A model for non-local electron heat transport

Microphysically, the electromagnetic electron temperature gradient (ETG) mode is studied within the framework of electron magnetohydrodynamics (EMHD). It is discovered that the dominant electromagnetic ETG instability in the core regime of low density plasma is a short-wavelength one. The instability-induced turbulent heating makes the core electron temperature (Te) to rise. The condition for the core Te rise in low density plasma, obtained from the ETG instability, is consistent with the experimental observation qualitatively. Furthermore, the electromagnetic ETG instability in high density plasma is also studied and compared with the experimental results. Macrophysically, a global energy balance equation is extended to tokamak plasma from a reversed pinch one. From the equation it is shown that the edge heat pulse weakens the core Te rise or even makes the non-local effect disappear, one phenomenon observed in experiments. Accordingly, the macro-parameter condition for the core Te rise is obtained. Finally, the analyses of electron heat transport coefficient indicate that when the core Te rises in response to the edge cold pulse, the heat transport coefficient reduces largely due to the excited short-wavelength electromagnetic ETG turbulence in low density plasma.