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An achievement in JT-60 gives a perspective for higher performance operation in ITER
- a plasma pressure can be 1.6 times with small rotational speed of 15% of previous estimation -
Jan. 26, 2007
In the large tokamak device JT-60 for fusion energy research in JAEA (Japan Atomic Energy Agency) [President Toshio Okazaki], it is found that a high plasma pressure corresponding to about 1.6 times of that is foreseen in ITER (International Thermonuclear Experimental Reactor) can be sustained stably with much smaller plasma rotation than that has been expected. This is the first result in the world that gives a perspective for extending ITER operational regime towards higher output density operation in future fusion reactors.
In order to realize a fusion reactor of high output density (small size and high output = high economy) it is necessary to increase the plasma pressure (temperature x density). However, since a phenomenon that deforms a donut shape plasma prevents increase in pressure, suppression of this phenomenon has been an important research objective. It has been predicted theoretically that rotating plasma by injecting high speed neutral beam with conducting wall surrounding the plasma suppresses this deformation and makes the pressure increase possible. However, it has been pointed that extra neutral beam power would be required to obtain enough rotational speed, since external driving force to rotate plasma in ITER and a future fusion reactor will be less than that in current experimental devices.
Therefore, determination of rotational speed that is required to suppress the plasma deformation has been an important issue. However, it has been difficult to perform an experiment with small rotational speed that simulates ITER and a future fusion reactor since in other devices on which directions of neutral beams are the same, the driving force of the rotation increases with a increase in heating power to obtain higher plasma pressure.
On the contrary in JT-60, several neutral beams with various injection directions are installed so that the rotational speed can be controlled artificially. Moreover, net injection power was increased by improvement in the magnetic filed structure done in 2005. Owing to these, we succeeded to realize a situation similar to ITER and a future fusion reactor in which the rotational speed is kept small with high power injection. As a result, it was found that a threshold value in the rotational speed obtained in other devices had been overestimated and that the deformation can be suppressed with only 15% of that had been obtained. The result indicates that a higher plasma pressure, corresponding to about 1.6 times of that is expected to be required in the long sustainment of a burning plasma in ITER (standard scenario), which is one of the main mission of ITER, can be maintained. And this is the first result in the world that gives a perspective for extending ITER operational regime towards higher output density operation in future fusion reactors.
This result will be published in the February 2nd issue of Physical Review Letters, the world authoritative journal in physics research.
•An achievement in JT-60 gives a perspective for higher performance operation in ITER -a plasma pressure can be 1.6 times with small rotational speed of 15% of previous estimation- (PDF)
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