deposition in tungsten surfaces

Chang

Alvarado

Marian

2018

Applied Surface Science

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We present calculations of secondary electron emission (SEE) yields in tungsten as a function of primary electron energies between 50 eV and 1 keV and incidence angles between 0 and 90 • . We conduct a review of the established Monte Carlo methods to simulate multiple electron scattering in solids and select the best suited to study SEE in high-Z metals. We generate secondary electron yield and emission energy functions of the incident energy and angle and fit them to bivariate fitting functions using symbolic regression. We compare the numerical results with experimental data, with good agreement found. Our calculations are the first step towards studying SEE in nanoarchitected surfaces for electric propulsion chamber walls. IntroductionSecondary electron emission (SEE) is the emission of free electrons from a solid surface, which occurs when these surfaces are irradiated with external (also known as primary) electrons. SEE is an important process in surface physics with applications in numerous fields, such as electric propulsion [1-5], particle accelerators [6], plasma-walls in fusion reactors [7][8][9][10][11], electron microscopy and spectroscopy [12,13], radio frequency devices [14-16], etc. In Hall thrusters for electric propulsion, a key component is the channel wall lining protecting the magnetic circuits from the discharge plasma. These channel walls are a significant factor in Hall thruster performance and lifetime through its interactions with the discharge plasma. These interactions are governed by the sheath formed along the walls, and so the properties of the sheath determine the amount of electron energy absorbed by the wall, which in turn affects the electron dynamics within the bulk discharge [1,[17][18][19]. Furthermore, the energy imparted by the sheath to the ions within the discharge determines the impact energy and incident angle of ions upon the surface, thus affecting the amount of material sputtered and consequently the wall erosion rate [20,21]. Thus, understanding how SEE affects sheath stability is crucial to make predictions of channel wall lifetime.Recently, a new wall concept based nano-architected surfaces has been proposed to mitigate surface erosion and SEE [22][23][24][25]. Demonstration designs based on high-Z refractory materials have been developed, including architectures based on metal nanowires and nanofoams [26][27][28][29][30]. The idea behind these designs is to take advantage of very-high surface-to-volume ratios to reduce SEE and ion erosion by internal trapping and redeposition. Preliminary designs are based on W, W/Mo, and W/Re structures, known to have intrinsically low sputtering yields secondary

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“…To do so, two common practices of experimental cathode research were used-(1) measurement of the voltage drop from the floating keeper to cathode potential, while correcting for the floating keeper sheath voltage drop, and (2) emissive probe measurement in the cathode plume using the inflection point method. 151 All measured voltages decrease with an increase in the discharge current. This typical cathode behavior is a result of the cathode emitter heating mechanism that relies on ion bombardment for maintaining sufficient emitter temperatures.…”

Section: Rafael's Heaterless Hollow Cathode For Micropropulsionmentioning

confidence: 92%

Space micropropulsion systems for Cubesats and small satellites: From proximate targets to furthermost frontiers

Levchenko

Bazaka

Ding

et al. 2018

Applied Physics Reviews

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267

104

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Rapid evolution of miniaturized, automatic, robotized, function-centered devices has redefined space technology, bringing closer the realization of most ambitious interplanetary missions and intense near-Earth space exploration. Small unmanned satellites and probes are now being launched in hundreds at a time, resurrecting a dream of satellite constellations, i.e., wide, all-covering networks of small satellites capable of forming universal multifunctional, intelligent platforms for global communication, navigation, ubiquitous data mining, Earth observation, and many other functions, which was once doomed by the extraordinary cost of such systems. The ingression of novel nanostructured materials provided a solid base that enabled the advancement of these affordable systems in aspects of power, instrumentation, and communication. However, absence of efficient and reliable thrust systems with the capacity to support precise maneuvering of small satellites and CubeSats over long periods of deployment remains a real stumbling block both for the deployment of large satellite systems and for further exploration of deep space using a new generation of spacecraft. The last few years have seen tremendous global efforts to develop various miniaturized space thrusters, with great success stories. Yet, there are critical challenges that still face the space technology. These have been outlined at an inaugural International Workshop on Micropropulsion and Cubesats, MPCS-2017, a joint effort between Plasma Sources and Application Centre/Space Propulsion Centre (Singapore) and the Micropropulsion and Nanotechnology Lab, the G. Washington University (USA) devoted to miniaturized space propulsion systems, and hosted by CNR-Nanotec—P.Las.M.I. lab in Bari, Italy. This focused review aims to highlight the most promising developments reported at MPCS-2017 by leading world-reputed experts in miniaturized space propulsion systems. Recent advances in several major types of small thrusters including Hall thrusters, ion engines, helicon, and vacuum arc devices are presented, and trends and perspectives are outlined.

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Recommended Practice for Use of Emissive Probes in Electric Propulsion Testing

Cited by 47 publications

References 125 publications

Boundary-induced effect on the spoke-like activity in E × B plasma

Boundary-induced effect on the spoke-like activity in E × B plasma

Calculation of secondary electron emission yields from low-energy electron deposition in tungsten surfaces

Space micropropulsion systems for Cubesats and small satellites: From proximate targets to furthermost frontiers

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