A Helias-Heliac hybrid stellarator

Abstract

Placing an 1 = 1 continuous helical coil with a pitch modulation in an axisymmetric toroidal magnetic field, a helical axis configuration was obtained with characteristics similar to the Heiias configuration for Wendelstein 7-X (W7-X). In the four pitch case, a device with an aspect ratio of 4-5 and good accessibility becomes possible, although a very weak magnetic hill exists.In a particular finite 0 magnetohydrodynamic (MHD) equilibrium, the magnetic well appears in the whole region for a central beta value of p(0) -1%. About a quarter of the particles at half radius are lost at f l = 0; however, both the radial electric field and the finite f l effect improve the particle orbit confinement significantly. The possibility of an open divertor is shown.

Study of a helical axis heliotron

“…However, it is noted that for the I TB = 0 case, total trapped particles increase and minor radius decreases. Thus, for realizing an aspect ratio of eight, R TF = 2.5 seems to be close to the optimum, and it does not contradict the MHD stability property that the Mercier stability criterion is satisfied up to β ≈ 4% [4]. In Ref.…”

“…It has been shown from the analytical expression for a simple magnetic field model that a negative value of ε b /ε h reduces the neoclassical ripple transport if ε b /ε h is finite, though these are symmetry breaking components [4]. We will show the physical mechanism of ripple transport reduction due to negative ε b /ε h .…”

“…In a small size experimental device (major radius ≈ 1 m), in order to allow experimental flexibility and easy access to the plasma, we employ a continuous helical field (HF) coil. Here the configuration produced by an L = 1/M = 4 continuous HF coil with pitch modulation of α = −0.4 has been chosen, where the helical coil winding law is defined as θ = π + (M/L)φ − α sin{(M/L)φ} [4]. Here θ (φ) is a poloidal (toroidal) angle variable.…”

Magnetic diagnostics: General principles and the problem of reconstruction of plasma current and pressure profiles in toroidal systems

“…We should also note that in quasi-helical systems, irrespective of their particular realization, the spectrum of the magnetic field contains only a few harmonics [48][49][50][51][52][53][54][55][56], and the amplitudes of only two or three of these are changed appreciably with growing β. Hence, also in this case, little information could be potentially extracted from magnetic measurements.…”

Realization and classification of symmetric stellarator configurations through plasma boundary modulations

“…The proposal for the next experimental device at Kyoto University is based on the modulated L = 1 helical coil system [3]. It should be noted that this magnetic configuration has been obtained through co-operation with P. Garabedian (cf., the Helias-Heliac Hybrid (HHH) stellarator) [4,5].…”