CONTENTS

This report provides an overview of research and development activities at Department of Fusion Plasma Research and Department of Fusion Facility, JAERI, during the period from April 1, 1995 to March 31, 1996. The activities in this period are highlighted by high-temperature plasma research in JT-60U and JFT-2M.

The objectives of JT-60U project are (1) confinement improvement, (2) impurity control and divertor studies, (3) steady-state study, and (4) energetic particle physics. The investigation on these subjects are aimed at contribution to the ITER physics R&D and formation of database for the concept development of fusion power reactors like SSTR.

The highest fusion triple product n_D(0) T_i(0) t_E of 1.2 x 10²¹ keV s m^-3 was marked in High-bp H-mode plasma. With a high-triangularity plasma cross section, giant ELM activity was suppressed. At high triangularity of d=0.4, the maximum edge pressure limited by giant ELMs and the central density increased by a factor of 2.8, and 1.6, respectively, from those without triangularity.

Improved confinement in a reversed shear plasma, previously predicted by the theoretical study in JAERI, was experimentally demonstrated. Significant reduction in electron and ion thermal diffusivity as well as particle diffusion coefficient was observed in the reversed shear region. Reversed shear configuration was sustained for a long period (7.5 s) by lower hybrid current drive (LHCD).

Heat removal and divertor plasma detachment were successfully established, for the first time, in reversed shear plasmas. The enhancement of the helium particle confinement and low diffusivity were observed as well. A neural network processor enabled accurate detection of plasma displacement, leading to successful feedback control of plasma position during the current quenching phase associated with a major disruption. Injection of 100 % neon-iced pellet (killer pellet) during the disruption drastically reduced the heat load at the divertor target.

The negative-ion-based neutral beam injection (NNBI) into the tokamak plasma was successfully conducted for the first time, with acceleration voltage, beam current, and pulse duration of 200 keV, 3.2 A, and 0.47 s, respectively. The design for divertor modification has proceeded in preparation for its installation in FY 1996.

In JFT-2M, the divertor configuration was modified from an open divertor to a closed divertor in FY 1995, and initial results on the closed divertor have been obtained. Progress was also made in understanding on the L/H transition physics by applying the divertor biasing and intense gas puffing. In DIII-D, introduction of high-resolution bolometer and divertor Thomson enabled accurate determination of divertor plasma properties in the detached and attached plasma regimes. Operation of discharges with negative shear has led to significant increases in the plasma performance and reactivity.

The Numerical EXperiment of Tokamak (NEXT) project was started in 1995. Its main focus is a simulation study of tokamak plasmas using particle and fluid simulation models on the developing technology of massively parallel computers.

Keywords: fusion research, JAERI, JT-60, JFT-2M, DIII-D, plasma physics, ITER, ITER-EDA, annual report

Editors: Shimada, M.(Chief), Asakura, N., Moriyama, S., Yamanishi T., Seki, M., Takahashi, I.