Description of work and role of partners

Task 1: “Active target” TPC

After the successful construction of a small-size GEM-based TPC and its operation in various test beams with standard gas mixtures, a novel idea will be investigated with GEM-TPCs. The idea is to use the gas contained in the TPC not only as the ionisation medium but also as a low-mass active target. In this way charged nuclear reaction products may be tracked and identified inside the target. This new detection technique needs a low-mass detector framework and very pure gases such as Hydrogen, Deuterium, Helium-3, Helium-4 are desirable although mixtures are possible if reaction products can be identified unambiguously. First test measurements have already demonstrated the possibility to reach a detector gain up to 104 without damage or instability in a triple GEM filled with pure helium gas. However, one has to remember the low number of primary clusters for the pure gas with respect to a standard Ar/CO2 (70/30) gas mixture. In a TPC, the electric field is applied in the longitudinal direction along the detector axis. The transverse position of the charged particle interaction is simply given by the location of the pads on which a signal is induced. The longitudinal position is determined by the drift time of the primary electrons to the readout anode. The granularity of the front-end electronics both in space and time should be sufficiently small in order not to deteriorate the resolution.
Simulation studies with GARFIELD and GEANT-4 have to be performed and compared with test measurements
using pure gases (hydrogen, deuterium, helium) in a prototype TPC.
This work will be lead by LNF and SMI in cooperation with IFIN-HH, TUM and UGlasgow.

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).
Using the LNF solutions we want to optimize the global production process and try to find possible standards for:

The final goal will be to draw up a practical, operational production scheme suitable for possible industrialization (technology transfer) of the construction process of the detector.
This work will be lead by GSI and LNF in cooperation with IFIN-HH, TUM, SMI and UH.

Task 3: Large readout structures, ASIC and FEE adaption and optimisation

Development of thin, flexible and large-size readout 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.
This work will be lead by GSI and TUM in cooperation with CEA-Saclay and UGlagow.