R & D of the production target for the next long-baseline neutrino oscillation experiment

Based on the success of the ongoing K2K long-baseline neutrino experiment, design of the next neutrino beam line in JHF project at the Tokai-site is now under way. This beam line is designed to produce the neutrino beam aming at Super-Kamiokande (295 km away from Tokai) with 100 times higher intensity than the existing beam line for the K2K experiment. We are developing a graphite target to produce the strongest neutrino beam in the world. The proton beam accelerated to 50 GeV in JHF 50GeV proton synchrotron is transported into the graphite rod with 3cm in diameter and 90cm in length. The positive pions with different momentum among many kinds of secondary particles generated on the target are selectively focused by the magnetic horns, and precisely aligned to the direction of Super-Kamiokande. After pions decay into muons and muon-neutrinos in the decay volume with 150m length, muon-neutrino beam is produced and running to Kamioka.

In order to produce high intensity neutrino beam, the production target is irradiated by proton beam with very high intensity. As a result, large amount of secondary particle is produced, but about 60k Joule heat is loaded on the target within very short period (about 5 microseconds). The following figure illustrates the ongoing test of cooling the graphite rod by water. Currently, the heat source is Joule heat of the rod itself, loading large current of 3000 A by the power supply.