Damped structure for JLC X-band linac

Accelerating structures with damping ports for higher modes have been investigated to apply to the JLC X-band linac. The external Q values were evaluated by Slater's tuning method using the computer code MAFIA. It was found by examining the dependence of the external Q value on the geometry of the iris of the damping ports that the structure with circumferential waveguides 11 mm wide was effective in damping the TM110 mode . The external Q values for some of the other higher modes were evaluated and it was found that TE111 mode is hard to damp in such a structure, though its impedance is expected not to be high. To estimate the degradation of the accelerating mode due to the damping ports, the dependence of the Q value and r/Q value on the geometry of the damping port were calculated. Those were about 16% and 4.2%, respectively. (Author) 7 refs., 7 figs., tab