KEK Proton Synchrotron

KEK Proton Synchrotron. The KEK Proton Synchrotron was a major particle accelerator located at the KEK laboratory in Tsukuba, Ibaraki, Japan. Operational from 1976, it served as a primary proton source for fixed-target experiments, playing a pivotal role in advancing particle physics and nuclear physics research in Asia. Its 12 GeV proton beam enabled groundbreaking studies in hadron spectroscopy and provided crucial support for the development of subsequent accelerators like the TRISTAN and KEKB colliders.

History and development

The project was initiated in the early 1970s by the KEK (then known as the National Laboratory for High Energy Physics) to establish a domestic high-energy physics research capability in Japan. Its design and construction were heavily influenced by international collaborations and knowledge transfer from institutions like CERN and the Zero Gradient Synchrotron at Argonne National Laboratory. Key figures in its development included physicists such as Shoji Shibata and Yoshio Yamaguchi. The accelerator achieved its first beam in 1976, marking a significant milestone for the Asian physics community and positioning KEK as a major center for hadron physics research alongside facilities like Brookhaven National Laboratory and the Institute for High Energy Physics in Protvino.

Technical specifications

The machine was a strong-focusing synchrotron with a design proton energy of 12 GeV. Its ring had a circumference of 339.3 meters, utilizing a FODO lattice structure for beam focusing. Protons were initially injected at 500 MeV from a Cockcroft-Walton pre-injector and a linear accelerator, later upgraded to a radio frequency quadrupole system. The magnet system consisted of 80 dipole magnets and 160 quadrupole magnets. It could extract beam via a fast resonant extraction method to multiple experimental areas, supporting simultaneous operations. The vacuum system maintained an ultra-high pressure to minimize beam loss from interactions with residual gas.

Scientific contributions and experiments

The facility hosted numerous landmark experiments, particularly in the spectroscopy of particles containing strange and charm quarks. The E62 experiment, led by researchers like Kazuo Abe, made precise measurements of hyperon polarization. The KEK-PS E135 experiment provided critical data on charmed baryon production. Another major program studied kaon-nucleus interactions and the properties of Ξ hypernuclei. These experiments tested predictions of quantum chromodynamics and the quark model, contributing significantly to the global understanding of strong force phenomena. The data were often analyzed in conjunction with results from Fermilab and the Super Proton Synchrotron at CERN.

Operation and upgrades

After achieving its design energy, the synchrotron underwent several upgrades to improve beam intensity and reliability. A major upgrade in the 1980s involved replacing the original pre-injector with a more efficient radio frequency quadrupole linac, significantly boosting the proton current. The control system was modernized in the 1990s, integrating new computer technologies. It operated for three decades, with its final dedicated proton beam run occurring in 2006. Following this, parts of its infrastructure, including the linac, were repurposed to serve as an injector for newer facilities like the J-PARC project and to provide beam for test stands.

Role in particle physics research

The accelerator established KEK as a leading international laboratory, fostering a generation of physicists and engineers in Japan. It created a strong research community in hadron physics, with its user program attracting scientists from across Asia, Europe, and North America. The technological expertise gained, particularly in synchrotron design, magnet fabrication, and beam diagnostics, was directly applied to the construction of Japan's first electron-positron collider, TRISTAN, and later the KEKB factory. Its legacy is evident in the continued operation of its injector chain and the foundational role it played for the high-intensity proton facility J-PARC. Category:Particle accelerators Category:High Energy Accelerator Research Organization Category:Buildings and structures in Ibaraki Prefecture