M.A. Spezziga

THE MICRO-GAP CHAMBER

Abstract 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.

The WELL detector

Abstract We introduce the WELL detector, a new type of position-sensitive gas proportional counter produced using advanced Printed Circuit Board (PCB) technology. The WELL is based on a thin kapton foil, copper-clad on both sides. Charge amplifying micro-wells are etched into the first metal and kapton layers. These end on a micro-strip pattern which is defined on the second metal plane. The array of micro-strips is used for read-out to obtain 1-D positional information. First results from our systematic assessment of this device are reported.

The micro-groove detector

We introduce the Micro-Groove Detector (MGD), a new type of two-dimensional position-sensitive gas proportional counter produced using advanced Printed Circuit Board (PCB) technology. The MGD is based on a thin kapton foil, clad with gold-plated copper on both sides. An array of micro-strips at a typical pitch of 200 lm is defined on the top metal layer. Using as a protection mask the metal left after the patterning, charge amplifying micro-grooves are etched into the kapton layer. These end on a second micro-strip pattern defined on the bottom metal plane. The two arrays of micro-strips can have an arbitrary relative orientation and so can be used for read-out to obtain 2-D positional information. First results from our systematic assessment of this device are reported: gas gain ’15 000, rate capability above 106 mm~2 s~1, energy resolution 22% at 5.4 keV, no significant charging or aging e⁄ects up to 5 mC/cm and full primary charge collection eƒciency even at high drift fields. ( 1999 Published by Elsevier Science B.V. All rights reserved.

What is the real gas gain of a standard GEM

We have observed very high gains (up to 7000) from GEMs with ‘standard’ parameters (kapton thickness 50 lm, pitch 120 lm, copper hole diameter 65 lm, kapton hole diameter 30 lm). This was achieved using GEMs coupled to a simple array of copper read-out strips. From the measurements of the current on all the electrodes, we conclude that the high observed gains are fully attributable to electron multiplication in the holes of the mesh, and not to electronics related e⁄ects as had been previously suggested. Furthermore, we report that this large gain may only be fully exploited when the field in the second GEM gap is high. The e⁄ect on the gain of coupling a GEM to another charge amplifying device was investigated using a GEM—PMGC combination. ( 1998 Elsevier Science B.V. All rights reserved.

A large area, high gain Micro Gap Chamber

Abstract A new approach to the construction of the Micro Gap Chamber is presented. A 10 × 10 cm 2 MGC has been built using a 8 μm thick polyimide layer as anode-cathode insulator. Studies on gas gain, uniformity of response along the strip and charging-up have been carried out in laboratory by using X-ray sources. Very large proportional gains, up to ∼ 210 4 , have been reached working with gas mixtures based on Ne-DME. The simplified technology for the detector fabrication opens the possibility to produce very large area MGCs.

Development of a very large area microstrip gas chamber for the CMS central tracking system

A very large area microstrip gas chamber (250 × 100 mm2), thought to be the building block of the CMS barrel tracker, has been built and undergone extensive tests with X-ray sources and particle beams. Rate capability, uniformity of response along the strip and charging-up effect for different gas gain and bias schemes have been measured in laboratory. A systematic study on the long-term stability of its performance (ageing) at high rates has been carried out both with standard and “clean” mechanical assemblies. Stability measurements under high voltage were performed. Studies of spatial resolution and efficiency for minimum ionizing particles were carried out with different gas gap, gas mixture, angle of incidence and avalanche gain.

A thin, large area microstrip gas chamber with strip and pad readout

Abstract The design, construction and test of a thin (200 μm overall substrate thickness), large area (10 cm × 10 cm) microstrip gas chamber (MSGC) with both strip and pad readout is described. The device is built on a 6 in. silicon wafer. The characteristics of this detector make it suitable as a building block of a tracking system at LHC/SSC.

FURTHER TEST AND DEVELOPMENT OF THE MICRO-GAP CHAMBER

Abstract 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 MGCs structure to avoid edge effects is discussed.

Operation of MSGCs with gold strips built on surface-treated thin glasses

Abstract We report the results of tests of MicroStrip Gas Chambers with gold strips fabricated on surface-treated thin glasses. The electrical properties of glass substrates are discussed and different solutions for surface coatings are presented. Short- and long-term measurements of stability of the response have been carried out on MSGCs with diamond-like coatings, under different experimental conditions. The tested detectors differed in the technology adopted for the processing of gold.

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.