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Run 1 experience with diamond BCM detectors at CMS

Run 1 experience with diamond BCM detectors at CMS. Moritz Guthoff On behalf of CMS/BRIL 17 th May 2014 RD42 collaboration meeting. Overview. Reminder: our diamond systems: BCM1F and BCM2/1L Operational success BCM1F: good background measurement (timing), suitable as luminometer .

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Run 1 experience with diamond BCM detectors at CMS

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  1. Run 1 experience with diamond BCM detectors at CMS Moritz Guthoff On behalf of CMS/BRIL 17th May 2014 RD42 collaboration meeting

  2. Overview • Reminder: our diamond systems: BCM1F and BCM2/1L • Operational success • BCM1F: good background measurement (timing), suitable as luminometer. • BCML: working well, no erratics at 0.5V/um (1L in 4T good up to 500V). UFO events, blabla. • Operational problems • BCM1F: non linearities(monster pulses), electric field effects (sugar coated), reduction in saturation peak (damage to laser driver) • BCML: signal decrease, rate dependency (turn on), erratic currents • System removal and detector analysis. • CCE measurements, TCT like on defence poster. • PSI test beam (needs some analysis) • Lessons learned • Select pCVD for BCML by leakage current • Need ways to mitigate non linearities. • Signal up to 300fb-1, -> test new prototypes now.

  3. Installation in CMS BCM2 BCM2 IP BCM1F BCM1L Z = +/-1.8 m R = 4.5 cm 4 modules per ring 1 module: BCM1L: - pCVD - leakagecurrentreadout BCM1F: - sCVD - fast MIP counter 1cm Z = +/-14.4m Inner ring: 4 pCVD, R = 5 cm Outer ring: 8 pCVD, R = 28 cm Leakagecurrentreadout

  4. BCM electronics • BCM1F • Front-end: Amplifier & optical driver. • Back-end: • ADC for signal analysis • Scaler for pulse counting • histograming for bunch by bunch analysis and separation of beam background • BCM2/1L • LHC BLM electronics: Current measurement, 40us shortest integration time • No manpower to develop and maintain own system. 200V ~0.5 V/μm

  5. BCM1F performance • Good measurement of beam background by exploiting timing of incoming background and outgoing luminosity particles. • Bunch by bunch luminosity measurement possible. BACKGROUND MESUREMENT CMS DP-2013/032

  6. Saturation CMS DP-2012/021 • Seen in ADC: Rare events of huge signal result in undershoot. • Long dead time result in filling scheme dependence of hit rates. CMS DP-2013/032

  7. BCM1F radiation damage • Radiation damage to linear laser driver observed • Electric field effects in diamond detectors reduce signal height, visible in switch-on behavior. CMS DP-2013/032 CMS DP-2013/032

  8. UFO beam loss event • Dust particles vaporized by the beam create beam loss events with Gaussian timing profile with duration O(1ms). • Potentially dangerous event, active protection effective. • During Run 1, three “mini”-UFOs found, no beam dump. T.Bär et al., ``UFOs in the LHC’’ IPAC'11, TUPC137, 09/2011 Thesis: M.Guthoff, IEKP-KA/2014-01

  9. Signal decrease • Section fits Thesis: M.Guthoff, IEKP-KA/2014-01

  10. k-factors as function of fluence • Fit to decay curves only in sections. • K factor not constant. • Not perfect hyperbolic shape. • Generally k factors not in agreement with RD42 irradiations Thesis: M.Guthoff, IEKP-KA/2014-01

  11. Signal loss prediction • Beam abort thresholds can be adapted for reduced sensitivity. • At “minimum efficiency” thresholds can not be lowered any more due to electronic noise. • BCM2/1L will survive LHC phase. • New strategies required for HL-LHC. • Hoping for new front-end electronics with less noise. Thesis: M.Guthoff, IEKP-KA/2014-01

  12. Turn on behavior • Rate dependence of signal visible in fast change of particle flux (when beams are brought into collision) • Highly damaged and low damaged detectors behave differently. Thesis: M.Guthoff, IEKP-KA/2014-01

  13. Rate dependency, compare w. testbeam • Leakage current readout (E~0.5V/um) • Signal efficiency lower at high rates. • Not an electronics effect. (BLM ionization tube close by is linear) • Not clear if effect is radiation damage induced. • Likely electric field effect. Data from one single LHC fill CMS DP-2012/029 0 2.7 5.4 8.1 10.8 13.6 16.3 19.0 x 107 Simulated MIPs [cm-2s-1] Luminosity scan at end of fill Normal luminosity span of this fill. (starts with highest luminosity.)

  14. High rate test beam at PSI • “High” rate test beam at PSI (pions) in the shadow of a PLT test beam

  15. First results (very preliminary) sCVDs multiplied with 4 (to obtain comparable number) No saturation visible with this measurement so far At 10 MHz new sCVD gives about ~60 nA. Expect ~23 nA at 10 MHz MIP rate

  16. Diamond feature? • HV 0->400V. Red curve goes down and comes back up. • Apparently this is normal behavior for diamond. How can this be explained?

  17. Erratic currents. • System sensitive to erratic currents. • Diamond giving erratic signals could lead to false beam abort. • Less problematic for BCM1L, since in 3.8T field. • Fringe field at BCM2 • Abort channels have no problems with magnet on at 200V. During CMS magnet failure several channels went erratic. • New E6 pCVD diamonds show bad current behavior. • Select new sensors by their HV stability. Lab measurements.

  18. Summary • Detectors performed well enough to serve their purpose. • Several issues with BCM1F and BCML

  19. THANK You

  20. BCM1L signal decrease compared with RD42 • Use FLUKA monte-carlo simulation to estimate the fluence at diamond location. CMS DP-2012/029

  21. k as function of phi (BCML) Thesis: M.Guthoff, IEKP-KA/2014-01

  22. Fit shape Thesis: M.Guthoff, IEKP-KA/2014-01

  23. An other UFO Thesis: M.Guthoff, IEKP-KA/2014-01

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