Essential aspects of beam physics in high intensity and high energy circular accelerators are described. Main issues such as tune spread, nonlinear resonances, and halo formation associated with space-charge effects are discussed. Typical coherent instabilities which had been the primary objections to upgrading the KEK 12 GeV proton synchrotron are introduced.

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Intense particle beams driven by pulse power generators, are basically high current and low energy. A strong coupling between the high current beams and the electromagnetic field not only degrades the beam quality in the acceleration gap but also makes difficult to transport them. Although indactive acceleration poses many problems, which remain unsolved, it seems to be an effective way to avoid this interaction. In this report, characteristics of pulse powered beams are reviewed and issues regarding them are briefly discussed.

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The concept and technology of collective accelerators using an intense electron beam which were studied extensively in the ’70s to ’80s, are reviewed briefly. The two most prominent kinds of acceleration schemes during this period were the type of linear arrangement of the system and that using an Electron Ring as a vehicle. Although only very small activity of experimental studies has been pursued beyond late ’80s, the result of the research on collective acceleration remains relevant to the significant phase of recent plasma science and to particle dynamics in the present high energy accelerators.

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Large current accelerator, in which the current is larger than a kilo-ampere, has various potential applications in industrial fields. Such accelerators have a long life, good reliability, high pulse repetition rates, and high efficiency. Although large current accelerators with energies larger than 10 MeV do not exist at present, various research and developments for the construction of such high energy and large current accelerators are being performed. Each research group has its peculiar application purpose. In this paper, several topics of large current accelerator applications are described in order to demonstrate the potential of the large current accelerator.

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Past particle transport studies on FRC plasmas are reviewed. In the closed field region, the long-held belief that the lower-hybrid-drift mode is responsible for particle transport is disproved and the possibility of the importance of an electromagnetic mode is pointed out. A kinetic-theoretical study on the transport in the open field region, in which mirror trapping, self-consistent ambipolar potential, classical collision, and collisionless pitch angle scattering near the magnetic X-point are taken into account, is introduced. In experiments, detailed measurements in the open field region were made possible by the realization of a low density FRC plasma using the technique of translation. From these measurements, plasma which diffused across the separatrix is shown to flow along the magnetic lines of force, while the flow velocity approaches the sound velocity, as with fluid flow through a duct. On the other hand, the fact that the empirical scaling law for particle confinement time does not depend on the plasma length seems to suggest that particles are lost through the loss cone in velocity space.

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Wall conditioning can control impurity and hydrogen isotope. So various methods of wall conditioning have been adopted in JT-60U. After the vacuum vessel is closed and pumping system works, tokamak discharges can be obtained within a week. The conditioning can also make a good condition that recycled particles are so low as to correspond to injected NB particles. An equivalent Q_DT up to 1.25 can be transiently achieved in reversed shear plasmas because of both optimization of wall conditioning and improved confinement. Wall conditioning in JT-60U is discussed in this paper.

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