The AGILE silicon tracker:: an innovative γ-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 (1 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 x 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 (<400 μW/channel) with full analog readout. The trigger of the satellite is given by the tracker. The total number of readout channels is around 43 000. 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. (C) 2002 Elsevier Science B.V. All rights reserved.