Evaluation of crucible for cold hearth transverse electron beam vapour generator

Abstract

Electron beam guns are extensively used as concentrated energy source in various material processing applications. A transverse 270° bend e-beam evaporator is generally used as a vapour generator for laser-based isotope separation process. In such an evaporator a condition is imminent where direct impingement of the beam on crucible wall happens when charge level is less than a critical level during continuous operation. Hence, in absence of online level measurement or charge feeding system, electron guns are susceptible to safety issues related to direct impingement of electron beam on molten charge containment. Reported literature on these safety aspects of the vaporizer addressing the crucible materials is scanty. The objective of this study was to identify a crucible material and desired wall thickness to produce vapour of a metal which requires 1500 W to achieved desired vapour for laser-based isotope separation process. In this study tantalum and tungsten were investigated as candidate crucible materials experimentally. Experiments were carried out on Tantalum and Tungsten discs of different thickness to obtain the damaging power in case of direct impingement. Puncture power was estimated by a commercial software for the coupons used in the experiments. The simulation results are in good agreement with the experimental results with certain deviations. The deviations can be attributed to the uncertainties in the scatter in thermo-physical data at high temperature and experimental conditions. The use of a 2 mm thick tantalum crucible was found to be safe with the electron beam power of vaporizer up to 1500 W.