F. Angelini

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.

A microstrip gas avalanche chamber with two-dimensional readout

A microstrip gas avalanche chamber with a 200 μm anode pitch has been built and successfully tested in our laboratory. A gas gain of 104 and an energy resolution of 18% (FWHM) at 6 keV have been measured using a gas mixture of argon-CO2 at atmospheric pressure. A preliminary measurement of the positional sensitivity indicates that a spatial resolution of 50 μm can be obtained.

Reading a GEM with a VLSI pixel ASIC used as a direct charge collecting anode

Abstract In MicroPattern Gas Detectors (MPGD) when the pixel size is below 100 μ m and the number of pixels is large (above 1000) it is virtually impossible to use the conventional PCB read-out approach to bring the signal charge from the individual pixel to the external electronics chain. For this reason a custom CMOS array of 2101 active pixels with 80 μ m pitch, directly used as the charge collecting anode of a GEM amplifying structure, has been developed and built. Each charge collecting pad, hexagonally shaped, realized using the top metal layer of a deep submicron VLSI technology is individually connected to a full electronics chain (pre-amplifier, shaping-amplifier, sample & hold, multiplexer) which is built immediately below it by using the remaining five active layers. The GEM and the drift electrode window are assembled directly over the chip so the ASIC itself becomes the pixelized anode of a MPGD. With this approach, for the first time, gas detectors have reached the level of integration and resolution typical of solid-state pixel detectors. Results from the first tests of this new read-out concept are presented. An Astronomical X-ray Polarimetry application is also discussed.

A microstrip gas chamber with true two-dimensional and pixel readout

A true two-dimensional μstrip gas chamber has been constructed and successfully tested. This new detector has an effective substrate thickness of less than 2 μm. An ion implanted oxide layer of 1.8 μm thickness provides the necessary insulation between the front and back plane and permits collection on the back electrodes of a large fraction of the induced charge. The back electrode signal is used to measure the coordinate along the anode strips (X-Y readout) or to provide true space points (pixel readout). Very good imaging capabilities have been obtained in both cases. A flux of 107 particles/mm2 s has been measured without significant gain loss. No charging effect has been observed after three days continuously running at a flux of 104 particles/mm2 s, while a 15% gain loss, probably due to ageing effects, has been measured after collection on the strips of a charge corresponding to the more than six years of running at the design luminosity of LHC, at 50 cm from the beam axis.

Results from the first use of microstrip gas chambers in a high-energy physics experiment

Abstract The first use of microstrip gas chambers in a high-energy physics experiment is described. The forward magnetic spectrometer of NA12 (GAMS) experiment at CERN-SPS has been equipped with 8 planes of microstrip gas chambers for a total of 1100 low-noise analog channels. The detectors have been exposed for 100 days to a high flux proton beam. A 0.2% momentum resolution at 450 GeV/c, a rate capability higher than 5 × 105/s−1mm−2 and a 9 ns time resolution have been measured.

Novel gaseous x-ray polarimeter: data analysis and simulation

We report on the development of a new higly efficient polarimeter, based on the photoelectric effect in gas, for the 2-10 keV energy range, a particularly interesting band for x-ray astronomy. We derive the polarization information by reconstructing the direction of photoelectron emission with a pixel gas detector. Attention is focused on the algorithms used in data analysis in order to maximize the sensitivity of the instrument. Monte Carlo simulation is also discussed in details.

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.

The microstrip gas chamber

Abstract We describe the operating principles of the microstrip gas chamber and the main results of measurements realized with several prototype devices in the detection of X-rays and charged particles. Detectors with 3, 5 and 10 μm anode widths and 125 or 200μm pitch have been successfully tested. A gas gain of 10 4 and an energy resolution of 12.2% fwhm at 6 KeV have been measured. A localization accuracy for minimum ionizing particles of 30 μm rms, a two track resolution of 250 μm and a high rate capability (above 2·10 7 cm −2 s −1 ) make the device a good candidate for tracking at high luminosity colliders.

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.