On the heating mix of ITER (invited paper)

This paper considers the heating mix of ITER for the two main scenarios. Presently, 73MWof absorbed power are foreseen in the mix 20/33/20 for ECH, NBI and ICH. Given a sufficient edge stability, Q = 10 the goal of scenario 2 can be reached with 40MW power irrespective of the heating method but depends sensitively inter alia on the H-mode pedestal temperature, the density profile shape and on the characteristics of impurity transport. ICH preferentially heats the ions and would contribute specifically with Q 0.5, and strong off-axis current drive (CD). The findings presented here are based on revised CD efficiencies γ for ECCD and a detailed benchmark of several CD codes. With ECCD alone, the goals of scenario 4 can hardly be reached. Efficient off-axisCDis only possible with NBI.With beams, inductive discharges with fni > 0.8 can be maintained for 3000 s. The conclusion of this study is that the present heating mix of ITER is appropriate. It provides the necessary actuators to induce in a flexible way the best possible scenarios. The development risks of NBI at 1MeV can be reduced by operation at 0.85MeV

Recent Advance in LHD Experiment

In the first four years of LHD experiment, several encouraging results have emerged, the, most significant of which is that MHD stability and good transport are compatible in the inward shifted axis configuration. The observed energy confinement at this optimal configuration is consistent with ISS95 scaling with an enhancement factor of 1.5. The confinement enhancement over the smaller heliotron devices is attributed to the high edge temperature. We find that plasma with an average beta of 3 % is stable in this configuration even though the theoretical stability conditions of Mercier modes and pressure driven low n modes are violated. In the low density discharges heated by NBI and ECR heatings, ITB(internal transport barrier) and an associated high central temperature (> 10 keV) are seen. The radial electric field measured in these discharges is positive (electron root) and expected to play a key role in the formation of the ITB. The positive electric field is also found to suppress the ion thermal diffusivity as predicted by neoclassical transport theory The width of the externally imposed island (n/m=1/1) is found to decrease when the plasma is collisionless with finite beta and it increases when the plasma is collisional. The ICRF heating in LHD is successful and a high energy tail ( up to 500keV) has been detected for minority ion heating, demonstrating good confinement of the high energy particles. The magnetic field line structure unique to the heliotron edge configuration is confirmed by measuring the plasma density and temperature profiles on the divertor plate. A long pulse (2minute) discharge, with an ICRF power of 0.4 MW has been demonstrated and energy confinement characteristics are almost the same as those in short pulse discharges

The large tokamak JT-60: a history of the fight to achieve the Japanese fusion research mission

Fusion research was driven by the oil shocks in 1970’s and the concern about climate change during 20th century. This paper addressed the scientific research history of JT-60, the tokamak that achieved record fusion performances and opened the way toward the continuous operation of a tokamak fusion reactor through its scientific discoveries. The paper also highlighted technical struggles to improve machine capabilities and to solve technical issues faced during the JT-60 project. The missions of JT-60 were to achieve equivalent energy break-even ( Q = PDTequi. / Pheat ≥ 1 Q=PDTequi.∕Pheat≥1 ) and to establish a scientific basis for fusion reactor. The JT-60 made several modifications to reach equivalent break-even condition and continued efforts were made by the JT-60 team to solve critical technical issues during 23 years of research operation. Scientific success of JT-60 led to current ITER projects and the modification of JT-60 to a superconducting tokamak, JT-60SA. This paper is intended to be useful for the future researchers and managers of large-scale project by giving dynamical evolutions and highlighting key players. I dedicate this paper to Hiroshi Kishimoto, who made an outstanding contribution in managing the JT-60 research project