1. January 25, 2003Richard Talaga1 High Voltage Distribution for RPCs Simple Model of Detector & HV Specifications & Requirements Simple HV Distribution Layout Parts & Costs for Simple Model Alternative Implementations +HV to Anode and – HV to Cathode C-W supplies

2. January 25, 2003Richard Talaga2 Simple Model of Detector & HV Detector –300 repetitive layers –20m x 20m cross section –2m x 2m per RPC  100 RPCs per layer HV –Operating Voltage: ~ 8 kV for ~2mm gap –1µA/m 2 dark current (BELLE result) mostly through noryl spacers up to ~ 5µA/m 2 if there are problems …(HV drop limits the current) –  400 µA per layer with properly-operating RPCs –Typical commercial HV channel provides ~1mA @10kV –HV System: 1ch/layer  300 channels for entire detector 1HV channel/100 RPCs; 1 current measurement for an “entire layer”

3. January 25, 2003Richard Talaga3 Specifications & Requirements HV distribution: 1 HV channel “per layer” –Ability to turn on/off Any one RPC?  No daisy chains “Simple Layout” Any of one cluster of RPCs ?  Limited daisy chains –Ability to provide more than 1 value of HV per plane Could accommodate two different HV/plane. “Less Simple” –Ability to track down bad RPC (high current) Current meters per RPC or cluster of RPCs could be a big help. “Less Simple”

4. January 25, 2003Richard Talaga4 Simple HV Distribution Layout 100 RPC/layer Here each HV channel serves 2 “1/2 layers” Assume 100 RPC connections to the outside Four HV distribution boxes per layer (25 ch/box) –100 pairs of HV connectors/layer + 8 pairs for boxes –240m of cables per quadrant  960 m/layer HV Channel Distribution box Detector cross section

5. January 25, 2003Richard Talaga5 Parts and Costs: Simple Model HV System: CAEN SY1527 (replaces SY 127) $332k –Module A1526: 6 HV ch @ 1mA/15kV per ch 50 modules  300 channels (1 per layer)$250k –Crate SY1527: fits 8 Modules A1526 7 crates (6 full & 1 with two modules) $82k RG58 cable –960m/layer x 300 layers =288,000m = 950,000 ft $136/1000ft spool  $129k SHV connectors: one pair per RPC –RPC end is soldered 30,000 RPCs x $23/pair (for qty of 100) $690k Distribution boxes 1200 boxes @ ~$100/box (no fanout connectors)$120k 10 kV connectors to PS 300 x $35 $10k Total HV M&S costs$1.3M

6. January 25, 2003Richard Talaga6 Parts and Costs: Notes CAEN HV modules –10 kV are being discontinued: SY 127 model A328 2mA @10kV ($1,400/channel) –15 kV model A1526 may be built to provide 10 kV with increased current ~1.3 mA and less potent HV connectors Note: $830/channel for standard model Connector cost –10kV connectors cost $70/pair $36 for bulkhead; $34 for cable –8kV SHV connectors cost $23/pair $9 for bulkhead; $14 cable SHV connector cost may be less because quote for qty 100 Attaching SHV connectors to cables –Assumed no cost in the estimate

7. January 25, 2003Richard Talaga7 “Less Simple”: Choice of 2 Values of HV per Layer HV Channel (high) Layers 1-4 HV Channel (low) Layers 1-4 Repeated pattern of higher/lower HV distribution boxes (On left and right sides of detector)

8. January 25, 2003Richard Talaga8 Alternative: +HV to anode and – HV to cathode Advantages (as in the BELLE experiment) –“Reduces the potential to ground on connectors, cables and surfaces as a precaution against external discharges through and around insulators” –“Helps reduce the overall HV system cost since modules capable of producing voltages in excess of 7.5 kV are less common and therefore more costly” Available CAEN SY1527 hardware CAEN A1732(N/P) 6kV @1mA $3,980/12ch  $246k system CAEN A1733(N/P) 4kV @2mA $3,825/12ch  $123k system Compare: A1549 15kV @1mA $5,045/6ch  $332k system –Note: Save on HV supplies but double the number of HV connectors, distribution boxes and cables

9. January 25, 2003Richard Talaga9 Alternative: Cockroft-Walton Supplies * Each RPC can have its own C-W supply, mounted nearby One low voltage cable replaces HV cable & connectors Safer: No HV outside the detector C-W board: part of RPC “package”; no HV connectors –Can be potted to reduce corona discharge –Can be shielded to reduce rf radiation Individual RPC HV control possible “Less Simple” Individual RPC current monitor possible “Less Simple” Cost compared to $1.3M conventional system – $40/channel seems possible $40/ch x 30,000 ch = $1.2M Note: $40/ch is for a “Simple System”; Individual RPC controls/monitors will cost more but are a “natural extension” of the C- W system * Used in ZEUS @2kV

10. January 25, 2003Richard Talaga10 Block Diagram of +/- 4kV C-W Supply + 4 kV - 4kV OSC AMP ~ Current V-mon V-ref C-W

11. January 25, 2003Richard Talaga11 Summary “Simple” HV system will cost ~ $1.3M –labor costs for terminating connectors not included Largest cost is for HV connectors Several enhancements to “simple” scheme are probably desirable –RPC current monitoring is important –Positive & Negative Voltage reduces potential to ground Cockroft-Walton HV system has advantages (adjustable voltage and current monitoring). This could be an interesting R&D project