• C. Rossi, P. Bourquin, J.-B. Lallement, A.M. Lombardi, S.J. Mathot, M.A. Timmins, G. Vandoni, M. Vretenar
  CERN, Geneva
• S. Cazaux, O. Delferrière, M. Desmons, R.D. Duperrier, A. France, D. Leboeuf, O. Piquet
  CEA, Gif-sur-Yvette

The first stage of acceleration in Linac4, the new 160 MeV CERN H^- injector, is a 352 MHz, 3 m long Radiofrequency Quadrupole (RFQ) Accelerator. The RFQ will capture a 70 mA, 45 keV beam from the rf source and accelerate it to 3 MeV, an energy suitable for chopping and injecting the beam in a conventional Drift Tube Linac. Although the RFQ will be initially operated at low duty cycle (0.1%), its design is compatible with higher duty cycle (10%) as the front-end for a possible high-intensity upgrade of the CERN linac facility. The RFQ will be of the brazed-copper design and will be built and assembled at CERN. Beam dynamics design allows for a compact structure made of a single resonant unit. Field symmetry is ensured by fixed tuners placed along the structure. In this paper we present the rf and mechanical design, the beam dynamics and the sensitivity to fabrication and to rf errors.

• 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.