A beam-driven proton irradiation setup for precision radiation damage tests of silicon detectors

A proton irradiation site for silicon detectors has been developed and commissioned at the Bonn Isochronous Cyclotron. The accelerator provides 14 MeV proton beams of up to 1 μA at beam widths of a few mm to the setup. Devices Under Test (DUTs) are irradiated inside a cooled, thermally-insulated box at ≤-20C, while being moved through the beam in a row-based scan pattern to achieve uniform fluence distributions. Custom-made diagnostics allow for beam-based, on- and offline dosimetry, enabling a beam-driven irradiation routine which produces uniform fluence distributions with standard deviations ≪ 1 %. Dedicated irradiations of thin titanium foils are performed to compare the commonly-used dosimetry via metallic foil activation to the beam-based approach. Within the error margins, both methods are in agreement, whereas the beam-based technique yields lower uncertainties of typically ≤ 2 %. Simulations indicate a reduction of the initial proton energy to 12.28(6) MeV on the DUT. Characterization of six, 150 μm-thin, passive LFoundry sensors before and after irradiation yield a proton hardness factor of κ_p=3.71(11), which is in agreement with expectations, allowing to irradiate up to 10^16n_eq / cm^2 within a few hours.