Diagnostic Systems on Alcator C-Mod

Basse, N. P.; Dominguez, A.; Edlund, E.; Fiore, C. L.; Granetz, R.; Hubbard, A.E.; Hughes, J. W.; Hutchinson, I. H.; Irby, J.; LaBombard, B.; Lin, L.; Lin, Y.; Lipschultz, B.; Liptac, J.; Marmar, E.; Mossessian, D.; Parker, R.; Porkoláb, M.; Rice, J. E.; Snipes, J.; Tang, V.; Terry, J.; Wolfe, S.; Wukitch, S.; Zhurovich, K.; Bravenec, R. V.; Phillips, P. E.; Rowan, W. L.; Kramer, G. J.; Schilling, G.; Scott, Steve; Zweben, S. J.

doi:10.13182/fst07-a1434

Cited by 68 publications

(49 citation statements)

References 129 publications

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“…Several key C-Mod diagnostic [23] with a multi-frequency, outer midplane reflectometer system [25] and gas-puff imaging (GPI [26]). Edge and pedestal rotation and impurity analysis from B 5+ charge-exchange recombination spectroscopy (CXRS) is presently limited to only a few cases at q 95~4 .8, I p =0.8 MA [15,27].…”

Section: Methodsmentioning

confidence: 99%

I-mode: an H-mode energy confinement regime with L-mode particle transport in Alcator C-Mod

Whyte

Hubbard

Hughes³

et al. 2010

Nucl. Fusion

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370

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An improved energy confinement regime, I-mode is studied in Alcator C-Mod, a compact high-field divertor tokamak using Ion Cyclotron Range of Frequencies (ICRF) auxiliary heating. I-mode features an edge energy transport barrier without an accompanying particle barrier, leading to several performance benefits. H-mode energy confinement is obtained without core impurity accumulation, resulting in reduced impurity radiation with a high-Z metal wall and ICRF heating. I-mode has a stationary temperature pedestal with Edge Localized Modes (ELMs) typically absent, while plasma density is controlled using divertor cryopumping. I-mode is a confinement regime that appears distinct from both L-mode and H-mode, combining the most favorable elements of both. The I-mode regime is obtained predominately with ion ∇B drift away from the active X-point. The transition from L-mode to I-mode is primarily identified by the formation of a high temperature edge pedestal, while the edge density profile remains nearly identical to Lmode. Laser blowoff injection shows that I-mode core impurity confinement times are nearly identical with those in L-mode, despite the enhanced energy confinement. In addition a weakly coherent edge MHD mode is apparent at high frequency ~ 100-300 kHz which appears to increase particle transport in the edge. The I-mode regime has been obtained over a wide parameter space (B=3-6 T, I p =0.7-1.3 MA, q 95 =2.5-5). In general the I-mode exhibits the strongest edge T pedestal and normalized energy confinement (H 98 >1) at low q 95 (<3.5) and high heating power (P heat > 4 MW). I-mode significantly expands the operational space of ELM-free, stationary pedestals in C-Mod to T ped~1 keV and low collisionality ν* ped~0 .1, as compared to EDA H-mode with T ped < 0.6 keV, ν* ped >1. The I-mode global energy confinement has a relatively weak degradation with heating power; W th ~ I p P heat 0.7 leading to increasing H 98 with heating power.2

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Section: Methodsmentioning

confidence: 99%

I-mode: an H-mode energy confinement regime with L-mode particle transport in Alcator C-Mod

Whyte

Hubbard

Hughes³

et al. 2010

Nucl. Fusion

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290

370

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“…Electron densities were in the range from 0.25 to 1.80×10 20 /m 3 , with plasma currents between 0.55 and 1.1 MA (5.9 ≥ q 95 ≥ 3.2). Electron densities were determined from a two color interferometer, fast electron temperature evolution using electron cyclotron emission and Z eff from visible bremsstrahlung [38]. Toroidal rotation, ion temperature and argon emissivity profiles were measured with a high resolution imaging x-ray spectrometer system [39,40], and electron density and temperature profiles were provided by Thomson scattering [38].…”

Section: Methodsmentioning

confidence: 99%

Non-local heat transport, rotation reversals and up/down impurity density asymmetries in Alcator C-Mod ohmic L-mode plasmas

Rice¹,

Gao²,

Reinke³

et al. 2013

Nucl. Fusion

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155

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Several seemingly unrelated effects in Alcator C-Mod Ohmic L-mode plasmas are shown to be closely connected: non-local heat transport, core toroidal rotation reversals, energy confinement saturation and up/down impurity density asymmetries. These phenomena all abruptly transform at a critical value of the collisionality. At low densities in the linear Ohmic confinement regime, with collisionality ν * ≤ 0.35 (evaluated inside of the q=3/2 surface), heat transport exhibits non-local behavior, core toroidal rotation is directed co-current, edge impurity density profiles are up/down symmetric and a turbulent feature in core density fluctuations with k θ up to 15 cm −1 (k θ ρ s ∼ 1) is present. At high density/collisionality with saturated Ohmic confinement, electron thermal transport is diffusive, core rotation is in the counter-current direction, edge impurity density profiles are up/down asymmetric and the high k θ turbulent feature is absent. The rotation reversal stagnation point (just inside of the q=3/2 surface) coincides with the non-local electron temperature profile inversion radius. All of these observations can be unified in a model with trapped electron mode prevalence at low collisionality and ion temperature gradient mode domination at high collisionality.

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“…Electron density and temperature profiles were measured using Thomson scattering [23], Z eff was determined from visible bremsstrahlung [23] and core toroidal rotation and ion temperatures were measured with a high resolution imaging x-ray spectrometer system [24]. The energy confinement time was evaluated both from magnetics measurements [23] and from complete density and temperature profiles. All observations presented here were from diverted Ohmic L-mode plasmas, and the results are all averaged over sawtooth oscillations.…”

Section: Methodsmentioning

confidence: 99%

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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Diagnostic Systems on Alcator C-Mod

Cited by 68 publications

References 129 publications

I-mode: an H-mode energy confinement regime with L-mode particle transport in Alcator C-Mod

I-mode: an H-mode energy confinement regime with L-mode particle transport in Alcator C-Mod

Non-local heat transport, rotation reversals and up/down impurity density asymmetries in Alcator C-Mod ohmic L-mode plasmas

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

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