Charge injectors of ALICE Silicon Drift Detector

Large area, 7.25 × 8.76 cm 2 , Silicon Drift Detector (SDD) has been developed for the ALICE experiment at CERN [A. Vacchi, et al., Nucl. Instr. and Meth. A 306 (1991) 187; A. Rashevsky, et al., Nucl. Instr. and Meth. A 461 (2001) 133–138; A. Rashevsky, et al., Nucl. Instr. and Meth. A 485 (2002) 54; P. Burger, C. Piemonte, A. Rashevsky, A. Roncastri, A. Vacchi, INFN/TC-02/07; C. Piemonte, A. Rashevsky, INFN/TC-02/08; C. Piemonte, A. Rashevsky, D. Nouais, INFN/TC-00/04. C. Piemonte, A. Rashevsky, A. Vacchi, ALICE-INT-2002-15, 2002; Inner Tracking System, CERN/LHCC, June 1999]. SDDs form two out of six cylindrical layers of the ALICE inner tracking system. The 260 high-quality SDDs needed to equip these two layers have been selected. One of the detector design elements devoted to allow controlled operating conditions is the on-board arrays of point-like charge injectors [D. Nouais, et al., CERN-ALICE-PUB-99-31; V. Bonvicini, et al., Il Nuovo Cimento 112AN (1–2) (1999) 137–146]. In the case of an SDD they are essential to trace, with the required frequency and precision, the changes in drift velocity induced by temperature variations. In order to ensure operating stability during the 10 years of the ALICE experiment the bias scheme of the charge injectors exploits the electrical properties not only of a detector itself, but also those of the cables mounted onto it, thus constituting a module. Computer simulations of the equivalent circuit revealed a significant improvement of the injection efficiency. Subsequent experimental tests of the first assembled modules confirmed the predicted performances. We report the layout of the charge injectors integrated in the ALICE SDD, as well as test results.