The 3-GeV rapid cycling synchrotron (RCS) of the Japan Proton Accelerator Research Complex (J-PARC) is now in the final beam commissioning phase, aiming for a design output beam power of 1 MW. With a series of injector linac upgrades in 2013 and 2014, RCS developed a high-intensity beam test, and launched 1-MW beam tuning in October 2014. The most important issues in realizing such a high-power continuous beam operation are to control and minimize beam loss for maintaining machine activations within permissible levels. In RCS, numerical simulation was successfully utilized along with experimental approaches to isolate the mechanism of beam loss and find its solution. By iteratively performing actual beam experiments and numerical simulations, and also by several hardware improvements, we have recently established a 1-MW beam operation with very low fractional beam loss of a couple of 10 −3 . In this paper, our recent efforts toward realizing such a low-loss high-intensity beam acceleration are presented as a follow-up of our previous article, H. Hotchi et al. Phys. Rev. ST Accel. Beams 12, 040402 (2009), in which the initial beam commissioning status of RCS has been reported.

A tabletop experimental system has been developed for the study of various collective effects in space-charge-dominated beams. It is based on the recently proposed idea that the dynamic motion of a one-component plasma in a trap can be made physically equivalent to that of a charged-particle beam propagating through a linear transport channel. In this paper, we report on the details of the system and on results of test experiments with a compact Paul trap that is divided into several independent sections. The trap design is carried out in consideration of practical constraints. A Maxwell equation solver is used to calculate the properties of the plasma confinement potential. Experimental observations are compared with numerical data obtained by a tracking simulation code that enables us to approximately predict the three-dimensional trajectories of particles in the system. Low-density N 2 þ plasmas are employed to examine the basic performance of the multi-section trap. The initial temperature, density and lifetime of a confined plasma are estimated from experiments and simulations.

The dynamic behavior of a bunched one-dimensional crystalline beam is studied theoretically. It is shown that, owing to the existence of momentum dispersion, a Coulomb chain traveling in a storage ring performs a complex periodic oscillation whenever it is exposed to a longitudinal radio-frequency force. The equations of motion are derived to predict the oscillation pattern in an arbitrary lattice structure. The validity of the present theory is confirmed through multiparticle simulations. Various features of an oscillating string beam, such as the lattice-parameter dependence of the orbit, the stability, and critical line density, etc., are also discussed.

Polycrystalline diamond films have been deposited on ceramic alumina substrates by microwave plasma chemical vapor deposition method. Variation of the emission spectra in the microwave plasma with the microwave power and the vapor pressure in the reaction chamber is studied, respectively. Relationships between the hydrogen atomic spectra and the average energy of the electrons in the plasma, as well as the mechanism of diamond film deposition on ceramic alumina are discussed.