Description
Within the HBS (High Brilliance neutron Source) project, the Jülich Centre for neutron Science (JCNS) at Forschungszentrum Jülich has developed a new kind of HiCANS which shall serve as a competitive user facility. One of its key components is the neutron target designed to operate at a 70 MeV proton beam. It is designed as a stationary solid tantalum target consisting of three layers as shown in figure 1. The first layer is the neutron producing layer. It is made of tantalum with an integrated microchannel cooling structure for heat dissipation. The second layer is the beam stop. The approx. 98 % of the proton beam is stopped in this water layer. The third layer serves as an enclosure for the beam stop.
A particular focus of the target development was on minimising hydrogen embrittlement and the compactness of the target. Due to the parameters, the realisation of heat dissipation emerged as a particular engineering challenge. The heat is dissipated through a cooling structure eroded into the neutron-producing layer. The geometry of this cooling structure is optimised to minimise temperature transients to reduce stresses and to homogenise the proton range to reduce hydrogen implantation. The thermal efficiency and power limit of the cooling structure have already been successfully measured experimentally. The crucial performance tests in a proton beam is still pending:
a) Measurement of the ratio of stopped to penetrated protons behind the first layer at 70 MeV in order to verify the resistance against hydrogen embrittlement
b) Measurement of the neutron yield and neutron spectrum at 70 MeV to verify the performance
c) Measurement of the temperature distribution on the back side of the target to verify the coolant capability at real operation conditions
For the SPES-LNL experiment, we are planning to produce a target that only consists of the first layer. This allows a two-dimensional temperature field to be measured using a thermal camera on the back side of the target. In addition, the proton beam behind the target should be measured to determine the proportion of stopped protons inside the target. Finally, the neutron yield should be measured outside the proton beam using suitable measuring devices (e.g. Bonner sphere).
We apply for beam time at 70 MeV and at least 86.4 µA to focus these on an area of 6 cm² in order to achieve the design dimensioning of 1 kW/cm² and hence provides the best results for a reliable validation of the simulation results as well as the first experimental proof of the functionality of the HBS target.
More details regarding the HBS target are published:
https://doi.org/10.1016/j.nima.2024.169912
