原子力機構サイクロトロンにおけるパルスビ一ム形成技術の開発

摘要

The intervals of extracted beam pulses from a cyclotron are tens of nano-seconds because an acceleration frequency of a cyclotron is generally tens of MHz, and they are too short for experiments such as pulse radiolysis and time of flight measurement of secondary particles. A beam chopping system, consisting of two types of high voltage kickers, is used to drastically increase the intervals of the beam pulses at the JAEA cyclotron. The first kicker installed in the beam injection line generates beam pulses with repetition period over 4.2 μs. The pulse width of the beam is about a cycle length of the acceleration frequency. The other kicker downstream of the cyclotron thins out needless beam pulses caused by multi-turn extraction. However, we could not provide the pulse beam stably over 30 min since the magnetic field of the cyclotron gradually decreased on the order of 0.01% and the number of multi-turn extraction increased. The magnetic field was stabilized within 0.001% by keeping temperature of the cyclotron magnet constant. In addition, a new technique to control an acceleration phase has enabled us to reduce the number of multi-turn extraction. As a result of these improvements, we have succeeded to stably provide a variety of pulse beams such as 65 MeV proton, 50 MeV ~4He~2+, 320 MeV ~(12)C~(6+) and 350 MeV ~(20)Ne~(8+).