News releases

Achievement of long sustainment of
a high-confinement, high-pressure plasma in JT-60
- A big step towards extended burn in ITER with the use of ferritic steel -

May. 9, 2006

In the large tokamak device JT-60 for fusion energy research in JAEA (Japan Atomic Energy Agency) [President Yuichi Tonozuka], a plasma with high confinement and high pressure equivalently required for ITER (International Thermonuclear Experimental Reactor) was successfully sustained for 28 seconds, which is the longest world record, through an improvement in the magnetic field structure using ferritic steel. This result contributes to ensuring the accomplishment of extended burn, a major objective in ITER.

It is one of the principal research objectives in ITER to sustain a magnetically confined plasma with a fusion gain (the ratio of fusion power to external heating power) of larger than 10 and with a high fusion power output for a long time, in order to establish burning plasma control technique toward the realization of fusion power plants. Since the fusion power is proportional to the square of the plasma pressure (temperature times density), this goal is accomplished only when
    (1) to increase the plasma pressure for larger fusion power output
    (2) to maintain high confinement in order to reduce the heating power required for sustainment of the high plasma pressure
are achieved simultaneously.
A "normalized plasma pressure" is used as a measure of the plasma pressure, while a "confinement enhancement factor" is used as a measure of the confinement performance.

In JT-60, a plasma is heated with fast ions generated inside by neutral beam injection. Since recent studies have revealed the possibility of confinement degradation caused by a loss of fast ions, ferritic steel (ferromagnet) was installed in the vacuum vessel last year in order to correct the magnetic field structure and hence reduce the loss of fast ions.
In the experiment after the ferritic steel installation, a reduction of fast ion losses was confirmed together with confinement improvement as predicted. As a result, we have sustained a high normalized plasma pressure stably with confinement performance higher than before, and extended the duration of a plasma with a value of (normalized plasma pressure) x (confinement enhancement factor) required for ITER up to 28 seconds, which was limited by the available maximum duration of neutral beam injection in JT-60. The result contributes to ensuring the accomplishment of extended burn in ITER.

The above result will be presented at the European Physics Society conference on controlled fusion and plasma physics during June 19 to 23 in Italy.

•Long sustainment of high-confinement, high-pressure plasma in the JT-60 tokamak

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