Annual Report

from April 1, 1996 to March 31, 1997

Department of Plasma Research and Department of Fusion Facilities

Naka Fusion Research Establishment
Japan Atomic Energy Research Institute
Naka-machi, Naka-gun, Ibaraki-ken, Japan 311-01

"Inside of the JT-60 vaccum vessel with W-shaped semi-closed divertor."

This report provides an overview of research and development activities at Department of Fusion Plasma Research and Fusion Facilities, JAERI, during the period from April 1, 1996 to march 31, 1997. The activities in this period are highlighted by high temperature plasma research in JT-60 and JFT-2M.

The objectives of the JT-60 project are to contribute to the ITER physics &D and to establish the physics basis for a steady state tokamak fusion reactor like SSTR.

To achieve these objectives, improvements and regulation of the facilities and developments of the instruments were performed. The highlights are as follows. The construction for the divertor modification from the original open type to the W-shaped semi-closed type for improving the particle control was started on February 1997. In the power supply system, the thyristor converter was partially rearranged to increase the plasma current with the high triangularity. The world record of plasma input power 40 MW was achieved by NBI with the beam energy of 90 keV using positive ion source. Also in negative-ion based NBI, the beam output of 18.4 A/350 keV(6.4 MW) with hydrogen and 13.5 A/400 keV(5.4 MW) with deuterium were achieved as the world record. Furthermore, a plasma input power of 3.2 MW/350 keV to JT-60 was realized with the single ion source. In LHRF system, a protection system of the antenna from the arcing was developed by means of detection of the light caused breakdown.

The followings are the results concerning the plasma performance. By extending the operational region of the high pH-mode, the world record of the fusion triplet, nDETi0 = 1.53x1021 keV s m-3, was achieved. It was found that the fusion triplet became maximum in the same region of the safety factor as the ITER operation. electron density 0.97x1020 m-3, the fusion triplet 0.78x1021 keV s m-3. The fusion power by D-D reaction was 53 kW, and assuming that the half of the fuel was tritium, the expected fusion output was 10.6 MW. The ratio of the output to the input power becomes 1.05, therefore it can be concluded that the plasma is in an equivalent break even condition. Moreover, in a reversed shear plasma, the highest values of the energy confinement time and the stored energy on JT-60 (1.08 s and 10.9 MJ) were recorded. Generation of radiative divertor, confinement of high energy ions, current profile control by RF current drive and impurity confinement in reversed shear plasmas were investigated systematically.

The poloidal coil system was modified so as to increase the triangularity. As the result an instability driven by the pressure gradient at the plasma edge was drastically suppressed, then a plasma with the confinement improvement factor of more than two and the fusion triple product of 0.27x1021 keV s m-3 was successfully maintained for 2.6 seconds. Furthermore, by raising the triangularity a full current drive plasma was successfully maintained with high confinement property and high fraction (60%) of the bootstrap current for three times longer than was formally achieved. A driven current of 270 kA was demonstrated by the negative ion based neutral beam injector (N-NBI) for the first time, and a profile of the current was estimated. The current drive efficiency by N-NBI was proved to be better by 1.6 times than that by standard energy (90 keV) positive ion based NBI.

Objectives of the JFT-2M program are (1) advanced and basic researches for the development of high-performance plasmas for nuclear fusion and (2) contribution to the physics R&D for ITER, with a merit of flexibility of a medium-size device. The modified closed divertor was found to improve compatibility of the H-mode with the dense and cold divertor plasma. In an H-mode plasma, suppression of the density fluctuation was found to occur in a high shear region of the radial electric field. It was demonstrated that the m=2 tearing mode was suppressed by the O-mode ECH for the first time in an elongated plasma. Plasma coupling experiment of the combline antenna for FWCD was carried out in collaboration with General Atomics. Planning of the Advanced Material-Tokamak Experiments (AMTEX) was initiated.

The primary objective of theory and analysis is to improve the physical understanding of the magnetically confined tokamak plasma. Remarkable progress has been made on understanding of physics of the reverse shear plasma, stability properties of ideal MHD, TAE and kinetic ballooning modes. Progress was also made in understanding of VDE mechanism and nature of divertor asymmetry. New Implicit Monte Carlo method is also developed for the analysis of impurity ionization and recombination. Selective He ash exhaust is also demonstrated using OFMC code simulation.

The main focus of the NEXT (Numerical Experiment of Tokamak) project is to simulate tokamak plasmas using particle and fluid models on the developing technology of massively parallel computers.

Keywords; Funsion Research,JAERI,JT-60,JFT-2M,DIII-D,Plasma physics,Fusion
Engineering,ITER,ITER-EDA,Fusion Reactor Design,Annual Report

Editors:Shimizu M.(chief).,Ide S.,Matsukawa M.,Kurihara R.,Koizumi K.,Takahashi I.