-- RoumyanaHadjiiska - 2019-07-04

Longevity study & HF production in CMS-RPC

Definitions

definitions.png Ohmic current is defined as current with no beam, up to around 7000V, in the range where there is no gas amplification contribute and the current follows the ohmic law. The ohmic current values are monitored at 6500 V, between Inject Warning and Squeeze. Cosmic current is defined as current with no beam, at working point voltage, in the region of the gas amplification. The cosmic current values are monitored between Beam Dump and Inject Warning.

Figures:

ohmic_vs_time.png Currents measured in four RPC stations are shown on the plot -W0 in the barrel and RE+1, RE+4, RE-4 in the endcap. The measured currents are plotted vs time. From the beginning of 2018 to September, a higher ohmic current has been observed in RE-4 comparing to RE+4 . After the gas flux was doubled in RE-4 (Mid-September) a significant change in its behavior has been observed, up to the point in which it drops below RE+4 curve. The ohmic current increase is directly correlated with the background. In the low background regions such as W+0, a very slow increase in the ohmic current has been observed. In RE+1 and W+0 the background rate is less than 10 Hz/cm2 and both have similar gas flows (0.7 V/h and 0.6 V/h respectively), while in RE4 the background rate is about 40Hz/cm2 and the gas flow is 1.1 V/h. Contact: cms-dpg-conveners-rpc@SPAMNOTcernNOSPAMPLEASE.ch

ohmic_vs_lumi.png Currents measured in four RPC stations are shown on the plot -W0 in the barrel and RE+1, RE+4, RE-4 in the endcap. The measured currents are plotted vs integrated luminosity. From the beginning of 2018 to September, a higher ohmic current has been observed in RE-4 comparing to RE+4 . After the gas flux was doubled in RE-4 (Mid-September) a significant change in its behavior has been observed, up to the point in which it drops below RE+4 curve. The ohmic current increase is directly correlated with the background. In the low background regions such as W+0, a very slow increase in the ohmic current has been observed. In RE+1 and W+0 the background rate is less than 10 Hz/cm2 and both have similar gas flows (0.7 V/h and 0.6 V/h respectively), while in RE4 the background rate is about 40Hz/cm2 and the gas flow is 1.1 V/h . A clear linear dependence is observed when LHC fills with similar run conditions, i.e. periods in which the integrated luminosity grows at a constant rate. Contact: cms-dpg-conveners-rpc@SPAMNOTcernNOSPAMPLEASE.ch

ohmic_decay.png Currents measured in four RPC stations are shown on the plot - W0 in the barrel and RE+1, RE+4, RE-4 in the endcap. RE-4 has double gas flow compared to RE+4. The ohmic currents were measured during the Heavy Ion period, which have very low luminosity, and this allows the RPCs to enter in a “recovery” period. The ohmic currents measured during this period show a clear decrease. The curves were fitted using an exponential function: i(t) = p0 + p1 * exp(-p2 * t) and it was found that the RE-4 current decreases faster than it is in RE+4. Contact: cms-dpg-conveners-rpc@SPAMNOTcernNOSPAMPLEASE.ch

p1_barrel.png Currents vs Instantaneous luminosity - Slopes: The RPC currents depend linearly on the instantaneous luminosity [1]. For each LHC fill the linear distributions were fit to a linear function in order to obtain the slope (P1) a.k.a. physics current (i = P1 * L). Due to the nature of the linear fit, P0 (Offset) absorbs the cosmic current (offset + ohmic + gas gain). The slopes (P1) as a function of a time for the five barrel wheels are shown on the plot. As it might be seen from it, P1 is stable in time. The changes in the middle of August are due to different applied HV working points. Wheels, located at equal distances from the interaction point along the beam pipe, have similar slopes (P1 values). They also have very similar rates [1]. No increase due to integrated luminosity is observed for the slopes for the entire year. Contact: cms-dpg-conveners-rpc@SPAMNOTcernNOSPAMPLEASE.ch

p1_endcap.png Currents vs Instantaneous luminosity - Slopes: The RPC currents depend linearly on the instantaneous luminosity [1]. For each LHC fill the linear distributions were fit to a linear function in order to obtain the slope (P1) a.k.a. physics current (i = P1 * L). Due to the nature of the linear fit, P0 (Offset) absorbs the cosmic current (offset + ohmic + gas gain). The slopes (P1) as a function of a time for the endcap stations are shown on the plot. As it might be seen from it, P1 is stable in time. The changes in the middle of August are due to different applied HV working points. Endcap staions, located at equal distances from the interaction point along the beam pipe, have similar slopes (P1 values). They also have very similar rates [1]. No increase due to integrated luminosity is observed for the slopes for the entire year. Contact: cms-dpg-conveners-rpc@SPAMNOTcernNOSPAMPLEASE.ch

ohmic_vs_HV.png The currents, measured in different years, as a function of the HV, for an example RPC chamber are shown in the plot. The lowest curve depicts for the currents measured in middle of September in 2016. The blue and green markers corresponds to currents measured in July and October in 2017, and the purple ones - to currents measured in the beginning of 2018. As it might be seen from the plot, the current increases as collisions go on. From the near end of 2017 to April 2018 we observe that the current decreases significantly during the YETS (Year End Technical Stop). Contact: cms-dpg-conveners-rpc@SPAMNOTcernNOSPAMPLEASE.ch

HF_vs_time.png The Hydrogen Fluoride (HF), produced in the gas under high electrical discharge may accelerate the detectors aging and may represents a possible cause for inner detector surface damaging and relative ohmic current increase, due to its electrical conductivity and high chemical reactivity. The HF measurements have been performed using an ion-selective electrode (ISE), which is a transducer (or sensor) that converts the activity of a specific ion [F-] dissolved in a solution into an electrical potential. The measurements have been performed at the gas exhaust of 3 regions: W0 in the barrel and RE+1, RE+4 in the endcap. The HF concentration is shown as a function of the time. The amount of HF is accumulated as collisions take place in CMS hence the increasing value. RE+1 and W+0, have a similar HF concentration, gas flow (0.7 V/h and 0.6 V/h ) and background (less than 10 Hz/cm2). In RE+4 the amount of HF accumulated is around 2 times higher, higher background (~ 40Hz/cm2) and the gas flow is 1.1 V/h, 2 times more than W+0 and RE+1. Contact: cms-dpg-conveners-rpc@SPAMNOTcernNOSPAMPLEASE.ch

HF_vs_lumi.png The Hydrogen Fluoride (HF), produced in the gas under high electrical discharge may accelerate the detectors aging and may represents a possible cause for inner detector surface damaging and relative ohmic current increase, due to its electrical conductivity and high chemical reactivity. The HF measurements have been performed using an ion-selective electrode (ISE), which is a transducer (or sensor) that converts the activity of a specific ion [F-] dissolved in a solution into an electrical potential. The measurements have been performed at the gas exhaust of 3 region: W0 in the barrel and RE+1, RE+4 in the endcap. The HF concentration is shown as a function of the integrated luminosity. There is a clear linear dependence between the HF concentration and the integrated luminosity. RE+1 and W+0, have a similar HF concentration, gas flow (0.7 V/h and 0.6 V/h ) and background (less than 10 Hz/cm2). In RE+4 the amount of HF accumulated is around 2 times higher, higher background (~ 40Hz/cm2) and the gas flow is 1.1 V/h, 2 times more than W+0 and RE+1. Contact: cms-dpg-conveners-rpc@SPAMNOTcernNOSPAMPLEASE.ch

ohmic_vs_HF.png The Hydrogen Fluoride (HF), produced in the gas under high electrical discharge may accelerate the detectors aging and may represents a possible cause for inner detector surface damaging and relative ohmic current increase, due to its electrical conductivity and high chemical reactivity. The HF measurements have been performed using an ion-selective electrode (ISE), which is a transducer (or sensor) that converts the activity of a specific ion [F-] dissolved in a solution into an electrical potential. The measurements have been performed at the gas exhaust of 3 region: W0 in the barrel and RE+1, RE+4 in the endcap. The ohmic current as a function of HF concentration is shown on the plot. RE+1 and W+0, have a similar HF concentration, gas flow (0.7 V/h and 0.6 V/h ) and background (less than 10 Hz/cm2). In RE+4 the amount of HF accumulated is around 2 times higher, higher background (~ 40Hz/cm2) and the gas flow is 1.1 V/h, 2 times more than W+0 and RE+1. There is a clear linear dependence between the ohmic current and HF concentration. HF trapped in the gap may form a thin conductive layer that increase the ohmic current, therefore it is necessary to fine tune the gas flow as a function of the background rate so that the HF is efficiently removed. Contact: cms-dpg-conveners-rpc@SPAMNOTcernNOSPAMPLEASE.ch

HF_CONCENTRATION_umol_liter_vsRATE.png The Hydrogen Fluoride (HF), produced in the gas under high electrical discharge may accelerate the detectors aging and may represents a possible cause for inner detector surface damaging and relative ohmic current increase, due to its electrical conductivity and high chemical reactivity. The HF production has been studied at GIF++ as a function of the background rate and gas flow. For the test a spare CMS-RPC chamber and standard gas mixture have been used. The HF measurements, at gas exhaust, have been performed using an ion-selective electrode (ISE), which is a transducer (or sensor) that converts the activity of a specific ion [F-] dissolved in a solution into an electrical potential. *The results show a linear dependence of the HF concentration rate on the background rate (and its corresponding current on the top X-axis), indeed the current increase linearly with the background increases. The blue markers represent the results, obtained with the lowest gas flow, while the red ones - with the higher. The slopes of the measured curves dependent on the gas flow - higher is the gas flow, less is the HF concentration. Contact: cms-dpg-conveners-rpc@SPAMNOTcernNOSPAMPLEASE.ch

ratio.png Ratio of the fluoride concentration measured in RPC at GIF++, at different gas volume exchanges with respect to 1 gas volume exchange per hour. Contact: cms-dpg-conveners-rpc@SPAMNOTcernNOSPAMPLEASE.ch

HF_TRAPPED_umolh_vsRate.png Fluoride concentration trapped inside the RPC gas gap and not efficiently removed. The HF concentration was measured at GIF++ at different background rate, and with three different gas flow. The estimation was done considering the HF accumulated during 8 hours of measurements, just after the detector switch off. Contact: cms-dpg-conveners-rpc@SPAMNOTcernNOSPAMPLEASE.ch

noise_rate.png ohmic_GIF.png Few spare RPC chambers are under gamma irradiation at GIF++ for the CMS-RPC system certification at HL-LHC. After having collected ~ 600 mC/cm2 from 2016 the detector performance and parameters are stable. Left: Irradiated chamber noise rate profile at 9.8kV, after having collected different amount of charge. The noise rate remains low, less than 1 Hz/cm2, and the profile is stable. Right: Ohmic current versus the integrated charge, for the irradiated (blue) and reference (red) chamber, at 6.5 kV. Ohmic current is low and almost stable in time after having collected around 600 mC/cm2. Contact: cms-dpg-conveners-rpc@SPAMNOTcernNOSPAMPLEASE.ch

ratioRE2.png Contact: cms-dpg-conveners-rpc@SPAMNOTcernNOSPAMPLEASE.ch
darkcurrent_IRR_REF_AT_WP.png Contact: cms-dpg-conveners-rpc@SPAMNOTcernNOSPAMPLEASE.ch
noiserate_IRR_REF_AT_WP.png Contact: cms-dpg-conveners-rpc@SPAMNOTcernNOSPAMPLEASE.ch
RE2-2-NPD-BARC-9_CurrentTOT_ALL-overlap.png Contact: cms-dpg-conveners-rpc@SPAMNOTcernNOSPAMPLEASE.ch
RE2_ResistivityRATIO_RatioCurrent_overlapped.png Contact: cms-dpg-conveners-rpc@SPAMNOTcernNOSPAMPLEASE.ch

References

[1] RPC Detector Performance Results for 2016 and 2017, CMS-DP-2018-001 ; CERN-CMS-DP-2018-001
Topic attachments
I Attachment History Action Size Date Who Comment
PNGpng HF_CONCENTRATION_umol_liter_vsRATE.png r1 manage 30.4 K 2019-09-30 - 18:25 AndreaGelmi  
PNGpng HF_TRAPPED_umolh_vsRate.png r1 manage 20.4 K 2019-09-30 - 18:25 AndreaGelmi  
PNGpng HF_vs_current_GIF.png r1 manage 25.8 K 2019-07-04 - 10:36 RoumyanaHadjiiska  
PNGpng HF_vs_lumi.png r1 manage 22.5 K 2019-07-04 - 10:36 RoumyanaHadjiiska  
PNGpng HF_vs_time.png r1 manage 18.1 K 2019-07-04 - 10:37 RoumyanaHadjiiska  
PNGpng RE2-2-NPD-BARC-9_CurrentTOT_ALL-overlap.png r1 manage 99.1 K 2020-01-27 - 16:30 AndresCabrera  
PNGpng RE2_ResistivityRATIO_RatioCurrent_overlapped.png r1 manage 19.2 K 2020-01-27 - 16:30 AndresCabrera  
PNGpng darkcurrent_IRR_REF_AT_WP.png r1 manage 22.1 K 2020-01-27 - 16:30 AndresCabrera  
PNGpng definitions.png r1 manage 69.8 K 2019-07-04 - 10:45 RoumyanaHadjiiska  
PNGpng noise_rate.png r1 manage 18.5 K 2019-07-04 - 10:36 RoumyanaHadjiiska  
PNGpng noiserate_IRR_REF_AT_WP.png r1 manage 22.8 K 2020-01-27 - 16:30 AndresCabrera  
PNGpng ohmic_GIF.png r1 manage 32.6 K 2019-07-04 - 10:36 RoumyanaHadjiiska  
PNGpng ohmic_decay.png r1 manage 88.6 K 2019-07-04 - 10:37 RoumyanaHadjiiska  
PNGpng ohmic_vs_HF.png r1 manage 19.0 K 2019-07-04 - 10:36 RoumyanaHadjiiska  
PNGpng ohmic_vs_HV.png r1 manage 34.8 K 2019-07-04 - 10:36 RoumyanaHadjiiska  
PNGpng ohmic_vs_lumi.png r1 manage 272.3 K 2019-07-04 - 10:36 RoumyanaHadjiiska  
PNGpng ohmic_vs_time.png r1 manage 294.8 K 2019-07-04 - 10:36 RoumyanaHadjiiska  
PNGpng p1_barrel.png r1 manage 246.2 K 2019-07-04 - 10:36 RoumyanaHadjiiska  
PNGpng p1_endcap.png r1 manage 275.7 K 2019-07-04 - 10:36 RoumyanaHadjiiska  
PNGpng ratio.png r1 manage 12.4 K 2019-09-30 - 18:25 AndreaGelmi  
PNGpng ratioRE2.png r1 manage 20.0 K 2020-01-27 - 16:30 AndresCabrera  
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Topic revision: r4 - 2020-01-27 - AndresCabrera
 
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