CURRENT STATUS OF A 1.2 GeV BOOSTER ELECTRON SYNCHROTRON AND IMPLEMENTATION FOR NUCLEAR STUDY AT TOHOKU UNIVERSITY

A 1.2 GeV booster electron synchrotron (STB ring) with combined use of pulse-beam stretcher at Laboratory of Nuclear Science (LNS) [1], Tohoku University was constructed for study of nuclear physics, which is also supposed to be an injector for a planned future 3rd generation light source. Currently the STB ring is routinely operated with a booster-storage mode to supply high energy γ-rays for nuclear study produced via Bremsstrahlung using an internal target wire. Since finite range of a tagging counter array mounted in a bending section, the booster has to be also operated at another flat-top energy lower than 1.2 GeV to extend the γ-ray energy toward lower side. Because characteristics of the STB ring have not been well understood, various beam properties such as betatron tunes and instabilities are not completely controlled at the moment. In order to improve performance of the machine and to study the beam dynamics in a circular accelerator, fundamental properties of the STB ring is now being measured. 1 LNS ACCELERATOR COMPLEX An injector S-band linac consisted with 19 accelerating structures provides multi-bunch beam with a long-pulse duration of 1 ~ 3 µs. The linac has been operated for multi-purpose use with high repetition rate up to 300 Hz, e.g., the lower energy beam than 50 MeV is able to branch off and often used for radioisotope production. Though the unloaded maximum energy is 300 MeV, an energy of 200 MeV is normally employed for the beam injection into the STB ring because of sufficient beam current. The beam energy is analyzed at a dispersive section in the transport line and selected to be within certain width (typically ± 1.5 %). Since there is an additional function of pulse-beam stretcher to the STB ring, the beam extraction system is also equipped. The quasi cw-beam extracted from the STB ring is transported to a couple of experimental stations