Abrupt reduction of core electron heat transport in response to edge cooling on the Large Helical Device

Abstract

Cold pulse inversion in a helical plasma is observed in the Large Helical Device (LHD) and thus the strong non-local effects are evident in the helical device as well as in tokamaks. A hydrogen pellet or tracer encapsulated solid pellet is injected into the edge of the LHD plasmas. A significant rise of the electron temperature is observed in the central region in response to the edge cooling. Transient analysis indicates a heat flux jump despite the absence of a change in the local temperature gradient. The non-local temperature rise takes place in the low density and high temperature regime just as predicted by the TFTR scaling.

Explaining Cold-Pulse Dynamics in Tokamak Plasmas Using Local Turbulent Transport Models

“…In contrast to the electron temperature, which is measured in the experiment with a time resolution of 0.05ms, the time resolution of the measured ion temperature was 24ms, making it challenging to perform direct comparison of timing of core and edge ion temperature rises. This work, however, does show that a large core ion temperature increase is not needed to recover the electron temperature inversion, contrary to past modeling work [17] and consistent with the fact that a temperature increase in the electron channel is observed in other experiments regardless of the ion response [7,33]. Unlike the TGLF-SAT1 simulations, TGLF-SAT0 did not recover an ion temperature increase at the plasma core.…”

How turbulence fronts induce plasma spin-up

“…This effect is a key for understanding why "the tail wags the plasma," i.e., why jogging edge flows by changing magnetic geometry leaves a footprint in the core flow. A perturbative experiment [23][24][25][26][27][28] is proposed as a further critical test.…”

“…Another important consequence that the nonlinear flux can induce is the dynamic response of the core flows against the edge perturbation [23][24][25][26][27][28]. As discussed above, the nonlinear flux allows the fluctuation momentum to propagate faster than the mean momentum.…”

Characteristics of Nonlocally‐Coupled Transition of the Heat Transport in LHD

“…One of the well-known examples of such phenomena is an abrupt rise of the core electron temperature T e in response to edge cooling (so-called "nonlocal transport phenomenon") [1]. The nonlocal transport phenomenon has been observed in many tokamaks [2][3][4] and recently in helical devices [5,6]. Since the phenomenon seems not to be accompanied by the premonitory change in the thermodynamic values, such as the temperature and its gradient, in the core region, the core T e rise induced by the edge cooling is considered to be a result of non-locality (it means spatial interaction between two distant points) in the electron heat transport.…”