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Glass Resistive Plate Chambers

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.

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Glass Resistive Plate Chambers

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  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 Resistive paint Signal pickup (x) Glass plates 8 kV Signal pickup (y) Resistive paint +++++++++++++++ _ _ _ _ _ _ _ _ _ _ _ +++ +++++ _ _ _ _ _ _ _ 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 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”

  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

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