Design and performance of the shielded DTL4 Faraday cup for the commissioning of the high-power ESS proton linac

The final as-built version of the DTL4 Faraday cup for the ESS proton accelerator is presented; the beam-interceptive device acted as beam dump to support the commissioning and tuning of the ESS proton accelerator up to the DTL4 section. The DTL4 Faraday cup was designed, optimized and validated via MCNPX/ANSYS simulations in order to dump [21, 74] MeV protons, proton pulses up to 50 μs long, repetition rates up to 14 Hz and an unprecedented proton beam current up to 62.5 mA. The maximum volumetric power density was computed to be 20 GW/cm3 and 25 MW/cm3 for 21 MeV and 74 MeV protons, respectively. During the DTL4 commissioning, the DTL4 Faraday cup absorbed and safely dissipated the proton beam power, measured in real-time the proton beam current as well as the pulse duration. Examples of measured proton pulses are included to demonstrate the transport and acceleration of the high-power proton beam all the way down to the ESS DTL4 section. The control system for the data acquisition, operation under vacuum, motion control and cooling water system was based on EPICS. The operational parameters are presented following the results of thermo-mechanical calculations. In the most demanding operational condition, the predicted temperature of the core was around 1010 °C. The cooling water temperature was continuously monitored and remained below 23 °C during the operational period. Neutronics simulations were performed in order to quantify the activation, residual dose rates, radiation shielding and necessary decay time to be waited after the end of the commissioning. After four weeks of decay, a residual dose rate of 1.1 mSv/h was measured at 30 cm from the device. The DTL4 Faraday cup and its shielding were uninstalled in order to proceed with the installation of the DTL5 section. The Faraday cup is planned to be permanently installed in the DTL4 intertank once the DTL5 section is in place.