Perturbative thermal diffusivity from partial sawtooth crashes in Alcator C-Mod

Creely, A. J.; White, A. E.; Edlund, E. M.; Howard, N. T.; Hubbard, A. E.

doi:10.1088/0029-5515/56/3/036003

Perturbative thermal diffusivity from partial sawtooth crashes in Alcator C-Mod

Journal Article · Fri Feb 05 00:00:00 EST 2016 · Nuclear Fusion

DOI:https://doi.org/10.1088/0029-5515/56/3/036003· OSTI ID:1897509

Creely, A. J. ^[1]; White, A. E. ^[2]; Edlund, E. M. ^[3]; Howard, N. T. ^[4]; Hubbard, A. E. ^[2]

MIT Plasma Science and Fusion Center, Cambridge, MA (United States); OSTI
MIT Plasma Science and Fusion Center, Cambridge, MA (United States)
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Oak Ridge Inst. for Science and Education (ORISE), Oak Ridge, TN (United States)

Perturbative thermal diffusivity has been measured on Alcator C-Mod via the use of the extended-time-to-peak method on heat pulses generated by partial sawtooth crashes. Perturbative thermal diffusivity governs the propagation of heat pulses through a plasma. It differs from power balance thermal diffusivity, which governs steady state thermal transport. Heat pulses generated by sawtooth crashes have been used extensively in the past to study heat pulse thermal diffusivity, but the details of the sawtooth event typically lead to non-diffusive 'ballistic' transport, making them an unreliable measure of perturbative diffusivity on many tokamaks. Partial sawteeth are common on numerous tokamaks, and generate a heat pulse without the 'ballistic' transport that often accompanies full sawteeth. This is the first application of the extended-time-to-peak method of diffusivity calculation to partial sawtooth crashes. Furthermore, this analysis was applied to over 50 C-Mod shots containing both L- and I-Mode. Results indicate correlations between perturbative diffusivity and confinement regime (L- versus I-mode), as well as correlations with local temperature, density, the associated gradients, and gradient scale lengths (a/L_Te and a/L_n). In addition, diffusivities calculated from partial sawteeth are compared to perturbative diffusivities calculated with the nonlinear gyrokinetic code GYRO. We find that standard ion-scale simulations (ITG/TEM turbulence) under-predict the perturbative thermal diffusivity, but new multi-scale (ITG/TEM coupled with ETG) simulations can match the experimental perturbative diffusivity within error bars for an Alcator C-Mod L-mode plasma. Perturbative diffusivities extracted from heat pulses due to partial sawteeth provide a new constraint that can be used to validate gyrokinetic simulations.

View Accepted Manuscript (DOE)

Research Organization:: Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). Plasma Science and Fusion Center

Sponsoring Organization:: USDOE Office of Science (SC), Fusion Energy Sciences (FES); USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)

Grant/Contract Number:: FC02-99ER54512; SC0006419

OSTI ID:: 1897509

Alternate ID(s):: OSTI ID: 1236974

Journal Information:: Nuclear Fusion, Journal Name: Nuclear Fusion Journal Issue: 3 Vol. 56; ISSN 0029-5515

Publisher:: IOP ScienceCopyright Statement

Country of Publication:: United States

Language:: English

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