Optimizing the high power input to the LBL 400 MHz proton RFQ

Based on the initial design values and results of the alignment and low-power testing of the novel 400-MHz RF quadrupole (RFQ) produced at Lawrence Berkeley Laboratory, the RF input power requirement at design gradient with full beam loading is approximately 160 kW. As the quadrant size and design limit the RF drive loop dimensions, the drive port was chosen to accept commercially available equipment of 1 5/8 in. in diameter. Available RF power sources provide 3 1/8 in. diameter coax at the output. The interface between the two coax sizes was chosen to be a 1/4 wavelength tapered section with a constant Zo of approximately 500 Ω. The 1 5/8-in. end of the tapered section is mounted directly to the RFQ cavity body. The following items are described: the method used to distribute the power handling limits more evenly; gradients and relative safety factors along the length of the tapered section; impedance matching sections; limiting factors and their subsequent treatment; and high-power test results