Heat transfer intensity and current density distributions at the anode of high current arcs in predominantly inert gas atmospheres were determined experimentally. Measurements were made for stable, axially symmetric arcs having a small diameter refractory metal cathode and a plane, cooled copper anode. The experimental method consisted of splitting the anode, measuring the heat flux and the current to one of the sections as a function of arc position relative to the splitting plane, and calculating therefrom the distribution functions. The work encompassed the effects of gas pressure (195–790 mm Hg), cathode geometry and material (tungsten and W-1% ThO2), electrode separation (1.6–12.7 mm), arc current (100–300 amp), gas composition (argon, helium, and diatomic gas-argon mixtures), and localized constriction of the plasma column. Peak heat transfer intensities ranged from 1.0 to 20 kw/cm2 and peak current densities from 100 to 2500 amp/cm2. The heat and current distribution curves were of similar shape and were generally sharper than Gaussian. The heat distributions were partially resolved according to transfer mechanism. An upper limit was set on the average kinetic energy of electrons arriving on axis at the anode. This was used to specify limits on gas heat transfer intensities for certain conditions. The space charge sheath at the anode was estimated to be 10−4 to 10−3 cm thick at the arc axis.
Selected aspects of NaI(Tl), Bi4Ge3O12 and CdWO4 growth are addressed. Purity and growth control, dopant level effects, specific imperfections and plastic deformation in large scale commercial production are considered.
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