Transport hysteresis of core plasma, isotope effect, and H-mode physics

Abstract

This article assesses the understanding of and impact by the hysteresis in transport relation. The rapid changes of fluxes compared to slow changes of plasma parameters are overviewed for both edge barrier and core plasmas. The theoretical approaches to understanding the direct influence of heating power on turbulent transport are addressed. Based on this new theoretical framework, the ‘isotope effect’ of plasma confinement time is discussed. A trial explanation is given for this unresolved mystery in plasma confinement. The advanced data analysis method to research the hysteresis in gradient-flux relation is explained.

Isotope effect in transient electron thermal transport property and its impact on the electron internal transport barrier formation in LHD

“…Because of this ingredient, the turbulence amplitude is allowed to change immediately after an additional heat source is applied and before the local parameters change. This response results in the bifurcation of the trajectory in the flux-gradient diagram depending on the applied ECH power [25][26][27]. In particular, under a modulation ECH (MECH) application, the trajectory in the flux-gradient diagram draws a loop, which we call the transport hysteresis.…”

“…When the transport hysteresis emerges, a single scalar transport coefficient is found to be no longer valid for representing the transport property of the high temperature plasmas [28][29][30][31]. A theoretical model predicts that the magnitude of the hysteresis is more enhanced in lighter isotope mass plasmas, which results in the confinement degradation and therefore explains the isotope effect [27].…”

“…This response results in the bifurcation of the trajectory in the flux-gradient diagram depending on the applied ECH power [25,26,27]. In particular, under a modulation ECH (MECH) application, the trajectory in the flux-gradient diagram draws a loop, which we call the transport hysteresis.…”

“…[27,34,35].There are two different dynamics in the heat flux evolution having fast and slow time constants. When the ECH is turned on, the heat flux increases with a fast time scale and a slight change in the electron temperature gradient.…”

Transport hysteresis and zonal flow stimulation in magnetized plasmas

“…Several observations of a hysteresis in the modulation electron cyclotron heating experiments have been reported, for instance on DIIID plasma [18] or on large helical device (LHD) [19,20]. Sharp and fast changes of heat flux at the switchon and switchoff of heating have been reported which has lead to the explained hypothesis that the heating power has an immediate influence on turbulent plasma transport even without a change of mean parameters or mean distribution function.…”