Engineering design of the RF input coupler for the IFMIF prototype RFQ linac

For the IFMIF/EVEDA RFQ linac, engineering design of the RF input coupler is carried out. The RF input coupler with a cooling port (L = λ/4), based on a 6 1/8 in. co-axial waveguide, is designed for the CW operation. Three cooling channels are installed into the inside of loop antenna, the outer-conductor and the inner-conductor around RF window. For the loop size, RF coupling factors on beam loading are evaluated with based on the measured S11 parameter and Q value on aluminum RFQ module. In order to fulfill the acceptance Q0 value of 9000 for the RFQ, the insertion depth of L = 45 mm is chosen. For this loop antenna size, magnetic field strength around the loop and surface loss density on the loop are evaluated, it is found to satisfy with the RF coupler acceptance values. Coupling cavity with ridge-type structure is also designed for the RF transmitted power test. It is evaluated to be 7.2 kW and 0.5 W/cm2 for RF power dissipation and RF surface loss density on the RF transmitted power of 200 kW.