• A. Jeff, S. Bart Pedersen, A. Boccardi, E. Bravin, T. Lefèvre, A. Rabiller, F. Roncarolo
  CERN, Geneva
• A.S. Fisher
  SLAC, Menlo Park, California
• C.P. Welsch
  The University of Liverpool, Liverpool

Synchrotron radiation is currently used on LHC for beam imaging and for monitoring the proton population in the 3 microsecond abort gap. In addition to these existing detectors, a study has been initiated to provide longitudinal density profiles of the LHC beams with a high dynamic range and a 50ps time resolution. This would allow for the precise measurement both of the bunch shape and the number of particles in the bunch tail or drifting into ghost bunches. A solution is proposed based on counting synchrotron light photons with two fast avalanche photo‐diodes (APD) operated in Geiger mode. One is free‐running but heavily attenuated and can be used to measure the core of the bunch. The other is much more sensitive, for the measurement of the bunch tails, but must be gated off during the passage of the core of the bunch to prevent the detector from saturating. An algorithm is then applied to combine the two measurements and correct for the detector dead time, after pulsing and pile‐up effects. Initial results from laboratory testing of this system are described in this paper.

• D. Egger
  EPFL, Lausanne
• A.E. Dabrowski, S. Döbert, D. Egger, T. Lefèvre, O. Mete
  CERN, Geneva

To improve the quality of the CLIC Test Facility 3 drive beam, it has been proposed that a photo injector replaces the actual thermionic gun. This would produce a lower emittance beam and minimize beam losses in the injector since the RF bunching and sub‐harmonic bunching systems would not be needed anymore. Such a photo injector, named PHIN, is currently being developed at CERN. One of the difficulties is to provide a high intensity beam (3.5A) with a stable (0.1%) beam energy over 1.5us as well as a relative energy spread less than 1%. A 90° spectrometer line featuring a segmented dump and an Optical Transition Radiation screen has been constructed and commissioned in order to study the time evolution of the beam energy along the pulse duration. In the following paper, we present the design as well as the results from the previous two PHIN runs.

• T. Lefèvre, E. Bravin, G. Burtin, A. Guerrero, A. Jeff, A. Rabiller, F. Roncarolo
  CERN, Geneva
• A.S. Fisher
  SLAC, Menlo Park, California

On the Large Hadron Collider (LHC), the continuous monitoring of the transverse sizes of the beams relies on the use of synchrotron radiation and intensified video cameras. Depending on the beam energy different synchrotron light sources must be used. A dedicated superconducting undulator has been built for low beam energies (450 GeV to 3 TeV), while edge and centre radiation from a beam separation dipole magnet are used respectively for intermediate and high energies (up to 7 TeV). The emitted visible photons are collected using a retractable mirror, which sends the light into an optical system adapted for acquisition using intensified CCD cameras. This paper presents the performance of the imaging system in terms of spatial resolution, and comments on the light intensity obtained and the cross calibration performed with the wire scanners. Upgrades and future plans are also discussed.

• A.E. Dabrowski, S. Bettoni, E. Bravin, R. Corsini, S. Döbert, T. Lefèvre, A. Rabiller, P.K. Skowronski, L. Søby, F. Tecker
  CERN, Geneva
• D. Egger
  EPFL, Lausanne
• A. Ferrari
  Uppsala University, Uppsala
• C.P. Welsch
  The University of Liverpool, Liverpool

The CTF3 facility is being built and commissioned by an international collaboration in order to test the feasibility of the proposed CLIC drive beam generation scheme. Central to this scheme is the use of RF deflectors to inject bunches into a Delay Loop and a Combiner Ring, in order to transform the initial bunch spacing of 1.5 GHz from the linac to a final bunch spacing of 12 GHz. The optimization procedure relies on several steps. The active length of each ring is carefully adjusted to within a few millimeters accuracy using a two‐period undulator. The transverse optics of the machine must be set-up in a way so as to ensure the beam isochronicity. Diagnostics based on optical streak cameras and RF power measurements have been designed to measure the longitudinal behaviour of the beam during the combination. This paper presents their performance and highlights recent measurements.

• M. Olvegård, E. Bravin, F. Carra, N.C. Chritin, A.E. Dabrowski, A. Dallocchio, S. Döbert, T. Lefèvre
  CERN, Geneva
• E. Adli
  University of Oslo, Oslo

The CLIC study is based on the so‐called two‐beam acceleration concept and one of the main goals of the CLIC Test Facility 3 is to demonstrate the efficiency of the CLIC RF power production scheme. As part of this facility a Test Beam Line (TBL), presently under commissioning, is a small scale version of a CLIC decelerator. To perform as expected the beam line must show efficient and stable RF power production over 16 consecutive decelerating structures. As the high intensity electron beam is decelerated its energy spread grows by up to 60%. A novel segmented beam dump for time resolved energy measurements has been designed to match the requirements of the TBL. As a complement, a diffusive OTR screen is also installed in the same spectrometer line. The combination of these two devices will provide both a high spatial resolution measurement of both the energy and energy spread and a measurement with a few nanoseconds time response. This paper describes the design of the new segmented dump and presents the results from the first commissioning of the TBL spectrometer line.

• M. Micheler, G.A. Blair, G.E. Boorman, V. Karataev, K. Lekomtsev
  JAI, Egham, Surrey
• R. Corsini, A.E. Dabrowski, T. Lefèvre
  CERN, Geneva
• S. Molloy
  Royal Holloway, University of London, Surrey

A setup for the investigation of Coherent Diffraction Radiation (CDR) from a conducting screen as a tool for non-invasive longitudinal electron beam profile diagnostics has been designed and installed in the Combiner Ring Measurement (CRM) line of the CLIC Test Facility (CTF3, CERN). In this report the status of the monitor development and results on the interferometric measurements of CDR spectra are presented. The CDR signal correlation with an RF pickup and a streak camera is reported. The future plans for the system improvements are also discussed.

• T. Lefèvre, S. Bart Pedersen, A. Boccardi, E. Bravin, A. Goldblatt, A. Jeff, F. Roncarolo
  CERN, Geneva
• A.S. Fisher
  SLAC, Menlo Park, California

The LHC beam dump system relies on extraction kickers that need 3 microseconds to rise up to their nominal field. As a consequence, particles crossing the kickers during this rise time will not be dumped properly. The proton population during this time should remain below quench and damage limits at all times. A specific monitor has been designed to measure the particle population in this gap. It is based on the detection of Synchrotron radiation using a gated photomultiplier. Since the quench and damage limits change with the beam energy, the acceptable population in the abort gap and the settings of the monitor must be adapted accordingly. This paper presents the design of the monitor, the calibration procedure and the detector performance with beam.

• M. Meddahi, S. Bart Pedersen, A. Boccardi, A.C. Butterworth, B. Goddard, G.H. Hemelsoet, W. Höfle, D. Jacquet, M. Jaussi, V. Kain, T. Lefèvre, E.N. Shaposhnikova, J.A. Uythoven, D. Valuch
  CERN, Geneva
• A.S. Fisher
  SLAC, Menlo Park, California
• E. Gianfelice-Wendt
  Fermilab, Batavia

Unbunched beam is a potentially serious issue in the LHC as it may quench the superconducting magnets during a beam abort. Unbunched particles, either not captured by the RF system at injection or leaking out of the RF bucket, will be removed by using the existing damper kickers to excite resonantly the particles in the abort gap. Following beam simulations, a strategy for cleaning the abort gap at different energies was proposed. The plans for the commissioning of the beam abort gap cleaning are described, and the first results from the beam commissioning are presented.

• M. Petrarca, E. Chevallay, A.E. Dabrowski, M. Divall Csatari, S. Döbert, D. Egger, V. Fedosseev, T. Lefèvre, R. Losito, O. Mete
  CERN, Geneva

The high charge PHIN photo injector is studied at CERN as an electron source for the CLIC Test Facility (CTF3) drive beam as an alternative to the present thermionic gun. The objective of PHIN is to demonstrate the feasibility of a laser-based electron source for CLIC. The photo injector operates with a 2.5 cell, 3 GHz RF gun using a Cs2Te photocathode illuminated by UV laser pulses generated by amplifying and frequency quadrupling the signal from a Nd:YLF oscillator running at 1.5GHz. The challenge is to generate a beam structure of 1908μbunches with 2.33nC perμbunch at 1.5GHz leading to a high integrated train charge of 4446nC and nominal beam energy of 5.5MeV with current stability below 1%. In the present test stand, a segmented beam dump has been implemented allowing a time resolved measurement of the energy and energy spread of the electron beam. In this paper we report and discuss the measured transverse and longitudinal beam parameters for both the full and time gated train of bunches, and the obtained photocathode quantum efficiency. Laser pointing and amplitude stability results are discussed taking into account correlation between laser and electron beam.