Résumé du preprint DAPNIA-07-36

Micromegas TPC studies at high magnetic fields using the charge dispersion signal
M. Dixit, D. Attie, A. Bellerive, K. Boudjemline, P. Colas, A. Giganon, I. Giomataris, V. Lepeltier, S. Liu, J.-P. Martin, K. Sachs, Y. Shin, S. Turnbull
The International Linear Collider (ILC) Time Projection Chamber (TPC) trans-
verse space-point resolution goal is 100 μm for all tracks including stiff 90◦ tracks
with the full ∼2 m drift. A Micro Pattern Gas Detector (MPGD) readout TPC
can achieve the target resolution with existing techniques using 1 mm or narrower
pads at the expense of increased detector cost and complexity. The new MPGD
readout technique of charge dispersion can achieve good resolution without resort-
ing to narrow pads. This has been demonstrated previously for 2 mm 6 mm pads
with GEMs and Micromegas in cosmic ray tests and in a KEK beam test in a 1 T
magnet. We have recently tested a Micromegas-TPC using the charge dispersion
readout concept in a high field super-conducting magnet at DESY. The measured
Micromegas gain was found to be constant within 0.5 % for magnetic fields up to
5 T. With the strong suppression of transverse diffusion at high magnetic fields,
we measure a flat 50 μm resolution at 5 T over the full 15 cm drift length of our
prototype TPC.


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