Divertor IR thermography on Alcator C-Mod

Terry, J. L.; LaBombard, B.; Brunner, D.; Payne, J.; Wurden, G. A.

doi:10.1063/1.3478669

Cited by 39 publications

(25 citation statements)

References 13 publications

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“…19 It views the ramped tiles by looking both down and in the toroidal direction from a periscope in a vertical port ($90 away toroidally), such that it can view the otherwise hidden vertical segment of the tile surface. A reference image used for camera alignment is shown in Fig.…”

Section: A Divertor Heat Flux Diagnosticsmentioning

confidence: 99%

Scaling of the power exhaust channel in Alcator C-Mod

LaBombard¹,

Terry²,

Hughes³

et al. 2011

Physics of Plasmas

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Parametric dependences of the heat flux footprint on the outer divertor target plate are explored in EDA H-mode and ohmic L-mode plasmas over a wide range of parameters with attached plasma conditions. Heat flux profile shapes are found to be independent of toroidal field strength, independent of power flow along magnetic field lines and insensitive to x-point topology (single-null versus double-null). The magnitudes and widths closely follow that of the "upstream" pressure profile, which are correlated to plasma thermal energy content and plasma current. Heat flux decay lengths near the strike-point in H-and L-mode plasmas scale approximately with the inverse of plasma current, with a diminished dependence at high collisionality in L-mode. Consistent with previous studies, pressure gradients in the boundary scale with plasma current squared, holding the magnetohydrodynamic ballooning parameter approximately invariant at fixed collisionality-strong evidence that critical-gradient transport physics plays a key role in setting the power exhaust channel.

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Section: A Divertor Heat Flux Diagnosticsmentioning

confidence: 99%

Scaling of the power exhaust channel in Alcator C-Mod

LaBombard¹,

Terry²,

Hughes³

et al. 2011

Physics of Plasmas

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“…The thermography and heat flux code are described in more detail in [12,4]. A typical heat flux profile from an I-mode plasma is shown in Fig.1 shown, the peak in the target heat flux is not perfectly aligned with the EFIT-located strike point.…”

Section: Experimental Details and Analysesmentioning

confidence: 99%

Heat-flux footprints for I-mode and EDA H-mode plasmas on Alcator C-Mod

Terry

LaBombard

Brunner

et al. 2013

Journal of Nuclear Materials

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IR thermography is used to measure the heat flux footprints on C-Mod's outer target in Imode and EDA H-mode plasmas. The footprint profiles are fit to a function with a simple physical interpretation. The fit parameter that is sensitive to the power decay length into the SOL, λ SOL , is ~1-3x larger in I-modes than in H-modes at similar plasma current, which is the dominant dependence for the H-mode λ SOL . In contrast, the fit parameter sensitive to transport into the private-flux-zone along the divertor leg is somewhat smaller in I-mode than in Hmode, but otherwise displays no obvious dependence on I p , B t , or stored energy. A third measure of the footprint width, the "integral width", is not significantly different between Hand I-modes. Also discussed are significant differences in the global power flows of the Hmodes with "favorable" drift direction and those of the I-modes with "unfavorable" drift direction.

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“…The line-integrated brightness measurements are Abel inverted to obtain radial emissivity profiles, which are then integrated within the last closed flux surface (LCFS) to obtain the total core radiated power P rad,core . Divertor heat flux is inferred using an infrared (IR) camera viewing a segment of the outer divertor and utilizing a 2D heat transport model for the divertor tiles to transform measured surface temperatures into heat flux profiles [ 19 ]. These profiles are then integrated over the divertor surface, assuming toroidal symmetry, to produce the total power conducted to the outer divertor P o-div .…”

Section: Experimental Descriptionmentioning

confidence: 99%

Power requirements for superior H-mode confinement on Alcator C-Mod: experiments in support of ITER

et al. 2011

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Power requirements for maintaining sufficiently high confinement (i.e., normalized energy confinement time H 98 ≥1) in H-mode and its relation to H-mode threshold power scaling, P th , are of critical importance to ITER. In order to better characterize these power requirements, recent experiments on the Alcator C-Mod tokamak have investigated H-mode properties, including the edge pedestal and global confinement, over a range of input powers near and above P th . In addition, we have examined the compatibility of impurity seeding with high performance operation, and the influence of plasma radiation and its spatial distribution on performance. Experiments were performed at 5.4T at ITER relevant densities, utilizing bulk metal plasma facing surfaces and ion cyclotron range of frequencies waves for auxiliary heating. Input power was scanned both in stationary enhanced D α (EDA) H-modes with no large ELMs and in ELMy H-modes in order to relate the resulting pedestal and confinement to the amount of power flowing into the scrape-off layer, P net , and also to the divertor targets. In both EDA and ELMy H-mode, energy confinement is generally good, with H 98 near unity. As P net is reduced to levels approaching that in L-mode, pedestal temperature diminishes significantly and normalized confinement time drops. By seeding with low-Z impurities such as Ne and N 2 , high total radiated power fractions are possible, along with substantial reductions in divertor heat flux (>4x), all while maintaining H 98 ~ 1. When the power radiated from the confined vs. unconfined plasma is examined, pedestal and confinement properties are clearly seen to be an increasing function of P net , helping to unify the results with those from unseeded H-modes. This provides increased confidence that the power flow across the separatrix is the correct physics basis for ITER extrapolation. The experiments show that P net /P th of one or greater is likely to lead to H 98~1 operation, and also that such a condition can be made compatible with a low-Z radiative impurity solution for reducing divertor heat loads to levels acceptable for ITER.

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Divertor IR thermography on Alcator C-Mod

Cited by 39 publications

References 13 publications

Scaling of the power exhaust channel in Alcator C-Mod

Scaling of the power exhaust channel in Alcator C-Mod

Heat-flux footprints for I-mode and EDA H-mode plasmas on Alcator C-Mod

Power requirements for superior H-mode confinement on Alcator C-Mod: experiments in support of ITER

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