Free boundary three-dimensional anisotropic pressure magnetohydrodynamic equilibria with nested magnetic flux surfaces are computed through the minimisation of the plasma energy functionalThe plasma-vacuum interface is varied to guarantee the continuity of the total pressure [p ⊥ + B 2 /(2μ 0 )] across it and the vacuum magnetic field must satisfy the Neumann boundary condition that its component normal to this interface surface vanishes. The vacuum magnetic field corresponds to that driven by the plasma current and external coils plus the gradient of a potential function whose solution is obtained using a Green's function method. The energetic particle contributions to the pressure are evaluated analytically from the moments of the variant of a biMaxwellian distribution function that satisfies the constraint B · ∇F h = 0. Applications to demonstrate the versatility and reliability of the numerical method employed have concentrated on high-β off-axis energetic particle deposition with large parallel and perpendicular pressure anisotropies in a 2-field period quasiaxisymmetric stellarator reactor system. For large perpendicular pressure anisotropy, the hot particle component of the p ⊥ distribution localises in the regions where the energetic particles are deposited. For large parallel pressure anisotropy, the pressures are more uniform around the flux surfaces.

A low-aspect-ratio quasi-axisymmetric stellarator CHS-qa was designed. An optimization code was used to design a magnetic field configuration with evaluations of physical quantities of quasi-axisymmetry, rotational transform, MHD stability and alpha particle collisionless confinement. It is shown that the electron neoclassical diffusion coefficient is similar to tokamaks for the low collisional regime. A self-consistent equilibrium with bootstrap current confirms the global mode stability up to 130 kA for R = 1.5 m and Bt = 1.5 T device. The evaluation of plasma rotation viscosity is greatly suppressed compared with conventional stellarators. Engineering design was completed with 20 main modular coils and auxiliary coils which provide flexibility of configuration study for confinement improvement and MHD stability.

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Inward turbulent particle transport observed in the rf heated plasma of the H-1 toroidal heliac is reproduced in the CHS heliotron/torsatron by generating a region of positive radial electric field shear (E'(r)>0) using electron cyclotron resonance heating of the plasma edge. Empirical condition of the radial reversal of the turbulent flux derived from two experiments indicates that the shear electric field might be universally responsible for the recorrelation of the density and plasma potential fluctuations leading to the inward transport.

The purpose of this work is to reveal the effects of the energetic particle mode (EPM) on fast-ion transport and consequent fast-ion loss in the compact helical system (CHS). For this purpose, fast particle diagnostics capable of following fast events originating from the EPM (f < 100 kHz) and from the toroidicity-induced Alfvén eigenmode (TAE) (f = 100-200 kHz) are employed in CHS. Experiments show that the EPM excited by co-circulating fast ions in an outward-shifted configuration is identified as a mode of m/n = 3/2 and can enhance fast-ion loss when its magnetic fluctuation amplitude exceeds ∼4 × 10 −5 T at the magnetic probe position. The lost fast-ion probe (LIP) located at the outboard side of the torus indicates that bursting EPMs lead to periodically enhanced losses of co-going fast ions having smaller pitch angles in addition to losses of marginally co-passing fast ions. Coinciding with EPM bursts, the Hα light detector viewing the peripheral region at the outboard side also shows large pulsed increases similar to that of the LIP whereas the detector viewing the peripheral region at the inboard side does not. This is also evidence that fast ions are expelled to the outboard side due to the EPM. The charge-exchange neutral particle analyser indicates that only fast ions whose energy is close to the beam injection energy E b are strongly affected by EPM, suggesting in turn that observed EPMs are excited by fast ions having energy close to E b .