Einzel lens chopper and behavior of the chopped beam in the KEK digital accelerator

Abstract

The KEK digital accelerator (KEK-DA), which is a small-scale rapid-cycle induction synchrotron (IS), has commenced operation. A permanent magnet x-band electron cyclotron resonance ion source serves as the KEK-DA ion source and delivers various ions. A new Einzel lens beam chopper has been developed to provide the necessary pulse width of a few microseconds. The chopper is implemented by applying a rectangular pulse voltage generated by a solid-state Marx generator to the middle electrode of the Einzel lens. Momentum modulation at the bunch head and tail resulting from chopping in longitudinal direction has been observed. This intrinsic property of the chopped pulse has been clearly observed in a long drift (a free run in the circular ring) in KEK-DA.

Wideband induction acceleration and its intrinsic nature in the KEK digital accelerator

“…Meanwhile, the assumed momentum spread, taken as one sigma of the Gaussian distribution, was Δp/p ¼0.18%. The momentum deviation caused by the einzel lens chopper [7] was not included. This is reasonable because the actual particle fraction with a large , where the set pulse and reset pulse are in red and blue, respectively.…”

“…The combined-function bending magnets with a bending radius of 3.3 m are operated at a frequency of 10 Hz, where the magnetic flux density at injection depends on the mass-to-charge ratio of the accelerated ion and the maximum flux density changes below 0.84 T, depending on the experimental requirements. Heavy-ion beams are generated in the ECRIS, extracted with an extraction voltage of 15 kV, chopped into lengths of several microseconds by the einzel lens chopper [7], and post-accelerated at 185 kV before entering the low-energy beam transport line. The heavy-ion beams are injected into the ring by the electrostatic injection kicker [8].…”

Racetrack-shape fixed field induction accelerator for giant cluster ions

“…Such an ion source is embedded in the 200 kV high voltage platform. Ion beams will be chopped by any longitudinal chopper, such as the Einzel lens chopper [18,19], so as to meet the bunch length required for the RAFFIA. The ion bunch is guided to the RAFFIA through the low energy beam transport line (LEBT) by including an appropriate momentum analyzer and charge-state selector.…”

Fast chopper for single radio-frequency quadrupole bunch selection for neutron time-of-flight capabilities

“…These structures require high voltage (HV) pulse rise and fall times of several nanoseconds to avoid partially deflected pulses that generate unwanted beam loss. Novel examples for high current include an E × B field chopper system described by Wiesner et al [8], and a chopping system based on a new Einzel lens described by Leo et al [9].…”