• R. Chamizo, H.-H. Braun, N.C. Chritin, D. Grenier, J. Hansen, Y. Kadi, L. Massidda, Th. Otto, R. Rocca, R. Zennaro
  CERN, Geneva

The CERN CLIC test facility (CTF3) aims at assessing the feasibility of the future multi-TeV Compact Linear Collider (CLIC). The CTF3 Tail Clipper Collimator (TCC) will serve to adjust the bunch train length of the beam extracted from the combiner ring, in combination with a fast kicker magnet. In addition, the TCC will operate, when required, as an internal beam dump. The challenge of the TCC design is to meet the requirements of both collimator and dump operational modes for a low energy e^- beam (100-300 MeV) of 35 A peak intensity. The TCC collimator will be installed at the end of 2008 in the TL2 transfer line of CTF3. This paper describes the final design of the TCC and the main issues related to its integration in the line.

• A. Grudiev, H.-H. Braun, D. Schulte, W. Wuensch
  CERN, Geneva

Recently the CLIC study has changed the operating frequency and accelerating gradient of the main linac from 30 GHz and 150 MV/m to 12 GHz and 100 MV/m, respectively. This major change of parameters has been driven by the results from a novel main linac optimization procedure. The procedure allows simultaneous optimization of operating frequency, accelerating gradient, and many other parameters of CLIC main linac. It takes into account both beam dynamics (BD) and high power rf constraints. BD constraints are related to emittance growth due to short- and long-range transverse wakefields. Rf constraints are related to rf breakdown and pulsed surface heating of the accelerating structure. The optimization figure of merit includes the power efficiency, measured as a ratio of luminosity to the input power as well as a quantity proportional to investment cost.

• A.E. Dabrowski, S. Bettoni, H.-H. Braun, E. Bravin, R. Corsini, S. Döbert, C. Dutriat, T. Lefèvre, M. Olvegård, P.K. Skowronski, F. Tecker
  CERN, Geneva

In the CLIC Test Facility 3 (CTF3), the strong coupling between the beam and the accelerating cavities (full beam loading) induces transient effects such that the head of the pulse is accelerated almost twice as much as the steady-state part of the pulse. The beam optics in the machine is tailored for the steady-state and not for the higher energy electrons, which are gradually lost. This can lead to inefficiency and contributes to the activation of the machine. A beam loading compensation scheme has been proposed to minimize this effect. By delaying appropriately the arrival time of rf pulse in accelerating cavities with respect to the beam, the transient energy can be brought close (to within a few percent) of the steady-state one. This paper presents the measurements done on CTF3 using time resolved energy measurements.

• A.E. Dabrowski, S. Bettoni, H.-H. Braun, R. Corsini, S. Döbert, T. Lefèvre, H. Shaker, P.K. Skowronski, F. Tecker
  CERN, Geneva
• J.J. Jacobson, M. Velasco
  NU, Evanston

The CLIC Test Facility CTF3, being built at CERN by an international collaboration, should demonstrate the feasibility of the CLIC two-beam technology by 2010. One of the issues addressed is the control of the electron bunch length in the whole complex. A bunch length measurement system with good resolution is therefore paramount. Two different systems are presently used in CTF3, based on microwave spectroscopy and on transverse rf deflectors, respectively. In the paper we describe the two systems, we discuss the different experimental methods used and present the results of the latest measurement campaigns.