Status of the ALICE TPC upgrade C. Garabatos

Running at 50 kHz Pb-Pb after LS2 No GG triggering, continuous readout This leads to electric field distortions of the order of the electric field -> space point distortions of order 1 m –MWPC are not an option S. Rossegger TPC Upgrade - LHCC2

In addition, space-charge in the amplification region Maximum particle rate of kHz/cm 2 -> sizeable gain drop -> deterioration of dE/dx D. Gonzalez-Diaz 1 et al TPC Upgrade - LHCC3

Alternative: GEMs No issue with rate capability Possibility to efficiently block ions Lower (effective) gain (all (electron) signal is collected): TPC Upgrade - LHCC4

However R&D is needed to settle a few issues with GEMs – Ion back-flow – typically few % if optimised for position resolution only – Gain stability – charging up processes, rate dependence… – Position and momentum resolution – not a show stopper – Stability under LHC conditions – to be tested – New electronics needed (speed, signal polarity) – profit from a common ALICE effort TPC Upgrade - LHCC5

Start work Need collaborators: so far no official Collaboration, but the reaction of the community has been very positive and helpful Decisive support from – CERN RD51 (L. Ropelewski, E. Oliveri) – GSI (U. Frankenfeld, J. Hehner) – Lund (A. Oskarsson, P. Christiansen) Institutions which are already working with us – TUM Munich (L. Fabbietti, B. Ketzer, M. Berger, P. Gasik) – Universidad Nacional Autónoma, Mexico (V. Peskov) – University of Tokyo, Japan (Y. Yamaguchi, T. Gunji, H. Hamagaki, …) Institutions which wish to work with us – Comenius University, Slovakia – Helsinki Institute of Physics, Finland – Yale University, United States TPC Upgrade - LHCC6

Ion back-flow (IBF) issue Opacity of GEMs to ions depends on field configuration, GEM geometry, gas, etc –needs systematic studies For the ALICE TPC, IBF ~ 0.25% at gain 2000 leads to reasonable distortions – this is our goal S. Rossegger TPC Upgrade - LHCC7

R&D on IBF in the lab TPC Upgrade - LHCC8 Set-up a stand in the RD51 GEM lab – conveniently change any gain or field Started measurements with 10x10 cm 2 foils in April

ALICE IFB measurements in GEM lab Systematic scans of voltages and fields have started in the lab, in order to understand – minimise- ion back flow Y. Yamaguchi TPC Upgrade - LHCC9

ALICE IBF simulations with Garfield++ Code for full charge transport and development of avalanches in C++ available from R. Veenhof First results before tuning code to measurement, by T.Gunji Pursue a configuration with low E T2 and low  V GEM TPC Upgrade - LHCC10

IBF status First measurements and simulations have started We are already twithin a factor 2 Next: play with geometry –GEM optical transparency TPC Upgrade - LHCC11

dE/dx: gain dependence of GEMs Gain increases at switch-on (30%) Effect depends on foil properties and rate (mins-hour) Slow decrease with time (hours/days) Slow decrease at switch-off (days) Gain depends on rate ☞ Calibration issue TPC Upgrade - LHCC F. Sauli et al, NIM A409 (2002) B. Azmoun et al, 2006 IEEE NSS F. Simon et al, IEEE TNS 54-6 (2007)

Gain stability with time and rate We have produced GEM foils at CERN (10x10 cm 2 ), with cylindrical, rather than bi-conical, holes Time (min) Current (nA) Ne+12%CO2, beta source Gas gain 200 Switch off the HV First look by V. Peskov TPC Upgrade - LHCC13

Gain stability –next steps Systematic studies of Gain vs. time for various initial conditions, particle flux, hole geometry, hole pitch (optical transparency) Study Japanese GEMs made in LCP and laser+plasma etching technology (cylindrical holes) Study the charging-up effects, and others, with simulations (R. Veenhof) Consider adding some ppm of H 2 O (we already have it) TPC Upgrade - LHCC14

Performance simulations - Position resolution 20% deterioration due to lack of PRF – with present pad planes Further deterioration at short drift distances TPC Upgrade - LHCC15 H. Appelshaeuser

Performance simulations – Momentum resolution 20% difference visible for TPC standalone tracking difference diminishes when constrained to vertex or combined with IST difference probably negligible when TRD is also included existing pad pattern OK! TPC Upgrade - LHCC16

Prototype: IROC machined and ready with box for shipment to Munich Chamber will be instrumented with single-mask GEMs for tests in lab, PS and LHC GEM foils expected for end of June TPC Upgrade - Test prototype17

Operation in LHC conditions The best it to build a prototype and put it in the ALICE cavern, close to the beam, during the forthcoming p-Pb period in November Use a spare IROC, remove the wires, put GEMs, and install it in ALICE – Single mask GEMs – HV, gas, simple readout, … – No dE/dx possible in these conditions; monitor gain TPC Upgrade - LHCC18 IROC prototype

Test beam in the PS Measure dE/dx for p,  from 1 to 6 GeV/c 10 FECs from ILCTPC – Lund – RCU readout with DATE and LTU Parasite ALICE test beams (VHMPID, TOF) Prepare DAQ, online, external PID (TOF), modify chamber box, … Aim for September 2012 – expect help from several people … TPC Upgrade - LHCC19

Prototype time line 6 foils ordered at CERN, to be delivered end of June Chamber body ready; to be shipped to Munich ~now Mounting of GEMs and tests in Munich till beginning of August Ship to CERN, equip with 10 FECs, final tests in La Total lab PS test beam in September Installation in ALICE cavern end of October TPC Upgrade - LHCC20

LS2: chamber options Existing pad-planes and chamber bodies with GEMs – cheaper, but short time to replace and test New chamber bodies with equal pad sizes – more money, more time to test New chamber bodies and smaller pads – even more money, ‘full’ performance TPC Upgrade - LHCC21

Electronics TPC Upgrade - LHCC22

Conclusions Prospects of a TPC upgrade with GEMs have produced excitement in the community and in ALICE – groups are joining A lot of activity has started, but nothing is official yet We hope to settle all issues by end TPC Upgrade - LHCC23

Backup TPC Upgrade - LHCC24

TPC Upgrade - LHCC25

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Possible run at the PS We might get a couple of days or nights in some of these slots. The later, the better TPC Upgrade - Test prototype27

TPC Upgrade - LHCC28