Abstract
An axial thermionic electron beam emitter assembly with a special geometry of the cathode along with particular spacing of the electrodes has been used to produce a stable, sharp and high power density image at an acceleration voltage of 10kV only. A hairpin-like tungsten wire, with diameter of 0.7mm having semi-spherical emitting area at the crown with an angle of 45 degree at the vertex was used as a cathode. A direct heating method was used to heat the cathode. The emission current of the gun is in accordance with the Langmuir relation. An electromagnetic coil was used for focusing the beam at the target. A two dimensional programmable movement was applied to control the work site in the x–y direction. Focusing of the beam has been achieved up to 1mm in diameter at an acceleration voltage of 10kV.Thermionic efficiency of the gun is 4mAW−1 and the power density measured is ∼105Wcm−2.The gun was used for welding and surface modification of different materials including refractory metals.
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