Speaker
Description
The Proton Power Upgrade (PPU) project at Spallation Neutron Source (SNS) is progressing well towards completion in 2024, when it is to deliver a 2MW 1.3 GeV proton beam at 60 Hz repetition rate to the SNS first target station (FTS). It thus imposes a further challenge to the engineering design of the mercury target to mitigate increased cavitation and high-cycle fatigue damage from ~45% more energy deposited into the system, which is mostly met by gas injection into the mercury flow. However, at the same time the target designs must maintain the moderator performance at a high level to serve the core mission of SNS of producing high-intensity neutron beams for material science. Taking advantage of an automated high fidelity modeling method with the coupling of DAGMC to MCNP6, at SNS we are able to directly track particle transport in CAD models generated from engineering designs for the Monte Carlo simulations of the SNS Target-Moderator-Reflector system. Thus detailed energy deposition analyses in the target were able to be performed for various target designs under different incident beam conditions, revealing subtle but destructive flaws and improving design efficiency. An original tapered-node design of the target front, which improved the mercury flow but impacted the moderator performance by > 5% loss, had to be revised to reduce the performance losses to ~2%. On the other hand, the more energetic proton beam shifts the peak neutron production zone slightly further into the target and a study of the optimized target length was thus performed to find out whether a more desirable position of the target could be achieved. While a slightly shorter target showed performance benefits averaged over moderators, such a gain was washed down if averaged over instruments since the upstream moderators host two times more instruments than the downstream ones.
