H-mode of W7-AS stellarator

In W7-AS the H-mode has been observed for the first time in a currentless stellarator plasma. H-modes are achieved with 0.4 MW Electron Cyclotron Resonance Heating with 140 GHz at 2.5 T and high density, with 70 GHz at 1.25 T and lower density and with neutral beam injection. The H-phases display all characteristics known from tokamak H-modes including the development of an edge transport barrier, an increase of the poloidal impurity flow velocity at the edge, the reduction of edge turbulence and ELMs. The power threshold for the H-mode seems to be lower than that in tokamaks and is in agreement with an neBT scaling. Major differences to the divertor H-mode is the small increase in energy content of maximally 30%, the lack of a strong isotope effect both in threshold and in H-mode characteristics and a peculiarly narrow operational range in iota.

[1]  G. M. Staebler,et al.  Particle and energy confinement bifurcation in tokamaks , 1993 .

[2]  Drake,et al.  Spontaneous poloidal spin-up of tokamaks and the transition to the H mode. , 1991, Physical review letters.

[3]  R. Neu,et al.  H-mode results in ASDEX Upgrade , 1994 .

[4]  F. Sardei,et al.  The Impact of Boundary Plasma Conditions on the Plasma Performance of the Wendelstein 7-AS Stellarator , 1992 .

[5]  W. Kerner,et al.  Studies of edge localized modes on ASDEX , 1992 .

[6]  E. Ascasibar,et al.  Detailed investigation of the vacuum magnetic surfaces on the W7-AS stellarator , 1993 .

[7]  A. Fukuyama,et al.  The impact of improved confinement on fusion research , 1991 .

[8]  ASDEX-Upgrade team,et al.  The H-Mode of ASDEX , 1989 .

[9]  E. C. Crume,et al.  Bifurcation theory of poloidal rotation in tokamaks: A model for L-H transition. , 1989, Physical review letters.

[10]  McGuire,et al.  Peaked density profiles in circular-limiter H modes on the TFTR tokamak. , 1990, Physical review letters.

[11]  G. Staebler,et al.  Turbulent viscosity bifurcation and the H-mode , 1993 .

[12]  R. J. Groebner,et al.  An emerging understanding of H-mode discharges in tokamaks , 1993 .

[13]  E. Strumberger,et al.  Magnetic field line diversion in Helias stellarator configurations: perspectives for divertor operation , 1992 .

[14]  U. Stroth,et al.  Transport in toroidal devices-the experimentalist's view , 1992 .

[15]  Y. Takeiri,et al.  Scalings of energy confinement and density limit in stellarator/heliotron devices , 1990 .

[16]  Paul W. Terry,et al.  Influence of sheared poloidal rotation on edge turbulence , 1990 .

[17]  V. Lebedev,et al.  Dynamics of L to H bifurcation , 1994 .

[18]  L. Giannone,et al.  Physics optimization of stellarators , 1992 .

[19]  H. Zohm,et al.  The isotope effect in ASDEX , 1993 .

[20]  F. Sardei,et al.  Transport in Stellarators , 1993 .

[21]  Geist,et al.  H mode of the W 7-AS stellarator. , 1993, Physical review letters.

[22]  Itoh.  Model of L- to H-mode transition in tokamak. , 1988, Physical review letters.

[23]  Stroth,et al.  Dimensionally similar discharges in the W7-AS stellarator. , 1993, Physical review letters.

[24]  E. Doyle,et al.  Physics of the L-mode to H-mode transition in tokamaks , 1992 .

[25]  Fujita,et al.  Edge electric-field profiles of H-mode plasmas in the JFT-2M tokamak. , 1990, Physical review letters.

[26]  K. Lackner,et al.  Tokamak Confinement in Relation to Plateau Scaling , 1990 .