Energy-varying beam extraction assisted by large momentum deviation and charge exchange

Abstract

Two energy-varying beam extraction schemes for energy sweeping compact rapid cycling therapy are discussed. One is one-turn (fast) extraction of a C^{6+} bunch from a fast-cycling hadron driver accelerator assisted by an off-momentum bump orbit, in which a combination of a kicker and a septum magnet are fired at a desired timing (or energy). The other is energy sweeping extraction, in which a C^{5+} bunch delivered from the laser ablation ion source is injected and accelerated in the barrier bucket up to the final energy. A fraction of the trapped C^{5+} ions is continuously released from the bucket on the way to the final energy to form a coasting beam over an expected time (or energy) region, and the beam drifts inward in the large flat momentum dispersion region. The drifting C^{5+} beam hits the stripper carbon foil located at the front of the bending magnet and near the inner surface of the vacuum chamber in the large flat dispersion region and is converted to a C^{6+} beam. The combination of the enhanced bending radius and septum magnet allows easy C^{6+} beam extraction by the single septum magnet downstream.