J-PARC

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The particle accelerators (3 and 50 GeV protons - synchrotron ) and experimental halls at the Japanese research complex J-PARC, about 120 km north of Tokyo on the Pacific coast .
The hall for experiments with neutron beams at J-PARC. The spallation neutron source is located behind the blue shield , with which 23 beam lines can be operated; Here you can see number 21 behind the red shield.
Superconducting magnets of the beam line from the 50 GeV main ring (currently only 30 GeV) of the J-PARC to the T2K experiment.

J-PARC ( J apan P roton A ccelerator R esearch C omplex) is a Japanese research complex at Tōkai in Ibaraki Prefecture , about 120 kilometers north of Tokyo on the Pacific coast area. Two proton synchrotrons with maximum particle energies of 3 and 50  GeV are operated here as part of a cooperation between the Japanese Atomic Energy Agency JAEA and the Research Center for High Energy Physics KEK . They are used to generate secondary beams such as muon and neutron beams for materials and life sciences as well as neutrino and kaon beams for particle and nuclear physics .

history

The J-PARC is the successor to the 12 GeV Proton Synchrotron ( KEK-PS ) operated at the KEK in Tsukuba from 1976 to 2005 . Construction of the complex was in 2001. With the smaller synchrotron was achieved the targeted proton energy of 3 GeV then 2008 and the end of the same year were the Spallation - targets the first muons - and neutron rays experiments are provided. At the end of 2008, a proton energy of 30 GeV was reached with the main ring and in the first half of the following year the beam line to the hadron experiment hall and the one for the T2K experiment were put into operation.

The Tōkai-to-Kamioka experiment (T2K) is the successor to the K2K experiment (KEK-to-Kamioka) , in which by the end of 2005 with the help of the KEK-PS neutrino from Tsukuba to the Super-Kamiokande detector 250 km west located Kamioka (today Hida ) were sent. The first neutrino event of the beam from J-PARC from Tōkai, 295 km away, was registered by the detector in February 2010. The aim of the experiments is to investigate the neutrino oscillation to determine the neutrino mass.

Since the J-PARC was only about 200 km from the epicenter of the Tōhoku earthquake in 2011 , there was considerable damage to the infrastructure on March 11, 2011, as well as to the accelerators and experiments. However, the tsunami only reached a height of 3 meters here and the flood protection devices designed for 8 meters prevented the area from being flooded. By the end of December 2011, the damage was repaired and operations resumed.

On May 23, 2013, an incident occurred in the hadron experiment hall in which radioactive material was released and 34 people were exposed to a radiation dose of up to 1.7  mSv (the maximum permitted annual effective dose for occupationally exposed persons is 20 mSv in Germany). The malfunction was an unusually fast extraction of protons from the 50 GeV main ring (within 5 milliseconds instead of the typical 2 s), which led to the destruction of a target and thus to the release of radioactivity. All accelerators and experiments were then switched off or discontinued for the time being and investigations initiated.

Construction and operation

The J-PARC has three particle accelerators which are supposed to accelerate protons one after the other to (in the final stage) up to 50 GeV.

A multi-stage linear accelerator (LINAC) brings it to 181 MeV. In a further expansion stage, it should reach 400 MeV for feeding into the first synchrotron and - for planned separate experiments on the transmutation of radioactive waste - to 600 MeV.

The first synchrotron has a circumference of 348 m and accelerates the protons from the LINAC to 3 GeV. Because of the relatively high repetition frequency of the circulating proton packets, 25 Hz, it is called Rapid Cycle Synchrotron (RCS). About 96% of the protons in the RCS are guided via a beam line into the experimental hall for materials and life sciences, where they are used to generate muon and neutron beams as secondary beams. The hall is located within the 50-GeV main ring .

The remaining four percent of the 3 GeV protons are introduced into the second synchrotron, the main ring, approximately every 3 s. This synchrotron has a circumference of 1568 m and accelerates the protons of the RCS to currently (2013) 30 GeV; a further increase to 50 GeV is planned. The main ring feeds the beam lines to the hadron experiment hall and the T2K experiment.

A special feature of the J-PARC is the targeted high beam power of the proton synchrotrons of up to 1 megawatt , which enables particularly powerful secondary beams to be generated. This requires beam currents of over 300 µA for the RCS and approx. 10–20 µA for the main ring; by 2011 stable beam powers of 100–200 kW had been achieved. Along with the Spallation Neutron Source (SNS) of the Oak Ridge National Laboratory in the USA and the ISIS of the British Rutherford Appleton Laboratory , the J-PARC is one of the world's most powerful systems for generating muon and neutron beams.

Web links

Commons : J-PARC  - collection of images, videos and audio files

literature

Individual evidence

  1. ↑ a b c Shoji Nagamiya: Introduction to J-PARC. In: Prog. Theor. Exp. Phys. 02B001, 2012, pp. 1–13, doi : 10.1093 / ptep / pts025 .
  2. ↑ a b c d Yoshishige Yamazaki: FROM KEK-PS TO J-PARC. (PDF; 1.1 MB) In: IPAC'10 - Special Lectures to Commemorate the 120th Anniversary of Birth of Yoshio Nishina. Kyoto, Japan, May 23, 2010.
  3. ↑ T2K Neutrino Beamline Started Operation. ( Memento of November 10, 2010 in the Internet Archive ) KEK Press Release, April 23, 2009.
  4. ↑ Limit values ​​in occupational radiation protection. ( Memento from April 24, 2015 in the Internet Archive ) Federal Office for Radiation Protection, as of May 7, 2013.
  5. ↑ 2nd Accelerator Facility Accident Report to Nuclear Regulation Authority. Japan Atomic Energy Agency (JAEA) and High Energy Accelerator Research Organization (KEK), June 18, 2013. Retrieved September 30, 2013 ( PDF ).
  6. ^ T. Sasa: Status of J-PARC transmutation experimental facility. 2008, oecd-nea.org (PDF).
  7. ^ T. Sasa: Design of J-PARC transmutation experimental facility. (Status around 2014). In: Ken Nakajima (Ed.): Nuclear Back-end and Transmutation Technology for Waste Disposal. Springer, 2014, ISBN 978-4-431-55110-2 , pp. 73-79.
  8. ↑ Takahiro Sato, Toshiyuki Takahashi, Koji Yoshimura (eds.): Particle and Nuclear Physics at J-PARC (Lecture Notes in Physics 781). Springer, 2009, pp. 3–8.


Coordinates: 36 ° 26 ′ 42 ″  N , 140 ° 36 ′ 21 ″  E