Impurity growth in single bunch operation of PF

Growth of the single bunch impurity was observed in the Photon Factory storage ring. The phenomenon caused by recapture of electrons that are thrown out of main bucket by Touschck effect was analyzed theoretically. Agreement of the observed rate of the impurity growth and the theoretical estimation was fairly well. In order to cure the effect, the RF knockout method was employed. The betatron tune of a bunch depends on the number of electrons in it. If the knockout frequency is adjusted to that corresponds to weak bunches to remove them, the betatron motion of the main bunch is scarcely affected. This method is routinely used in the single bunch operation of Photon Factory.