New observations with the gas electron multiplier (GEM)

We describe recent measurements realized with the Gas Electron Multiplier (GEM) mesh added as pre-amplification element to a multiwire and a micro-strip chamber. Large, stable combined gains are obtained, with good uniformity and energy resolution, in a wide range of filling gases including non-flammable mixtures; coupled to a micro-strip plate, the pre-amplification element allows to maintain the high rate capability and resolution at considerably lower operating voltages, completely eliminating discharge problems. Charge gains are large enough to allow detection of signals in the ionization mode on the last element, permitting the use of a simple printed circuit as read-out electrode; two-dimensional read-out can then be easily implemented. The absence of charge multiplication in the last stage avoids charge build-up on the substrate and prevents ageing phenomena. A new generation of simple, reliable and cheap fast position sensitive detectors seems at hand

The gas electron multiplier (GEM)

We describe operating priciples and results obtained with a new detector component: the Gas Electrons Multiplier (GEM). Consisting of a thin composite sheet with two metal layers separated by a thin insulator, and pierced by a regular matrix of open channels, the GEM electrode, inserted on the path of electrons in a gas detector, allows to transfer the charge with an amplification factor approaching ten. Uniform response and high rate capability are demonstrated. Coupled to another device, multiwire or micro-strip chamber, the GEM electrode permit to obtain higher gains or less critical operation; separation of the sensitive (conversion) volume and the detection volume has other advantages, as a built-in delay (useful for triggering purposes) and the possibility of applying high fields on the photo-cathode of ring imaging detectors to improve efficiency. Multiple GEM grids in the same gas volume allow to obtain large amplification factors in a succession of steps, leading to the realization of an effective gas-filled photomultiplier

Progress with diamond over-coated microstrip gas chambers

We describe recent observations and measurements with Micro-Strip Gas Chambers coated, after manufacturing, with a thin diamond-like layer in order to increase their rate capability. Compared to the more widely used solution consisting in coating the insulating support with a conductive layer before photo-lithography (the so-called undercoating), over-coating has the advantage of avoiding possible problems with adherence of metals to the layer, damages during the etching process and reduced quality of the artwork resulting from imperfections or dust inclusions in the layer. Early tests have however indicated that, possibly because of damages to the layer due to electron and ion bombardment during the avalanche process, irreversible structural modifications and fatal breakdown could be encountered at very high integral radiation fluxes. The present paper summarizes these results, and describes recent developments demonstrating that a better choice of the parameters of the over-coat may allow to withstand the radiation doses anticipated for LHC detectors with the intrinsically simpler over-coating solution. We discuss also several possible applications of the use of thin, controlled resistivity layers for other families of detectors used or in development for CERN¹s high luminosity collider

High rate operation of micro-strip gas chambers on diamond-coated glass

Very high rate operation of micro­strip gas chambers can be achieved using slightly conducting substrates. We describe preliminary measurements realized with detectors manufactured on boro-silicate glass coated, before the photo-lithographic processing, with a diamond layer having a surface resistivity of around 1014 /o. Stable medium-term operation, and a rate capability largely exceeding the one obtained with identical plates manufactured on uncoated glass are demonstrated. If these results are confirmed by long-term measurements the diamond coating technology appears very attractive since it allows, with a moderate cost overhead, to use thin, commercially available glass with the required surface quality for the large-scale production of gas micro-strip detectors

Operation of high rate microstrip gas chambers

We describe recent measurements carried out in well controlled and reproducible conditions to help understanding the factors affecting the short and long term behaviour of Microstrip Gas Chambers. Special care has been taken concerning the gas purity and choice of materials used in the system and for the detectors construction. Detectors built on glasses with surface resistivity in the range $10^{13}-10^{15} \Omega/\Box$ have shown satisfactory performance as they do not show charging-up process at high rate and stand the large doses required for the future high luminosity experiments (~10 mC·cm-1·yr-1). Concerning the lifetime measurements, it has been observed that chambers manufactured on high-resistivity glass are far more susceptible of suffering ageing than detectors made on low resistivity, electron-conducting supports, independently of the metal used for the artwork (chromium or gold) at least in clean gas conditions. The successfully operation in the laboratory of detectors manufactured on diamond-coated glass with a surface resistivity around $10^{15} \Omega/\Box$ confirms the last statement. Results from a long-term, high rate beam test are also reported

Study of ageing and gain limits of microstrip gas chambers at high rates

The CMS experiment comprises MSGCs as one of the key detection elements for high luminosity tracking at LHC. In addition to the high dose rate of 10 mC/year per cm of strip, these detectors have to survive the hostile presence of highly ionizing particles, neutrons low energy gammas and hadrons. In this report we present the results of systematic tests on maximum safe operational gain limits in MSGCs before the discharge. Long term ageing tests performed on prototype open Ibanana¹ modules envisaged to be arranged around the interaction region in the forward part of the CMS tracker show no evidence of gain drop up to equivalent ~ 10 years of LHC operation. A comparison is made between argon and neon gas mixtures with DME in equal proportions by investigating long term irradiation effects on chamber operation by introducing controlled and reproducible pollution in the gas lines

Nuclear astrophysics with radioactive ions at FAIR

The nucleosynthesis of elements beyond iron is dominated by neutron captures in the s and r processes. However, 32 stable, proton-rich isotopes cannot be formed during those processes, because they are shielded from the s-process flow and r-process, β-decay chains. These nuclei are attributed to the p and rp process. For all those processes, current research in nuclear astrophysics addresses the need for more precise reaction data involving radioactive isotopes. Depending on the particular reaction, direct or inverse kinematics, forward or time-reversed direction are investigated to determine or at least to constrain the desired reaction cross sections. The Facility for Antiproton and Ion Research (FAIR) will offer unique, unprecedented opportunities to investigate many of the important reactions. The high yield of radioactive isotopes, even far away from the valley of stability, allows the investigation of isotopes involved in processes as exotic as the r or rp processes