The Establishment of a Self-Consistent Nuclear Energy System (SCNES) attempts to meet the following four requirements -energy production, fuel production, the burning of radionuclides, and system safety with a strong reliance on excess neutron generation. Based on several milestone studies, it has been pointed out that a fast fission reaction provides an appreciable neutron excess to incinerate fission products, while MA (Minor Actinides) may be treated as a fuel along with Pu in this system. To improve both the quality and quantity of neutron excess for the transmutation of radiowastes, neutron generation in the external neutron sources based on accelerator and/or fusion technologies was evaluated. Our results suggest that multi-component SCNES supplemented by accelerator-driven and fusion-based neutron sources may approach the final goal of the development of a nuclear energy system that is safe, wasteless, and supported by reliable fuel resources.

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Contents of a special topic article ’Fundamentals of Burn Control’ are explained briefly as an introduction.

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We review the early and more recent studies regarding thermal instability due to alpha particle heating and its control. The first subsection explains generally the physics of thermal instability and the control methods proposed for achieving a steady state operation. The last two subsections are devoted to present research and topics as well as future issues related to the operation scenario for ITER in relation to thermal instability.

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Helium exhaust is required in steady state D-T burning operations. The recycling of deuterium and tritium should be controlled in order to achieve an operation margin for profile control, etc. These requirements are met by the active pumping of a divertor. The present status of particle control studies and plasma facing materials are described.

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Physics issues in burn control of tokamak reactor are reviewed with an emphasis on improved confinement with an internal transport barrier. Long-time control of current profile in negative shear con-figuration, thermal instability in high poloidal beta mode, and the influence of various instabilities are discussed. Results of one-dirnensional transport simulation are presented to demonstrate the suppression of ideal MHD instability and sawtooth oscillation using off-axis anti-current drive.

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Characteristics of disruptive plasma termination, its amelioration and avoidance, and fast plasma shut-down are described in relation to designing tokamak fusion reactors.

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The issue of burn control in FDR-ITER, the design of which was completed in 1998, is introduced, Controllability was studied based on the ID transport code, PRETOR, during the burn phase with self-ignition, as well as during start-up and shut-down. The results of the present study have helped us to identify the importance of controlling the fuel supply, impurity injection, and heating power to maintain fusion power and power to the divertor.

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Burn control in helical fusion reactors is overviewed, focusing on LHD (Large Helical Device)-type helical reactors. For the ignition projection of these reactors, several confinement scalings are adopted with the assumption of an improvement factor. In particular, the primarily effects of neoclassical transport loss on ignition and burn control are described. Recent LHD experiments have justified reactor design with a confinement improvement factor of 2. Density and beta limits are also evaluated in the POPCON plots, and issues of steady-state burn control in helical reactors are summarized.

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The plasma control technique for use in large tokamak devices has made great developmental strides in the last decade, concomitantly with progress in the understanding of tokamak physics and in part facilitated by the substantial advancement in the computing environment. Equilibrium control procedures have thereby been established, and it has been pervasively recognized in recent years that the real-time feedback control of physical quantities is indispensable for the improvement and sustainment of plasma performance in a quasi-steady-state. Further development is presently undertaken to realize the “advanced plasma control” concept, where integrated fusion performance is achieved by the simultaneous feedback control of multiple physical quantities, combined with equilibrium control.

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Issues regarding plasma equilibrium control in helical systems are overviewed focusing on the control of plasma cross-sectional shape and bootstrap current in high-temperature helical plasmas. The role and characteristics of equilibrium control in helical devices are described first, and the definitions of magnetic configuration parameters of three-dimensional helical plasmas are given in the following section. Typical examples of equilibrium control in the present medium-sized helical systems are then described, and the operational domain and the feedback control planning for LHD plasmas are shown in the final section.

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The present status of plasma control with magnetic fields in reversed-field pinches (RFPs) is briefly reviewed. Since the RFP is a low-q, high-magnetic-shear configuration, field error (toroidally asymmetric equilibrium) control is quite important, in addition to global equilibrium control. The development of sophisticated techniques of RFP plasma control has resulted in the attainment of improved confinement modes. The locked modes, resulting from the nonlinear interaction of several dominant tearing modes, have been controlled with external magnetic field perturbations in the RFX experiment. Plasma control issues related to the future steady state RFP are discussed.

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Beam-circuit code is presented to simulate a Traveling-Wave Direct Energy Converter (TWDEC), which recovers the energy of fusion protons escaping from a FRC/D³He fusion reactor. A transmission line loop for propagation of the electrostatic traveling wave is designed using lumped constant elements L.C.R. Electrostatic coupling between proton beam and circuits is treated by directly solving Poisson’s equation. Circuit equations are transformed to temporal finite-difference equations, which are solved following the leap-flog scheme. Simulation results display desirable performance characteristics. Traveling wave with a fixed frequency is excited spontaneously without any external power supply. The wave is kept its equilibrium state under loading, and the wave is stable to variation of the load.

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