A method of forming a semiconductor material of a photovoltaic device that includes providing a surface of a hydrogenated amorphous silicon containing material, and annealing the hydrogenated amorphous silicon containing material in a deuterium containing atmosphere. Deuterium from the deuterium-containing atmosphere is introduced to the lattice of the hydrogenated amorphous silicon containing material through the surface of the hydrogenated amorphous silicon containing material. In some embodiments, the deuterium that is introduced to the lattice of the hydrogenated amorphous silicon containing material increases the stability of the hydrogenated amorphous silicon containing material.

Method of stabilizing hydrogenated amorphous silicon and amorphous hydrogenated silicon alloys

http://mwalker.gatech.edu/papers/ProgAerospace_Singh_V75_2015_pp15-25.pdf

A review of research in low earth orbit propellant collection

The first direct experimental measurements of electron current due to rotating spokes in a modern highpower Hall thruster are presented. A segmented anode consisting of 12 equally spaced azimuthal sections has been retrofitted onto the H6 6-kW class Hall thruster and operated at power levels up to 3 kilowatts. Independent discharge current measurements on each anode segment at 1 MHz and synchronous high-speed video of the discharge at 87,500 frames per second reveal that visible rotating spoke structures in the thruster channel correspond to local electron current oscillations with amplitude approximately 30% of the mean local discharge current through each segment. Discrete Fourier transforms of discharge current oscillations on each segment reveal peaks at spoke rotation frequencies an order of magnitude larger than at the well-known breathing mode frequency. The apparent dominance of the breathing mode in traditional Hall thruster discharge current frequency spectra is revealed to be an artifact of the use of a contiguous ring-shaped anode. Based on the magnitude of local discharge current oscillations on each segment, the magnitude of plasma density oscillations are inferred to be of the order of the mean plasma density and the net discharge current carried by the spoke mechanism is calculated to be up to 50% of the total thruster discharge current.

/pdf/measurement-of-cross-field-electron-current-in-a-hall-33fv5vagng.pdf

Measurement of Cross-Field Electron Current in a Hall Thruster Due to Rotating Spoke Instabilities

The helicon Hall thruster is a two-stage thruster that was developed to investigate whether a radio frequency ionization stage can improve the overall efficiency of a Hall thruster operating at high thrust and low specific impulse. This paper describes an experiment that measured the single-stage and two-stage performance of the helicon Hall thruster operating at 10–25  mg/s anode mass flow rates of xenon at 100–200 V discharge voltages, and also for 6  mg/s of argon at 300 V, and 2.6  mg/s of nitrogen at 200 V. The helicon Hall thruster performance during operation with argon and nitrogen is characterized by low beam divergence efficiency and low propellant utilization efficiency. During two-stage operation, the thrust of the helicon Hall thruster marginally increased with radio frequency power, but the propulsive efficiency and thrust-to-power both decreased with increasing radio frequency power. Probe diagnostics suggest that gains were realized by a slight increase in propellant efficiency, but that t...

/pdf/performance-of-a-helicon-hall-thruster-operating-with-xenon-35qyeh1hef.pdf

Performance of a Helicon Hall Thruster Operating with Xenon, Argon, and Nitrogen

This work presents recent results of ongoing investigations into rotating spoke instabilities in Hall thrusters. Recent work by the authors demonstrated large amounts of electron current carried by spokes in the nearanode region in the H6 6-kW laboratory model Hall thruster, and raises the question of whether spokes may play a larger role in electron transport throughout the Hall thruster plume. Spokes have since been observed via high speed imaging in several Hall thrusters, including the H6, the NASA 173Mv1, the X2 dual nested channel Hall thruster, the Helicon Hall thruster, and the Busek BHT-600. While this work focuses on the H6 Hall thruster, visual examples of spoke presence in these other thrusters are also presented. A parameter study of the dependence of spoke amplitude and propagation velocity on magnetic field strength and discharge voltage in the H6 shows that the magnetic field strength has a strong influence on spoke properties. Spokes appear to be omnipresent in Hall thrusters, though with widely variable strength and stability, and appear even at very highly efficient operating conditions with high voltage and high magnetic field strength – the most prominent spoke mode in the H6 is observed at a 600 V, 65% total efficiency operating condition. In response to earlier studies that have observed spokes exclusively at low voltage or in inefficient operating regimes, a study of spoke behavior at a very low voltage operating condition links a transition to higher efficiency operation with the formation of stabilized spoke structures. Finally, we present visual evidence from high-speed imaging of spokes bridging the centrally mounted cathode to the discharge channel.

http://www.umich.edu/~peplweb/pdf/IEPC-2011-242.pdf

Parametric Investigation of the Rotating Spoke Instability in Hall Thrusters

: The development status of a two-stage Hall thruster, the Helicon Hall Thruster, is presented. The Helicon Hall Thruster combines the efficient ionization mechanism of a helicon source with the favorable plasma acceleration properties of a Hall thruster. Conventional Hall thrusters rely on direct current electron bombardment to ionize the flow in order to generate thrust. Electron bombardment typically results in an ionization cost that can be on the order of ten times the ionization potential, leading to reduced efficiency, particularly at low specific impulse and discharge voltage. Helicon sources have been demonstrated to be an efficient means of producing a high-density, low-temperature plasma. The goals of the program are to design, manufacture, and test a thruster that operates efficiently over a range of input power from 3 to 10 kW with discharge voltages ranging from 150 to 500 V and discharge currents ranging from 12 to 40 A. The potential benefits of a reduced ionization cost with the helicon ionization stage are outlined. The design and manufacturing challenges involved in the development of the thruster are discussed, followed by plans for testing.

Development Status of the Helicon Hall Thruster

The invention is generally related to process for generating one or more molecules having the formula SixHy, where x and y are integers ≥1, such as silane, comprising the steps of: providing a silicon containing material, wherein the silicon containing material includes at least 20 weight percent silicon atoms based on the total weight of the silicon containing material; generating a plasma capable of vaporizing a silicon atom, sputtering a silicon atom, or both using a plasma generating device; and contacting the plasma to the silicon containing material in a chamber having an atmosphere that includes at least about 0.5 mole percent hydrogen atoms based on the total moles of atoms in the atmosphere; so that a molecule having the formula SixHy; (e.g., silane) is generated. The process preferably includes a step of removing one or more impurities from the SixHy (e.g., the silane) to form a clean SixHy (e.g., silane). The process may also include a step of reacting the SixHy (e.g., the silane) to produce a high purity silicon containing material such as electronic grade metallic silicon, photovoltaic grade metallic silicon, or both.

Peter Young Peterson

Papers

Development Status of the Helicon Hall Thruster

Plasma processes for producing silanes and derivatives thereof