• S. Ramberger, P. Bourquin, Y. Cuvet, A. Dallocchio, G. De Michele, F. Gerigk, J.-M. Giguet, J.-B. Lallement, A.M. Lombardi, E. Sargsyan, M. Vretenar
  CERN, Geneva

The design of the Drift Tube Linac (DTL) for the new linear accelerator Linac4 at CERN has been made ready for production: H–ion beams of up to 40 mA average pulse current are to be accelerated from 3 to 50 MeV by three RF tanks operating at 352.2 MHz and at duty cycles of up to 10%. In order to provide a margin for longitudinal matching from the chopper line, the longitudinal acceptance has been increased. The synchronous phase starts at -35° in tank1 and ramps linearly to -24° over the tank while it went from -30° to -20° in the previous design. The accelerating gradient has been lowered to 3.1 MV/m in Tank1 and increased to 3.3 MV/m in Tank2 and Tank3 for a better distribution of RF power between tanks that is compatible with a mechanical design. To make the transverse acceptance less sensitive to alignment and gradient errors, the focusing scheme has been changed to FFDD over all 3 tanks. Design features that were demonstrated in earlier reports have been improved for series production. Results of high power RF tests of the DTL prototype equipped with PMQs are reported that test the voltage holding in the first gaps in presence of magnetic fields.

• F. Grespan
  INFN/LNL, Legnaro (PD)
• G. De Michele, S. Ramberger, M. Vretenar
  CERN, Geneva

Post Couplers (PC's) are devices used in order to reduce the effect of perturbations on the operating mode of a DTL, using the resonant coupling stabilization method. In this paper an equivalent circuit for a DTL equipped with PC's is presented, together with a 3D simulation analysis, which can explain the post coupler stabilization principle and define a new tuning strategy for DTL cavities. The PC tuning procedure based on the equivalent circuit and on frequency measurements has been tested and validated with measurements on the Linac4 DTL aluminum model.