Progress in tokamak research at MIT

Parker, R.; Greenwald, M.; Luckhardt, S.C.; Marmar, E.S.; Porkoláb, M.; Wolfe, S.

doi:10.1088/0029-5515/25/9/023

Cited by 103 publications

(78 citation statements)

References 28 publications

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“…It has been widely observed that Ohmic energy confinement in tokamaks increases linearly with electron density, and then saturates at a critical density [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15]. An example of this behavior is shown in Fig.1 was obtained from a shot by shot scan of the electron density in 5.2 T, 0.81 MA (q 95 = 4.3) plasmas from Alcator C-Mod [13].…”

Section: Introductionmentioning

confidence: 91%

Ohmic energy confinement saturation and core toroidal rotation reversal in Alcator C-Mod plasmas

et al. 2012

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Ohmic energy confinement saturation is found to be closely related to core toroidal rotation reversals in Alcator C-Mod tokamak plasmas. Rotation reversals occur at a critical density, depending on the plasma current and toroidal magnetic field, which coincides with the density separating the linear Ohmic confinement regime from the saturated Ohmic confinement regime. The rotation is directed co-current at low density and abruptly changes direction to counter-current when the energy confinement saturates as the density is increased. Since there is a bifurcation in the direction of the rotation at this critical density, toroidal rotation reversal is a very sensitive indicator in the determination of the regime change. The reversal and confinement saturation results can be unified since these processes occur at a particular value of the collisionality.

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Section: Introductionmentioning

confidence: 91%

Ohmic energy confinement saturation and core toroidal rotation reversal in Alcator C-Mod plasmas

et al. 2012

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“…For most discharges, the measured TE is greater than the neoAlcator value 3 . The increase in stored energy with ip suggested an L-mode behavior; a linear regression can be performed to calculate the best fit to a power law scaling for the data.…”

Section: A Ohmic L-modementioning

confidence: 75%

Transport experiments in Alcator-C-Mod

et al. 1995

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A series of transport experiments has been carried out in Alcator C-Mod. [Phys Plasmas 1 1511 (1994)] It is found that data from both ohmic and ICRF heated plasmas can be fitted with an L-mode scaling law. The ohmic TE's show no scaling with density in any regime and can reach values of 2-3 times neo-Alcator. Impurity confinement has been studied with the laser blow-off technique with T, showing nearly linear scaling with plasma current. Ohmic and ICRF H-modes are obtained over a wide range of discharge parameters, extending the range in the international database for nB, by almost a factor of 10. The power threshold for ELM-free discharges is in rough agreement with the scaling P/S = .044 nB. Energy diffusivities of ohmic and ICRF heated plasmas have been measured from local analysis of plasma profiles and power fluxes. The same analysis produces a value for plasma resistivity which lies between the Spitzer and neo-classical calculations. Analysis of plasma transients have yielded values for particle diffusivity and convection velocity.

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“…The components in the RF section and the first amplifier for 2-18 GHz signals are installed in front of the diagnostic port as shown in Figure 2(b). The current CECE IF section has 8 channels, two of which are tunable (6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18). More details about Correlation ECE diagnostic in C-Mod can be found in [5] and upgrades in the IF section will be published in the future [6].…”

Section: Description Of the Correlation Ece Diagnostic In Alcator C-modmentioning

confidence: 99%

“…One hypothesis is that a change of the dominant type of turbulence is responsible for the ohmic confinement transition: Trapped Electron mode (TEM) is dominant in the LOC regime and Ion Temperature Gradient (ITG) mode is dominant in the SOC regime. Although the LOC/SOC transition has been studied extensively in the past [8][9][10][11][12][13], the transition still remains a mystery in fusion transport research. In previous studies, only line integrated n e fluctuations were measured across the LOC/SOC transition [9,13], and local turbulence changes and other fluctuating quantities, such as potential and temperature fluctuations, were not available.…”

Section: T E Fluctuation Measurements Across Rotation Reversalsmentioning

confidence: 99%

Correlation ECE diagnostic in Alcator C-Mod

Sung

White

Howard

et al. 2015

EPJ Web of Conferences

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Abstract. Correlation ECE (CECE) is a diagnostic technique that allows measurement of small amplitude electron temperature, T e , fluctuations through standard cross-correlation analysis methods. In Alcator C-Mod, a new CECE diagnostic has been installed [Sung RSI 2012], and interesting phenomena have been observed in various plasma conditions. We find that local T e fluctuations near the edge (ρ ∼ 0.8) decrease across the linearto-saturated ohmic confinement transition, with fluctuations decreasing with increasing plasma density [Sung NF 2013], which occurs simultaneously with rotation reversals [Rice NF 2011]. T e fluctuations are also reduced across core rotation reversals with an increase of plasma density in RF heated L-mode plasmas, which implies that the same physics related to the reduction of T e fluctuations may be applied to both ohmic and RF heated L-mode plasmas. In I-mode plasmas, we observe the reduction of core T e fluctuations, which indicates changes of turbulence occur not only in the pedestal region but also in the core across the L/I transition [White NF 2014]. The present CECE diagnostic system in C-Mod and these experimental results are described in this paper.

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Progress in tokamak research at MIT

Cited by 103 publications

References 28 publications

Ohmic energy confinement saturation and core toroidal rotation reversal in Alcator C-Mod plasmas

Ohmic energy confinement saturation and core toroidal rotation reversal in Alcator C-Mod plasmas

Transport experiments in Alcator-C-Mod

Correlation ECE diagnostic in Alcator C-Mod

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