Fusion Science and Technology / Volume 58 / Number 1 / July 2010 / Pages 141-149
Chapter 3. Confinement and Transport / Special Issue on Large Helical Device (LHD)
The magnetic configuration of the Large Helical Device (LHD) changes with the increment in beta. To distinguish between the beta effect and the configuration effect on the gradual degradation of the global confinement property in the high-beta LHD plasmas, the local transport characteristics are studied by considering the change in the major radius of the magnetic flux surface with the beta value. A model transport coefficient that has the same nondimensional parameter dependence as the international stellarator scaling 2004 (ISS04) is introduced and used as the reference. The dependence of the local transport characteristics in high-beta plasmas on the major radial position of a geometric center of the magnetic flux surface is compared with that in low-beta plasmas. The dependence of the local transport in the peripheral region is correlated more with beta itself than the magnetic configuration effect, whereas the core transport appears to be correlated more with the configuration effect. The comparison of the experimental transport coefficients and the calculation results shows that the resistive pressure gradient-driven turbulence can be considered as one of the causes of this degradation.