• S. Ramberger, N. Alharbi, P. Bourquin, Y. Cuvet, F. Gerigk, A.M. Lombardi, E.Zh. Sargsyan, M. Vretenar
  CERN, Geneva
• A. Pisent
  INFN/LNL, Legnaro, Padova

The Drift Tube Linac (DTL) for the new linear accelerator Linac4 at CERN will accelerate H^- ion beams of up to 40mA average pulse current from 3 to 50MeV. It is designed to operate at 352.2MHz and at duty cycles of up to 10%, if required by future physics programmes. The accelerating field is 3.2MeV/m over the entire length. Permanent magnet quadrupoles are used as focusing elements. The 3 DTL cavities consist of 2, 4 and 4 segments of about 1.8m each, are equipped with 35, 41 and 29 drift tubes respectively, and are stabilized with post-couplers. Several new features have been incorporated in the basic design. The electro-magnetic design has been refined in order to reduce peak field levels in critical areas. The mechanical design aims at reducing the complexity of the mechanical structure and of the adjustment procedure. Drift tubes and holders on the tanks that are machined to tight tolerances do not require adjustment mechanisms like screws or bellows for drift tube positioning. A scaled cold model, an assembly model and a full-scale prototype of the first half tank have been constructed to validate the design principles. The results of metrological and rf tests are presented.

• G. Bellodi, M. Eshraqi, J.-B. Lallement, S. Lanzone, A.M. Lombardi, E.Zh. Sargsyan
  CERN, Geneva
• R.D. Duperrier, D. Uriot
  CEA, Gif-sur-Yvette

Linac4 is a normal conducting H^- linac to be built at CERN as a new injector to the PS Booster and later on as a front end of a Superconducting Proton Linac (SPL). The layout consists of a H^- rf source, a magnetic LEBT, a RFQ (accelerating the beam from 45 keV to 3 MeV), a chopper line, a conventional Drift Tube Linac (from 3 MeV to 50 MeV), a Coupled Cavity Drift Tube Linac (from 50 MeV to 100 MeV) and a pi-mode structure (PIMS, from 100 to 160 MeV), all operating at a frequency of 352 MHz. End-to-end beam dynamics simulations have been carried out in parallel with the codes PATH and TRACEWIN to optimise the design and performance of the accelerator and at the same time to guarantee a cross-check of the results found. An extensive statistical campaign of longitudinal error studies (static and dynamic) was then launched for validation of the proposed design and to assess the maximum level of RF jitter/inaccuracies (in both phase and amplitude) the system can tolerate before beam quality at injection in the PS Booster - and later in the SPL- is compromised.

• K. Hanke, G. Bellodi, J.-B. Lallement, A.M. Lombardi, B. Mikulec, M. Pasini, U. Raich, E.Zh. Sargsyan
  CERN, Geneva
• H. Hori
  MPQ, Garching, Munich

Linac 4 is a 160 MeV H^- linac which will become the new injector for CERN's proton accelerator chain. The linac will consist of 4 different rf structures, namely RFQ, DTL, CCDTL and PIMS running at 352.2 MHz with 2 Hz repetition rate and 0.4 ms pulse length. A chopper line ensures clean injection into the PS Booster. The combination of high frequency and a high-current, low-emittance beam calls for a compact design where minimum space is left for diagnostics. On the other hand, diagnostics is needed for setting up and tuning of the machine during both commissioning and operation. A measurement strategy and the corresponding choice of the diagnostic devices and their specific use in Linac4 are discussed in this paper.