Comparative study of cavities for Iinac at SAMEER

Our group at SAMEER has established standing wave side coupled structure operating at π/2 mode at 2.998 GHz frequency. We have successfully established this mechanically challenging structure and made 6 MeV as well as 15 MeV linac tubes which are delivering desired beam parameter for patient treatment. It is proposed to design and develop 30 MeV, high beam power accelerator for medical applications. The present structure has ∼ 90MΩ/m shunt impedance after final processing. The drift tube diameter of 6 mm is just sufficient to deliver output beam of less than 2 mm diameter. In the existing setup, the beam with power of about 1.2 KW collides with a 6 mm tungsten target and generates Bremsstrahlung X-rays. For the new design, we plan to have 8-10 KW beam and hence the heat dissipation will be very high. We propose to increase the drift tube diameter up to 12 mm so as to ensure beam with large diameter can pass through so as to increase the beam spot size on target. This will help to reduce the thermal issues at the target location. This paper presents comparative study of cavity design with various drift tube diameters. We present the effects arising due to changing dimensions of the cavity profile on the critical parameters of the linear accelerator tube such as the shunt impedance, quality factor and power dissipation. The design of cavity is done using Super Fish code of LANL. (author)