Configuration flexibility and extended regimes in Large Helical Device

Fusion Science and Technology

et al. 2006

Substantial progress has been achieved to raise the plasma beta in stellarators and helical systems by high power neutral beam heating, approaching reactor relevant values [1][2][3]. The achievement of high-β operation is closely linked with configuration effects on the confinement and with magnetohydrodynamic (MHD) stability. However, the observed pressure gradients indicate some mitigation of the effects on the plasma confinement, presumably because of the high collisionality of high-β plasmas and island healing effects ). As far as operational limits by pressure driven MHD instabilities are concerned, only weak confinement degradation effects are usually observed, even in linearly unstable regimes.The impact of the results concerning high-β operation in W7-AS and LHD on the future stellarator programme will be discussed, including relations to tokamak research. Some of the future key issues appear to be: -the control of the magnetic configuration (including toroidal current control), -the modification of confinement and MHD properties towards the low collisional regime, -and the compatibility of high-β regimes with power and particle exhaust requirements to achieve steady state operation.

Section: High-β Operation In W7-as and Lhd: Global Confinement And Opmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Significance of MHD Effects in Stellarator Confinement

Weller

Sakakibara

Fusion Science and Technology

et al. 2006

“…In this paper, the collisionless zonal-flow response in helical systems with E r is theoretically described with a modified expression for the probability of the transition from the toroidally-trapped orbit to the helical-ripple-trapped orbit. Besides, the linear gyrokinetic Vlasov simulation over the poloidally global domain [5] is done to investigate effects of the E × B rotation on the residual zonal flow in a model magnetic geometry which corresponds to an inward-shifted LHD configuration [12]. Comparing the theory and simulation results, we examine the validity of the theoretical prediction about enhancement of the residual zonal-flow level due to E r .…”

Section: Introductionmentioning

confidence: 99%

Enhancement of Residual Zonal Flows in Helical Systems with Equilibrium Radial Electric Fields

Sugama

2010

Contrib. Plasma Phys.

The collisionless response of the zonal-flow potential to the initial particle distribution and turbulence source is theoretically described for helical systems with equilibrium radial electric fields driving the poloidal E × B rotation of helical-ripple-trapped particles. Theoretically predicted enhancement of the residual zonal-flow potential due to the E × B rotation is verified by the linear gyrokinetic Vlasov simulation using the poloidally global domain for a model magnetic geometry corresponding to the inward-shifted LHD configuration.

“…In the past designs of LHD-type heliotron reactors, FFHR-2 and FFHR-2m1 [2], γ = 1.15 and outward-shifted configuration (R ax /R c = 3.75/3.9) were adopted to get as a large blanket space as possible with a compact size. On the other hand, relatively good particle confinement has been observed in LHD with inward-shifted configuration (R ax = R c ) because of the decrease in effective helical ripple loss of neoclassical and anomalous transport [3].…”

Section: Introductionmentioning

confidence: 99%

Core Plasma Design of a Heliotron Reactor

Goto

Suzuki

et al. 2010

Contrib. Plasma Phys.

The design of a core plasma with the LHD-type heliotron configuration has been advanced. Recent design study of a LHD-type heliotron reactor has shown that the increase in the reactor size is a possible solution to secure a sufficient blanket space. The increase in the reactor size enables a flexible selection of plasma configurations. In this respect, a commercial plant design with the plasma configuration which has a similar shape to that of LHD high-beta plasma discharge was carried out. A parametric scan with a system design code showed that there exists the design window with engineering constraints and the physics constraints which can be extrapolated from the present experimental achievements. Finite-beta equilibrium calculations by VMEC code showed that the last closed flux surface which has almost the same shape as that in vacuum equilibrium can be obtained by applying an appropriate additional vertical field.