AGILE silicon tracker: an advanced gamma- and x-ray detector for space

AGILE is a light and effective instrument for the detection of gamma-ray sources in the energy range 30 MeV - 50 GeV within a large field of view. The instrument is planned to fly in the years 2002 - 2005, a period in which no other gamma-ray mission in the same energy range is foreseen. AGILE is made of a tungsten-silicon tracker, a CsI minicalorimeter, an anticoincidence system and an X-ray detector (10 - 40 keV). The tracker consists of 14 planes, each made of 2 layers of 16 single-sided, AC coupled, 410 micrometer thick silicon detectors. Each detector covers an area of 9.5 X 9.5 cm² and has a readout pitch of 242 micrometer with one floating strip. Four silicon detectors are bonded together creating a 'ladder' 38 cm long. The total number of readout channels is around 37000. The readout chip is the TAA1 (IDE- AS, Norway), an analog-digital, self triggering chip used in a very low power configuration (400 (mu) W/channel). A prototype silicon ladder and the complete readout chain have been tested at the CERN PS in July 1999. The final ladder has been tested in May 2000. We present the noise performances of the readout electronics in the very low power configuration, and the testbeam results obtained with the full AGILE ladder. The results are compared with GEANT simulations.