Bergmann, J.

Dickel, T.

Diwisch, M.

Geissel, H.

Knöbel, R.

Nazarenko, S.

Plaß, W. R.

Scheidenberger, C.

Weick, H.

GSI Repository

Experimental Investigations and Technical Design for The Time-OF-FlightDetectors in the CR at FAIR.∗M. Diwisch1, J. Bergmann1, T. Dickel1,2, H. Geissel1,2, R. Kno¨bel1,2, S. Nazarenko3, W. R. Plaß1,2, C.Scheidenberger1,2, and H. Weick21Justus-Liebig Universita¨t Gießen, Gießen, Germany; 2GSI, Darmstadt, Germany.; 3Tomsk Polytechnic University ,Tomsk, RussiaTechnical design and performancesimulations of a larger TOF detectorTo perform isochronous mass spectrometry (IMS) [1] inthe future CR at FAIR, investigations in instrumentationand designs for a about a factor 2 larger Time-Of-Flight(TOF) detector have been conducted. For future applica-tions of IMS simulations of the CR have been performedand showed, that the currently used 40 mm diameter carbonfoil (areal density: 10µg/cm2) would be too small for thelarge emittance of the beam in the CR and too many ionswould be lost in each turn. This challenge has been metby the the design of an improved and larger TOF detector.The carbon foil size will be increased from 40 mm to 80mm diameter and will be used for the first time. Simply in-creasing the size of the detector leads to decreased timingperformance of the detector. To compensate for this onecan apply higher voltages to the detector to transport thesecondary electrons faster from a carbon foil to the MCPs[2]. As part of the improved design of the larger TOF detec-tor the transport efficency is improved to almost 100% andthe timing resolution to 40 ps. All this is achieved whilekeeping the stringent spatial requirments at the CR.Figure 1: CAD drawing of the new TOF detector sur-rounded by a Helmholtz magnet for the CR which providesthe detector with a homogenious (10−3) magnetic field inthe transport area.∗Work supported by the BMBF under contract No.06GI9115I, bythe HGF (NAVI) and by GSI (strategic university cooperation GSI-JLU-FAIR)Testing of Larger Carbon Foil Properties fora TOF Detector in the CRIn order to investigate the feasibility and the propertiesof those large carbon foils a test chamber has been built. Inthis test chamber the possible changes of the physical prop-erties of larger foils compared to the currently used smallfoils (e.g. flatness of the surface after evacuation of thedetector volume) in the timing performance are measured.The test chamber has been operated in a first step with thecurrently used 40 mm diameter carbon foils. This allowsus to see the differences between small and large foils di-rectly. Measurements are performed with an alpha-sourcefrom which alpha-particles penetrate the carbon foil in thecenter of the chamber and emits secondary electrons whichare detected by two MCP detectors. Simulations predictedthat the secondary electron transport in the setup only con-tributes with only 2 ps to the timing of the whole measure-ment. Experimental predictions state, that the measuredtime uncertainty will therefore be approximately 25 ps andis solely due to effects in the MCPs and flatness of the foil[3].Figure 2: Photography of the assembled test chamber. Thecarbon foil is placed in the center inbetween two grids. Byapplying voltages to the grids the secondary electrons areguided to two MCPs on the side. The diameter of the gridsis 80 mm and therefore has the same size as the future car-bon foils.As soon as the large foils will be available they will betested and compared to the small foils.References[1] J. Tro¨tscher et al., NIM B 70 (1992) 455-458[2] M. Diwisch, Master Thesis, JLU Giessen, (2011)[3] M. Diwisch, PhD Thesis in progress, JLU Giessen, (2014)NUSTAR-FRS-11 GSI SCIENTIFIC REPORT 2013108 doi:10.15120/GR-2014-1-NUSTAR-FRS-11

Experimental Investigations and Technical Design for The Time-OF-Flight Detectors in the CR at FAIR

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Experimental Investigations and Technical Design for The Time-OF-Flight Detectors in the CR at FAIR

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