Amend, W.

Arend, A.

Blume, C.

Dillenseger, P.

Glässel, S.

Roether, F.

GSI Repository

Construction and first performance studies of a CBM TRD prototype withalternating wires developed in Frankfurt∗S. Gla¨ßel, W. Amend, A. Arend, C. Blume, P. Dillenseger, and F. RoetherInstitut fu¨r Kernphysik, Goethe-Universita¨t, Frankfurt am Main, GermanyIntroductionThe Transition-Radiation Detector (TRD) for the Com-pressed Baryonic Matter (CBM) experiment at the Facil-ity for Antiproton and Ion Research (FAIR) has to deliverelectron identification and tracking performance in a highparticle-density environment. To deliver the required fastdetector response for the expected high signal rates, a thinMulti-Wire Proportional Chamber (MWPC) without driftregion has been developed [1].One key challenge of this setup is the sensitivity of thefield geometry to deformations of the cathode planes. Witha thin foil as front cathode, even minor internal pressurevariations can affect the gas gain [2]. In order to mini-mize this effect, the robust field geometry of an alternat-ing wire structure, as proposed for the ALICE VHMPID[3], has been explored. Field wires are introduced betweenthe sense wires to generate field lines from the field to thesense wires that are independent of the front cathode. Con-sequently, the electrical field in the sensitive area near theentrance window becomes significantly lower.Construction and experimental set-upTo study the effects of an alternating wire set up on thegas gain, a small aluminium prototype with dimensions of21,8 x 21,8 cm2 has been built. Thin sense wires (gold-plated tungsten, 20 µm) and thicker field wires (copper,79 µm) are arranged on the anode plane with a pitch of2.5 mm. A thin aluminized Mylar-foil (19 µm) serves asfront cathode and entrance window at the same time. Apadplane with 15 read-out pads is used as rear cathode.Both, front and rear cathode, have a distance of 4 mm tothe anode plane, leading to a total gas gap of 8 mm (seeFig. 1).Figure 1: Schematic profile with field lines of the new pro-totype with alternating wires.First measurements in a laboratory environment were∗Work supported by BMBF and HIC for FAIR.performed with an 55Fe source. The sense wire current wasmeasured for different positions at various differential pres-sures. Field wires were on ground potential. A standardprototype without field wires and with similar dimensionswas employed for reference measurements.ResultsThe first tests give a clear indication for a superior per-formance in terms of gas gain stability for the new proto-type. The effect that the gas gain shows variations up to60 % in the case of internal overpressure, as seen for thestandard set up, is drastically reduced for the setup withalternating wires (variations are below 10 %, as shown inFig. 2).Figure 2: Gas gain as function of position at 0.5 mbar over-pressure for standard (left) and new prototype (right).OutlookThe superior performance of the new prototype will befurther investigated to confirm it on a quantitative level.Measurements with different field wire potentials and ofthe energy resolution will be performed.A second prototype with alternating wires and an asym-metric structure, i.e. the wire plane is moved towards thereadout cathode, has been built and will be tested as well.References[1] P. Dillenseger et al., “In-beam performance studies of the firstfull-size CBM-TRD prototypes developed in Frankfurt ”, GSIScientific Report 2012 (2013) 66.[2] E. Hellba¨r et al., “Construction and simulations of full-sizeCBM-TRD prototypes without drift region”, GSI ScientificReport 2012 (2013) 60.[3] D. Varga et al., “Close cathode chamber: Low material bud-get MWPC”, Nuclear Instruments and Methods in PhysicsResearch, 2013, p. 11-18.NQM-CBM-30 GSI SCIENTIFIC REPORT 201346 doi:10.15120/GR-2014-1-NQM-CBM-30

Construction and first performance studies of a CBM TRD prototype with alternating wires developed in Frankfurt

http://repository.gsi.de/record/67776/files/NQM-CBM-30.pdf

Construction and first performance studies of a CBM TRD prototype with alternating wires developed in Frankfurt

Abstract

Similar works

Full text

Available Versions

GSI Repository