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February 9, 2015
The 18th Plasma Experiment Cycle Concluded: Advances in High-Performance Plasma

The plasma experiments on the Large Helical Device (LHD) conducted during this academic year concluded on February 5, 2015. Since beginning in 1999, this was the eighteenth round of experiments. This year’s experiments began on November 6, 2014, and over forty-four days we conducted more than 6,400 plasma discharges. During this period, working together with researchers from universities and research institutes in Japan and also with foreign researchers, we moved forward with various experiments and research. During this research period, on January 23, 2015, or seventeenth year since the initiation of these experiments in 1999, we surpassed 130,000 plasma discharges. On the LHD, based upon the high-level operation reliability of the superconducting coil system, experiments progressed at a high pace that is not seen on other large devices. Because of this, we are able to continuously introduce various results.

In this year’s experiments, too, in addition to the high performance of LHD plasma advancing still further, we were able to obtain numerous results and to greatly develop our research. Through electron heating experiments that utilized the higher power of microwaves at the frequency of 154 gigahertz, we surpassed an electron temperature of 100 million degrees at an average density heretofore higher than in the past. Further, we investigated in detail high-temperature plasma whose ion temperature and electron temperature were nearly equal. And research aimed at achieving the future fusion energy advanced through confining the high-pressure plasma at the comparatively high magnetic field strength of one Tesla (10,000 Gauss). At the same time, we also investigated in detail the stability of plasma confined in the magnetic field container. Further, we actively conducted physics experiments for the purpose of clarifying the complicated phenomena that accompany high-performance plasma, and we deepened further the necessary academic understanding for the design of the future fusion power plant. Regarding the experimental successes this year, we will report again after conducting data analyses.

Accompanying the completion of the plasma experiments, since February 6, we have been conducting on the LHD an operation in which we raise the temperature of the superconducting coils from -270 degrees Celsius to room temperature. To reach room temperature will take four weeks, and we will raise the temperature little by little. Then, from early March, after reaching room temperature, we plan to begin maintenance and inspection procedures. Tours of the LHD were limited during the plasma experiment period. From now until the beginning of the next round of plasma experiments we invite everyone to visit and to view the LHD.