High-frequency edge turbulence in wide pedestal QH-modes at DIII-D

New insights regarding high-frequency edge turbulence in DIII-D wide pedestal QH-modes are obtained through comparisons of experimental phase contrast imaging (PCI) measurements with gyrokinetic simulations from the GENE code, utilizing a synthetic PCI diagnostic. Measurements from the DIII-D PCI system [1] indicate high-frequency (> 600 kHz), low-wavenumber (< 5/cm) turbulence near the edge of wide pedestal QH-mode plasmas. The observed phase velocities closely follow the E×B velocity at the bottom of the radial electric field well, suggesting that the mode emerges as a consequence of the lower shearing rate in wider pedestals. These hypotheses are tested through comparisons with gyrokinetic simulations from the GENE code. Linear simulations indicate rapidly growing kinetic ballooning-like modes at the bottom of the radial electric field well with wavenumbers below the PCI detection range. Nonlinear simulations are used to determine the signal at wavenumbers measurable using PCI and are compared to experimental observations by computing synthetic PCI signals [2].

References

[1] E. M. Davis et al. Rev. Sci. Instrum. 89, 10B106 (2018)

[2] S. K. Hansen et al. Plasma Phys. Controlled Fusion 64, 095011 (2022)