Modifications in turbulence and edge electric fields at the L–H transition in the DIII‐D tokamak

The L to H transition in the DIII‐D tokamak [Plasma Physics and Controlled Nuclear Fusion Research, 1986 (IAEA, Vienna, 1987), Vol. I, p. 159] is associated with two clear signatures: edge density fluctuations are abruptly suppressed (in ≊100 μsec), while the edge poloidal rotation velocity vθ increases, implying that the radial electric field Er becomes more negative. Detailed new spectroscopic profile measurements show that the changes in vθ and Er generate a region of sheared electric field and poloidal flow of width ≊3–5 cm. This region develops simultaneously with, and has the same spatial extent as, the edge fluctuation suppression zone as measured using a reflectometer system. Furthermore, the radial extent of the shear and fluctuation suppression zones encompass the location of the H‐mode edge transport barrier. These observations are consistent with recent theoretical models of the L–H transition, and a comparison with these theories is presented. Data are also presented on the evolution of edge ...

[1]  E. Doyle,et al.  Physics of the L to H transition in the DIII-D tokamak , 1990 .

[2]  Tadashi Sekiguchi,et al.  Plasma Physics and Controlled Nuclear Fusion Research , 1987 .

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

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

[5]  R. Slusher,et al.  New fluctuation phenomena in the H-mode regime of poloidal-divertor tokamak plasmas , 1984 .

[6]  V. Lynch,et al.  Low‐n stability calculations for three‐dimensional stellarator configurations , 1990 .

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

[8]  P. Diamond,et al.  Neoclassical poloidal and toroidal rotation in tokamaks , 1991 .

[9]  Brown,et al.  H-mode behavior induced by cross-field currents in a tokamak. , 1989, Physical review letters.

[10]  E. Doyle,et al.  Far‐infrared heterodyne scattering to study density fluctuations on the DIII‐D tokamak , 1990 .

[11]  F. Wagner,et al.  Regime of Improved Confinement and High Beta in Neutral-Beam-Heated Divertor Discharges of the ASDEX Tokamak , 1982 .

[12]  W. A. Peebles,et al.  X‐mode broadband reflectometric density profile measurements on DIII‐D , 1990 .

[13]  M. Keilhacker,et al.  Confinement Studies in L and H-Type ASDEX Discharges , 1984 .

[14]  B. G. Logan,et al.  Enhanced confinement in tokamaks , 1990 .

[15]  L. Lao,et al.  Plasma shaping, edge ballooning stability and ELM behaviour in DIII-D , 1990 .

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

[17]  Lao,et al.  Study of giant edge-localized modes in DIII-D and comparison with ballooning theory. , 1988, Physical review letters.

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

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

[20]  K. Burrell,et al.  High spatial and temporal resolution visible spectroscopy of the plasma edge in DIII‐D , 1990 .

[21]  Burrell,et al.  Role of edge electric field and poloidal rotation in the L-H transition. , 1990, Physical review letters.

[22]  D. Brower,et al.  Fluctuation measurements in the DIII‐D and TEXT tokamaks via collective scattering and reflectometry , 1990 .

[23]  P. Gohil,et al.  Multipoint Thomson scattering diagnostic for DIII-D , 1988 .

[24]  K. Burrell,et al.  Spectroscopic study of edge poloidal rotation and radial electric fields in the DIII‐D tokamak (invited) , 1990 .

[25]  F. Hinton,et al.  Theory of plasma transport in toroidal confinement systems , 1976 .

[26]  F. Wagner,et al.  Development of an Edge Transport Barrier at the H-Mode Transition of ASDEX , 1984 .

[27]  Wootton,et al.  Evidence for confinement improvement by velocity-shear suppression of edge turbulence. , 1990, Physical review letters.

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