Sanae Tamura

Effect of Toroidal Field Ripple on Fast Ion Behavior in a Tokamak

Computational studies have been performed for fast ion behavior in a Tokamak with toroidal field ripple. Collisionless behavior of fast ions relating to rippletrapping, ripple-detrapping and banana drift is of essential importance in fast ion loss processes in case of quasi-perpendicular neutral beam injection. The collisionless ripple trapping and ripple-enhanced banana drift produce a large number of loss bands in velocity space and enhance the loss of fast ions. The fast ion loss associated with ripple can be categorized into two groups; ripple-trapped loss and banana-drift loss. The amount of loss particles due to the respective loss process is significantly influenced by the effect of finite banana size of fast ions. The ripple-trapped loss particles are localized in a specific region on the first wall surface.

Parallel Interruption of Heavy Direct Current by Vacuum Circuit Breakers

A newly developed d.c. circuit breaker successfully interrupts the current up to 130 kA d.c. under 44 kV d.c. recovery voltage. The breaker also can carry out the respective 4000 times operations of the above breaking duty every ten minutes without any trouble. The essential breaking mechanism is composed of two series and four parallel construction of vacuum valves with current commutation capacitor.

JT-60 power supplies

The paper gives a description of the electric power supplies of the JT-60 tokamak system, required to energize the magnetic field coils for plasma excitation and confinement.

Determination of Optimum Positions of the Poloidal Field Coils of a Large Tokamak

A set of two numerical methods is presented for determining optimum configuration of the poloidal field coils of a large tokamak. The first method is an application of the virtual-casing principle developed by Zakharov and determines both the currents and the positions of a system of the coils. The second one used a simplex method of non-linear programming for optimization calculations of the coil positions in a given area in the two dimensional space. This is needed to meet various practical requirements in the design of tokamaks. These methods have been applied in the design of JT-60 (JAERI large tokamak) to determine the positions of the ohmic heating coils, and shown to be effective when they are used in combination.

Design study of fusion experimental reactor at JAERI

Conceptual design studies of a next generation tokamak fusion reactor, the Fusion Experimental Reactor (FER) at JAERI are described. Recent design efforts have been focused on elaborating two typical design concepts, one based on the best existing physics data bases and the other on rather conservative physics basis, to be capable of achieving a self-ignited, long burning DT plasma and demonstrating the feasibility of key fusion reactor technologies. Various flexibility scenarios to enhance the machine capabilities to realize higher reactor-core performance have also been developed and incorporated in the design in accordance with an overall plan of phased construction and operation program of FER.

JT-60 Ohmic Heating Power Supply

The JT-60 ohmic heating power supply system is now being manufactured. The system has an additional inductive energy storage coil other than the ohmic heating coil to make a stepped build-up of plasma current and is designed to meet a variety of operations required for the JT-60 experimental program. In this paper, the overall design and operation of the system are described. A detailed description is also given of some important components whose performances need to be tested under various conditions.

Ergodic Behavior of Magnetic Field Lines in a Poloidal Divertor Tokamak

The ergodic behavior of magnetic field lines is investigated numerically in a Tokamak divertor system under the influence of magnetic perturbations. The entropylike quantity introduced into the magnetic system characterizes the property of the magnetic field lines and is related closely to the width of the ergodic layer. The metric entropy of the ergodic field lines is given in terms of the entropylike quantity.

Low-Beta Plasma Equilibrium and Stability in Linear Filamentary Multipole Magnetic Fields

Analytical results are presented for two stability integrals along a field line and for a class of low-β plasma equilibria in linear multipole magnetic fields. The integral \ointdl calculated for quadrupole and hexapole fields, \ointdl/B for quadrupole, hexapole and octopole fields. They are expressed in terms of the complete elliptic integral of the first kind. The stability limit lines defined by (∂/∂ψ)\ointdl=0 and (∂/∂ψ)\ointdl/B=0 (ψ: flux function) are determined together with the magnetic mirror ratio on those field lines. The magnetic well depth is also estimated. Low-β plasma equilibria in multipole fields are obtained by the perturbation technique. Variations of the field lines due to the plasma diamagnetism are calculated up to the linear terms in plasma pressure.

STUDY OF OHMIC HEATING (OH) POWER SUPPLY SYSTEM USING DC THYRISTOR CIRCUIT BREAKER

A thyristor circuit breaker (TCB) and an electromagnetic scaled model of an Ohmic Heating (OH) power supply system were made as a JT-60 R&D. In this paper, the test results of the TCB interruption are described, and also various OH power supply systems using the TCBs and their experimental results by the scaled model are shown and compared.

Behaviour of Fast Ions in a Large Tokamak Plasma during NBI Heating

Abstract The slowing-down process of fast ions produced by the neutral beam injection into a tokamak plasma has been studied by a simulation code using Monte-Carlo techniques. The energy transfer from the beams to the plasma and the loss of fast ions due to charge exchange and drifting motion are investigated in detail for quasi-perpendicular injection of the 75 keV hydrogen beam into the JT-60 (JAERI large tokamak) plasma.