Study of MHD Equilibrium and Stability for Heliotron/Torsatron with Helical Axis

• Published in: Journal of the Physical Society of Japan Vol. 64; no. 11; pp. 4175 - 4184
• Main Authors: MATSUMOTO, T, NAKAMURA, Y, WAKATANI, M
• Format: Journal Article
• Language: English
• Published: Tokyo Institute of Pure and Applied Physics 01-11-1995; Physical Society of Japan; The Physical Society of Japan
• Subjects: Exact sciences and technology; Magnetic confinement and equilibrium; Physics; Physics of gases, plasmas and electric discharges; Physics of plasmas and electric discharges; Stellarators, spheromaks, compact tori, bumpy tori, and other toroidal confinement devices; Stellarators, torsatrons, heliacs, bumpy tori, and other toroidal confinement devices; Theoretical study; LHD device; Heliotron; MHD equilibrium; Torsatron stellarators; MHD stability
• ISSN: 0031-9015; 1347-4073
• DOI: 10.1143/JPSJ.64.4175

MHD equilibrium and stability of LHD (Large HelicalDevice) are studied when circular plane magnetic axis is distortedinto spatial helical one by introducing unbalance between two helicalcoil currents. The helical axis effect increases rotational transformwith enhancing magnetic hill at zero beta, where beta is the ratio ofplasma pressure to magnetic pressure. The significant effect ofhelical magnetic axis is reduction of average radius of the outermostflux surface or elimination of edge region with large magnetichill. For finite beta plasmas this reduction of average plasma radiushas substantial stabilizing effect on pressure driven MHD modesthrough enhancement of magnetic well produced by both Shafranov shiftand helical shift of magnetic axis. However, by comparing the helicalaxis configuration of LHD to planer axis configuration with the sameradius produced by using limiter, the change of equilibrium andstability due to the helical axis is found weak in the LHD case. Themerit of the helical axis configuration is controllability of averageplasma radius without limiter.