• K. Yoshimura, Y. Hashimoto, Y. Hori, Y. Igarashi, S. Mihara, H. Nishiguchi, Y. Sato, M. Shimamoto, Y. Takeda, M. Uota
  KEK, Ibaraki
• M. Aoki, N. Nakadozono, T. Tachimoto
  Osaka University, Osaka

Proton beam extinction, defined as a residual to primary ratio of beam intensity, is one of the most important parameters to realize the future muon electron conversion experiment (COMET) proposed at J-PARC. To achieve the required extinction level of 10^-9, we started measuring beam extinction at main ring (MR) as the first step. The newly developed beam monitor was installed into the abort beam line and the first measurement was successfully performed by using the fast-extracted MR beam. We found that empty RF buckets of RCS, in which all protons were considered to be swept away by a RF chopper before injection to RCS,, contained about 10^-5 of the main beam pulse due to chopper inefficiency. We are now developing a new beam monitor with improved performance for further studies at the abort line. In addition, we have started new measurements at the different stage of proton acceleration, i.e. at Linac, 3-50 BT line, and the main ring. In this paper, we present recent results and future prospect of beam extinction measurements.

• M. Uota, Y. Hashimoto, Y. Hori, H. Matsumoto, Y. Saitoh, M. Shimamoto, M. Tomizawa, T. Toyama
  KEK, Ibaraki

In J-PARC 50GeV synchrotron ring, large vacuum pressure rises above 10^-3 Pa are found at 30GeV acceleration final stage of intensity over 10¹³ protons per pulse in the chambers of the in-vacuum electrostatic septum magnet for the slow-extraction(SX), magnetic septum for SX, and the kicker magnet for the fast-extraction. This pressure rise depends on beam intensity and peak-current, and can be reduced by continuous beam operations, such as scrubbing with proton beam, secondary emission electrons and other cations of remaining gasses or desorptions.

• G.H. Wei
  KEK/JAEA, Ibaraki-Ken
• A. Ando, Y. Hashimoto, T. Koseki, J. Takano
  J-PARC, KEK & JAEA, Ibaraki-ken
• S. Igarashi, K. Ishii, M. Tomizawa, M. Uota
  KEK, Ibaraki
• P.K. Saha, K. Satou, M.J. Shirakata
  JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken

The beam commissioning of J-PARC (Japan Proton Accelerator Research Complex) MR (Main Ring) was started from May 2008 and is in progress. As usual, injection tuning is in the first stage and strongly related to other tuning items. Starting with design schemes, making adjustment due to leakage field influence from injection septum, doing envelope matching considering dilution of beam profile in Main Ring are reported in this paper. The 'Without bump' scheme was got on June 15th 2008, while 'With bump' scheme on February 15th 2009. Beam orbit betatron oscillation to the MR close orbit which cause by injection error is less than 1 mm both in horizontal and vertical direction. Meanwhile, Beam Optics matching for 3 GeV beam from 350BT to MR has been well done too, which is also very important.

* T. Koseki, Challenges and Solutions for J-PARC Commissioning and Early Operation, in these proceedings

• G.H. Wei
  KEK/JAEA, Ibaraki-Ken
• A. Ando, T. Koseki, J. Takano
  J-PARC, KEK & JAEA, Ibaraki-ken
• K. Fan, S. Igarashi, K. Ishii, T. Nakadaira, M. Tomizawa, M. Uota
  KEK, Ibaraki
• H. Harada, P.K. Saha
  JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken

The beam commissioning of J-PARC/MR has been started from May 2008 and is in progress*. One key purpose of MR commissioning is the 30 GeV beam fast extraction to Neutrino beam line, which reflect the overall commissioning result. In the MR, the third straight section is assigned for the fast extraction. 5 kickers and 8 septa were installed there, which can give beam a bipolar kick to inside or outside of MR. Inside kick means beam to Neutrino Oscillation Experiment, while outside kick means beam dumped to abort line. However before commissioning, the measured magnetic field distribution of each septa shows non-linear profile along the horizontal direction. In order to find the influence, a simulation with these measured field has been performed. Depends on this study and some OPI (Operation Interface) made by code SAD for orbit modification online, fast extraction of 30 GeV beam to Neutrino line has been achieved on April 23rd 2009. Beam orbit have been tuned to less than 0.5 mm and 0.1 mrad in both horizontal and vertical at the beginning of Neutrino line, which is also the end of MR fast extraction. And so far, 100 kW continual operation to neutrino line have been achieved, too.

* T. Koseki, "Challenges and Solutions for J-PARC Commissioning and Early Operation", in these proceedings