High Voltage Distribution for RPCs Simple Model of

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 January 25, 2003 Richard Talaga 1

Simple Model of Detector & HV • Detector – 300 repetitive layers – 20 m x 20 m cross section – 2 m x 2 m per RPC • 100 RPCs per layer • HV – Operating Voltage: ~ 8 k. V for ~2 mm 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 ~1 m. A @10 k. V – HV System: 1 ch/layer 300 channels for entire detector • 1 HV channel/100 RPCs; 1 current measurement for an “entire layer” January 25, 2003 Richard Talaga 2

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” January 25, 2003 Richard Talaga 3

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 – 240 m of cables per quadrant 960 m/layer Distribution box HV Channel Detector cross section January 25, 2003 Richard Talaga 4

Parts and Costs: Simple Model • HV System: CAEN SY 1527 (replaces SY 127) $332 k – Module A 1526: 6 HV ch @ 1 m. A/15 k. V per ch • 50 modules 300 channels (1 per layer) $250 k – Crate SY 1527: fits 8 Modules A 1526 • 7 crates (6 full & 1 with two modules) $82 k • RG 58 cable – 960 m/layer x 300 layers =288, 000 m = 950, 000 ft • $136/1000 ft spool $129 k • SHV connectors: one pair per RPC – RPC end is soldered • 30, 000 RPCs x $23/pair (for qty of 100) $690 k • Distribution boxes • 1200 boxes @ ~$100/box (no fanout connectors) $120 k • 10 k. V connectors to PS • 300 x $35 $10 k • Total HV M&S costs January 25, 2003 $1. 3 M Richard Talaga 5

Parts and Costs: Notes • CAEN HV modules – 10 k. V are being discontinued: SY 127 model A 328 • 2 m. A @10 k. V ($1, 400/channel) – 15 k. V model A 1526 may be built to provide 10 k. V with increased current ~1. 3 m. A and less potent HV connectors • Note: $830/channel for standard model • Connector cost – 10 k. V connectors cost $70/pair $36 for bulkhead; $34 for cable – 8 k. V 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 January 25, 2003 Richard Talaga 6

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

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 k. V are less common and therefore more costly” • Available CAEN SY 1527 hardware • CAEN A 1732(N/P) 6 k. V @1 m. A $3, 980/12 ch $246 k system • CAEN A 1733(N/P) 4 k. V @2 m. A $3, 825/12 ch $123 k system • Compare: A 1549 15 k. V @1 m. A $5, 045/6 ch $332 k system – Note: Save on HV supplies but double the number of HV connectors, distribution boxes and cables January 25, 2003 Richard Talaga 8

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. 3 M conventional system – $40/channel seems possible • $40/ch x 30, 000 ch = $1. 2 M • Note: $40/ch is for a “Simple System”; Individual RPC controls/monitors will cost more but are a “natural extension” of the CW system * Used in ZEUS @2 k. V January 25, 2003 Richard Talaga 9

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

Summary • “Simple” HV system will cost ~ $1. 3 M – 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 January 25, 2003 Richard Talaga 11