The KEK-Digital Accelerator (DA) has been constructed, and it is in commission now. This accelerator is a rapid cycle synchrotron. Its acceleration principle is based on the induction synchrotron (IS) concept which was demonstrated in 2006 using the existing KEK 12 GeV proton synchrotron. Even before this demonstration, the small IS not employing any large scale injector had been proposed as All Ion Accelerator, which has the capability to accelerate all kinds of ions with their possible charge-state. Similarly, there is no large-scale injector in the KEK-DA. For KEK- DA, an ion beam is extracted from an ion source, chopped, post-accelerated and immediately guided to be injected to the DA ring. Presently, a permanent magnet type of Electron Resonance Ion Source (ECRIS) is utilized as the ion source for the KEK-DA. In order to mitigate the space charge effect and closed orbit distortion caused by a remanent field in the ring, the ion beam must be accelerated after extraction. Therefore, the KEK-DA ECRIS is embedded inside a 200 kV High Voltage Platform (HVP).In order to accelerate an ion beam in a synchrotron, a beam pulse length must be less than revolution time period in the ring. Since the typical revolution time is ~10 µs in our case, a ms ion beam which is produced from an ECRIS must be chopped before injection into the ring. For such purpose, a novel chopper device has been developed after our examination and consideration of various chopping systems. The novel chopper, so-called Einzel lens chopper, has been developed and demonstrated. Its principle is rather simple: by modulating a voltage applied to the middle electrode of the Einzel lens, it is worked as a longitudinal gating device as well as the focusing device. This performance can be realized by introducing a Marx generator to provide a pulse voltage in a desired duration time. The Marx generator used in the present studies has the fast response of rising and falling times with the solid-state switching device.For this implementation, the functionality and performance of the Marx generator have been confirmed by measurement and simulation. At first, in order to obtain a voltage for beam blocking and another voltage for beam optics matching of the Einzle lens, a beam blocking experiment was carried out by using the helium and nitrogen ion beams. In addition, a simulation was also performed by using the IGUN code. The chopping performances with different chopping timings and time durations have been investigated by observing time profiles of the chopped beam at a Faraday cup. The results were further confirmed and explained by using the circuit model of the Faraday cup. Reconstruction of a beam profile from the observed signal, which is modified by the Faraday cup response, is important to investigate a chopper performance. By solving the inverse problem, the beam profile was reconstructed successfullyA chopped beam is transported through a transport line and injected into the ring. In order to avoid a beam loss during transportation, it is important to know a beam emittance. Therefore, a beam emittance measurement was carried out by using a pepper pot emittance monitor. Through this experiment, the measurement and analysis procedures have been established. The optimization of the LEBT parameter was performed to reduce the beam losses.For further investigation of the transient beam behavior from the Einzel lens to the DA ring, a simple code was developed. By using the simulation result, we can identify the intrinsic characteristic of the Einzel lens chopper. Such an intrinsic nature is that the bunch head is retarded and bunch tail is moving forward. This source is originated from the transient time region of the Einzel lens chopper voltage, which modulates a momentum at the bunch head and tail. This phenomenon, which is called as “drift compression”, has been confirmed by comparing the bunch profile at the entrance and exit of transportation line. For the beam motion in the ring, beam diffusion or spread is also observed in the experimental and simulation results. For a long distance beam motion in the ring, the space charge effect is clearly seen: the particles are diffused from the bunch in time. The experimental results for the longitudinal motion can be quantitatively reproduced by using our simulation code.Presently, the Einzel lens chopper has been operating successfully with its stable and reliable performances and without causing any trouble during the KEK-DA beam commissioning
