Fusion Science and Technology / Volume 58 / Number 1 / July 2010 / Pages 12-28
Chapter 2. LHD Progress / Special Issue on Large Helical Device (LHD)
Progress in the integrated development of the helical system in the Large Helical Device (LHD) is described in this paper. Understanding of net current-free plasmas has been deepened in the extended operational regime. Geometrical optimization based on neoclassical theory has revealed that good confinement, equivalent to the tokamak H-mode, can be obtained in the collisionless regime. This approach has also demonstrated that anomalous transport is reduced simultaneously, which poses a working hypothesis that optimization of neoclassical transport suppresses turbulent anomalous transport as well. With regard to the magnetohydrodynamic instability, LHD has discovered that interchange instability is benign in the magnetic hill. These two findings have produced a synergistic effect on the enhancement of confinement and plasma . Remarkable proof of the advantage of helical systems can be seen in very high density operation, which is not accessible in tokamaks. Abundant integrated knowledge about three-dimensional physics has been extracted from these achievements. This progress is important in the assessment of the potential of a helical fusion reactor and makes a significant complementary contribution to tokamaks as well.