• M. Vretenar, Y. Cuvet, G. De Michele, F. Gerigk, M. Pasini, S. Ramberger, R. Wegner
  CERN, Geneva
• E. Kenzhbulatov, A. Kryuchkov, E. Rotov, A.G. Tribendis
  BINP SB RAS, Novosibirsk
• M.Y. Naumenko
  RFNC-VNIITF, Snezhinsk, Chelyabinsk region

The 352 MHz CCDTL will accelerate the Linac4 beam from 50 to 102 MeV. It will be the first CCDTL used in a proton linac. Three short DTL tanks, each having two drift tubes, are connected by coupling cavities and form a chain of 5 resonators operating in the stable π/2 mode. The CCDTL section is made of 7 such chains, each fed by a 1.3 MW klystron. Focusing quadrupoles are placed between tanks, easing their alignment with respect to a conventional DTL thus making the structure less sensitive to manufacturing errors. In order to validate the design and to develop the production technology, two prototypes have been constructed and successfully tested. The first prototype, built at CERN, consists of two half-cavities and one coupling cell, whereas the second, with two full cavities and one coupling cell, was built at VNIITF and BINP in Russia in the frame of an R&D contract funded by the ISTC Organisation. Both prototypes have been tested at CERN slightly beyond their nominal power level, at the design duty cycle of 10%. In this paper we present the results of high-power tests, the results of the technological developments prior to production, and the final design of the CCDTL.

• M. Vretenar, P. Bourquin, R. De Morais Amaral, G. Favre, F. Gerigk, J.-M. Lacroix, T. Tardy, R. Wegner
  CERN, Geneva

The high-energy section of Linac4, between 100 and 160 MeV, will be made of a sequence of 12 seven-cell accelerating cavities of the Pi-Mode Structure (PIMS) type, resonating at 352 MHz. Compared to other structures used in this energy range, cavities operating in pi-mode with a low number of cells have the advantage of simplified construction and tuning, compensating for the fact that the shunt impedance is about 10% lower because of the lower frequency. Field stability in steady state and in presence of transients is assured by the low number of cells and by the relatively high coupling factor of 5%. Standardising the linac rf ystem to a single frequency is considered as an additional economical and operational advantage. The mechanical design of the PIMS will be very similar to that of the 352 MHz normal conducting 5-cell LEP accelerating cavities, which have been successfully operated at CERN for 15 years. After reviewing the basic design principles, the paper will focus on the tuning strategy, on the field stability calculations and on the mechanical design. It will also report the results of measurement on a cold model and the design of a full-scale prototype.