Organization legal name	Short name	Activity leaders*	Logo
Istituto Nazionale di Fisica Nucleare, INFN-LNF	INFN	G. Bencivenni, C. Curceanu
Oesterreichische Akademie der Wissenschaften, SMI	OeAW	J. Zmeskal
Gesellschaft für Schwerionenforschung mbH	GSI	B. Voss
Technische Universität München	TU München	B. Ketzer
Helsingin yliopisto	UH	F. García
Commissariat à l’Énergie Atomique	CEA-Saclay	D. Neyret
Institutul National de Fizica – Horia Hulubei	IFIN-HH	M. Bragadireanu
University of Glasgow	UGlasgow	J. Annand

* in bold the spokesperson

 

The next generation of experiments in hadron physics aims at studying rare processes with dramatically improved sensitivity. The technical requirements to reach this goal include high beam intensities and luminosities, fast detectors with large acceptance and high resolution. Examples are the KLOE2 and AMADEUS experiments at DAFNE-LNF, Frascati, Italy, and PANDA and CBM at FAIR, Darmstadt and Olympus at DESY, Hamburg, Germany. An essential part of all these experiments is a detector for charged particles possesing excellent tracking capabilities and covering large areas or volumes. An extremely low material budget is vital in order not to spoil the energy and mass resolution of the apparatus. Micropattern gas detectors (MPGD) based on the Gas Electron Multiplier (GEM) technology provide a very promising path towards these goals. Introduced in 1996 by F. Sauli, a GEM consists of a thin (50μm) copper-kapton-copper composite in which is chemically etched a set of holes, arranged in a hexagonal pattern (typically 70 μm diameter with 140 μm spacing). Applying a potential difference across the two sides of the GEM generates a suitable electric field inside its holes: electrons released by the ionization in the gas will drift into the holes and are multiplied in the high electric field (50-70 kV/cm). Cascading the avalanche multiplication over three adjacent foils allows to operation of triple-GEM detectors at an overall gain above 104, while eliminating the risk of hazardous discharges (<10-12 per charged particle) - the major advantage of the GEM technology.

Task 1: "Active target" TPC

The next generation of experiments in hadron physics aims at studying rare processes with dramatically improved sensitivity. The technical requirements to reach this goal include high beam intensities and luminosities, fast detectors with large acceptance and high resolution. Examples are the KLOE2 and AMADEUS experiments at DAFNE-LNF, Frascati, Italy, and PANDA and CBM at FAIR, Darmstadt and Olympus at DESY, Hamburg, Germany. An essential part of all these experiments is a detector for charged particles possesing excellent tracking capabilities and covering large areas or volumes. An extremely low material budget is vital in order not to spoil the energy and mass resolution of the apparatus. Micropattern gas detectors (MPGD) based on the Gas Electron Multiplier (GEM) technology provide a very promising path towards these goals. Introduced in 1996 by F. Sauli, a GEM consists of a thin (50μm) copper-kapton-copper composite in which is chemically etched a set of holes, arranged in a hexagonal pattern (typically 70 μm diameter with 140 μm spacing). Applying a potential difference across the two sides of the GEM generates a suitable electric field inside its holes: electrons released by the ionization in the gas will drift into the holes and are multiplied in the high electric field (50-70 kV/cm). Cascading the avalanche multiplication over three adjacent foils allows to operation of triple-GEM detectors at an overall gain above 104, while eliminating the risk of hazardous discharges (<10-12 per charged particle) - the major advantage of the GEM technology.

Task 2: Large area foils and support structures

The CERN TS-DEM workshop has developed a new manufacturing procedure based on a single-mask photolithography. This technique allows the fabrication of GEM foils as large as 2000x500 mm2, which are the largest high quality foils produced up to now in the world. There are two main schools of thought concerning the construction and assembly procedure of detectors: those of CERN and LNF. The CERN group, in order to mechanically support the GEM foils and then to avoid large sags and possible oscillations of the foil itself (the typical distance between foils is of the order of 2-3 mm), generally use very thin (200 μm) glass fibre grid frames placed between the foils. This technique, successfully applied in COMPASS and TOTEM, has some drawbacks: The glass fibre grid, made of special non-stratified composite material and realized by very fine machining, is expensive and, from the point of view of detector operation, results in an increase of the material budget as well as an efficiency loss inside the active region of the detector. For very large detectors the possibility to realize such thin grids is also to questions and in any case the handling and stocking of this component could certainly be an issue.

The construction procedure developed by the LNF group (member of this proposal) is based on the so-called stretching technique of the GEM foil. By means of a custom-built tool (GEM-stretcher) the foil, clamped around its perimeter by suitable jaws, is mechanically tensioned at a value of about 1 kg/cm (the jaws are connected to gauge meters, allowing the readout of the mechanical tension). Finite element simulations (ANSYS) indicate that, on foils up to ~1000x400 mm2, the maximum sag, due to combined gravitational and electrostatic effects, is of the order of tens of microns. This technique has been successfully applied to the construction of medium area (200x240 mm2) LHCb GEMs, and more recently to a first large area planar GEM prototype (700x400 mm2 active area). This technology will allow the building of fully efficient detectors, in a simplified and less expensive way, but it has to be proven that the same technique could be used for the construction of chambers of larger dimensions (>1000x400mm2).

Task 3: Large read-out structures, ASIC and FEE adaption and optimisation

Development of thin, flexible and large-size read-out structures with high granularity, using Kapton technology, are required for large area GEM detectors as well as for a large GEM-TPC. Here we will concentrate on the development and the optimization of the manufacturing process, on the development of hybrid structures with combined pixel and strip readout matching the expected occupancies, and on the optimization of the readout patterns and the signal routing.

Design of a generic readout system for fast micropattern gas detectors. A fully custom-made readout chip for MPGD (Micro Pattern Gas Detector) will need to be highly integrated to match the high density of readout channels. It should have very low noise so that very high gain is unnecessary and extremely low power consumption in order to avoid undue heat dissipation in the detector. For the envisaged applications, it should additionally feature zero suppression already on the level of analogue data, and a data driven readout. Such a chip, combined with a preamplifier/shaper chip suited for the particular detector, would find application in a wide range of experiments and for a large range of particle detectors. The TUM groups has proposed the basic architecture of such a ‘hit detection ASIC’. While the production of the final ASIC is clearly out of the scope of this JRA, we plan, in collaboration with GSI, to progress with the design of the ASIC, and to test first samples of single-channel prototypes. As a prerequisite, work will continue on testing and implementing existing ASICs, which already include some of the features of the final ASIC, such as analog pipeline (e.g. APV25, AFTER T2K), data driven readout (XYTER), etc. For these tests, a common portable readout system for analog data, based on a pipelined ADC with USB readout will be developed. Such a system will find applications in many groups in the MPGD community, where a lack of suitable, highly integrated readout electronics has been one of the limiting factors since long.