Turbulent Cross Phase Control using Differential RF Heating: A Mechanism for Controlling Transport in Fusion Plasmas (and other turbulent systems)?
 

In fusion plasmas, the I-mode and similar relatively new transport regimes offer both good energy confinement properties and reduced density limit issues with potentially better control. All of these make fusion a more attainable energy source.  While a number of different mechanisms have been identified for the formation and maintenance of enhanced confinement regimes few if any allow enhanced confinement in one channel (energy) but not another (density) which is seen in the I-mode.  We have earlier (TTF15) proposed differential cross-phase modification controlled by the dominant instability as a possible mechanism for the different transport in different channels and have investigated potential control tools.  Simple dynamical models (Phys. Plasmas 98,99) have been able to capture a remarkable amount of the dynamics of the core and edge transport barriers found in many devices. By including in this rich though simple dynamic transport model an additional simple model for cross phase effects, driven by the inclusion of multiple instabilities, we can investigate whether the dynamics of more continuous transitions such as the I-mode can be captured and understood.  This allows different cross phases between the transported fields such as density and temperature which can then allow for different transport in these fields.  The logical question is then, if this mechanism is valid, what can the model tell us about control knobs for these promising regimes? Here we show results found by using differential electron and ion heating to control the I-mode regime. By using both location modification and modulation of the amplitude and duration of both the electron and ion heating as the control knobs we demonstrate the ability to modulate the confinement in the I-mode without slipping into the H-mode regime.  With this simple model, schemes for optimization of both exhaust and core temperature can be envisioned.