EE EDR Workshop CERN March 2002 R M Brown - RAL 1 The VPT HV System lOverview of the architecture lThe HV filter card lRadiation tolerance lPower supply specification lFault analysis lSummary

EE EDR Workshop CERN March 2002 R M Brown - RAL 2 VPT Gain vs bias voltage  G<5% for  V=10%  Single operating voltage for all VPTs (apart from handling fault conditions)

EE EDR Workshop CERN March 2002 R M Brown - RAL 3 Overview of EE HV System

EE EDR Workshop CERN March 2002 R M Brown - RAL 4 HV Distribution inside a Dee One quadrant is shown

EE EDR Workshop CERN March 2002 R M Brown - RAL 5 HV Distribution inside a SC Three of five filter cards are shown

EE EDR Workshop CERN March 2002 R M Brown - RAL 6 Filter network in SC Anode HV Dynode HV Signal to FPPA VPT

EE EDR Workshop CERN March 2002 R M Brown - RAL 7 5-Channel filter card Anode filter side Dynode filter side

EE EDR Workshop CERN March 2002 R M Brown - RAL 8 HV filter cards in SC

EE EDR Workshop CERN March 2002 R M Brown - RAL 9 Radiation tolerance HV filter card components have been irradiated under bias to: > 200kGy ( 60 Co)(~ 4x 10 year dose at  = 3) ~ n/cm 2 (~ 10 year neutron fluence) No failures occurred (A capacitor showed  C ~ 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 10 Fault analysis - typical examples

EE EDR Workshop CERN March 2002 R M Brown - RAL 11 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= 50  A,  V= -50V 2.4% with 2 bad VPT  I=100  A,  V= -100V 0.2% with 3 bad VPT  I=150  A,  V= -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  V= -100V) However, if the Dynode shorts, but not the Anode, then V A -V D increases on the other VPTs  potentially damaging Therefore, need possibility to change V A or V D on one S/C. (Should be incorporated in HV fan-out in Control Room)

EE EDR Workshop CERN March 2002 R M Brown - RAL 12 Power supply specifications Output voltage:+1200V maximum remotely set with  V = 10V (or less) Output current:> 5mA (source) (to handle fault conditions) > 5  A (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 13 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 ~ 250  A (not a problem) a VPT may draw ~100nA for a short time (<< 200  A/quadrant) V A -V D Must not exceed 300V  Anode and Dynode Power Supplies must be interlocked

EE EDR Workshop CERN March 2002 R M Brown - RAL 14 Summary lThe HV system for the VPTs presents no special problems lPower supplies meeting the specification are available off- the-shelf (eg Iseg NHQ202) lSystem costs are dominated by distribution and on-detector filters lA systematic fault analysis has been made Initial irradiation studies of components with  and n are encouraging