1. Glass Resistive Plate Chambers
BELLE Experiment:
Virginia Tech (barrel)
Tohoku (endcaps)
Dan Marlow, Princeton (seminar at Rice), Norm Morgan (Virginia Tech)
Monolith Experiment (proposed at Grand Sasso):
Carlo Gustavino
Virginia chambers at Fermilab
Valery Makeev

2. RPC Principles of Operation
Signal pickup (x)
Resistive paint
Glass plates
8 kV
Signal pickup (y)
Spacers
_ _ _ _ _ _ _ _ _ _ _
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.
Before
_ _ _ _ _ _ _
The discharged area recharges slowly through the high-resistivity glass plates.
After

3. 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.

4. Principles of Operation: I vs V Curve
Glass RPCs have a distinctive
and readily understandable current versus voltage relationship.
Low voltage
High voltage

5. Pulse Shape
One interesting feature of RPCs is that the signal can be observed both using a pickup electrode and by viewing the light signal using a PMT.
The pulses are large (~100 mV into 50 ohms) and fast (FWHM ~ 15ns)
There is a very good correlation between the electronic and the light signal.

6. Current, pulse shape, efficiency
Pulse height, currents, plateau depend on:
Gas mixture
Electric field (HV/gap size)
Resistivity of the ink

7. Principles of Operation: Rate Capability
As noted, each discharge locally deadens the RPC. The recovery time is approximately
_ _ _ _ _ _ _
Numerically this is (MKS units)
Assuming each discharge deadens an area of , rates of up
to can be handled with 1% deadtime or less. This is well below what is expected in our application.

8. Gas Mixture (Belle) Traditional Gas Mixture
64% Argon : 6% Freon % Isobutane
Constraints
Safety: gas should be non flammable:
mixture ---> 30% Argon : 62% Freon :8% Butane
Environment: Freon 116--> Freon R134A
Cost: Isobutane ---> Butane “silver”

9. Virginia Chambers at Fermilab
Valery Makeev
Chambers have been stored in an ambient atmosphere for three years
Eventually (see next slide) they work with efficiency >90%

10. Summary
Glass RPC chambers are simple to build, reliable detectors, but applicable only for low rate experiments
The only known (so far) damage mechanism to glass RPC’s is related to freon+water vapor+HV combination
Combination of reversible (short term exposure?) and irreversible (long term exposure) effects
Chemistry of deposits on both electrodes is not very well understood
Water vapor proof gas lines are sufficient to avoid the problem
Even in the case of accidental damage a recipe exists for chamber recovery through chemical cleaning of the glass surfaces