Microgap Chamber Research Articles

An aging study of semiconductive microstrip gas chambers and a gas electron multiplier

The aging behavior of wire chambers have been of great interest for many years. Recently a new generation of proportional chambers have been developed including the microstrip gas chamber (MSGC) microgap chamber (MGC) and gaseous electron multiplier (GEM). Aging studies of these detectors are of particular interest to the LHC (Large Hadron Collider) community because the baseline design of the CMS experiment includes MSGCs as part of the tracking system. In this work we report aging studies of two MSGC's and a GEM detector with a MSGC used for readout. The GEM is constructed from Kapton and copper, the MSGC's are constructed from semiconductive glass and gold. When the MSGC's are operated in argon and dimethyl ether (DME) gas mixture and irradiated with a 6 KeV photon beam, > 100 mC/cm charge can be accumulated without degradation of the detector performance while the GEM+MSGC can tolerate 220 mC/cm without degradation of performance, corresponding to about 20 years of operation at the LHC.

An aging study by semi-conductive microstrip gas chambers

The aging behavior of wire chambers have been of great interest for many years. Recently, a new generation of proportional chambers have been built including the microstrip gas chamber (MSGC) microgap chamber (MGC) and gaseous electron multiplier (GEM). Aging studies of these detectors are of particular interest to the Large Hadron Collider (LHC) community because the baseline design of the CMS experiment includes MSGCs as part of the tracking system. We have performed a series of aging tests of large pitch, 1 mm MSGC’s constructed on semiconductive glass substrates operated in argon and dimethyl ether (DME). The quencher, DME is believed to chemically react with some materials of organic origin commonly used in gas systems, shortening the lifetime and deteriorating the performance of the detectors. Great care was taken to minimize unwanted chemical reactions and all materials suspected to react with DME were removed from areas where the DME gas flows. With these precautions, we have demonstrated that the MSGC can tolerate about 150 mC/cm of accumulated charge without significant degradation of the chamber performance. This corresponds to about 15 yr of operation at the LHC.

A microgap photomultiplier for the read-out of a LaF 3:Nd(10%) scintillator

A LaF 3:Nd(10%) scintillator crystal has been placed in a microgap gas chamber to obtain a position-sensitive detector for γ-rays. Directly on the crystal a thin layer of nickel is evaporated and on top of that a thin semi-transparant CsI photocathode. γ-rays absorbed in the scintillator crystal produce a UV-light flash, which liberates electrons in the photocathode. These electrons are multiplied and detected in the microgap chamber. By comparing the spectrum measured when this detector is irradiated with 511 keV γ-rays with a spectrum that is computed in a Monte Carlo simulation it is concluded, that the probability that a UV-light photon created in the scintillator produces a photoelectron in the photocathode, is about 2.5%. The signals from this detector can be distinguished better from the background than when a similar crystal is mounted on a standard photomultiplier tube.

Performance of a small gap chamber

The design of the Small Gap Chamber combines features of the MicroStrip Gas Chamber [1] and of the MicroGap Chamber [2]. It is a detector for a single coordinate read-out with the single metal layer pattern of a MSGC and the anode-cathode separation of a MGC. A polyimide layer, suitably patterned on top of the metal, ensures an insulation at the edge of the electrodes and defines the conductive areas in front of the gas. We report on the performance measured in a test beam at CERN and with an X-ray tube in the laboratory.

A LaF 3 : Nd(10%) scintillation detector with microgap gas chamber read-out for the detection of γ-rays

A LaF 3 : Nd(10%) scintillator crystal has been placed in a microgap gas chamber to obtain a position-sensitive detector for γ-rays. Directly on the crystal a thin layer of nickel is evaporated, and on top of that a thin semi-transparant CsI photocathode. γ-rays absorbed in the scintillator crystal produce a UV-light flash, which liberates electrons in the photocathode. These electrons are multiplied and detected in the microgap chamber. By comparing the spectrum measured when this detector is irradiated with 511 keV γ-rays with a spectrum that is computed in a Monte Carlo simulation, it is concluded that the probability that a UV-light photon created in the scintillator produces a photo-electron in the photocathode, is about 2.5%.

Performance of three variants of micro-gap chambers

Measurements with variants of micro-gap chambers built on silicon wafers are reported: • - we compare the ability of the detectors to sustain high voltage on the cathodes for two fabrication processes; • - we present results on the measurement of the second coordinate with small stereo angle cathodes and for two kinds of insulating layer on the silicon; • - we discuss a first attempt to build a one-dimensional micro-gap chamber with a single metal layer.

The Micro-Gap Chamber: new developments

To fully exploit the capabilities of the Micro-Gap Chamber, new geometries are examined in the light of the recent work performed in our labs. Results on the usage of neon in the gas mixtures necessary to operate the chamber at high gas gain and of ageing tests with these new mixtures are also discussed.

A large area MicroGap Chamber with two-dimensional read-out

A 10/spl times/10 cm/sup 2/ MicroGap Chamber with a small stereo angle read-out has been developed for the inner tracking system of CMS. The anode strips are 9 /spl mu/m wide with a pitch of 200 /spl mu/m. The sampling pitch of the back cathode is 400 /spl mu/m at a stereo angle of 50 mrad. Both coordinates are read-out from the same side of the detector substrate. Measurements of gain stability, fraction of induced charge on the back electrode, uniformity of response along the strip and rate capability have been performed in laboratory, using X-ray sources. Detection efficiency, spatial resolution, charge and space correlation have been measured with minimum ionizing particle beams at CERN.

A UV light photo-detector based on a MicroGap Chamber with single electron response

Abstract A MicroGap Chamber (MGC) used as a fast UV light detector with single electron sensitivity is presented. The detector has a semitransparent or reflective CsI photocathode, 100–200 μm anode pitch and 2D capability. It works with gas mixtures based on DME and light noble gases at atmospheric pressure. A gas gain >106 has been achieved with a two-stage gas amplification (G > 102 in the drift region and G ≈ 104 in the strip region). The use of light noble gases, like neon, has brought to a sensible reduction of VUV light output (hence photon feedback) during electron multiplication in gas. Due to the very thin gap (5 μm) a very large fraction of the avalanche charge is quickly delivered to the fast amplifier (20 ns peaking time) thus improving the single electron detection capability of the MGC. Because of its higher gain the MGC with a semitransparent CsI photocathode provides a better single electron detection efficiency (>90%) than the MGC with a reflective photocathode. This latter, vice versa, has a higher quantum efficiency and a faster response. Experimental results on gas gain, drift properties, positional sensitivity and single electron detection efficiency are reported.

The MicroGap Chamber: a new detector for the next generation of high energy, high rate experiments

The concept of MicroGap Chamber (MGC) is introduced. Results from a large MGC (10 × 10 cm 2) with a small stereo angle read-out are presented. Both coordinates are read out from the same side of the detector substrate. Measurements of gain stability, fraction of induced charge on the back electrode, uniformity of response along the strip and rate capability have been performed in the laboratory, using X-ray sources. Detection efficiency, spatial resolution, charge and space correlation have been measured with minimum ionizing particle beams at CERN.

Further test and development of the micro-gap chamber

Results from a beam test of the micro-gap chamber with minimum ionizing particles are reported. The dependence of the spatial resolution on the incidence angle of the beam with respect to the detector plane has been studied. Laboratory tests on new amplification structures, designed to increase gain and stability and to reduce the detector capacitance, are also shown. A maximum gas gain of 6000 and a specific capacitance of 0.5 pF/cm have been obtained. An optimised layout of the MGC's structure to avoid edge effects is discussed.

The micro-gap chamber

The micro-gap chamber (MGC), a new type of position sensitive proportional gas counter, is introduced. The device is built using microelectronics technology. In this detector the separation between the electrodes collecting the avalanche charge (the anode-cathode gap) is only a few microns. The time it takes to collect the positive ions is therefore very short ( ≈ 10 ns). The speed of the device now equals that of solid state detectors but it is more than three orders of magnitude higher than in standard proportional counters and one order of magnitude higher than in the recently introduced microstrip gas chamber (MSGC). As a result, the rate capability is extremely high (> 9×10 6 c/mm 2 s). The amplifying electric field around the thin anode microstrip extends over a small volume but is very intense (270 kV/mm). It provides a gas gain of 2.5 × 10 3 at 400 V with 14% (FWHM) energy resolution at 5.4 keV. The anode pitch is 100 μm and the readout is intrinsically two-dimensional. Because there is practically no insulating material in view, charging was not observed even at the highest rate. This device seems very well suited for instrumentation of the tracking system at the new hadron colliders (LHC/SSC) as well as in many other fields of research.