Speaker
Michael T. Ronan
(LBL)
Description
We present final analyis results of cosmic ray data taken with a Large-Area
Micromegas TPC by the Berkeley-Orsay-Saclay (BOS) collaboration. The TPC gas chamber
for these R&D studies was 50 cm diameter and 50 cm long and was operated with three
gas mixtures, Ar:CF4 3%, ArCH4 (P10) and Ar:Isobutane 5% in magnetic fields up to 2
tesla. A large-area, 38 cm diameter, copper Micromegas electro-mesh with 60 micron
pitch, and 50 micron mesh to anode pad plane gap provided gains up to 3000. Over 1000
channels of TPC readout electronics, with 1X10 and 2X10 mm^2 anode pads, have been
used to cover the detector area. The detector ran very smoothly with excellent gain
uniformity. Precision measurements of drift velocity, diffusion and electron
attachment have been made and compared to MagBoltz simulations. We have obtained a
Micromegas TPC extrapolated zero-drift, point resolution of 50 microns. We compare
the measured resolution dependence on drift distance, up to 50 cm, to parameterized
simulations of the drift and avalanche of individual ionization electrons for the
gases studied.
Primary author
Michael T. Ronan
(LBL)
