Summary of Experimental Results in LHD

Since the successful production of the first plasma in l998, outstanding plasma parameters have been achieved. The eLectron temperature of 10 keV, ion temperature of 13.5 keV, plasma stored energy of l.3 MJ have been recorded independently during 7 years operation in LHD. These results show that LHD has plasma confinement properties comparable to those of the world's largest fusion machines. The specific feature of steady state operation of LHD is also demonstrated by a more than 1 hour discharge or by sustaining a long pulse discharge with 1.3 GJ of input energy.

Attained Plasma Parameters

Beta value is the figure of merit which indicates the efficien cy of the plasma confinement.It is defined as the ratio of the plasma pressure to the magnetic Pressure.Economical magnetic fusion confinement devices are required to achieve a beta value of more than 5%.The figure on the right shows the recorded beta values in world wide helical plasma confinement devices.The beta value in LHD extends year by year and is breaking new ground.

Experimental Highlight

All of the confining magnetic field is produced by super con ducting magnets in LHD and the magnetic configuration is in principle suitable for steady state operation. ln the 8th experimental campalgn, high temperature plasma produc tion and long time duration sustainment was demonstrated using a steady state heating scheme.Figures on the right show the wave forms of a shot achieved using a heating input energy of 1.3GJ.This is a new area in the fusion plas ma experiment.The traces in the top column show the input power.powers from an ion and electron cyclotron heating system are 520 kW andl 110kW, respectively.NBI power of 25 sec pulse length is injected repetitively.The sec ond and third columns show the behaviors of ion tempera ture and electron density respectively.Plasma with a central ion temperature of 2 keV and an electron density of 7-8x 1018m-3 is maintained steadily and stably for more than 30 min. Bottom second column show the plasma radiation mainly emitted by impurities.This shows the accumulation of impurities is not yet a severe problem in this discharge. Bottom blue and red lines indicate the variation of the tem perature rise in different diverter positions.The bottom green line shows the time variation of the magnetic axis position, which is actively varied in order to mitigate heat concentration on the diverter plates. The figure on the left shows the progress of several import ant plasma parameters, electron and ion temperatures and plasma duration time by experimental campaign. Each experimental campalgn of about a half of a year was performed once a year except the first and second cam palgns in 1998.

Recent Results of Theory and Computer Simulation Researches

A new super computer system has been introduced since 2003 (main memories;1.3tera Bytes, calculation speed;1.41tera Flops) and is now in full operation pro ducing new knowledge and information on fusion plasmas and complexity science.Fur ther,remarkable progress has been made in computational techniques and related utilites. The new system achieved a world record in calculation effi ciency.

Result > Summary of Experimental Results in LHD
Result > Summary of Experimental Results in LHD