Beam-extraction method from a synchrotron effective for the spot scanning method

A new method for slow beam extraction from a synchrotron ring is proposed, based on controlling a quadrupole field with a fast response (FQ), assisted by a transverse RF-field (RF-knockout). This method works as follows: 1) particles of a circulating beam are diffused by RF-knockout to just inside the boundary of a separatrix produced under a resonant condition, 2) exciting the FQ shrinks the separatrix to a certain size, and the particles outside the separatrix can be extracted, 3) the fast Q-field is turned off, and 4) the above process is repeated until all of the circulating beam is completely extracted. This method can extract prescribed particles at required timings quickly and precisely, because it is controlled with only the fast Q-field. A proof-of-principle experiment was carried out at the HIMAC synchrotron. As a result, it was verified that the beam was extracted only with exciting the FQ, but not with turning the RF-knockout on. (author)