A DRIFT-TUBE LINAC INCORPORATING A RAMPED ACCELERATING FIELD*

A short, high-power linac structure has been designed drift tubes are copper and use new neodymium-iron-boron quadrupoles. The linac is tuned using conical-sweep post couplers and is driven by multiple rf loops. Rapid ac-celeration of the beam occurs from low to high gradients in a short, compact, and lightweight structure. Because this linac will also be used to test open drift tubes, test results are included on vacuum measurements of high-grade epoxies and plastics that might be used in a drift-tube body. Design Features Proton drift-tube linacs today are capable of reachin accelerating gradients of 5 MVim in UHF band. An RF % functions as the injector for these powerful, compact machines; most RFQ accelerating sections reach gradients of only about 2 MVlm. It is necessary, therefore, to provide a matching section between the RFQ and the high-gradient DTL. One way of accomplishing this is to estab-lish a field ramp that smoothly joins the two gra-dients. ’ Such a machine has been conceptually designed at Los Alamos for 5 % duty factor at 425 MHz and is now under final design and fabrication for us by the Grumman Aircraft Co. of Bethpage, New York. It is called a ramped-adient drift-tube linac (RGDTL). Grumman is doing the ma1 design and fabrication of several major components while Los Alamos is providing the drift tubes, quad-rupoles, and end walls. The RGDTL operates between 2.07 and 6.7 MeV with a lOO-mA hydrogen beam at a maximum of 4.4 MVlm and is connected to a 5-MV/m flat gradient DTL that takes the beam to 50 MeV. From outward a pearances, the RGDTL design re-sembles any typical K at-gradient tank, as shown in Fig. 1. The drift tubes are supported by a girder structure as ha