Current Status of the High Intensity Pulsed Spallation Neutron Source at J-PARC

Abstract

At the Japan Proton Accelerator Research Complex, a pulsed spallation neutron source has been providing neutron beams with high intensities and narrow pulse widths since 2008 for various materials science experiments. The neuron-pulse characteristics measured during early low-power operations indicated that this source is capable of providing the world's highest peak neutron intensities and pulse resolution at the 1-MW operation level, which is the goal of the facility. To achieve this operational goal, efforts have been underway to solve a critical issue affecting the target operation, i.e. mitigation of cavitation damages at the front end of the mercury target vessel, by injecting gas micro-bubbles and using a fast flow of the mercury through a narrow channel. Another issue is that the target vessel needs to be redesigned to ensure its robustness against the cyclic thermal stress produced by the temperature swings when the proton-beam trips because the water shroud surrounding the mercury target vessel failed during 500-kW operation in 2015.

Cavitation Damage Prediction in Mercury Target for Pulsed Spallation Neutron Source Using Monte Carlo Simulation

“…The temperature of the target material rises rapidly due to the spallation reaction of the target materials, and the amount of temperature rise increases as the power of the proton beam increases. A liquid heavy metal, mercury, having functions of a cooling medium and a spallation material, was applied in order to efficiently remove a large amount of heat from the target and generates high-intensity neutrons in J-PARC (Japan Proton Accelerator Research Complex) and SNS (Spallation Neutron Source) [7,8]. When high-intensity proton beams are injected into the mercury in a mercury vessel, pressure waves in mercury induce the growth, shrinkage and collapse of cavitation bubbles scatted in the mercury.…”