Magnetohydrodynamic equilibrium configurations with hollow current density profiles in the HL-2A tokamak are reconstructed for pellet injection discharges. The experimental data of pressure profiles, resulting from electron temperature measurements and a model density profile, analogous to that measured in the JET experiment, and Mirnov pickup coil signals are employed in the reconstructions. It is explicitly shown for the first time that configurations with hollow current density profiles may be realized by multiple pellet injection in HL-2A tokamak experiments. The reconstructed results show there exists a negative magnetic shear region in the plasma core which would benefit confinement improvement.
Hydrogenated amorphous silicon (a-Si:H) films are prepared using a windowless photochemical vapor deposition system. Vacuum ultraviolet light of 121.6 nm from hydrogen-helium mixture plasma is thought to decompose silane molecules into mainly SiH and SiH2 radicals. Contributions of these radicals to film growth result in growth rate dependence upon substrate temperature (T
s). The apparent sticking probability of both radicals is determined to be 0.84 at T
s=100° C and 0.68 at T
s=250° C, from the variation of step coverage as a function of T
s. Adjusting the substrate position close to the light source brings about an increase of incident SiH and SiH2 radicals through primary photolysis by 121.6 nm light, as well as decrease of gas-phase reactions, which allows us to control the Si–H2 bond density in the film. The effect of the Si–H2 bond in the film is also shown.
Penta-di-methyl-amino-tantalum (Ta[N(CH3)2]5), a new source chemical of Ta in TaO chemical vapor deposition (CVD), has been studied. TG and DTA measurements show that Ta[N(CH3)2]5 is chemically stable up to about 150°C and vaporizes at a temperature of 80°C. TaO films were deposited by LP-CVD at temperatures of 380∼520°C, by using the new chemical Ta[N(CH3)2]5 and O2. The deposition rate of TaO with Ta[N(CH3)2]5 is higher than that with Ta(OC2H5)5, a conventional Ta source. The TaO CVD using Ta[N(CH3)2]5 and O2 yields a good step coverage. Although the as-deposited TaO films are oxygen poor in film composition, annealing in an oxidizing ambient improves the stoichiometry and reduces the leakage current.
Previous work on a slowly rotating mass shell with Rat interior in a Friedman" universe is extended to second order in the angular velocity w. The rotational perturbations of order w lead to density perturbations and gravihdonal waves in the perturbed Friedman" cosmos of order w2, The density perturbations are discussed with the help of gauge-invariant variables. It is shown that the flatness condition inside the shell can be preserved in order wz if the geameuy of the shell is suitably chosen, though there are gravitational waves in the exterior region. The deformation of the shell is discussed for the very early and late stlges of the universe. PACS numbers: 04201,0430, 9880 t Present address: Max-Planck-Gesellschfc Arkitsgruppe Gravitationstheorie an der Univenilar Iena, Max-Wen-Platz 1. D-07743 ]en& Federal Republic of Germany.
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