AIP Digital Archive
Electrical Engineering, Measurement and Control Technology
A 150-MeV pulsed-racetrack microtron (RTM)1 is being developed as an injector for a 650-MeV SR ring by Sumitomo Heavy Industries, (SHI). The ring has a superconducting weak-focusing single-body magnet with an orbital diameter of 1.0 m. This light-source system, named AURORA,2 is designed for industrial use, especially for x-ray lithography with a critical wavelength of 1.02 nm. A unit of AURORA consists of the RTM injector, the compact storage ring, and sixteen SR light beamlines at the maximum. The RTM, which is 1.5 m in width, 3.7 m in length, and 1.5 m in height, is mainly composed of an injection system, a 6-MeV accelerating column, two main magnets with reverse field magnets, beam focusing, and correction elements. The injection system boosts a 20-keV electron beam from a gun up to an energy of 120 keV, using a single-gap cavity. This system, about 1.7 m in length, also bunches the beam with two re-entrant type bunchers in order to increase the acceleration efficiency of the RTM. The accelerating column, the resonant frequency of which is 2856 MHz, is of the conventional side-coupled standing-wave type. The rf power supplied by a pulsed 5.5-MW klystron is delivered not only to the accelerating column but also to the single-gap cavity and the two bunchers. The main magnets are characterized by slightly inclined poles in order to obtain a vertical focusing strength. The mean value of the magnetic field in the main magnets is 1.2 T. The reverse field magnets act as horizontal steerers as well as for turning back the first accelerated 6-MeV beam to the accelerating column. The focusing and correction elements include many permanent quadrupole magnets and some vertical steerers.The specifications of the extracted beam are as follows. The pulse width is variable from 0.5 to 2 μs, and the repetition rate is up to 180 Hz. Emittances are to be 1π mm mrad in both the horizontal and vertical directions, and the energy spread is to be less than 0.1%. More than 5-mA peak current is expected after 25 turns with 6-MeV energy gain per each. All of the components have been manufactured and successfully tested.3 The assembly of the microtron has been completed and installed at SHI Tanashi Works, Tokyo. The test operation has started and the first 6-MeV electrons have been already observed. Further acceleration is being developed.
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