Characterization of enhanced Dα high-confinement modes in Alcator <i>C</i>-Mod

Greenwald, M.; Boivin, R. L.; Bonoli, P. T.; Budny, R.; Fiore, C. L.; Goetz, J. A.; Granetz, R.; Hubbard, A.; Hutchinson, I. H.; Irby, J.; LaBombard, B.; Lin, Y.; Lipschultz, B.; Marmar, E.; Mazurenko, A.; Mossessian, D.; Pedersen, T. S.; Pitcher, C.S.; Porkoláb, M.; Rice, J.E.; Rowan, W. L.; Snipes, J. A.; Schilling, G.; Takase, Y.; Terry, J. L.; Wolfe, S.; Weaver, James L.; Welch, B.; Wukitch, S.

doi:10.1063/1.873451

Cited by 189 publications

(124 citation statements)

References 16 publications

(19 reference statements)

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“…Systematic studies of the parameters which favour access to the regime have been performed. As has previously been reported 24 , the most consistently important conditions are the safety factor, q, and the plasma triangularity, δ. In deuterium plasmas, low q 95 (< 3.5) and low δ (< 0.3) favour ELM-free discharges.…”

Section: Conditions To Access the Eda Regimementioning

confidence: 74%

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Pedestal profiles and fluctuations in C-Mod enhanced D-alpha H-modes

et al. 2001

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High resolution measurements on the Alcator C-Mod tokamak [I.H. Hutchinson et al,Phys. Plasmas 1, 1551 (1994)] of the transport barrier in the "Enhanced D α " (EDA) regime, which has increased particle transport without large edge localized modes, show steep density and temperature gradients over a region of 2-5 mm, with peak pressure gradients up to 12 MPa/m. Evolution of the pedestal at the LH transition is consistent with a large, rapid drop in thermal conductivity across the barrier. A quasi-coherent fluctuation in density, potential and B pol , with f o~5 0-150 kHz and k θ~ 4 cm -1 , always appears in the barrier during EDA, and drives a large particle flux. Conditions to access the steady-state EDA regime in deuterium include δ=> 0.35, q 95 > 3.5 and L-mode target density e n > 1.2 x 10 20 m -3 . A reduced q 95 limit is found for hydrogen discharges.2

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Section: Conditions To Access the Eda Regimementioning

confidence: 74%

“…The lower τ p in EDA has been shown most clearly by impurity ablation experiments 24 , and is also reflected by a decrease in the rates of rise of both density and radiated power. n e and P rad usually reach a steady state, as shown in Fig.…”

Section: A Global Characteristicsmentioning

confidence: 98%

Pedestal profiles and fluctuations in C-Mod enhanced D-alpha H-modes

et al. 2001

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“…Surface films can dramatically alter the relationship between surface temperature and heat flux, and if not properly considered, can lead to erroneous negative heat fluxes [4]. We employ a novel Fourier analysis method to estimate the thermal resistance of films: (1) computing the complex thermal impedance of a bare surface using measured temperatures and modeled heat fluxes and (2) adding to this a minimal amount of surface thermal resistance to eliminate negative EDA H-modes are steady-state discharges in which the pedestal is regulated by a continuous 'quasi-coherent' edge mode, rather than by a regular procession of ELMs [5]. Figure 3 shows a representative 0.9 MA, 5.4 tesla EDA H-mode discharge, with 4 MW of ICRF power (80 MHz, second-harmonic, hydrogen-minority).…”

Section: New Divertor Heat Flux Diagnosticsmentioning

confidence: 99%

Divertor heat flux footprints in EDA H-mode discharges on Alcator C-Mod

LaBombard

Terry

Hughes

et al. 2011

Journal of Nuclear Materials

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The physics that sets the width of the power exhaust channel in a tokamak scrape-off layer and its scaling with engineering parameters is of fundamental importance for reactor design, yet it remains to be understood. An extensive array of divertor heat flux diagnostics was recently commissioned in Alcator C-Mod with the aim of improving our understanding.Initial results are reported from EDA H-mode discharges in which plasma current, input power, toroidal field and magnetic topology were varied. The integral width of the outer divertor heat flux footprint is found to lie in the range of 3 to 5 mm mapped to the midplane.Widths are insensitive to single versus double-null topology and the magnitude of toroidal field. Pedestal physics appears to largely determine these widths; a dependence of width on plasma thermal energy is noted, yielding a reduction in width as plasma current is increased for the best EDA H-modes.

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“…5,6,7 In an EDA H-mode, the particle transport is sufficiently enhanced over the ELM-free (edge localized mode) H-mode level to result in stationary density and impurity levels. 8 Previously, C-Mod ITB experiments have focused upon heating during current ramp-up with ICRF, 9 pellet enhanced performance mode, 10 and the enhanced neutron mode. 11 The latter is an ITB mode initiated by a transition from H to L-mode in which the density profile becomes peaked resulting from the ETB collapse.…”

Section: Introductionmentioning

confidence: 99%

Double transport barrier experiments on Alcator C-Mod

Wukitch¹,

Boivin²,

Bonoli³

et al. 2002

Physics of Plasmas

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Double transport barrier modes (simultaneous core and edge transport barrier) have been observed with off-axis ion cyclotron range of frequencies (ICRF) heating in the Alcator C-Mod tokamak [I. H. Hutchinson et al., Phys. Plasmas 1, 1511]. An internal transport barrier (ITB) is routinely produced in enhanced D α H-mode (EDA) discharges where the minority ion cyclotron resonance layer is at r/a ~ |0.5| during the current flat top phase of the discharge. The density profile becomes peaked without the presence of a particle source in the plasma core and continues to peak until the increased core impurity radiation arrests the improved energy confinement, ultimately leading to a barrier collapse. With the addition of moderate (0.6 MW) central ICRF heating, the double barrier mode was maintained for as long as the ICRF power was applied and modeling shows that the internal thermal barrier was maintained throughout the discharge. The presence of sawteeth throughout most of the ITB discharge allows sawtoothinduced heat pulse analysis to be performed. This analysis indicates that there is an abrupt radial discontinuity in the heat pulse time to peak profile when an ITB is present. Furthermore, this discontinuity appears to move into the core plasma from the edge region in about 0.2 sec, several confinement times. The deduced thermal diffusivity, χ hp , indicates a barrier exists in the electron thermal transport, the barrier is limited to a narrow radial region, and the transport is unaffected outside this narrow radial extent.

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Characterization of enhanced Dα high-confinement modes in Alcator C-Mod

Cited by 189 publications

References 16 publications

Pedestal profiles and fluctuations in C-Mod enhanced D-alpha H-modes

Pedestal profiles and fluctuations in C-Mod enhanced D-alpha H-modes

Divertor heat flux footprints in EDA H-mode discharges on Alcator C-Mod

Double transport barrier experiments on Alcator C-Mod

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