Kelvin-Helmholtz instabilities in tokamak edge plasmas

The parallel Kelvin–Helmholtz instability is investigated as a possible explanation for poloidal asymmetries of density fluctuations which reverse with the plasma current direction. It is shown that these modes are localized around the position where the radial gradient of parallel velocity is maximum. Two mechanisms lead to unstable Kelvin–Helmholtz modes; the acceleration of ions in a presheath and the anomalous Stringer spin-up due to asymmetries of the particle flux. Up–down asymmetries are explained by combining these two effects. Depending on the limiter configuration, the Stringer effect amplifies or weakens the flow due to presheath acceleration. This type of asymmetry reverses with the plasma current direction.

[1]  P. Diamond,et al.  DRIFT WAVE PROPAGATION AS A SOURCE OF PLASMA EDGE TURBULENCE , 1994 .

[2]  M. Rosenbluth,et al.  Electron‐temperature‐gradient‐driven instability in tokamak boundary plasma , 1993 .

[3]  T. Stringer,et al.  Diffusion in Toroidal Plasmas with Radial Electric Field , 1969 .

[4]  E. Doyle,et al.  Poloidally asymmetric response of turbulence to the H mode on the CCT tokamak , 1993 .

[5]  X. Garbet,et al.  Tokamak turbulence with stochastic field lines , 1998 .

[6]  K. L. Sidikman,et al.  Bifurcations and modulational interaction in negative compressibility turbulence , 1994 .

[7]  X. Garbet,et al.  Radial propagation of turbulence in tokamaks , 1994 .

[8]  D. Goebel,et al.  ALT-II toroidal belt pump limiter performance in TEXTOR , 1989 .

[9]  Y. Sarazin,et al.  Intermittent particle transport in two-dimensional edge turbulence , 1998 .

[10]  Ding Li,et al.  Non-ideal Kelvin-Helmholtz instabilities of a plasma edge with parallel mass flow , 1992 .

[11]  R. Chodura,et al.  Plasma–wall transition in an oblique magnetic field , 1982 .

[12]  A. Hassam,et al.  Loss of static equilibrium, flow generation and the development of turbulence at the edge of tokamaks , 1992 .

[13]  D. Brower,et al.  The spectrum, spatial distribution and scaling of microturbulence in the TEXT tokamak , 1987 .

[14]  M. Tendler,et al.  Different scenarios of transitions into improved confinement modes , 1997 .

[15]  J. Drake,et al.  Three-dimensional collisional drift-wave turbulence: Role of magnetic shear , 1996 .

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

[17]  P. Stangeby.  Plasma sheath transmission factors for tokamak edge plasmas , 1984 .

[18]  C. W. Horton,et al.  Amplitude Limitation of a Collisional Drift Wave Instability , 1971 .

[19]  A. J. Allen,et al.  Particle drift effects on the Alcator C-Mod divertor , 1996 .

[20]  P. C. Stangeby,et al.  Plasma boundary phenomena in tokamaks , 1990 .

[21]  P. Stangeby,et al.  The nature of plasma fluxes to surfaces nearly tangential to the magnetic field , 1992 .

[22]  S. Wolfe,et al.  Marfe: an edge plasma phenomenon , 1984 .

[23]  R. Slusher,et al.  Low‐frequency density fluctuations in a tokamak plasma , 1985 .

[24]  A. Rogister.  A plasma edge microinstability with up-down asymmetry , 1987 .

[25]  W. Horton,et al.  Structure of parallel-velocity-shear-driven mode in toroidal plasmas , 1998 .

[26]  Wilson,et al.  Shear damping of drift waves in toroidal plasmas. , 1993, Physical review letters.

[27]  J. Gunn.  Two-dimensional quasineutral PIC simulation of a Gundestrup probe , 1998 .

[28]  B. Lipschultz,et al.  Poloidal asymmetries in the scrape-off layer plasma of the Alcator C tokamak , 1987 .

[29]  N. D’angelo,et al.  Kelvin—Helmholtz Instability in a Fully Ionized Plasma in a Magnetic Field , 1965 .

[30]  Hutchinson,et al.  Ion collection by probes in strong magnetic fields with plasma flow. , 1987, Physical review. A, General physics.

[31]  M. Rosenbluth,et al.  Parallel velocity shear instabilities in an inhomogeneous plasma with a sheared magnetic field , 1973 .

[32]  V. Rozhansky,et al.  Analytical studies of multidimensional plasma transport in the scrape-off layer , 1992 .

[33]  E. Mazzucato,et al.  Scaling of density fluctuations in PDX , 1985 .

[34]  A. Chankin,et al.  Experimental study of plasma fluxes in the shadow of a scoop limiter on T-10 , 1987 .

[35]  C. Gil,et al.  Particle exhaust studies in Tore Supra with a pump limiter , 1990 .