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LHCb CALO commissioning meeting 03.06.08 Anatoli Konoplyannikov /ITEP/

ECAL CW base performance. Outline ECAL – HCAL CW base difference; CW base study with switching on/off Agilent power supply; Current limitation in the MV Agilent power supply; Possible improvements of the ECAL HV system.

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LHCb CALO commissioning meeting 03.06.08 Anatoli Konoplyannikov /ITEP/

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  1. ECAL CW base performance • Outline • ECAL – HCAL CW base difference; • CW base study with switching on/off Agilent power supply; • Current limitation in the MV Agilent power supply; • Possible improvements of the ECAL HV system. LHCb CALO commissioning meeting 03.06.08 Anatoli Konoplyannikov /ITEP/

  2. ECAL CW base performance • ECAL CW base features different from HCAL • wrongly soldered electrolytic capacitors -> mainly replaced; • unexpected DC current through the Agilent PS when power supply is off (it shows a MV to LV correlation); • LV protection fuses blowing up during the unexpected MV switching off (general power cuts, DSS action in case of alarm); • CW base pumping frequency impact on the PMT anode (CW noise); • Painful recovery from MV over current protection relay trip (needs: set ½ of all HV off, set Agilent off, switch on relays and repeat in back order). LHCb CALO commissioning meeting 03.06.08 Anatoli Konoplyannikov /ITEP/

  3. ECAL CW base performance Wiener PS ~ 12 m +- 7 V ~ 80 m PMT group Agilent PS Fuses +80 V +5.8 V CW -5.8 V LV regulators In CW 1 +80 V Current limiting R = 0 or 100 W 2 CW HV_LED_DAC board 8 ~ 4 m Sketch of the LV and MV distribution of the XCAL HV system LHCb CALO commissioning meeting 03.06.08 Anatoli Konoplyannikov /ITEP/

  4. ECAL CW base performance 47 nF 47 nF Test Point ECAL CW base circuit diagram. The main difference from HCAL case is the additional filtering and integrating capacitors (in my opinion, it leads to main differences) LHCb CALO commissioning meeting 03.06.08 Anatoli Konoplyannikov /ITEP/

  5. ECAL CW base performance HVout = 400 V, R=0 HVout = 100 V, R=0 HVout = 400 V, R=100 Original ECAL CW base oscillograms in Test Point, when Agilent 40 V goes down LHCb CALO commissioning meeting 03.06.08 Anatoli Konoplyannikov /ITEP/

  6. ECAL CW base performance HVout = 100 V, R=0 HVout = 400 V, R=0 No C+C ECAL CW base oscillograms in Test Point HVout = 400 V, R=100 HVout = 100 V, R=100 LHCb CALO commissioning meeting 03.06.08 Anatoli Konoplyannikov /ITEP/

  7. ECAL CW base performance CW noise impact on a PMT anode, in case of original CW CW noise impact on a PMT anode, in case of modified CW (without C+C) There is no change of the CW noise behavior for original and modified base LHCb CALO commissioning meeting 03.06.08 Anatoli Konoplyannikov /ITEP/

  8. ECAL CW base performance Unexpected current from Agilent PS LHCb CALO commissioning meeting 03.06.08 Anatoli Konoplyannikov /ITEP/

  9. ECAL CW base performance • Current limitation in the MV Agilent power supply • For improving the recovery procedure from MV current protection trip the current limiting resistors have been added for all HCAL boards. • The R=70 W allows: • limit max current of the protection relay up to 0.8 A; • decrease the cross talk on neighbor protection circuits and exclude collective effects; • maintenance the HV in smooth way. Unfortunately for ECAL HV system the current limiting resistor could increase the CW base instability (as was shown above), but may be it should be verified with more CW bases. LHCb CALO commissioning meeting 03.06.08 Anatoli Konoplyannikov /ITEP/

  10. ECAL CW base performance • What to do • Unfortunately not so much ! • Modification of 6000 CW bases is not realistic and decreasing a number of power cuts seems not realistic too. In the same time we can: • Decrease the pumping MV voltage for COSMIC runs as much as possible (for example in five times and set an ECAL trigger threshold five times lower) Now the max HV is about 1.55 kV and required MV is about 75 V (22 x 75) In case of Gain 5 times less the HV will be about 250 V less and required MV is about 60 V • Increase the ramping down time of the Agilent PS, but it will work only for planed operations ; • Modify one spare HV_LED_DAC board with MV current limiting resistors for performing the PMT noise test; • In case if the noise does not changed, modify all HV_LED_DAC boards. We have to be ready for some efforts during the ECAL HV system maintenance LHCb CALO commissioning meeting 03.06.08 Anatoli Konoplyannikov /ITEP/

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