Fabbietti, L.

Gasik, P.

Mathis, A.

Münzer, R.

GSI Repository

Development of a 4-GEM large-size prototype for the ALICE TPC upgrade ∗P. Gasik†1,2, L. Fabbietti1,2, A. Mathis1,2, R. Muenzer1,2, and the ALICE TPC collaboration1TU Mu¨nchen, Excellence Cluster ‘Origin and Structure of the Universe‘, Boltzmannstr. 2, 85748 Garching, Germany;2TU Mu¨nchen, Physik Department E12, James-Franck-Str. 1, 85748 Garching, GermanyALICE at the LHC at CERN is planning a major upgradeof the central barrel detectors, including the TPC, to copewith an increase of the LHC luminosity after 2018. A full-size prototype of a TPC Inner Read-Out Chamber (IROC)was produced and tested during the test-beam campaign inthe fall of 2014. It was equipped with a quadruple GasElectron Multiplier (GEM [1]) employing GEM foils witha pitch of 140µm (”Standard” - S) and 280µm (”LargePitch” - LP). The subsequent GEM foils in the stack havebeen installed according to the S-LP-LP-S configurationpresented schematically in fig. 1. The design and assem-bly procedure of the 4-GEM prototype follows closely thatof the triple GEM prototype built and tested in 2012 anddescribed in details in [2, 3]. A notable modification withFigure 1: Schematic picture of the 4-GEM IROCrespect to the 2012 setup is that the induction gap (betweenGEM4 and the pad plane) was reduced from 4 mm to 2 mm.The new 4-GEM IROC employs also a cover electrode,which is used to minimise drift-field distortions at the edgesof the GEM stack.Several HV settings were used with the prototype, in-cluding the one defined as ’baseline’ for the ALICE GEMreadout chambers optimised for the ion backflow and en-ergy resolution [4]. A resistor chain was used to supply thepotentials on the subsequent GEM electrodes. The GEMIROC was installed in a test field cage with a drift length of115mm and commissioned with radioactive sources. Theprototype is operated in Ne-CO2-N2 (90-10-5) gas mixture,which is the nominal gas mixture for the upgraded TPC.Figure 2 shows a gain curve obtained for the prototypeusing a 55Fe source. The gain is scaled with a commonscaling factor (SF ) applied to all GEM potentials. Thenominal gain of 2000 is obtained for SF ≈ 100%. Thevalue of ion backflow corresponding to this setting is 0.63%and the energy resolution of a 55Fe peak σ = 11.3% [4].The dE/dx resolution of the prototype was evalu-ated in a test beam campaign at the CERN PS with∗Work supported by GSI, BMBF, BMBF 05P12WOGHH, ExcellenceCluster ’Universe’† p.gasik@tum.deSF (%)95 96 97 98 99 100 101 102 103 104GAIN310 (90-10-5)2-N2Ne-COFigure 2: Gain curve obtained in Ne-CO2-N2 (90-10-5) forthe 4-GEM IROC using scaled ’baseline’ HV settings.1 GeV/c pions and electrons. The relative energy resolutionσ (dE/dx) /〈dE/dx〉 obtained for electrons (∼ 9.1%) andpions (∼ 10.4%) is comparable to the resolution of theMWPC IROC [4].Stability of the chamber was evaluated in a test beam atthe CERN-SPS. The discharge probability was measuredusing showers of hadrons produced by a high-intensity sec-ondary pion beam with a momentum of 150 GeV/c im-pinging on a 30-40 cm thick iron absorber. The averagebeam intensity was ∼6×106 particles per spill, resultingin an average in-spill rate of ∼1.2 MHz. The number ofparticles accumulated during the experiment is NSPStot =(4.7± 0.2) × 1011. The chamber was operated with the’baseline’ settings at the gain of 2000. In total, three dis-charges were detected in the detector. This translates intoa discharge probability of (6± 4) × 10−12 per incominghadron. This result is of the same order of magnitude asthe one obtained by the LHCb Collaboration where thedischarge probability of 3-GEM detectors operated withan isobutane-CF4-based gas mixtures was measured undersimilar conditions [5].References[1] F. Sauli, NIM A386 (1997) 531[2] P. Gasik, JINST 9 (2014) C040394[3] ALICE Collaboration, CERN-LHCC-2013-020 (2013)[4] ALICE Collaboration, CERN-LHCC-2015-002 (2015)[5] G. Bencivenni et al., NIM A494 (2002) 156MU-NQM-ALICE-06 GSI SCIENTIFIC REPORT 2014104 DOI:10.15120/GR-2015-1-MU-NQM-ALICE-06

Development of a 4-GEM large-size prototype for the ALICE TPC upgrade

http://repository.gsi.de/record/183872/files/MU-NQM-ALICE-06.pdf

Development of a 4-GEM large-size prototype for the ALICE TPC upgrade

Abstract

Similar works

Full text

Available Versions

GSI Repository