Differential Cross-Phase Modulation as a Control Knob for I-Mode Transport: New Results from a Reduced-Model and Non-linear GENE with Insights

Enhanced-confinement regimes such as the I-mode promise H-mode-like energy confinement without large particle and impurity retention, but the mechanism that decouples energy and particle transport remains an open question. We present the newest results from our previously proposed differential cross-phase modification mechanism, where multiple micro-instabilities shift the relative phase between fluctuating fields, altering their transport. Reduced-model Embedding these cross-phase responses in a six-field transport model reproduces continuous L → I transitions, including the weak E×B shear layer. Gyrokinetic simulations Linear and Nonlinear scans with GENE incorporating ITG, TEM and ETG drives confirm that modest adjustments to ion- versus electron-heating profiles can shift the dominant instability mix leading to different changes in the phases for the thermal vs particle channel. Control strategy Simulated heating sweeps (modulated ICRH + ECH) suggest that relatively low frequency modulation can nudge discharges back and forth from the I-mode to the L-mode providing a practical transport control knob for current and future devices.

These results support differential cross-phase as a viable explanation for I-mode’s channel-selective transport and offer control guidelines. Current experiments could investigate these mechanisms.