Speaker
Description
In the ESS Technical Design Report (TDR) (ISBN 978-91-980173-2-8, April 23, 2013), the fundamental design of the ESS spallation target is presented. It defines the target design, requirements, and the supporting systems necessary to operate the spallation target with a 5 MW, 2 GeV proton beam.
Since the ESS spallation target design—comprising pure tungsten cooled with helium gas—has no direct predecessor, the work to develop the concept design through final design, manufacture, and installation, has presented significant challenges. The final products must meet the basic requirements:
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The spallation material, tungsten, must withstand a proton beam pulse of 2 GeV, with a pulse length of 2.86 ms, at a repetition rate of 14 Hz, over a period of at least five years.
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The target wheel, which encapsulates the tungsten, must be mechanically designed and positioned relative to the neutron moderator to optimize neutron flux. This requires a flat target wheel placed very close to the moderator with minimal material interfering with the proton beam's interaction with the spallation material.
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The 5 MW proton beam will generate a heat load of 3 MW in the target wheel. To manage this heat load, a helium gas flow of 3 kg/s is required.
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The spallation properties, which produce a high neutron flux, also pose radioactive challenges. The helium gas must be free of particles and have a very low oxygen content.
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They high radiation and vacuum environment emphasize the target mechanical design must address the cold-welding phenomenon.
The concept design presented in the ESS TDR was never feasible for the final design without several major design modifications. The ESS In-Kind partners have significantly contributed to refining the TDR concept into a design that can be manufactured and operated within the challenging requirements.
Today, the ESS spallation target, including all supporting systems, is installed and ready for operation. Achieving this has involved resolving various issues and non-conformities, ranging from manufacturing challenges to late-identified design flaws—a reality faced by all non-proven design system and component projects.
Although the target system is now ready for operation, some requirements still need verification, which can only be performed once the proton beam is on target. The spallation target design accounts for this late verification and includes conservative measures to limit risks once the target is operational.