Resolving broadening of ECRH deposition due to edge turbulence in DIII-D by heat deposition measurement
- Univ. of Texas at Austin, Austin, TX (United States)
- Univ. of York, York (United Kingdom)
- General Atomics, San Diego, CA (United States)
- Univ. of California, Los Angeles, CA (United States)
- Univ. of Wisconsin, Madison, WI (United States)
Interaction between microwave power, used for local heating and mode control, and density fluctuations can produce a broadening of the injected beam, as confirmed in experiment and simulation. Increased power deposition width could impact suppression of tearing mode structures on ITER[1]. This work discusses the experimental portion of an effort to understand scattering of injected microwaves by turbulence on the DIII-D tokamak. The corresponding theoretical modeling work can be found in M.B. Thomas et. al.: Submitted to Nuclear Fusion (2017)[Author Note - this paper to be published in same journal]. In a set of perturbative heat transport experiments, tokamak edge millimeter-scale fluctuation levels and microwave heat deposition are measured simultaneously. Beam broadening is separated from heat transport through fitting of modulated fluxes[2]. Electron temperature measurements from a 500 kHz, 48-channel ECE radiometer are Fourier analyzed and used to calculate a deposition-dependent flux[3]. Consistency of this flux with a transport model is evaluated. A diffusive(∝ ∇˜ Te) and convective(∝ ˜ Te) transport solution is linearized and compared with energy conservation-derived fluxes. Comparison between these two forms of heat flux is used to evaluate the quality of ECRF deposition profiles, and a Χ2 minimization finds a significant broadening of 1D equilibrium ray tracing calculations from the benchmarked TORAY-GA ray tracing code[4] is needed. The physical basis, cross-validation, and application of the heat flux method is presented. The method is applied to a range of DIII-D discharges and finds a broadening factor of the deposition profile width which scales linearly with edge density fluctuation level. Furthermore, these experimental results are found to be consistent with the full-wave beam broadening measured by the 3D full wave simulations in the same discharges[5].
- Research Organization:
- General Atomics, San Diego, CA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- FC02-04ER54698
- OSTI ID:
- 1481199
- Journal Information:
- arXiv.org Repository, Vol. 2017; ISSN 9999-0017
- Publisher:
- Cornell University
- Country of Publication:
- United States
- Language:
- English
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