Validating a model based on interchange-drift-Alfvén turbulence for LH and HL transitions in DIII-D*

A model for transitions between low confinement (L-) mode and high confinement (H-) mode was recently reported to show strong agreement with ASDEX-U experiments [1]. The model, based on the power balance of interchange-drift-Alfvén turbulence, yields a transition boundary in terms of electron density and electron temperature evaluated at the separatrix. We report examination of this model using various DIII-D plasmas, including pre-H L-mode (before H mode entry), post-H L-mode (after HL back transition), type-I ELMy (edge- localized-mode dominated) H-mode, and type-III ELMy H-mode. It is found that the calculated LH transition boundary properly separates pre-H and post-H L-modes, similar to the finding in ASDEX-U [1]. The model suggests the pre-H L-mode is drift-Alfvén dominant, the post-H L-mode is resistive-ballooning mode dominant, and the type-III ELMy H-mode has marginal resistive-ballooning activity. This suggested picture appears consistent with confinement-correlated, edge-localized fluctuations measured by the Radial Interferometer Polarimeter (RIP) and Beam Emission Spectroscopy (BES) [2]: quasi-coherent fluctuations peaking at ~40 kHz arise in both the type-III ELMy H-mode and the post-H L-mode. Consideration of discharges with both favorable and unfavorable grad-B drift indicate the curve is robust to changes in drift direction.