On 31 October a team at the Japan Proton Accelerator Research Complex (J-PARC) accelerated a proton beam to the design energy of 3 GeV in the new Rapid-Cycling Synchrotron (RCS). This is an important step for this joint project between KEK and the Japan Atomic Energy Agency (CERN Courier March 2007 p5).

The team began beam commissioning the RCS during the run that started on 10 September. The linac was once again in operation and on 2 October the beam was successfully transported from the linac to the RCS. Two days later, the H beam was transported to the H-0 dump located at the injection section of the RCS without the charge-exchange foil.

The charge-exchange foil was installed during the following scheduled two-week shutdown. On 25 October the proton beam produced by the stripping of two electrons from the H ions in the foil was transported through one arc of the RCS and extracted to the beam transport to the muon and neutron production targets, known as 3BNT. As the targets are not yet ready, the beam currently goes to a 4 kW beam dump just beyond the extraction system. The following day, the beam circulated in the RCS and was extracted to 3NBT. Finally, on 31 October, the team accelerated a beam in the RCS to the design energy of 3 GeV and extracted it to the 3NBT dump via the kicker system.

One aim during commissioning has been to minimize the radioactivation of the accelerator components, because the team will have to replace items such as the charge-exchange foil-replacement system after the beam commissioning. To achieve this the team did the commissioning with one shot of the linac beam with a peak current of 5 mA and a pulse length of 50 μs. This allowed it to accumulate useful beam data "shot by shot" with a minimum radioactivation of the accelerator components.