Appelshäuser, H.

Arend, A.

Baumann, C.

Bel, T.

Blume, C.

Dillenseger, P.

Hellbär, E.

Reuß, K.

Roether, F.

Seidl, M.

GSI Repository

Construction and simulations of full-size CBM-TRD prototypes withoutdrift region∗E. Hellba¨r, H. Appelsha¨user, A. Arend, C. Baumann, T. Bel, C. Blume, P. Dillenseger, K. Reuß,F. Roether, and M. SeidlInstitut fu¨r Kernphysik, Goethe-Universita¨t, Frankfurt am Main, GermanyTo provide a fast and efficient e/π separation and chargedparticle tracking for the Compressed Baryonic Matter(CBM) experiment a Transition Radiation Detector (TRD)based on a thin Multiwire Proportional Chamber (MWPC)without an additional drift region is considered [1].Corresponding to this design two full-size prototypeshave been developed and built with an anode-cathode spac-ing of 4 mm and 5 mm, respectively, resulting in amplifi-cation regions of 8 mm and 10 mm depth. The gold-platedtungsten wires with a diameter of 20 μm have a pitch of2.5 mm. They are glued on distance ledges which are at-tached to the frame of the detector made out of aluminiumwith dimensions of 60 × 60 cm2. The back side con-sists of a honeycomb structure supporting the pad plane.The common pad plane design features different pad sizes,where the read-out pads used during tests have a size of7.125 × 75 mm2. A second frame to seal the MWPC in-cludes a thin aluminized mylar foil serving as the entrancewindow as well as an optional support structure. Figure 1shows a technical drawing of the prototypes with the afore-mentioned components.To avoid large changes of the gas gain due to its defor-mation the thin mylar foil has to be stretched uniformlyand with appropriate tension. To achieve this requirementa method based on thermal expansion is being used [2].The foil is fixed to a plexiglass frame which is heated upby heating coils resulting in the expansion of the frame andthus a mechanical stretching of the foil. To quantitativelyanalyse the bulge of the stretched foil caused by overpres-sure inside the chamber the deformation of the entrancewindow and the mechanical stress of the MWPC body aresimulated with the Abaqus software package [3]. Accord-ing to these simulations the entrance window stretched ata plexiglass temperature of 55◦C gets deformed by 160μm at an overpressure of 0.01 mbar which is verified bymeasurements. The resulting gain variation as a functionof the modified distance between the entrance window andthe anode wires is simulated with Garfield [4] and shownfor three detector geometries without drift region in Fig-ure 2. Keeping the deformation of the entrance windowbelow than 120 μm leads to a gain variation of less than10% and can be achieved by limiting the differential gaspressure variations to less than 0.01 mbar.The full-size prototypes described in this article weretested along with several other considered prototype geo-metries with dedicated drift regions at the common testbeam campaign at CERN-PS in October 2012 [5][6].∗Work supported by BMBF and HICforFAIRFigure 1: Technical drawing of a full-size TRD-prototypewithout drift region.m]μd [-300 -200 -100 0 100 200 300Gain(0)Gain(d)0.80.911.11.21.31.4 (20%) for2Relative gain with Xe(80%)/CO4+4mm MWPC 1940V, Gain(0)=22245+5mm MWPC 2220V, Gain(0)=22276+6mm MWPC 2500V, Gain(0)=2229Figure 2: Relative gain depending on the displacement ofthe entrance window for three detector types without driftregion.References[1] P. Reichelt, H. Appelsha¨user, and M. Hartig, CBM ProgressReport 2010, Darmstadt 2011, p. 39.[2] Michael Staib et al., RD51-Note-2011-004.[3] http://www.3ds.com/de/products/simulia/portfolio/abaqus/overview/[4] http://garfield.web.cern.ch/garfield/[5] P. Dillenseger et al., In-beam performance studies of the firstfull-size CBM-TRD prototypes developed in Frankfurt, thisreport.[6] D. Emschermann et al., Common CBM beam test of theRICH, TRD and TOF subsystems at the CERN PS T9 beamline in 2012, this report.PHN-NQM-EXP-31 GSI SCIENTIFIC REPORT 201260

Construction and simulations of full-size CBM-TRD prototypes without drift  region

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Construction and simulations of full-size CBM-TRD prototypes without drift region

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