M.C.S. Williams

A New type of resistive plate chamber: The Multigap RPC

Abstract This Letter describes the multigap resistive plate chamber (RPC). The goal is to obtain a much improved time resolution, keeping the advantages of the wide gap RPC in comparison with the conventional narrow gap RPC (smaller dynamic range and thus lower charge per avalanche which gives higher rate capability and lower power dissipation in the gas gap).

The multigap resistive plate chamber as a time-of-flight detector

Abstract The goal of this R&D has been to reach the time resolution needed for Time-of-Flight detectors using the Multigap Resistive Plate Chamber (MRPC). We present here a MRPC with a time resolution of 70 ps. This prototype has been studied within the R&D program for the very large area TOF array of the ALICE experiment at the CERN LHC.

The non-spark mode and high rate operation of resistive parallel plate chambers

Abstract The good time and position resolution of the resistive plate chamber (RPC) make it an attractive candidate for muon trigger systems at future colliders. However, this device has severe rate problems that make it unusable above 1 Hz/cm 2 in its present form. We have investigated various materials and have also discovered a new mode of operation that allowed us to operate the RPC at 150 Hz/cm 2 . We discuss further improvements that may extend operation to even higher rates. We also discuss spark formation and explain the cause for the abnormally late spark signals.

A study of the multigap RPC at the gamma irradiation facility at CERN

Abstract The selected device for the ALICE Time-of-Flight array is the Multigap Resistive Plate Chamber (MRPC). We have tested this device at the Gamma Irradiation Facility at CERN to evaluate the rate dependence. We find that the rate capability of the MRPC easily exceeds the 50 Hz/cm 2 maximum expected rate at the ALICE experiment. In addition, we have measured the power dissipated for an equivalent flux of 1.6 kHz/cm 2 of through-going muons to be 650 mW/m 2 .

Investigation of resistive parallel plate chambers

Abstract The resistive parallel plate chamber (RPC) has been developed during the last ten years. We have investigated two versions of these chambers, one with cellulose and the other with phenolic plates. We present a comparison between these two for various gas mixtures and the dependence on particle flux.

The wide gap resistive plate chamber

Abstract The resistive plate chamber (RPC) has good time and position resolution; these factors (coupled to its simple construction) make it an attractive candidate for muon trigger systems at future colliders. However, operated in spark mode, the RPC has severe rate problems that make it unusable above 10 Hz/cm 2 . We have previously published our results concerning the operation of the RPC in spark and in avalanche mode; we have shown that the rate limit can be increased to 150 Hz/cm 2 if the RPC is operated in avalanche mode. Here, we discuss the performance of chambers with 6 and 8 mm gas gaps (compared to the more usual 2 mm gap). We outline the reasons for this choice, and also discuss anode versus cathode strip readout. We have measured the efficiency versus flux, and also show that an enhanced rate limit can be obtained if only a small region of the chamber is exposed to the beam (spot illumination). Finally we have tested the performance of chambers constructed with other materials for the resistive plate and compare it to chambers constructed with our preferred plastic, melamine laminate.

Resistive plate chambers with secondary electron emitters and microstrip readout

Abstract We describe our attempt to develop Resistive Plate Chambers (RPCs). One study involves the use of secondary electron emitters that consist of porous photosensitive materials (CsI, diethylferocenil-mercury, SbCs and others) deposited on a cathode; this enhances efficiency, thus allowing the use of light, non-flammable gas mixtures. The other study concerns the operation of an RPC with a narrow strip readout - the “microstrip RPC”.

The multigap RPC: the time-of-flight detector for the ALICE experiment

Abstract The selected device for the ALICE time-of-flight is the multigap resistive plate chamber. This detector, consisting of a stack of glass plates, has a time resolution between 60 and 80 ps . We discuss the principle of operation of this detector and present the latest results from the ongoing R&D program.

Pure avalanche mode operation of a 2-mm gap resistive plate chamber

Abstract It is necessary to operate the resistive plate chamber (RPC) in avalanche mode to obtain high efficiency at elevated particle fluxes. We examine this mode of operation with a 2 mm gap RPC using gas mixtures containing C 2 F 4 H 2 and C 2 F 5 H. In order to explain the data we propose that the avalanche growth is strongly limited by space charge effects.

Further studies of avalanche mode operation of resistive parallel plate chambers

Abstract We have investigated the high rate operation of the resistive plate chamber and have discovered that melamine-phenolic laminates are good candidates for a plate material. We have previously shown that avalanche mode (rather than spark mode) gives a substantial improvement in the rate capability. There are two new encouraging results; the timing spectra are not affected by the rate; and particles at non normal incidence have a higher detection efficiency; these substantially increase the rate capability of this device. However there are two results that show that further RD and the fall off of the efficiency with increasing high voltage. Our goal is to produce a cheap large area detector that has good spatial and time resolution and has a rate capability suitable for the muon system at a future collider. We believe that these results show that this detector is already promising and should satisfy these requirements with further R&D.