The operation and performance of a micro-Hall thruster are characterized. The thruster is coaxial in design, with a 0.5 mm channel width and 4 mm outer diameter. The magnetic circuit includes a samarium cobalt permanent magnet generating approximately 0.7 T at the exit plane and 1 T inside the channel. Operation with a commercial hollow cathode neutralizer is achieved in the 10-40 W power range with an anode flow rate of 0:12-0:20 mg=s of xenon. The measured thrust is in the range of 0.6-1.6 mN for an anode flow rate of 0:17-0:20 mg=s and an applied voltage of 110-275 V. Anode thrust efficiency and specific impulse are in the range of 10-15% and 300-850 s, respectively, for the same conditions. Relatively broad ion energy distributions and large beam divergence are observed from an analysis of the plume using a retarding potential analyzer and ion current probe. The discharge exhibits the characteristic Hall thruster "breathing mode" instability in the 35-70 kHz frequency range.
A low pressure plasma spray (LPPS) process has been developed to operate at 3-4 kW and to deposit metals or ceramic compounds at rates of 0.1-10 g/min, with a Zoating spot diameter of 1-1.5 cm. The two novel features of this facility are the low power and deposition rate, 10 to 100 times below those of conventional plasma spray processes, and the capacity for reactive plasma spraying. fiese spray parameters lend themselves to applications in mesoscale (dimensions on order 0.1-1 mm) devices, including substrates for microelectronics. Low-rate spraying may facilitate the construction of mesoscale parts in a layered technique similar to VLSI fabrication. Traditional VLSI fabrication processes are ill-suited to build parts with thickness on the millimeter scale.In the case of non-reactive spraying, solid metal powders with particle sizes from 2 to 44 pm are injected into the plume of a 3-4 kW DC arcjet operating on a ;ombination of argon, hydrogen and nitrogen. The plasma jet melts and convects the powder toward a cooled substrate where it solidifies to form a coating. Reactive spraying is similar except that the plasma gases include a component which reacts with the solid powder to form a compound coating. Results will be presented for the reactive spraying of AW and the non-reactive spraying of Cu, in terms of density, mechanical strength, bond strength and thermal conductivity. In the case of pure Cu, for example, these coatings have achieved densities of 92-96% with shear strength exceeding that of pure rolled and annealed copper. These properties will be studied as functions of substrate temperature, particle size, and plasma parameters such as arc power and plasma temperature.High density plasma-enhanced chemical vapor deposition is a technology of growing importance in the deposition of materials for the semiconductor and optoelectronics industries.Direct current (DC) plasma jets (also known as arcjets) are a particular form of high density plasma source that produce a high velocity (5-10 km/sec) plasma stream (20-30% dissociation fraction, ne -lOI3 cm-3 ). The plasma jet provides large convective fluxes of chemically reactive radical species, in super-equilibrium concentrations, that are stagnated on a substrate on which film growth occurs. High quality films of materials such as diamond, cubic boron nitride, aluminum nitride, and gallium nitride have been grown by this method at growth rates that are high compared with other deposition methods.The radical species are key to the growth of these materials. To determine the concentrations of the important gas phase species and thus elucidate the growth kinetics of the deposited films, mass spectrometry is employed. A small amount of the plasma is passed through a hole in the substrate; the hole is sized to be comparable with the collisional mean free path. The sampled plasma is expanded into a nearly collisionless environment provided by differential pumping. Such effusive sampling guarantees that the plasma sampled will be representative of the chemistry withi...
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