Evaluation of the 3-GeV proton beam profile at the spallation target of the JSNS

Materials and Life Science Experimental Facility at the Japan Proton Accelerator Research Complex I: Pulsed Spallation Neutron Source

“…Then, we developed a method of sampling gaseous hydrogen from the circulating hydrogen in the hydrogen loop (1.5 MPa, 20 K) under high neutron irradiation at J-PARC, and measure the para-hydrogen fraction with a Laser Raman spectroscopy. The measured para-hydrogen fraction was consistent with the equilibrium level of para-hydrogen at 20 K (99.8%) at the 300 kW beam operation because a Fe(OH) 3 catalyst worked well in the loop. The measured pulse shape at 300 kW was also in good agreement with the calculated result for the 99.8% para-hydrogen [48].…”

“…Before removing the target, cover gas in the surge tank was transferred to an off-gas process system to reduce the radioactivity of gaseous radioactivity, especially 127 Xe and 3 H, accumulated in the cover gas. The transferred cover gas is stored in gas holders of the off-gas process system for about 12 months waiting for the decay of 127 Xe having half-life of 36.4 days, while 3 H is absorbed by a molecular sieve (synthetic zeolite) [23], and then released to the environment after checking the radioactivity. This gas transfer operation is repeated until the radioactivity of 127 Xe decreased down to 1/100 of its initial value, which is significantly below the allowable value even if the remaining 127 Xe in the loop is released through the stack of the building at any failure.…”

“…The proton beam is accelerated up to 0.4 GeV by a linac and accumulated in 2 short bunches, and then accelerated up to 3 GeV in the Rapid Cycling Synchrotron (RCS), resulting to have a structure of a 150 ns bunch width with a spacing of 600 ns per 1 macro pulse. The beam extracted from the RCS is delivered to the spallation neutron source through the 3 GeV RCS to Neutron Facility Beam Transport (3NBT) [2][3][4].…”

“…The high radiation zone including the target, the three moderators in wing configuration, and the reflector and central shielding are placed inside a helium-filled vessel. The helium vessel with its inactive helium filling prevents the production of corrosive gases such as O 3 , NO x and acts as protective boundary against possible spills of mercury and light water in case of serious failure incidents. The moderators' side surfaces are the origins of the neutron beamlines.…”

Beam commissioning of the 3-GeV rapid cycling synchrotron of the Japan Proton Accelerator Research Complex

“…For higher beam-power operations, the beam painting scheme will be a key to handle the beam loss especially at the injection through the early stage of the acceleration. The transverse painting also plays an important role in terms of mitigating a pressure wave on the neutron target [39,40]. In the second commissioning stage, our efforts will be dedicated to such a global parameter optimization including the beam painting scheme toward higher beampower operations.…”