Bräuning, H.

Frühauf, J.

Graf, Horst

Löchner, S.

Reiter, A.

Witthaus, M.

GSI Repository

Pilot study of beam position and profile monitoring for the pBar targetA. Reiter, H. Bra¨uning, J. Fru¨hauf, H. Graf, S. Lo¨chner, M. WitthausGSI, Darmstadt, GermanyAt secondary target installations like the FAIR antipro-ton target, monitoring of the beam-target-overlap is a cru-cial task for the beam instrumentation. For antiproton pro-duction an intense 29 GeV proton beam pulse is extractedwithin 50 ns from the SIS100 synchrotron. The primarybeam is focussed after a 3 m drift section in air on a 3 mmNickel target rod. Because the target station is surroundedby a 1 m iron shielding, the spot size must be derived fromdetectors in the short drift section. To this purpose the per-formance of two detectors operating in air has been studiedwith 300 MeV/u Nickel beams and fast extraction.Figure 1: Air-BPM (front) with two electrodes (Bottom andTop) shown on the left; SEM-Grid (at back) with HV elec-trodes that cover the arrays of Tungsten wires.Experiment Setup and ResultsTwo radiation-hard detectors were installed at the end ofthe HTP beam line next to the dump (see Figure 1):• ”Air-BPM”: This detector consists of two diagonally-cut 135 mm electrodes, separated by a ground guard,and was placed 50 mm from the beam axis. A verticalmotor drive typically moved the device in 1 mm steps.• SEM-Grid: This detector is an existing GSI designmounted on an external pneumatic drive 20 cm infront of the beam dump. No high voltage was applied.Both detectors were connected via pulse-stretchers tocharge-to-frequency converter POLAND units [1] and readout via FESA, the new FAIR standard for acquisition sys-tems. For each spill offset-corrected data were stored forfurther analysis. The Air-BPM signals were fed to thePOLAND units via 80 m long coaxial cables to emulatethe situation in the target hall where 150 m are required.Figure 2: Scan of Air-BPM for 1x109 Ni ions (A) and ver-tical SEM-Grid profile for 2.5x109 Ni ions (B).In Figure 2 detector signals of Air-BPM (A) and SEM-Grid (B) are presented. The Air-BPM was scanned throughthe beam in 1 mm steps. For each of the 15 positions tenspills were analysed and the normalised ratio ’difference-over-sum’ ∆/Σ calculated. The measured gradient of∆/Σ=(1.42±0.02)%/mm is in good agreement with thetheoretical value based on the electrode geometry.The vertical profile shows a smooth distribution with a kinkat 19 mm, which might be due to imperfections in the offsetsubtraction. The full profile width of 10 mm fairly agreeswith the data of Cromox screen and SEM-Grid in the up-stream diagnostic chamber. The calculated charge integralis only 20% lower than the prediction of Sternglas [2]. Sim-ilar ratios have been observed in ref. [3] and by the authorsfor other data sets of SEM-Grids installed in vacuum. How-ever, the present data are yet too sparce to conclude that thesecondary electron yield does not suffer significantly fromoperation in air. Further data need to back up the presentencouraging results.References[1] S. Lo¨chner et al., GSI Scientific Report 2013, Darmstadt.[2] E. J. Sternglas, Phys. Rev. 108 (1957) 1.[3] C. Nociforo et al., ”Profile Monitors for the Super-FRS”, ThisScientific Report.GSI SCIENTIFIC REPORT 2014 FG-GENERAL-32DOI:10.15120/GR-2015-1-FG-GENERAL-32 449

Pilot study of beam position and profile monitoring for the pBar target

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Pilot study of beam position and profile monitoring for the pBar target

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