Critical sub-systems of linac tube

Full text: Linac is a device in which electrons are accelerated linearly with the help of microwave power. The linac tube essentially consists of: (a) electron gun, (b) accelerating structure, (c) dielectric window, (d) electron output window and/or (e) target. The electron gun products beam of electrons and launches inside the interaction zone. The accelerating structure is a chain of coupled high-Q resonators, properly tuned to support π/2 mode. Microwave generated from a suitable high power source enters the interaction structure through the dielectric window. As the electron beam passes through the chain of cavities, power transfer takes place from microwave to the electron beam increasing its energy to the order of mega electron volts. Depending upon the application, accelerated electron beam may be taken out in the atmosphere through an electron output window or may be allowed to impinge on a high atomic number target material producing Bremsstrahlung x-rays. Out of these five sub-systems, in a hard baked and pinched-off Linac tube, a properly designed interaction structure rarely fails during the life span of the machine. Other four sub-systems are the vulnerable components in the accelerator system; which determine the performance and life of the machine. In SAMEER, couple of designs of these sub-systems has been optimised for accelerators of different energies and applications. Our past experience in the field has helped us making these components more rugged and reliable. Design, fabrication, and characterisation aspects of these sub-systems will be discussed in the paper. (author)