Electron cyclotron heating (ECH) is one of the intense methods of plasma heating, and which utilizes the collisionless electron-cyclotron-resonance-interaction between the launched electromag-netic waves (called electron cyclotron waves) and electrons which are one of the constituents of the high temperature plasmas. Another constituent, namely the ions which are subject to nuclear fusion, are heated indirectly but strongly and instantly (in about 0.1 s) by the collisions with the ECH-heated electrons in the fusion plasmas. The recent progress on the development of high-power and high-frequency millimeter-wave-source enabled the ECH experiments in the middle size tokamaks such as JFT-2M (Japan), Doublet III (USA), T-10 (USSR) etc., and ECH has been demonstrated to be the sure and intense plasma heating method. The ECH attracts much attention for its remarkable capabilities; to produce plasmas (pre-ionization), to heat plasmas, to drive plasma current for the plasma confinement, and recently especially by the localization and the spatial controllability of its heating zone, which is beneficial for the fine controls of the profiles of plasma parameters (temperature, current density etc.), for the control of the magnetohydrodynamic instabilities, or for the optimization/improvement of the plasma confinement characteristics. Here, the present status of the ECH studies on tokamak plasmas are reviewed.

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The experimental studies on the neutron transmission efficiencies of neutron guide tubes were carried out by using thermal neutrons from the JAERI electron linac. The neutron guide tube facility on a large scale have been planned on the reconstructed JRR-3 in JAERI. The neutron efficiencies of the 1/10 scale neutron guide tube, which is 2 mm width and 1.8 m length, with and without appreciable alignment errors were studied to evaluate the efficiencies of the planned ones. Calculated results by the Neutron Guide Tube Analysis Code 'NEUGT' were also assessed by these neutron experiments. The experimental results agree well with the calculated results by 'NEUGT' even with alignment errors. From this experimental study, the efficiency of the planned neutron guide tubes is estimated to be good enough for the neutron beam experiments.

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Statespace characterizations of two examples of a set of generalized, finite-dimensional, nonlinear reactor dynamics are presented. A power-law representation of reactivity feedback which captures some important kinetic characteristics is used. It is shown that the time domain of R³ statespace reactor dynamics-which incorporates prompt neutrons, delayed neutrons, and fuel temperature dynamics-affords an interesting and relevant set of new dynamic results and apparently does not admit evolution into compact trajectory trapping geometries; the latter suggests that the appearance of "chaotic" dynamical behavior is unlikely at this level of description.

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The identification method applying the projection operator for less small disturbances which do not instantly lead the alarm initiation has been extended to diagnose PWR plants operated with automatic frequency control. The authors previously proposed the non-linear transformation of the observed signals to satisfy with the linear relationship between the disturbances and the observed signals by utilizing several additional observed signals which are closely related with the non-linear characteristics of PWR plant. In addition, a method is proposed to compensate the fluctuation of observed signals due to automatic frequency control by utilizing both the input signal of the main steam valve control system and the input signal of the control rod control system. The effectiveness of the extended method has been examined by several computer experiments using a simple PWR plant simulation code.

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Ionization characteristics of two-step excitation by two intense nonmonochromatic (finite bandwidth) lasers are investigated. By approximating the laser fields by a stochastic model of a chaotic field, the stochastic atomic-density-matrix equations for three-level atoms are first obtained. Comparing with the analytical solution, the accuracy of our model is confirmed. By using this model, the ionization characteristics are studied in detail as a function of laser bandwidth. The dependence of laser bandwidth on the Doppler averaged ionization probability is also investigated.

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The depletion and production amounts of U, Pu, transplutoniums and fission products in the full-core fuel assemblies of Japan Power Demonstration Reactor-1 (JPDR-1) were obtained using codes for calculating three-dimensional nuclear-thermo-hydrodynamic performance, and depletion and production amounts. The results were investigated, compared with the recovery amounts in all the reprocessed fuel assemblies. As a result, the following has been found :
(1) The depletion and production amounts agree well with the recovery amounts except ²⁴⁰, Pu, ²³⁷Np and ^242mAm.
(2) It is necessary to calculate the depletion and production amounts by taking account of the axial distributions of void fraction and burnup of the fuel assembly.
(3) Enhancement for calculational accuracy of the depletion and production amounts calls for improvement of fission energies and systematic evaluation of neutron cross sections.

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