Professor Tony Weidberg

Abstract:

A large sample (96) of epitaxial Si PIN photodiodes has been irradiated by approximately 1 MeV neutrons and 24 GeV protons with fluences up to 10¹⁵ equivalent 1 MeV neutrons cm^-2 in order to test their suitability for use in the optical readout of the ATLAS semiconductor tracker and pixel detector at the CERN Large Hadron Collider. After an initial reduction of 30% the responsivity remains constant up to the maximum fluence. The rise and fall times are not significantly affected and remain below 1 ns. Although the dark current increases linearly with increasing neutron fluence, its level remains below 100 nA which is negligible in comparison to the operating photocurrent which is above 100 μA. Enhanced ageing studies at 60 °C have also been carried out and no failure has occurred after an equivalent of 360 years of operation.

Abstract:

A radiation hard optical readout system designed for the ATLAS Semiconductor Tracker (SCT) is described. Two independent versions of the front-end optical package housing two VCSEL emitters and an epitaxial Si PIN photodiode have been irradiated with neutron fluences over 10(15) n cm(-2), the level encountered in the ATLAS pixel detector. Environmental tests have been performed down to -20 degreesC. Extensive radiation and lifetime tests have also been carried out on the opto-electronic components and the front-end VCSEL driver and timing/ control ASICs. Bit error rate, cross-talk and single event upset measurements using irradiated devices show that the system meets the performance specification.

Abstract:

The ATLAS SCT optical links system is reviewed. The assembly and testing of prototype opto-hamesses are described. Results are also given from a system test of the SCT barrel modules, including optical readout.

Abstract:

The radiation tolerance of three multimode optical fibres has been investigated to establish their suitability for the use in the front-end data links of the ATLAS experiment. Both gamma and neutron irradiation studies are reported. A step-index fibre with a pure silica core showed an induced attenuation of approximately 0.05 dB/m at 330 kGy(Si) and 1×1015 n(1 MeV Si)/cm2 and is suitable for use with the inner detector links which operate at 40-80 Mb/s. A graded-index fibre with a predominantly germanium-doped core exhibits an induced attenuation of approximately 0.1 dB/m at 800 Gy(Si) and 2×1013 n(1 MeV Si)/cm2 and is suitable for the calorimeter links which operate at 1.6 Gb/s. Measurements of the dose rate dependence of the induced attenuation indicate that the attenuation in ATLAS will be lower.