Finding evidence for density fluctuation effects on electron cyclotron heating deposition profiles on DIII-D

Brookman, M. W.; Austin, M. E.; Petty, C. C.

doi:10.1063/1.4936542

Cited by 2 publications

(4 citation statements)

References 7 publications

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“…We can use this identity with z = −in α n β /σ 2 ⊥ and θ = φ N − φ N and only the term n = 0 gives a contribution. At last we obtain (10) and (iz) are the modified Bessel functions of first kind and, in particular, I 0 is even so that…”

Section: An Estimate Of the Effect Of Density Fluctuationsmentioning

confidence: 94%

“…and I n (z) = i −n J n (iz) are the modified Bessel functions of first kind and, in particular, I 0 is even so that I 0 (−n α n β /σ ⊥ ) = I 0 (n α n β /σ ⊥ ). Expression (10) is valid under the only assumption of long parallel correlation length k 0 L 1 which is usually satisfied in cases of interest. If in addition, we consider the limit σ ⊥ = (k 0 L ⊥ ) −1 → 0 + which is often the case for beams in the EC frequency range, the Hankel's large-argument expansion of the modified Bessel function,…”

Section: An Estimate Of the Effect Of Density Fluctuationsmentioning

confidence: 99%

“…Since these factors are particularly favorable for existing machines, beam broadening is fairly difficult to measure. However, some evidence of such of an effect has been recently reported [10] and more effort is put to further investigate the issue experimentally. Simultaneously, modeling efforts have been reported to study this effect [11,12].…”

Section: Introductionmentioning

confidence: 99%

“…Since these factors are particularly favorable for existing machines, most importantly the beams have a short propagation distance between the fluctuation regime and the absorption regime, beam broadening is expected to be small and hence fairly difficult to measure. However, some evidence of such of an effect has been recently reported [10] and more is put to further investigate the issue experimentally. Simultaneously, modeling efforts have been reported to study this effect [11][12][13][14][15].…”

Section: Introductionmentioning

confidence: 99%

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The effect of density fluctuations on electron cyclotron beam broadening and implications for ITER

et al. 2017

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We present state-of-the-art computations of propagation and absorption of electron cyclotron waves, retaining the effects of scattering due to electron density fluctuations. In ITER, injected microwaves are foreseen to suppress neoclassical tearing modes (NTMs) by driving current at the q = 2 and q = 3/2 resonant surfaces. Scattering of the beam can spoil the good localization of the absorption and thus impair NTM control capabilities. A novel tool, the WKBeam code, has been employed here in order to investigate this issue. The code is a Monte Carlo solver for the wave kinetic equation and retains diffraction, full axisymmetric tokamak geometry, determination of the absorption profile and an integral form of the scattering operator which describes the effects of turbulent density fluctuations within the limits of the Born scattering approximation. The approach has been benchmarked against the paraxial WKB code TORBEAM and the full-wave code IPF-FDMC. In particular, the Born approximation is found to be valid for ITER parameters. In this paper, we show that the transport in ITER is diffusive unlike in present experiments, thus causing up to a factor of 2 to 4 broadening in the absorption profile. However, the broadening depends strongly on the turbulence model assumed for the density fluctuations, which still has large uncertainties.

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Section: An Estimate Of the Effect Of Density Fluctuationsmentioning

confidence: 94%

Section: An Estimate Of the Effect Of Density Fluctuationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

The effect of density fluctuations on electron cyclotron beam broadening and implications for ITER

et al. 2017

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Resolving ECRH deposition broadening due to edge turbulence in DIII-D

et al. 2021

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Microwave heat pulse propagation experiments have demonstrated a correlation between millimeter-scale turbulence and deposition profile broadening of electron cyclotron (EC) waves on the DIII-D tokamak. In a set of discharges in DIII-D, a variation in edge density fluctuations on the mm-scale is associated with 40%–150% broader deposition profiles, expressed in terms of normalized minor radius, as compared with equilibrium ray tracing. The 1D power profile is determined from transport analysis of the electron temperature response to EC power modulation using perturbative analysis with a square wave power modulation at 20–70 Hz, producing a series of Fourier harmonics that are fit collectively to resolve transport. Fitting an integrated heat flux expressed in the Fourier basis of the modulation to diffusive, convective, and coupled transport terms in a linear model can resolve the broadened EC deposition width from the power perturbation to resolve a broadening in each case. The best fit degree of beam broadening observed scales approximately linearly with the Doppler backscattering measured fluctuation level in the steep gradient region. Quantifying the effect of edge fluctuation broadening on EC current drive power needs of future devices will require 3D full-wave codes that can be validated on the current generation of machines. These DIII-D experiments provide a quantitative measure of fluctuation effects and a dataset to benchmark full-wave simulations that can model and eventually predict nonlinear effects neglected by 1D equilibrium beam and ray tracing.

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Finding evidence for density fluctuation effects on electron cyclotron heating deposition profiles on DIII-D

Cited by 2 publications

References 7 publications

The effect of density fluctuations on electron cyclotron beam broadening and implications for ITER

The effect of density fluctuations on electron cyclotron beam broadening and implications for ITER

Resolving ECRH deposition broadening due to edge turbulence in DIII-D

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