Bozyk, L.

Kester, O.

Lavrik, V.

Reiter, A.

GSI Repository

Controlled beam loss experiment at SIS18L.Bozyk1, O.Kester1,2, V.Lavrik∗1,2, and A.Reiter11GSI, Darmstadt, Germany; 2IAP University of Frankfurt, Frankfurt m Main, GermanyThe FAIR beam loss monitoring (BLM) system is basedon different types of particle detectors. Its main purposeis the minimisation of beam losses around the SIS100 syn-chrotron and protection of machine components from un-necessary activation. As a part of a BLM feasibility studyan experiment with controlled losses on a scraper was per-formed at SIS18 section.The aim of this study is the production of beam losses ata well defined position and the measurement of the showerintensity with BLM detectors. In the present setup twoplastic scintillators of the existing BLM system were used.They are installed downstream of a scraper at a distance of2 and 5 meters, respectively. The scraper was positionedclose to the beam orbit. Uranium beams of different en-ergies and intensities in the range of 100-900 MeV/u and108-109 particles were utilized. The beam was injectedinto the SIS18 synchrotron, accelerated and then stored forseveral seconds. During that time the beam was excitedand was slowly impinging on the scraper. The resultingcount rates in the scintillators were monitored through theABLASS data acquisition system[1] and further analysedwith a ROOT code[2]. Figure 1 shows one BLM signal(blue curve) and the DC current transformer signal DCT(black curve) in arbitrary units. In the flattop region no sig-nificant BLM signal is detected. After 2 seconds the exciterwas turned on and produced the shown BLM signal. It wascarefully checked that no significant losses were producedat other locations around the sychrotron.Figure 1: Measured signals of DCT and scintillator in a.u.During the initial storage when the exciter is switchedoff only a small fraction of the beam is lost. In order todetermine the beam life time (see red curve in figure 1) the∗ v.lavrik@gsi.debeam current can be approximated by an exponential func-tion. When the beam exciter is switched on, one can cal-culate the number of lost particles on the scraper for eachtime-bin by taking the difference between the extrapolatedlife time function and the actual number of particles mea-sured by the DCT.For each energy, the data were approximated by a linearfit and the ratio between BLM signal and loss rate was re-trieved. One can interpret this ratio as a normalised showerintensity. This dependency between the ratio and the beamenergy is shown in Figure 2. At low energies it seemsto follow parabolic curve. Starting from 300 MeV/u theshower strength of the beam losses follows the expectedlinear trend which one expects from the results of MonteCarlo simulations. The experiment will be repeated withLHC type ionisation chambers[3] which will be installedduring the next short shutdown in order to measure theirresponse function and estimate their signal strength for pos-sible SIS100 beam loss scenarios.Figure 2: BLM signal to loss rate ratio in dependence onbeam energyReferences[1] T. Hoffmann et al., “Experiences on Counter Applicationsand Beam Loss Measurement at the GSI Synchrotron”, 11thBeam Instrumentation Workshop 2004 (BIW 04), Knoxville,Tennessee, USA, p.294[2] R. Brun, F. Rademakers, “ROOT: An Object-Oriented DataAnalysis Framework”; http://root.cern.ch[3] M. Stockner, “Beam loss calibration studies for high energyproton accelerators”, Ph.D. Thesis, Geneva, 2007.GSI SCIENTIFIC REPORT 2013 FG-SIS18-01doi:10.15120/GR-2014-1-FG-SIS18-01 FAIR@GSI 313

Controlled beam loss experiment at SIS18

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Controlled beam loss experiment at SIS18

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