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.
Highlights
From the results presented in this paper, we can conclude that the satisfactory performance of the Einzel lens as a beam chopper has been successfully demonstrated by using helium ion species
To verify the performance of the chopper, the chopped beam profile was reconstructed from the Faraday cup signal, taking into account its circuit response properties
The resultant bunch profile is consistent with the beam profile as predicted from the chopping voltage
Summary
The KEK digital accelerator (KEK-DA) is a small-scale induction synchrotron (IS) that was built as part of the renovation of the former KEK 500 MeV booster ring of the rapid-cycle proton synchrotron [1]. In principle KEK-DA is an injector-free accelerator, certain injection energy is required to mitigate the transverse space-charge effect and closed-orbit distortions caused by remnant fields in the ring. For these reasons, the electron cyclotron resonance ion source (ECRIS) is embedded in a high-voltage platform (HVP). The required pulse length should be shorter than the revolution time of the ion beam, or $12 s for He1þ. Various types of beam choppers are available for this purpose
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