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The VPT HV System Overview of the architecture The HV filter card Radiation tolerance Power supply specification Fault analysis Summary EE EDR Workshop CERN March 2002 R M Brown - RAL 1 VPT Gain vs bias voltage DG<5% for DV=10% Single operating voltage for all VPTs (apart from handling fault conditions) 12 10 Gain 8 6 V(A)=1000V V(A)=800V 4 2 0 0 200 400 600 800 1000 Dynode Voltage EE EDR Workshop CERN March 2002 R M Brown - RAL 2 Overview of EE HV System EE EDR Workshop CERN March 2002 R M Brown - RAL 3 HV Distribution inside a Dee One quadrant is shown EE EDR Workshop CERN March 2002 R M Brown - RAL 4 HV Distribution inside a SC Three of five filter cards are shown EE EDR Workshop CERN March 2002 R M Brown - RAL 5 Filter network in SC Signal to FPPA Anode HV VPT Dynode HV EE EDR Workshop CERN March 2002 R M Brown - RAL 6 5-Channel filter card Anode filter side Dynode filter side EE EDR Workshop CERN March 2002 R M Brown - RAL 7 HV filter cards in SC EE EDR Workshop CERN March 2002 R M Brown - RAL 8 Radiation tolerance HV filter card components have been irradiated under bias to: > 200kGy (60Co) (~ 4x 10 year dose at = 3) ~ 1015 n/cm2 (~ 10 year neutron fluence) No failures occurred (A capacitor showed DC ~ 17% - to be followed-up) Irradiation of HV cables is just starting Further studies are planned of filter operation under irradiation EE EDR Workshop CERN March 2002 R M Brown - RAL 9 Fault analysis - typical examples Fault Consequence Remedy Power supply Lose 1 Quadrant Change power supply (In control room) Cable Lose 1 Supercrystal Use spare cable (Requires access Inside or outside of Dee?) VPT (A or D short to Earth) Lose 1 Crystal (Voltage drops by 50V on other 24 Xtal in S/C) Change calibration for 24 channels. (Failed channel is lost) Filter component (open/short circuit) Affects 1 Crystal (Noisy or lost) None HV discharge (capacitor/cable/VPT) Noise induced triggers Reduce HV on one S/C EE EDR Workshop CERN March 2002 R M Brown - RAL 10 Fault analysis (2) ‘Extreme case’: 1% of all VPTs develop a short circuit from Anode/Dynode to earth. single S/Cs: 19.5% with 1 bad VPT I= 50mA, DV= -50V 2.4% with 2 bad VPT I=100mA, DV= -100V 0.2% with 3 bad VPT I=150mA, DV= -150V If Anode and Dynode both short to earth this is not a problem (the loss in gain on the other VPTs is < 5% for DV= -100V) However, if the Dynode shorts, but not the Anode, then VA-VD increases on the other VPTs potentially damaging Therefore, need possibility to change VA or VD on one S/C. (Should be incorporated in HV fan-out in Control Room) EE EDR Workshop CERN March 2002 R M Brown - RAL 11 Power supply specifications Output voltage: +1200V maximum remotely set with DV = 10V (or less) Output current: > 5mA (source) (to handle fault conditions) > 5mA (sink) Voltage ripple: 50mV maximum Ramp rate: ~10V/s (2 mins total) (Rise and Fall) Set in hardware (S/W control in addition?) Format: Rack-mounted (CAMAC or NIM/RS232) Integrity: Must be powered via UPS system EE EDR Workshop CERN March 2002 R M Brown - RAL 12 Ramp-up/down Ramp-down OPAL experience: Graceful ramp-up/down essential (Several VPTs lost before going to UPS and 2 min ramp-down) RIE experience: Many VPTs draw large currents at 0.2 < B < 0.8T Need to ramp-down HV following a fast quench (t ~ 280s) Ramp-up at 10V/s, current to charge cables is ~ 250mA (not a problem) a VPT may draw ~100nA for a short time (<< 200mA/quadrant) VA-VD Must not exceed 300V Anode and Dynode Power Supplies must be interlocked EE EDR Workshop CERN March 2002 R M Brown - RAL 13 Summary The HV system for the VPTs presents no special problems Power supplies meeting the specification are available offthe-shelf (eg Iseg NHQ202) System costs are dominated by distribution and on-detector filters A systematic fault analysis has been made Initial irradiation studies of components with g and n are encouraging EE EDR Workshop CERN March 2002 R M Brown - RAL 14