Development of high-rate timing RPCs L. Lopes 1,2, R. Ferreira Marques 1,2, P. Fonte 1,3, A. Pereira 1, V. Peskov 4, A. Policarpo 1,2 1 - Laboratório de Instrumentação e Física Experimental de Partículas (LIP), Portugal. 2 - Departamento de Física, Universidade de Coimbra,Portugal. 3 - Instituto Superior de Engenharia de Coimbra, Portugal. 4 - Royal Institute of Technology, Stockholm, Sweden.

P.Fonte CBM collaboration meeting GSI Rate capability – Standard RPCs Timing RPCs

P.Fonte CBM collaboration meeting GSI Rate capability – Special RPCs PPAC microRPC Si plate  =10 4  cm -HV mm Drift gap Amplification gap Resistive anode on a metal base  = 10 7  cm Wire meshes (50  m wires at 0.5 mm pitch) 15 mm 3.5 mm Protected PPAC microRPC Avalanche Charge (electrons) 1.0E E E+07 What about timing RPC? Gain is huge (G 0 ~10 12 ) Must be tested. [Fonte et al., 1999] [Carlson et al, NSS2001]

P.Fonte CBM collaboration meeting GSI Construction technique No spacers Resistive electrode ENSITAL ® SD (polimer)  ~ 4  10 9  cm Good surface finish Commercial material Gas system Gas filters used to prevent discharges due to gas impurities Gas Mixture: TFE (R-134a) / SF 6 = 90% / 10% Assembled under clean conditions

P.Fonte CBM collaboration meeting GSI Test Setup

P.Fonte CBM collaboration meeting GSI Event Generation Compton scattering Very low background counting rate during all the measurements. Less than 2 Hz/cm 2 below the streamer threshold. 511 keV photons from the annihilation of positrons 662 keV

P.Fonte CBM collaboration meeting GSI Acquisition System

P.Fonte CBM collaboration meeting GSI Results - Current & Counting Rate Tired chamber Current saturation due to electrode resistivity around 2.8 kV Linear due to space charge effect ( kHz/cm 2 ) Counting plateau

P.Fonte CBM collaboration meeting GSI Results – Charge Streamer Threshold 22 Na (0.8 mCi) Low rate: 2000 Hz/cm 2

P.Fonte CBM collaboration meeting GSI Time Resolution i0i0 beam  ~ 50 ps Wider initial current distribution photons  ~ 90 ps Compton electrons

P.Fonte CBM collaboration meeting GSI Results - Time Resolution 1 The time resolution remains essentially unchanged from 2 kHz/cm 2 to 25 kHz/cm 2 at a level around 90 ps . Typical time spectrum

P.Fonte CBM collaboration meeting GSI Results - Time Resolution 2 For a given counting rate, an increase of the applied voltage doesn't considerably improve the time resolution Counting Plateau

P.Fonte CBM collaboration meeting GSI Problems – Chamber Current I f  0.95I i at 1.55 m from source I f  0.90I i at 0.85 m from source Time elapsed between I i and I f, 8 min on average The counting rate presents a similar behaviour

P.Fonte CBM collaboration meeting GSI Problems - Electrode resistivity After 5 min with  V= 0 V  i+5 = 1.15  i on average. After 20 min with  V= 0 V  i+20 = 1.30  i External Measurement Short term behaviour

P.Fonte CBM collaboration meeting GSI Problems - Electrode resistivity External Measurement 0 V600 V100 V i=185 nA i=122 nA Full recovery also possible Average value during beam test 2x10 10

P.Fonte CBM collaboration meeting GSI Problems - Electrode Resistance Seems to be a typical behaviour of ionic conductors. Recoverable  may work in a low duty cycle situation. Not full solution  find something else

P.Fonte CBM collaboration meeting GSI Results - Current & Counting Rate ( kHz/cm 2 ) 60 Co (3000 Ci) Initially, when the electrode presents its lower volume resistivity, it is possible to reach much higher currents and counting rates.

P.Fonte CBM collaboration meeting GSI Conclusions Time resolution of 90 ps  was demonstrated at 25 kHz/cm 2. Commercial plastic material, ionic conductor  must find something else. Very active field within the ATOF/I3HP project... Up to 50 kHz/cm 2 with the lowest resistivity value (but no time information). Strict clean conditions must be observed. Considerably more difficult technology than low rate RPC.