GIF tests status report Work of several people: Test setup design - PowerPoint PPT Presentation

GIF tests status report • Work of several people: – Test setup design & construction • Oliver, Hubert, engineers, technicians, ... – Data taking & installation at Cern • Jurgen, Albert, Felix, Carl-Friedrich, Julia, Federica – Analysis framework • Felix and Oliver – Data analysis • Albert and Federica – Garfield simulations • Albert, Federica, (Carl-Friedrich, Julia) – MTGeant4 simulations for next GIF tests • Markus 02/08/08 F. Legger 1

GIF analysis 02/08/08 F. Legger 2

The test setup cosmic muon ref. chambers 50 cm long LHCb standard MDT tubes 6 small tubes (1 m long) COMPASS Trigger: 2 layers of 6 scintillators 02/08/08 F. Legger 3

The setup at the GIF DAQ LHCb MWPC chamber • 20 M events • Threshold scan: Source 34, 36, 38 mV Cs 137 • HV scan: 2700, 2745, 2760 V 590 GBq • Counting rate scan: 50, 800, 1100, 1400 Hz/cm 2 Gas 02/08/08 F. Legger 4

GIF measurements • Run length ~ 12 hours (1M evts ~ 40000 hits in small tubes/run) • Drift time spectra • r-t relationship • Efficiency as a function of background rate • Resolution as a function of background rate → – Needs 1000 tracks in 1 mm slices 75000 tracks 02/08/08 F. Legger 5

Analysis status: drift time spectrum • Tubes 67-68-69-70 only • track cuts Track in • CL1, CL2 > 0.02 ref. • |d1-d2| < 0.8 mm chamber • |d1+d2| < 14.2 mm 2 (top) . d2 Slightly different conditions in data d1 and simulations (T) Track in ref. chamber 1 Drift time spectrum for small tubes is not well reproduced by Garfield (bottom) refine t0? First hit or all hits? 02/08/08 F. Legger 6

Analysis status: tube swapped 02/08/08 F. Legger 7

Analysis status: hedgehock cards Upper multilayer: Hedgehock card type II In the analysis code both multilayers were assigned the same HH card type II -> big tubes were swapped Lower multilayer: Hedgehock card type I 02/08/08 F. Legger 8

Fix in Calib file (from Felix) 02/08/08 F. Legger 9

Distance from wire vs. slope (track ref. ch. 2) Before fix After fix Last tube 02/08/08 F. Legger 10

Old plots: efficiency & r-t relationship All tubes: still with HH card problem...will be redone 02/08/08 F. Legger 11

Old plots: resolution 50 Hz/cm2 800 Hz/cm2 σ = 190 +/- 2 µ m σ = 212 +/- 6 µ m σ (big) = 120 +/- 2 µ m σ (big) = 147 +/- 4 µ m σ (small) = 147 +/- 3 µ m σ (small) = 153 +/- 7 µ m 1100 Hz/cm2 σ = 240 +/- 15 µ m σ (big) = 171 +/- 11 µ m σ (small) = 170 +/- 18 µ m • CL1, CL2 > 0.02 • |d1-d2| < 0.8 mm • |d1+d2| < 14.2 mm All tubes: still with HH card problem...will be redone 02/08/08 F. Legger 12

Garfield simulations 02/08/08 F. Legger 13

Gas gain • electrons on the wire/primary electrons : NB: to have SAME electrical field in small and big tubes, HV = 2730 in – described by Townsend coefficient, however small tubes small uncertainties on Townsend coefficient Historically, HV = 2760 V in small lead to large uncertainties on gas gain -> tubes, which corresponds to HV = hardcoded in Garfield 3101 V in big tubes – for each electron, gain distributed with Polya New Garfield simulations function (x α e -(1+ α )x , 0< α <1) needed! • Diethorn formula: • • Small tubes: Big tubes: – E(a) = 195400 V/cm – ρ 0 / ρ gas = 1 bar/ 3 bar – E(a) = 193500 V/cm – b = 7.1 mm – b = 14.6 mm – E min ( ρ 0 ) = 23523 V/cm – a = 0.025 mm – a = 0.025 mm – ∆ V = 34 V – V = 3080 V – V = 2760 V – G = 20700 – G = 25500 02/08/08 F. Legger 14

Current signal • Only ion mobility taken into account • Ramo's theorem gives • ion mobility is constant (r > 100 µ m): µ = 0.51 cm 2 /Vs @ 3 bar • • Big tubes: Small tubes: – b = 14.6 mm – b = 7.1 mm – a = 0.025 mm – a = 0.025 mm – V = 3080 V – V = 2760 V – Max t = 4.3 ms – Max t = 1.1 ms 02/08/08 F. Legger 15

High rate effects • Electronics effects: • Big tubes: – Baseline shift and fluctuations – b = 14.6 mm – Shift effects reduced by using bipolar – Max t = 4.3 ms shaping (need the introduction of large dead time to prevent multiple hits) – N (50 Hz/cm 2 ) = 0.6 – N (800 Hz/cm 2 ) = 9.6 • Space-charge effects: – N (1100 Hz/cm 2 ) = 13.2 – Ion clouds drifting towards the cathod – N (1400 Hz/cm 2 ) = 16.8 change the electric field and the gas gain: important for non linear gases such as • Small tubes: Ar:CO2 – b = 7.1 mm – electrons drifting toward the wire see – Max t = 1.1 ms charge only within 1 cm – N (50 Hz/cm 2 ) = 0.075 – Ion clouds (Poisson distributed): – N (800 Hz/cm 2 ) = 1.2 – N (1100 Hz/cm 2 ) = 1.65 • n = (1 cm) * N c * t max – N (1400 Hz/cm 2 ) = 2.1 • N c background rate per unit wire length (i.e. Hz/cm 2 => Hz/cm 2 * tube x8 less ion clouds in small tubes!!! diameter [cm]) 02/08/08 F. Legger 16

Electric field for high background rates Solution: If k>>r : If k<<b , second term is dropped and we obtain the usual electric field (1/r) Boundary condition: Trascendental equation for k (numerical solution): However , one must take into account the gain drop due to the change of electric field, by calculating the line charge and insert it into the Diethorn formula -> Iterative process (convergence after a few steps) 02/08/08 F. Legger 17

Electric field parameters Albert's plots k >> r not valid at very high rates Small tubes: 1000 Hz/1.5cm2 = 666Hz/cm2 Average energy big tubes: 666Hz/cm2*3cm= 2000Hz/cm deposit: 36 keV 02/08/08 F. Legger 18

Electric field at high background rates Albert's plots no background ~1/r with background [cm] • Small (big) tubes: – E(high rate) < E(low rate) for r<2 (4) mm • E field variation: from less than 1% (positive, close to the wire) to a few percent (negative, close to the wall) 02/08/08 F. Legger 19

Garfield simulation: status Rate Evts • Implementation: (Hz/cm 2 ) – HEED (particle interaction with the gas) 0 300000 – MagBoltz (electron trasport properties) 800 0 1100 60000 – Ionisation along the track 1400 160000 – Drift of electrons – Current signal (ion part) – Response of ATLAS electronics To be changed – Low rate : gas gain only input OK – High rate effects • Gas gain from iteration of Diethorn formula OK • Adds background electric field (parameter k from iteration) To be checked • Scales with number of ion clouds Poisson -distributed OK • Response of ATLAS electronics To be changed • Simulation with no background: 60000 evts/day/CPU • Simulation with background: 10000 evts/day/CPU 02/08/08 F. Legger 20

Conclusions STILL A LOT TO DO 02/08/08 F. Legger 21

Spare slides 02/08/08 F. Legger 22

Electric field change due to space charge Q = 36 keV/ 22 eV e Gauss theorem: Differentiating both sides: 02/08/08 F. Legger 23

Tracking resolution • CL1, CL2 > 0.02 • |d1-d2| < 4 mm • |d1+d2| < 14.2 mm 02/08/08 F. Legger 24

GIF runs • 14 M + 4 M + 2 M + 120k = 20 M evts collected • Threshold scan (34-36-38 mV) ~ 1M evts each; • Counting rate scan (0, 800, 1100, 1500 Hz/cm2) ~ 1 M evts each; • HV scan (2700V, 2745V) with source on/off ~ 1 M evts each; • Atlas settings for electronics with source on/off ~ 1 M evts each; • Time over Threshold scan with source on/off and threshold scan (34-36-38-40-42-44 mV) ~ 10k evts each. 02/08/08 F. Legger 25

GIF counting rates (I) SOURCE Threshold Nb. evts Hit rate <- (small tubes) (mV) (Hz/cm 2) att. inf. 38 3772021 54.6174 att. Inf. 36 1099982 68.9975 att. inf. 34 1256475 71.7997 att. 1 (shielding) 38 3772021 1032.94 att. 1 (shielding) 36 1199981 1129.75 att. 1 (shielding) 34 1256475 1169.96 att. 2 (shielding) 38 1387269 806.269 att. 2 (shielding) 36 1060907 807.611 att. 2 (shielding) 34 1199979 863.51 To get the counting rate/tube multiply by att. 1 (NO shielding) 38 2481841 1427.56 150 cm 2 att. 1 (NO shielding) 36 1182973 1462.7 att. 1 (NO shielding) 34 1399971 1559.61 02/08/08 F. Legger 26