First Tests of a Micromegas TPC in a Magnetic Field First Tests of a Micromegas TPC in a Magnetic Field

Abstract Since the summer of 2003, a large Micromegas TPC prototype (1000 channels, 50 cm drift, 50 cm diameter) has been operated in a 2T superconducting magnet at Saclay. A description of this apparatus and first results from cosmic ray tests are presented. Additionnal measurements using simpler detectors with a laser source, an X-ray gun and radio-active sources are discussed. Drift velocity and gain measurements, electron attachment and aging studies for a Micromegas TPC are presented. In particular, using simulations and measurements, it is shown that an Argon-CF 4 mixture is optimal for operation at a future Linear Collider