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2001
The polarization current plays an important role in the evolution of magnetic islands with a width comparable to the characteristic ion orbit width. Understanding the evolution of such small magnetic islands is important for two reasons: (1) to investigate the threshold mechanisms for growth of large-scale islands (e.g., neoclassical tearing modes)…
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2000
H -mode operation has been achieved in high current I p . 200 kA plasmas in the START spherical tokamak for both neutral-beam-injection-heated and Ohmic discharges. The transition to H mode features the development of well-defined edge pedestals in density and temperature, which signifies the formation of an edge-transport barrier, and associated e…
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1999
The peeling mode restricts access to the second stability region of the ideal ballooning mode at the tokamak plasma edge. Using a two-dimensional, high toroidal mode number eigenmode code employing a model tokamak equilibrium, it is shown that a window to second stability exists for a sufficiently deep magnetic well. The different mode structures o…
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1999
The ideal magnetohydrodynamic (MHD) stability of the tokamak edge is analyzed, with particular emphasis on radially localized instabilities; it is proposed that these are responsible for edge pressure gradient limits and edge localized modes (ELMS). Data and stability calculations from DIII-D [to appear in Proceedings of the 16th International Conf…
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1998
A new formalism for analyzing the magnetohydrodynamic stability of a limiter tokamak edge plasma is developed. Two radially localized, high toroidal mode number n instabilities are studied in detail: a peeling mode and an edge ballooning mode. The peeling mode, driven by edge current density and stabilized by edge pressure gradient, has features wh…
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1995
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1995
A kinetic theory for magnetic islands in a low collision frequency tokamak plasma is presented. Self-consistent equations for the islands’ width, w , and propagation frequency, w , are derived. These include contributions from the perturbed bootstrap current and the toroidally enhanced ion polarization drift. The bootstrap current is ind…
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1995
A theory for the existence of noninteracting small-scale, "drift" magnetic islands in a high temperature tokamak plasma is presented. This situation contrasts with that discussed by Rebut and Hugon [Plasma Phys. Controlled Fusion 33, 1085 (1991)] which involves a background "sea" of magnetic turbulence caused by island overlap. The islands are driv…
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1995
Short wavelength fluctuations may be a source of anomalous transport in toroidal plasmas. Early investigations concerned electron and ion modes that occur only at a particular radius and have a localised eigenfunction: such modes do not seem important for transport. Recently, Connor, Taylor and Wilson [1] described electron modes that occur at all …
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1993
An important conclusion of earlier work using the ballooning representation is that shear damping of plasma drift waves may be suppressed in a torus. This application of the formalism requires that the diamagnetic frequency have a maximum and implies that drift modes can exist only at this maximum. Here we show that there is a far more general clas…
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