Non-monotonic radial structures of fluctuating temperatures and densities associated with fishbone activities in KSTAR

Abstract

General characteristics of a fishbone mode in KSTAR are investigated. Fishbone activities are observed with a Mirnov coil, an electron cyclotron emission radiometer (from the core to the edge of plasmas) and an beam emission spectroscopy system (core or edge plasmas) which are measuring fluctuations of poloidal magnetic fields, electron temperatures, and densities, respectively. Temporal evolutions of these fluctuations are similar to the observations from other tokamaks. An interesting and notable feature found in KSTAR fishbone modes is that radial coherence structures of electron temperature and density with respect to magnetic fluctuations are non-monotonic that they have a local minimum at [Formula: see text] and a maximum at [Formula: see text] in addition to the usual global peak near the q = 1 surface, where r/ a is the normalized minor radius and q is the safety factor. Furthermore, the associated temporal evolution of the electron temperatures in slow-time scale, i.e., less than 1 kHz, with the fishbone activities show that there exist a drop in temperature or increase in temperature depending on inside or outside the q = 1 surface, respectively, from the core to the edge plasmas except that there are almost no temperature changes in the intermediate region which seems to be correlated with the non-monotonic coherence profile. Such a non-monotonic structure and the slow temporal evolution of temperatures are explained with barely trapped resonating fast ions with the banana orbit widths of the order of the minor radius, so that they transit the core and the edge regions simultaneously without trespassing the mid-plane intermediate region.

Tokamak edge localized mode onset prediction with deep neural network and pedestal turbulence

“…As shown in figure 6(c), the temporal evolution of the broadband fluctuations from BES ch#45 and cross-power spectrum between the BES ch#45 and ch#53 are presented in the first two rows, together with the corresponding network outputs in the last row of the figure. Obviously, we can find that fast-ion induced fishbone activities recur during the ELM suppression phase [70], which confuses the network with their density fluctuating patterns. This is the reason why we encounter the recurring false predictions of the network which are turned out to be correlated with the fishbone activities.…”