JIRA ATO352 HV scan and busy time scan

[JIRA] (ATO-352) HV scan and busy time scan of the space charge distortion [JIRA] (ATO-347) Electron transparency measurement using black laser data [JIRA] (ATO-353) Instability of TPC correlation with beam background 20 th May 2016 1

Material Electron transparency gating grid scan using black laser data Can we see “hotspots” in IROC regions with high distortions? electron transparency maps Distortion scans: Is space charge originating in the proportional part ? Trigger rate scan HV scan GG voltage scan Cover voltage scan Distortion maps before/after gas accident, before fter gas exchange 20 th May 2016 Did space charge effect change after gas accident, or is the higher distortion related to Ne-Ar? Are the Ne and Ar distortion compatible ? Precise measurements needed O(0. 1 cm). DCA maps not enoght. 3 D-maps creation - request pending 2

Electron transparency scan 20 th May 2016 3

Electron transparency scan. IROC Relative electron relative transparency defined as a ratio of signals from laser central electrode T(VGG)=QCE(VGG)/QCE(VGG=0) Notice: CE signal obtained in standalone Runs at IR =0 Goals: 20 th May 2016 verify homogeneity provide maps for distortion simulation check for hot-spots at region with big distortion 4

Electron transparency scan. IROC Electron relative transparency estimated as a ratio of signals from laser central electrode <T(VGG)>pad-row= <QCE(VGG)/QCE(VGG=0)>pad-row Not hot-spots (region with almost full transparency) At 70 V electron transparency ~ 1. % rel. fluctuation ~ 100% 20 th May 2016 fluctuation bigger than statistical error estimated as <RMSpad/Qpad>~ 10% RMSpad after Fourier filtering ~ 0. 03 ADC 5

Electron transparency scan. IROC Electron relative transparency estimated as a ratio of Laser central electron signal T(VGG=70 V)=QCE(VGG=70 V)/QCE(VGG=0 V) At 70 V electron transparency ~ 1. % 20 th May 2016 rel. fluctuation ~ 100% 6

Electron transparency scan. OROC Electron relative transparency estimated as a ratio of Laser central electron signal T(VGG=70 V)=QCE(VGG=70 V)/QCE(VGG=0 V) At 70 V electron transparency ~ 1. % 20 th May 2016 rel. fluctuation ~ 100% 7

Distortion scans. Space charge scaling investigation 20 th May 2016 8

Scan analysis Fitting of the scaling function - correlation of corrected dist. maps vs corresponding reference maps - linear fit e. g Drfcorr(Run=253462, x, y, )vs Drfcorr(Run=253461, x, y, ) Comparison of distortion maps differences 20 th May 2016 e. g. Drfcorr(Run=253462, r, f)-Drfcorr(Run=253461, r, f): r: f 9

Data rate scan. Distortion maps scaling Is space charge originating in the proportional part ? Distortion maps at readout rate 200 Hz vs 200 Hz (IR ~500 k. Hz) A side - slope ~ 1 C side - slope ~ 1 3 bands visible Distortion independent of the trigger rate except of small region at C side 20 th May 2016 10

Data rate scan. Distortion maps difference Is space charge originating in the proportional part ? Drf at rate 400 Hz - Drf rate at 200 Hz (IR ~500 k. Hz) A side - slope ~0 C side - slope ~0 but 3 bands visible Distortion independent of the readout rate except of small region at C side 20 th May 2016 11

HV scan. Distortion maps scaling Is space charge originating in the proportional part ? Distortion maps for the HV scan (-19 and -37 V) at IR ~500 k. Hz A side - slope ~ 1 C side - slope ~ 1 Slope very close to 1. Space charge independent of the high voltage (or voltage not applied) some region with small deviation from ideal 1 slope details in the 2 D maps 20 th May 2016 12

Rate scan. Distortion maps scaling Is space charge originating in the proportional part ? Distortion maps at readout rate 200 Hz vs 200 Hz (IR ~500 k. Hz) A side - slope ~ 1 C side - slope ~ 1 3 bands visible Distortion independent of the trigger rate except of small region at C side 20 th May 2016 13

HV scan. Distortion maps scaling Is space charge originating in the proportional part ? Distortion maps at readout rate 200 Hz vs 200 Hz (IR ~500 k. Hz) A side - slope ~ 1 C side - slope ~ 1 3 bands visible Distortion independent of the trigger rate except of small region at C side 20 th May 2016 14

[JIRA] (ATO-353) Instability of TPC correlation with beam background 20 th May 2016 15

TPC HV instabilities - trending Hypothesis: Higher tripping rate in RUN 1 was caused by higher beam background and not by the differnce in gass mixture. Is Ne comparably stable to Ar? Quantitatively description of dependence of the TPC instabilities as function of the beam background attempt to compare different gas mixture HV instability estimators faction of time |VROC(t)-<VROC>|>DV Current instabilities (current sensor in OCDB only until 2012) Beam background instability estimators 20 th May 2016 LHCdata background estimators TPC data volume corrected for IR TPC sector occupancy corrected for IR 16

Conclusion Distortion dependence on the readout rate and on the HV is very week Most probably space charge does not originate in the proportional region To confirm 2 additional scanning points will be requested In case distortion does not depends on the GG and rate, expected improvement changing back to Ne is significant Ratio ~ wdr(Ar)/wdr(Ne) d. Ndx(Ne)/d. Ndx(Ar) ~ 4 (? ? ? exact number to be quoted) ==> 4(? ? ? ) times smaller fluctuation of the space charge 4 (? ? ? ) times reduced “dead zone” area Ar and Ne mixture - attempt for quantitative comparison of HV instabilities 20 th May 2016 17