Author: Doebert, S.     [Döbert, S.]
Paper Title Page
MOPMR024 A Versatile Beam Loss Monitoring System for CLIC 286
SUPSS070   use link to see paper's listing under its alternate paper code  
 
  • M. Kastriotou, S. Döbert, W. Farabolini, E.B. Holzer, E. Nebot Del Busto, F. Tecker
    CERN, Geneva, Switzerland
  • M. Kastriotou, E. Nebot Del Busto, C.P. Welsch
    The University of Liverpool, Liverpool, United Kingdom
  • M. Kastriotou, C.P. Welsch
    Cockcroft Institute, Warrington, Cheshire, United Kingdom
 
  The design of a potential CLIC beam loss monitoring (BLM) system presents multiple challenges. To successfully cover the 48 km of beamline, ionisation chambers and optical fibre BLMs are under investigation. The former fulfils all CLIC requirements but would need more than 40000 monitors to protect the whole facility. For the latter, the capability of reconstructing the original loss position with a multi-bunch beam pulse and multiple loss locations still needs to be quantified. Two main sources of background for beam loss measurements are identified for CLIC. The two-beam accelerator scheme introduces so-called crosstalk, i.e. detection of losses originating in one beam line by the monitors protecting the other. Moreover, electrons emitted from the inner surface of RF cavities and boosted by the high RF gradients may produce signals in neighbouring BLMs, limiting their ability to detect real beam losses. This contribution presents the results of dedicated experiments performed in the CLIC Test Facility to quantify the position resolution of optical fibre BLMs in a multi-bunch, multi-loss scenario as well as the sensitivity limitations due to crosstalk and electron field emission.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-MOPMR024  
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MOPMR039 Review of Emittance Diagnostics for Space Charge Dominated Beams for AWAKE e- Injector 337
 
  • O. Mete Apsimon, G.X. Xia
    UMAN, Manchester, United Kingdom
  • S. Döbert
    CERN, Geneva, Switzerland
  • C.P. Welsch
    The University of Liverpool, Liverpool, United Kingdom
 
  Funding: This work is supported by the Cockcroft Institute Core Grant and STFC.
For a low energy, high intensity beam, total beam emittance is dominated by defocusing space charge force. This is most commonly observed in photo-injectors. In this low energy regime, emittance measurement techniques such as quadrupole scans fail as they consider the beam size only depends on optical functions. The pepper-pot method is used for 2D emittance measurements in a single shot manner. In order to measure the beam emittance in space charge dominated regime by quadrupole scans, space charge term should be carefully incorporated into the transfer matrices. On the other hand, methods such as divergence interferometry via optical transition radiation (OTRI), phase space tomography using 1D projections of quadrupole scans can be suitably applied for such conditions. In this paper, the design of a versatile pepper-pot system for AWAKE experiment at CERN is presented for a wide range of bunch charges from 0.1 to 1nC where the space charge force increases significantly. In addition, other aforementioned methods and respective algorithms are introduced as alternative methods.
 
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-MOPMR039  
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TUOBB03 CERN AWAKE Facility Readiness for First Beam 1071
 
  • C. Bracco, M. Bernardini, A.C. Butterworth, H. Damerau, S. Döbert, V. Fedosseev, E. Feldbaumer, E. Gschwendtner, W. Höfle, A. Pardons, E.N. Shaposhnikova, H. Vincke
    CERN, Geneva, Switzerland
 
  The AWAKE project at CERN was approved in August 2013 and since then a big effort was made to be able to probe the acceleration of electrons before the "2019-2020 Long Shutdown". The next steps in this challenging schedule will be a dry run of all the beam line systems, at the end of the HW commissioning in June 2016, and the first proton beam sent to the plasma cell one month later. The current status of the project is presented together with an outlook over the foreseen works for operation with electrons in 2018.  
slides icon Slides TUOBB03 [10.682 MB]  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-TUOBB03  
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WEOBB02 Status of Wakefield Monitor Experiments at the CLIC Test Facility 2099
 
  • R.L. Lillestøl, E. Adli, J. Pfingstner
    University of Oslo, Oslo, Norway
  • N. Aftab, S. Javeed
    PINSTECH, Islamabad, Pakistan
  • R. Corsini, S. Döbert, W. Farabolini, A. Grudiev, W. Wuensch
    CERN, Geneva, Switzerland
 
  For the very low emittance beams in CLIC, it is vital to mitigate emittance growth which leads to reduced luminosity in the detectors. One factor that leads to emittance growth is transverse wakefields in the accelerating structures. In order to combat this the structures must be aligned with a precision of a few um. For achieving this tolerance, accelerating structures are equipped with wakefield monitors that measure higher-order dipole modes excited by the beam when offset from the structure axis. We report on such measurements, performed using prototype CLIC accelerating structures which are part of the module installed in the CLIC Test Facility 3 (CTF3) at CERN. Measurements with and without the drive beam that feeds rf power to the structures are compared. Improvements to the experimental setup are discussed, and finally remaining measurements that should be performed before the completion of the program are summarized.  
slides icon Slides WEOBB02 [2.928 MB]  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEOBB02  
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THPMB046 Status and Plans for Completion of the Experimental Programme of the Clic Test Facility Ctf3 3347
 
  • P.K. Skowroński, R. Corsini, S. Döbert, W. Farabolini, D. Gamba, L. Malina, T. Persson, F. Tecker
    CERN, Geneva, Switzerland
  • W. Farabolini
    CEA/DSM/IRFU, France
  • D. Gamba
    JAI, Oxford, United Kingdom
 
  The CLIC Test Facility CTF3 was build, commissioned and operated at CERN by an international collaboration, with the aim of validating the CLIC two beam acceleration scheme, in which the RF power used to accelerate e+/e beams is extracted from a high intensity electron beam. In the past years the main issues of such a scheme were assessed, demonstrating its feasibility. The CTF3 experimental programme is complementing these results by addressing cost and performance subjects, mainly using the CALIFES test beam injector and a full scale two-beam module. In this paper we document the present status and give an outlook to next year run, when the experimental programme should be completed.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-THPMB046  
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THPMB056 Witness Beam Production with an RF Gun and a Travelling Wave Booster Linac for AWAKE Experiment at CERN 3378
 
  • O. Mete Apsimon, G.X. Xia
    UMAN, Manchester, United Kingdom
  • R. Apsimon, G. Burt
    Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
  • S. Döbert
    CERN, Geneva, Switzerland
 
  Funding: This work is supported by the Cockcroft Institute Core Grant and STFC.
AWAKE is a unique experiment that aims to demonstrate the proton driven plasma wakefield acceleration. In this experiment, proton bunches from the SPS accelerator will be injected into a 10m long pre-formed plasma section to form wakefields of hundreds MV/m to several GV/m. A second beam, e.g., the witness beam, will be injected after the protons in an appropriate phase to gain energy from the wakefields. A photo-injector will be utilised to deliver this second beam. It consists of an S-band RF gun followed by a meter long accelerating travelling wave structure (ATS). The RF gun was recuperated from existing PHIN photo-injector. A 3D RF design of the ATS was done by using the CST code and the field maps produced were used to characterise the electron beam dynamics under space charge effect by using the PARMELA code. The impact of the mechanical errors on the beam dynamics were investigated.
 
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-THPMB056  
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THPMY039 RF Synchronization and Distribution for AWAKE at CERN 3743
 
  • H. Damerau, D. Barrientos, T. Bohl, A.C. Butterworth, S. Döbert, W. Höfle, J.C. Molendijk, S.F. Rey, U. Wehrle
    CERN, Geneva, Switzerland
  • J.T. Moody, P. Muggli
    MPI-P, München, Germany
 
  The Advanced Wakefield Experiment at CERN (AWAKE) requires two particle beams and a high power laser pulse to arrive simultaneously in a rubidium plasma cell. A proton bunch from the SPS extracted about once every 30 seconds must be synchronised with the AWAKE laser and the electron beam pulsing at a repetition rate of 10 Hz. The latter is directly generated using a photocathode triggered by part of the laser light, but the exact time of arrival in the plasma cell still depends on the phase of the RF in the accelerating structure. Each beam requires RF signals at characteristic frequencies: 6 GHz, 88.2 MHz and 10 Hz for the synchronisation of the laser pulse, 400.8 MHz and 8.7 kHz for the SPS, as well as 3 GHz to drive the accelerating structure of the electron beam. A low-level RF system has been designed to generate all signals derived from a common reference. Additionally precision triggers, synchronous with the arrival of the beams, will be distributed to beam instrumentation equipment. To suppress delay drifts of the several kilometer long optical fibres between AWAKE and the SPS RF systems, a compensated fibre link is being developed.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-THPMY039  
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THPOR033 Integration and Testing of 3 Consecutive CLIC Two-Beam Modules 3856
 
  • A.L. Vamvakas, M. Aicheler, S. Döbert, M. Duquenne, H.M. Durand, M. Sosin, J.I. Väinölä
    CERN, Geneva, Switzerland
  • V. Rude
    ESGT-CNAM, Le Mans, France
 
  CLIC (Compact LInear Collider) is a study of a 50 km long linear electron-positron collider, consisting of ap-proximately 20,000 repetitive 2 m long modules. Micron level manufacturing and alignment tolerances are re-quired for the RF and magnet components due to the nanometre beam size and luminosity goal. The effect of thermal, vacuum and mechanical loads needs to be as-sessed, both in transient and in steady state conditions. The dynamic behaviour of mock-ups was investigated on the prototype two-beam module. Two additional two-beam modules are installed to further investigate the interconnections between them, in a machine-like envi-ronment. The array of three consecutive modules allows for alignment tests of the module sequence, while thermal and vacuum tests can be executed simultaneously. A transportation experiment is foreseen, investigating the feasibility of installing prealigned modules. Finally, new design of components is being tested, based on the expe-rience gathered from the first module and leading to a new generation module.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-THPOR033  
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THPOR037 TW-Structure Design and E-Field Study for CLIC Booster Linac 3868
 
  • E. Darvish Roknabadi
    IPM, Tehran, Iran
  • S. Döbert
    CERN, Geneva, Switzerland
 
  Using the SUPERFISH code we present a design for a traveling wave (TW) structure of the Booster Linac for CLIC. The structure, consisting of thirty asymmetric cells attached to the beam pipes at two ends, works in 2Pi/3 operating mode at working frequency 2 GHz. The RF field transmitted through the designed cavity is prepared in an RF field data file to be used in the PARMELA code. We will then compare the resultant output PARMELA field with that of the ideal RF field which obtained from the usual method for a traveling wave structure.
* Based on CLIC Note 1051, 2015
 
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-THPOR037  
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THPOW015 Study of the Performance of Cs2Te Cathodes in the PHIN RF Photoinjector using Long Pulse Trains 3960
 
  • C. Heßler, E. Chevallay, S. Döbert, V. Fedosseev, F. Friebel, I. Martini, M. Martyanov, H. Neupert, V. Nistor, M. Taborelli
    CERN, Geneva, Switzerland
 
  The drive beam of CLIC requires unusually high peak and average currents which is challenging for the electron source. As an alternative to the thermionic electron gun foreseen in the baseline design, a photoinjector option is under study at CERN using the PHIN photoinjector, which was designed for a bunch charge of 2.3 nC and 1200 ns train length. During operation with nominal train length in 2014, a large pressure increase in the vacuum system, attributed to a heating of the Faraday cup, caused a degradation of the photocathode. To overcome this problem a vacuum window has been installed to separate the Faraday cup from the rest of the vacuum system. In addition the train length has been further increased to 1600 ns to advance the beam parameters towards CLIC requirements. In this paper recent improved photocathode lifetime measurements carried out under these new conditions will be presented and compared with earlier measurements. Furthermore, the utilized Cs2Te cathode has been analyzed with X-ray Photoelectron Spectroscopy (XPS) before and after its usage in PHIN to get a better understanding of photocathode surface deterioration effects, which will also be discussed.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-THPOW015  
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