The AGILE silicon tracker: An innovative gamma-ray instrument for space

AGILE (Light Imager for Gamma-ray Astrophysics) is the first small scientific mission of ASI, the Italian Space Agency. It is a light (100 kg for the scientific instrument) satellite for the detection of gamma-ray sources in the energy range 30 MeV-50 GeV within a large field of view (14 of the sky). It is planned to be operational in the years 2003-2006, a period in which no other gamma-ray mission in the same energy range is foreseen. AGILE is made of a silicon tungsten tracker, a CsI(Tl) minicalorimeter (1.5X//0), an anticoincidence system of segmented plastic scintillators and a X-ray imaging detector sensitive in the 10-40 keV range. The tracker consists of 14 planes, each of them made of two layers of 16 single-sided, AC coupled, 410 mum thick, 9.5 multiplied by 9.5 cm**2 silicon detectors with a readout pitch of 242 mum and a floating strip. The readout ASIC is the TAA1, an analog-digital, low noise, self-triggering ASIC used in a very low power configuration ( less than 400 muW/channel) with full analog readout. The trigger of the satellite is given by the tracker. The total number of readout channels is around 43000. We present a detailed description of the tracker, its trigger and readout logic, its assembly procedures and the prototype performance in several testbeam periods at the CERN PS.