Takatoshi Morishita

RF amplitude and phase tuning of J-PARC SDTL

A fine tuning has been performed for RF phase and amplitude of SDTL (Separate-type Drift Tube Linac) station in the beam commissioning of J-PARC LINAC. A phase-scan method is adopted to carry out the tuning. An adequate set-point is determined by matching measured absolute beam energy with those from a modeling. The tuning goal is satisfied using this method, which required within 1deg for phase and 1% for amplitude. This paper presents detail procedures of RF tuning of SDTL.

The precise survey and the alignment results of the J-PARC LINAC

J-PARC linear accelerator components have been installed. Before the beam commissioning, a precise survey for alignment has been performed. The reference points were set up on the tunnel wall to built a survey network. Based on the survey results, the magnets in the straight section were re-aligned finely. Then, the results of the displacement are confirmed to be tolerable for the beam commissioning.

The DTL/SDTL alignment of the J-PARC LINAC

The required alignment accuracy in the J-PARC linac is 0.1 mm in transverse direction. In the DTL/SDTL section, the fine alignment was carried out by using an optical alignment telescope along with the cavity installation. The displacement of the DTL by the unit tank connection was monitored by a laser tracker to obtain the tolerable displacement between unit tanks. The heights of cavities and magnets were compensated form the local settlement of the linac tunnel.

High power conditioning of the DTL for J-PARC

The high-power conditioning of the three DTL tanks for the J-PARC has been started in October 2006. The design rf peak-power levels for beam acceleration of the tanks are about 1.1 MW (DTL1), 1.2 MW (DTL2) and 1.0 MW (DTL3), respectively. As a result of the conditioning, we have achieved that the rf power levels are about 1.3 MW, 1.45 MW and 1.23 MW of which are 1.2 times the power levels of the desired one (the pulse length is 650 mus and the pulse repetition is 25 Hz). During the linac beam commissioning, the DTLs can keep the required rf power stable now.

An Alignment of J-PARC Linac

J-PARC linear accelerator components are now being installed in the accelerator tunnel, whose total length is more than 400 m including the beam transport line to 3GeV synchrotron. A precise alignment of accelerator components is essential for high quality beam acceleration. In this paper, planned alignment schemes for the installation of linac components and watching the long term motion of the building are described. Markings are placed on the floor, which act as a reference for the initial alignment at the installation. For a straight line alignment, the wire position sensor is placed on the offset position with respect to the beam center by a target holder. The hydrostatic levering system is used for watching the floor elevation over the long period.

Rf Tuning and Fabrication Status of the First Module for J-PARC ACS

J-PARC Linac starts with 180-MeV SDTL temporary, and it is upgraded to 400-MeV with 21 ACS (Annular Coupled Structure) modules and two ACS bunchers and two debunchers [1]. First buncher module is under fabrication, and second buncher and a few accelerating modules are also planed until FY2006. The first ACS module consists of two 5-cells ACS tanks and a 5-cells bridge cavity for the buncher module. Three RF tuners are installed to the bridge cavity for fine RF tuning. An operating frequency should be tuned to 972 MHz within the fine-tuning range before a brazing process in a factory. The tuning procedure has been studied with RF simulation analysis and cold-model measurements for ACS and bridge cells [2]. This paper describes RF tuning results, fabrication status and related development items.

Path to 1-MW at J-PARC Rapid Cycling Synchrotron

The accelerator system at Japan Proton Accelerator Research Complex (J-PARC) has been operational since May 2008 and has mainly been used to perform physics experiments. The accelerator system consists of a Linac, a Rapid Cycling Synchrotron (RCS), and a Main Ring Synchrotron. The originally designed RCS injection energy is 400MeV, but the first operation started at 181MeV. New acceleration cavities were installed in J-PARC Linac during the summer shutdown of 2013, and user operation by the Material and Life science Facility (MLF) at the injection energy of 400MeV was started from February 2014. Post beam commissioning of 400MeV injection energy, beam loss was small enough, and we established 300kW continuous operation. Subsequently, the peak current of the Linac was increased from 30mA to 50mA. This upgrade enabled us to try 1-MW beam acceleration. Finally, after some additional improvements, we successfully accelerated 1-MW equivalent protons.

Vacuum properties and operation stability of the radio-frequency quadrupole accelerator in Japan Proton Accelerator Research Complex linac

The Japan Proton Accelerator Research Complex accelerator comprises an injector linac, a 3-GeV rapid-cycling synchrotron (RCS), and a 30-GeV main ring. The linac provides a 400-MeV negative hydrogen ion beam to the RCS. For beam power upgrade, a new radio-frequency quadrupole (RFQ) was designed to increase the peak beam current from 30 to 50 mA. This RFQ was fabricated and installed in the front end of the linac beam line in the summer of 2014. Since then, the RFQ has been operated without serious problems for more than two years. However, operational stability of the RFQ can be improved further. The RFQ operation trips occasionally owing to sparking between vane tips. An increase in residual gas components is observed during beam operation. A part of the beam lost in the RFQ hits the inner surface of the cavity, which induces outgassing from the surface. Moreover, the trip rate depends on the beam operating condition. Under a higher trip rate, a larger increase in the carbon-related residual gas componen...

Present Status of the Laser Charge Exchange Test Using the 3-MeV Linac in J-PARC

The Accelerator-driven System (ADS) is one of the candidates for transmuting long-lived nuclides, such as minor actinide (MA), produced by nuclear reactors. For efficient transmutation of the MA, a precise prediction of neutronics of ADS is required. In order to obtain the neutronics data for the ADS, the Japan Proton Accelerator Research Complex (J-PARC) has a plan to build the Transmutation Physics Experimental Facility (TEF-P), in which a 400-MeV negative proton (H) beam will be delivered from the J-PARC linac. Since the TEF-P requires a stable proton beam with a power of less than 10 W, a stable and meticulous beam extraction method is required to extract a small amount of the proton beam from the high power beam using 250 kW. To fulfil this requirement, the Laser Charge Exchange (LCE) method has been developed. The LCE strips the electron of the H beam and neutral protons will separate at the bending magnet in the proton beam transport. To demonstrate the charge exchange of the H, a preliminary LCE experiment was conducted using a linac with energy of 3 MeV in JPARC. As a result of the experiment, a charge-exchanged H beam with a power of about 5 W equivalent was obtained under the J-PARC linac beam condition, and this value almost satisfied the power requirement of the proton beam for the TEF-P.

Upgrade and Operation of J-PARC Linac

Kazuo HASEGAWA*, Hidetomo OGURI, Takashi ITO, Etsuji CHISHIRO, Koichiro HIRANO, Takatoshi MORISHITA, Shinichi SHINOZAKI, Hiroyuki AO, Kiyonori OHKOSHI, Yasuhiro KONDO, Jun TAMURA, Saishun YAMAZAKI, Toshihiko HORI, Fumiaki SATO, Yasuo NEMOTO, Isao KOIZUMI, Nobuo OUCHI, Nobuhiro KIKUZAWA, Akira UENO, Akihiko MIURA, Shinpei FUKUTA, Akinobu YOSHII, Koichi SATO, Akira OZONE, Yuki SAWABE, Yusuke KAWANE, Hiroshi IKEDA, Yuichi ITO, Yuko KATO, Kazuo KIKUCHI, Fumio HIROKI, Toshio TAKAYASU, Tsutomu USAMI, Munetoshi YANAI, Kazuhiko TADOKORO, Kenji OHSAWA, Fujio NAITO, Yong LIU, Zhigao FANG, Takashi SUGIMURA, Kenta FUTATSUKAWA, Kiyoshi IKEGAMI, Masato KAWAMURA, Kesao NANMO, Yuji FUKUI, Tomoaki MIYAO, Tomofumi MARUTA and Akira TAKAGI