The quality of temperature field (Table 4.1) seems to increase as diameter increases from 4mm to 10mm. However there is a limit to continuous diameter increment in order for tungsten rod not to serve as heat sink to the heat shield under these prevailing physical conditions. This heat sinking effects have been discussed in section 3. The temperature curve is also presented in Fig.4.4 at 600A current rating which shows time dependent temperature values. It also shows that all selected tungsten diameters (except 10mm) have all attained steady state temperature values within 30 seconds.