ESS Proton Beam Window Design Update

Abstract

ESS target station is devised inside a large vessel that serves as confinement for the atmosphere surrounding main components of the neutron source. Such an environment can not be in contact with the accelerator one, where ultra high vacuum is needed to guarantee a good transporting media for the 2.0 GeV protons.The Proton Beam Window (hereon PBW) of the European Spallation source is an intricate component that behaves as a physical separator between the accelerator atmosphere and the target one; permitting to work with both environments and thus selecting the optimal vacuum level at each side.As the proton beam has to cross the window, scattering interactions will take place inside, releasing a considerable amount of energy of around 6 kW, and distorting the protons’ path. A thin and robust model has been designed while having to accomplish the crucial requirement founded on the desire to intrude the beam in the lowest way possible; besides a cooling system is conceived to evacuate all the power deposited.Recent discoveries on materials analyzed in other facilities have motivated a design change from the former beam wind model, together with the aim of improving the design and enhance the cooling capabilities to handle the power deposited. Therefore, the former helium-based cooling system has been replaced by light water, providing larger cooling rates and reducing the high design pressure in the old model. The new water-cooled PBW has a thinner cooling channel, as water can lead to undesired beam distortion, what results in a double cylindrical plate shape of 1 mm each, that leaves another 2 mm cooling channel inside. Solution presented includes the thermo-fluid and mechanical analysis of the PBW that led to the above design.Prototype manufacturing has started, and progress is presented.Together, the sealing system that will be mounted on to guarantee the requested leak rates has been design ad-hoc for this component, with a robust pneumatic system to actuate remotely and inflatable belows to bring the desired vacuum levels at both sides. Sealing system has also allowed for beam measuring instrumentation to control the beam parameters, and the mounting device and its cabling have been introduced in a modular way to facilitate the operation inside such aforementioned vacuum requirements.Moreover, a shielding analysis has been also performed to arrive to the final model, which includes neutron streaming evaluation through the cooling pipes, and thermal and mechanical analyses to assess whether an active or passive cooling should be implemented.