Filamentless operation of a high-power electron bombardment furnace used for refractory metals atom beam generation

Filamentless operation of a 10 kW electron bombardment vacuum furnace in th e temperature range 2000-3000 K is described. This novel mode of operation was useful in obtaining low magnetic field ambient around the furnace. This enabled us to carry out sensitive measurement of atomic properties of refr actory metal atoms with the help of well-collimated neutral atomic beams. I n this furnace, the necessary electron emission was derived from the innerm ost heat shield, which was coated with a low work-function metal and placed closer to the boat to attain high enough temperatures. The destabilizing e ffect of high degree of electrothermal feedback was effectively countered b y using a nonlinear ballast consisting of a bank of tungsten lamps. The ion ized fraction in the atomic beam was removed with the help of biased grids. This furnace has provided uninterrupted service to many users over the las t few years. (C) 2000 American Institute of Physics. [S0034- 6748(00)04408- 7].