Bunching beam dynamics and emittance growth in a final buncher of heavy ion fusion accelerator system are studied using a particle-in-cell simulation. The results indicate that while the beam current is increased by longitudinal compression, the beam particles dilute in phase space depending on the bunching history.

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The gyrokinetic theory is a basic framework for describing microinstabilities, turbulence, and resultant anomalous transport in magnetically confined plasmas. This article reviews basic governing equations of the gyrokinetic theory, namely, gyrokinetic equations for the gyrocenter distribution function, the electrostatic potential, and the magnetic vector potential, based on Lagrangian and Hamiltonian formulation. In this formulation, conservation laws for the magnetic moment, the phase space volume, and the total energy are rigorously treated.

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This paper reviews recent studies of tokamak MHD stability towards the achievement of a high beta steady state, where the profile control of current, pressure, and rotation, and the optimization of the plasma shape play fundamental roles. The key instabilities include the neoclassical tearing mode, the resistive wall mode, the edge localized mode, etc. In order to demonstrate an economically attractive tokamak reactor, it is neccesary to increase the beta value simultaneously with a sufficiently high integrated plasma performance. Towards this goal, studies of stability control in self-regulating plasma systems are essential.

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The recent dramatic progress in the study of helical systems related to achieving high beta plasmas is reviewed.Discharges with over 3% beta plasmas have been achieved in LHD and W7-AS experiments. Although MHD instabilities affect pressure gradients as a local effect, high beta plasmas have been achieved in a fairly stable region according to ideal MHD stability analysis. Heating power and/or radiation phenomena were shown to still limit the experimental beta values. Magnetic surfaces with good quality are considered to exit even in over 3% beta plasmas. The issues involved in achieving more than 5% beta plasmas are summarized.

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Recently, high-beta operations of Spherical Tokamak (ST) have received increased attention due to the compatibility achieved between high-beta and a long confinement time. In addition to the high normalized current I/aB achievable at a low aspect ratio, an important advantage of high-beta ST is its direct access to second stability for ideal ballooning modes. The mega-ampere class experiments, NSTX and MAST, renewed the record beta values up to β_T˜35%, increasing confinement time up to τ_E˜0.1 sec. Small-scale experiments produced the second-stable STs with diamagnetic toroidal field /absolute minimum-B by transforming oblate FRCs. Major issues for the second stable STs are achieving a stable startup/ profile control for kink and the ballooning stabilities and a concrete approach to high-ratio pressure driven currents .

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The recent progress in high-beta reversed-fieldpinch (RFP) studies is reviewed. Experimental efforts to suppress the RPF dynamo modes (core resonant tearing modes) have resulted in remarkable confinement improvement in large RFP experiments. The poloidal beta (≈total beta) value of ˜20% has been achieved with improved confinement. After suppressing the current-driven modes, the role of pressure-driven modes will become important in the RFP dynamics. Theoretical studies of pressure-driven modes have revealed that ideal-mode-stable RFP configurations with β_P≈30% exist, and that unstable mode spectra are sensitive to local current profiles as well as to pressure profiles. The role of the Suydam criterion on the stability of ideal modes is discussed briefly. From an experimental point of view, it is essential to investigate the beta limit in the RFP by increasing heating power density under conditions of improved confinement.

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Advanced fusion such as D-³He requires an ultra-high-β plasma. The field-reversed configuration (FRC) plasma is a candidate because of its intrinsic ultra-high-β: <β>≈1. The FRC can be produced by merging spheromaks with counter helicities. This result strongly implies that the FRC represents a new relaxed state, which is not a Taylor's state. Recently, the two-fluid relaxation theory has been developed to describe a relaxed state with finite pressure gradient such as FRC. The theory calls for an Alfvenic flow in the relaxed state. In order to drive such a fast flow, preliminary experiments have been performed to which external electrodes or non-neutral plasmas are applied.

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Pulsed electromagnetic wave generation by an ionization front created by a laser beam is reviewed. The laser created ionization front which propagates with a relativistic velocity can interact with a counterpropagating electromagnetic wave and results in the upshifted electromagnetic wave.

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Under the Numerical EXperiment of Tokamak (NEXT) research project, various fluid, particle, and hybrid codes have been developed. These codes require a computational environment which consists of high performance processors, high speed storage system, and high speed parallelized visualization system. In this paper, the performance of the JAERI Origin3800 system is examined from a point of view of these requests. In the performance tests, it is shown that the representative particle and fluid codes operate with 15˜40% of processing efficiency up to 512 processors. A storage area network (SAN) provides high speed parallel datatransfer. A parallel visualization system enables order of magnitude faster visualization of a large scale simulation data compared with the previous graphic workstations. Accordingly, an extremely advanced simulation environment is realized on the JAERI Origin3800 system. Recently, development of a storage grid is underway in order to improve a computational environment of remote users. The storage grid is constructed by a combination of SAN and a wavelength division multiplexer (WDM). The preliminary tests show that compared with the existing data transfer methods, it enables dramically high speed data transfer ˜100 Gbps over a wide area network.

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