Argon, krypton and xenon were puffed with and without simultaneous hydrogen gas puffing into Ohmically heated plasmas of the JT-60U tokamak with low plasma currents in order to study the capability of disruption mitigation. It was found that krypton gas puffing can provide a plasma termination with smaller amounts of runaway electrons in comparison to argon and xenon gas puffing.

Development of a SiC microwave absorber for a damped cavity is presented. The SiC studied has a resistivity of 101–102 Ω cm, which is the expected value to damp higher-order modes (HOMs) in the cavity and also has high thermal conductivity. The absorber is attached to the cavity as a part of the beam duct. Since the SiC duct receives a large amount of energy from the electron (or positron) stored beam, it is very important to estimate the dissipation power in the SiC duct and to design a cooling mechanism. The heat load problem of the SiC duct is discussed and the results of high power testing of the SiC duct are presented. The damping mechanism for HOMs is based on the power dissipation due to the resistivity of SiC. The fine control of the resistivity of SiC in fabrication is very important. The preliminary results on this problem are also presented.

A two-dimensional hydrodynamical calculation method of self-gravitating rotating system is presented. The equation of fluid motion is treated in a Lagrangian form, while the Poisson equation of the gravitational potential is solved by the Finite-Element-Method. The results show that, in disagreement with the results of previous authors, there is no evidence of the ring formation along the equator, in case the fluid is initially rotating as a rigid body. The discrepancy is, presumably, due to the exact conservation of the angular momentum in the Lagrangian method and the inexact conservation in the Eulerian method. In this connection, it is demonstrated that a ring-like structure is actually formed under the circumstances where the angular momentum is transferred inwardly or a differential rotation of the fluid is assumed in the initial state.

We have developed an initial-beam-loading compensation system by a new compensation method, where the system modulates the phase and amplitude of a low-level rf signal simultaneously, thereby optimizing a high-power rf waveform fed to an accelerating structure to compensate the beam energy spread. This compensation system is very compact and can easily be installed in and removed from a klystron system. This system was used in a beam test performed in the 125 MeV electron linac of the Laboratory for Electron Beam Research and Application in Nihon University. Experimental results demonstrate that this system effectively corrects the beam energy spread due to the initial-beam-loading effect. The new compensation method is expected to be effective in the compensation of energy spread in high-intensity and long-pulse beams in electron linacs.

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