Enhanced confinement in tokamaks

Stambaugh, R.D.; Wolfe, S.; Hawryluk, R. J.; Harris, J. H.; Biglari, H.; Prager, S. C.; Goldston, Robert James; Fonck, R. J.; Ohkawa, T.; Logan, B.G.; Oktay, Erol

doi:10.1063/1.859361

Cited by 51 publications

(25 citation statements)

References 104 publications

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“…L-Mode scaling has been theorized to be a manifestation of several underlying transport mechanisms and a lower bound for confinement [9]. When any of these mechanisms are suppressed, an enhanced confinement mode is entered.…”

Section: Previous Resultsmentioning

confidence: 99%

Measurement of particle transport coefficients on Alcator C-Mod

Luke¹

1994

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The study of particle transport is increasingly important for fusion research. During the 1993 and 1994 campaigns of Alcator C-Mod, one observed phenomenon was the divertor detachment. This phenomenon was characterized by reduced particle and energy flows to the divertor plates and is of interest as a solution to the heat loading problem of the first wall. A sharp rise in the central electron density was observed after detachment. The goal of this thesis was to study the behavior of the plasma transport during the divertor detachment in order to explain this density rise.The measurement of particle transport coefficients requires sophisticated diagnostic tools. A two color interferometer system was developed and installed on Alcator C-Mod to measure the electron density with high spatial (~ 2 cm ) and high temporal (5 1.0 ms) resolution. The system consists of 10 CO 2 (10.6 pm) and 4 HeNe ( .6328 4m) chords that are used to measure the line integrated density to within 0.08 CO 2 degrees or 2.3x 1016 m-2 theoretically.Using the two color interferometer, a series of gas puffing experiments were conducted. The density was varied above and below the threshold density for detachment at a constant magnetic field and plasma current. Using a gas modulation technique, the particle diffusion, D, and the convective velocity, V, were determined. Profiles were inverted using a SVD inversion and the transport coefficients were extracted with a time regression analysis and a transport simulation analysis. Results from each analysis were in good agreement.Measured profiles of the coefficients incriased with the radius and the values were consistent with measurements from other experiments. The values exceeded neoclassical predictions by a factor of 10. The profiles also exhibited an inverse dependence with plasma density. The scaling of both attached and detached plasmas agreed well with this inverse scaling. This result and the lack of change in the energy and impurity transport indicate that there was no change in the underlying transport processes after detachment. On the contrary, measurements of the Ha radiation and argon transport were consistent with a change in the electron source at the edge. Thus, the rise in central density was due to an increase in the overall electron source or a improvement in fueling efficiency and not due to an improvement in the core particle transport.

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Section: Previous Resultsmentioning

confidence: 99%

Measurement of particle transport coefficients on Alcator C-Mod

Luke¹

1994

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“…The damping ͑22͒ also supports an improvement in confinement with current and ion mass. 2 We also note that the assumption of large means that the L to H mode transition is triggered by a strong heat flow. The present results again emphasize the importance of toroidal effects and the perpendicular dynamics.…”

Section: ͑32͒mentioning

confidence: 99%

On the high-confinement-mode equilibrium in tokamak plasmas

Singh

Weiland

1999

Physics of Plasmas

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“…The traditional approach to the profile structure problem has been via transport analysis, using a theoretically or empirically predicted local transport coefficient. This method of approach has had variable success, 10 but has not yielded very much generic insight into the structure of profiles on account of the complexity of the local transport model. A naturally complementary method is via the methodology of selforganized criticality ͑SOC͒ theory.…”

Section: Introductionmentioning

confidence: 99%

On the statistical mechanics of self-organized profiles

1996

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The radial structure of tokamak profiles determined by anomalous transport is elucidated by studying the statistical mechanics of a sand pile automaton for which the toppling conditions depend on local gradient, alone. In this representation, the sand pile dynamics is Markovian, and spatial profiles may be obtained from calculated expectation values of the local gradient. The Markovian structure of the dynamics is exploited to analytically derive a local gradient probability distribution function from a generalized kinetic equation. For homogeneous, weak noise, the calculated expectation value of the gradient is well below the marginally stable state. In the over-driven limit ͑i.e., strong homogeneous noise͒, a region of super-critical gradient is shown to form near the bottom of the pile. For the case of localized noise, the mean self-organized profile is always sub-critical. These results are consistent with numerical studies of simple automata. Their relevance to and implications for tokamak confinement are discussed.

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Enhanced confinement in tokamaks

Cited by 51 publications

References 104 publications

Measurement of particle transport coefficients on Alcator C-Mod

Measurement of particle transport coefficients on Alcator C-Mod

On the high-confinement-mode equilibrium in tokamak plasmas

On the statistical mechanics of self-organized profiles

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