# Presentation: 557015

## 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

- Richard Talaga

- January 25, 2003

## 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/m2 dark current (BELLE result)
- mostly through noryl spacers
- up to ~ 5μA/m2 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”

- Richard Talaga

- January 25, 2003

## 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”

- Richard Talaga

- January 25, 2003

## 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

- Richard Talaga

- January 25, 2003

## 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

- Richard Talaga

- January 25, 2003

## 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

- Richard Talaga

- January 25, 2003

## “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)

- Richard Talaga

- January 25, 2003

## 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

- Richard Talaga

- January 25, 2003

## 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

- Richard Talaga

- January 25, 2003

## Block Diagram of +/- 4kV C-W Supply

- + 4 kV

- - 4kV

- OSC

- AMP

- ~ Current

- V-mon

- V-ref

- C-W

- Richard Talaga

- January 25, 2003

## 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

- Richard Talaga

- January 25, 2003