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JointGEM
Hadron Physics 2 - WP 24
Introduction:
With the invention of GEM-foils (GEM stands for Gas Electron Multiplication) by F. Sauli (CERN) in 1997 a new generation of tracking detectors was born. This new technology will allow the design of very light weight gas detectors with large areas in almost every necessary shape with reasonable costs.
Basic concept:
The idea is quite simple. In a plastic foil (Kapton), with both sides covered with an electric conductive material (copper), a lot of small holes are punched. By applying a voltage difference (a few hundred volts) a huge electric field will be generated in the small holes. A charged particle passing through an adequate gas mixture (e.g. argon and CO2) surrounding the GEM foils will produce a few electrons, which are amplified on their way through the small holes due to the strong electric field – a gas electron multiplication occurs.
Nevertheless, it has to be mentioned that the production of large area foils, with the necessary quality, involves special techniques with the necessary know-how, which is available only on a few places around the world - the best quality foils are produced at CERN.
Different detector concepts
- Large Area Planar GEM Detectors
Light weight detectors are planned with active areas of square meters, having high rate capabilities (more than 100.000 counts per cm2) and excellent spatial resolution, in the order of 100 µm. A prototype GEM foil with a size of 300mm x 700 mm is seen in the picture.
- Cylindrical Triple-GEM Detectors
Ultra-light cylindrical GEM detectors are planned as an inner tracking system for KLOE at LNF, with a spatial resolution of approximately 200 µm. In total for layers of such detectors with increasing size will be used. The dimension of the prototype (seen in the picture) is: diameter 300 mm, length 500 mm.
- Time-Projection-Chamber with GEM
A prototype TPC with GEM readout has been developed with minimized material budget around the active area. Test measurements were successfully performed at GSI, Germany using the FOPI apparatus. The dimension of the TPC (as seen in the picture) is: diameter (outer) 300 mm, length 750 mm.
Applications
The next generation of experiments in hadron physics aims to study rare processes with drastically improved sensitivity. To achieve this goal new machines like the Facility for Antiproton and Ion Research (FAIR) in Germany or improvements on existing facilities, like the proposed upgraded of DAFNE at LNF in Italy, are needed. These machines will provide higher beam intensities, which are essential for the new experiments in hadron physics. Beside the new facilities new fast detectors with large acceptance, high resolution and extremely low material budget must be developed.
