M.M. Massai

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.

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.

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.

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.

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.

Study of the π0π0 system in pp central collisions at 450 GeV/c

Abstract The effective mass spectrum of π0 pairs produced in pp central collisions (pp → pfπ0π0ps) at 450 GeV/c, s = 29 GeV , below 1 GeV differs from that observed in peripheral charge exchange reactions. In particular, there is a large number of events between ππ-threshold and 1 GeV, that interfere with f0(980) destructively. The possible existence of a broad S-wave state is suggested.

Ultrafast soft x-ray two-dimensional plasma imaging system based on gas electron multiplier detector with pixel readout

In the present article a new diagnostic device in the soft x-ray range, for magnetic fusion plasmas, is proposed based on a gas electron multiplier detector with 2.5×2.5 cm active area, equipped with a true two-dimensional readout system. The readout printed circuit board, designed for these experiments, has 128 pads. Each pad is 2 mm square and covers a roughly circular area. The operational conditions of the detector are settled to work in the x-ray range 3–15 keV at very high counting rates, with a linear response up to 2 MHz/pixel. This limitation is due to the electronic dead time. Images of a wrench and two pinholes were done at rates of 2.5 MHz/pixel with a powerful x-ray laboratory source showing an excellent imaging capability. Finally preliminary measurements of x-ray emission from a magnetic fusion plasma were performed on the Frascati tokamak upgrade experiment. The system was able to image the plasma with a wide dynamic range (more than a factor of 100), with a sampling frequency of 20 kHz and with counting rates up to 4 MHz/pixel, following the changes of the x-ray plasma emissivity due to additional radio frequency heating. The spatial resolution and imaging properties of this detector have been studied in this work for conditions of high counting rates and high gain, with the detector fully illuminated by very intense x-ray sources (laboratory tube and tokamak plasma).

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.

A MICROSTRIP GAS CHAMBER ON A SILICON SUBSTRATE

Abstract The operation of a microstrip gas chamber built on a silicon substrate is described. The insulation between the low-resistivity silicon and the anode-cathode structure is provided by a 2 μm thick thermal oxide layer. A gas gain of 10 4 has been measured at potential differences much lower than those usually needed with glass or quartz substrates. No surface charging or gain drift have been observed up to a measured flus of 5 × 10 5 particles/cm 2 s. A device with such a thin dielectric between strips and back plane, makes a true two-dimensional readout possible.