# Presentation: 273305

## Glass Resistive Plate Chambers

- Proof of principle: BELLE Experiment:
- Virginia Tech (barrel)
- Tohoku (endcaps)
- Dan Marlow, Princeton (seminar at Rice), Norm Morgan (Virginia Tech), Kazuo Abe (KEK)

- A. Para

- 5 years of operation,
- Full efficiency
- No chamber exchanged/replaced

## RPC Principles of Operation

- A passing charged particle induces an avalanche, which develops into a spark.  The discharge is quenched when all of the locally  (                  ) available charge is consumed.

- Spacers

- The discharged area recharges slowly through the high-resistivity glass plates.

- Before

- After

## Plateau Curve

- 2 mm gap RPCs plateau at a fairly high voltage.
- Note the slight falloff in efficiency well above the plateau.  This effect is real and typical.

## BELLE chamber design

- Two float glass sheets, 2 mm thick
- Noryl spacers
- Epoxy 3M 2216
- India ink (30%black + 70%white)
- Gas connectors

- Very simple device

## Gas Mixture (Belle)

- Traditional Gas Mixture
- 64% Argon :  6% Freon 116  30% Isobutane
- Constraints
-  Safety: _gas should be non flammable_:
- mixture ---> 30% Argon : 62% Freon :8% Butane
-  Environment: Freon 116--> Freon R134A
-  Cost: Isobutane ---> Butane “silver”
- Streamer mode operation: large, robust  signals 100-200 pC

## First result: signal from streamer mode

- Gas: Freon/Argon/IsoButane at 62:30:8
- High Voltage: 7.5 KV or above
- Cosmic ray signal (triggered by 3 layers of scintillator)

- 1 streamer

- 2 streamers

- 3 streamers

- PED

- avalanche

- PED + avalanche

- Repond, Lia, (Argonne)

## Production cost, materials

-      RPC  Material per m2
**	****	**Glass @ $0.40/lb                      $10
- 		Mylar  (5mil)                              $3
-            Spacers                                      $5
-            Conductive paint                         $1.50
-            Epoxy                                          $4
-            Gas fittings  (injection molded)  $2
-            Misc. supplies                             $2
-        Total                                 $27.50/m2
- _ _

## RPC production facility floor plan

## RPC production, Virginia model

-  Gllass is placed on a conveyor  that moves the glass or RPC through an automatic wash/rinse/dry cycle ready for epoxy or painting.
- Clean glass is diverted to a gluing station where  the spacers and edges are epoxied to the glass plate. Virginia Tech experience indicates that it will take 15-30 mins to glue the spacers. We will use 30 mins for the estimate.
- The second sheet is flipped  lowered onto the first epoxied sheet.
-  Epoxied RPCs are moved to a curing station. There are two curing stations. Freshly glued chambers are stacked on one.
- Cured RPCs from the previous day’s stack  are moved to a leak-check station. Chambers which fail the leak test are discarded (much less that 1% from Virginia Tech experience)
- Top surface of the chamber is cleaned and painted with Statguard Conductive Acrylic Paint (DESCO 10408)
- After inking the RPC is either flipped and sent back to the cleaning input line for the other side or passed to a station for HV connection application and packing

## RPC production shift personnel

-  Material movers – moving/opening crates and feeding glass into the assembly line and loading modules for shipment.                                       2
- line worker - monitoring cleaning process                                                  1
- line workers - laying down spacers and lowering top sheet of glass           3
- line worker - monitoring inking and drying	                                      1
- line worker – monitoring leak check and curing process and resupplying the assembly line                                                                                             1
- foreman – supervisor, quality control, procurement                                   1
** ****Total****	****per shift****	****	****                                             9**

## Expected yield

- 1 chamber is produced every 30 mins, 16 chambers per 8 hours shift.
- 2 shifts per  day, 220 days per year.
- 440 shifts per year give production capability of 7040 chambers per facility per year.
- Two factories will produce 48,000 chambers in 3.5 years

## Factory cost

- Assembly line equipment                             $400K
- Floor space 5000 ft2  @ $16.25/ft2/yr        $85K/year
- Labor                                                         $1000K/year
-       Labor breakdown:
-       16 technicians @  $50k/year          $800K/year
-         2 foremen      @  $60k/year          $120K/year
-         1 project manager                            $80K/year

## RPC Assembly at Va Tech

- To _reduce assembly time_, extruded strips were used instead of “button-like” spacers.

- This also provided a natural “mouse maze” to ensure uniform distribution of the gas.

- This is the slowest step in the production

## Improving the BELLE design

- Cut the corner,  make the gas manifold:
-  improve coverage/reduce dead area, improve robustness of a chamber
- Replace India ink by Static quard conductive acrylic paint :
- Do not depend on unspecified properties of the proprietory products
-  replace 2mm  glass by 3 mm glass:
- Reduce breakage, improve robustness
- Replace epoxy by transfer tape for gluing spacers:
- Enable full automation of the production process
- Reduce number of spacers, 20 cm pitch instead of 10:
- Take advantage of thicker glass, simplify the production.

## Off-axis RPC design

## Gaining experience/confidence with RPC’s

- Gas leaks. How big are they?
- Examine large area chambers from Virginia:
- Few have broken connectors
- One leaks 30 ccm/min
- Two  leak 3-5 ccm/min
- For the rest the leak rate is below the threshold of detectability
- Leaks? Do they  matter?
- Does a leaky chamber work?
- How poorly?

## Efficiency of a chamber with the biggest leak

- Despite a sizeable leak, the chamber shows a pretty good efficiency, ~ 90%
- But this efficiency seems do degrade with time ?

## Efficiency of a chamber with the biggest leak

- But this efficiency seems do degrade with time ?
- This chamber was operated with no gas flow
- Indication that the gas composition/contamination is not very important ?

## Building small chambers

- Some 20 chambers constructed this summer by a TRAC teacher
- Efficiency in excess of 95%
- Constructed a setup for long term studies of a large collection of chambers

## Further ideas to test ?

- Glass with embedded resistive layer?
- Simplify the production ( no washing, painting of one side)
- Laminate with  an insulating plastic?
- Simplify the process
- Improve the safety of the production process

## Conclusions

- Experience, so far, is very positive: confirming the BELLE conclusion, albeit on a very much smaller scale, that glass RPC’s  are very robust detectors suitable for large detectors
- A systematic studies of the glass RPC has commenced, but it will be a long time before we can add much to the BELLE experience
- Production of chambers lends itself to the automation, thus offering a significant potential for further cost reductions
- Commercial: today, 5 pm, LabF: show and tell. See for yourself small chambers and large chambers, production process,  cosmic rays test stand.