Stochastic fluctuation and transport of tokamak edge plasmas with the resonant magnetic perturbation field

Abstract

We present that a statistical method known as the complexity–entropy analysis is useful to characterize a state of plasma turbulence and flux in the resonant magnetic perturbation (RMP) edge localized mode (ELM) control experiment. The stochastic pedestal top temperature fluctuation in the RMP ELM suppression phase is distinguished from the chaotic fluctuation in the natural ELM-free phase. It is discussed that the stochastic temperature fluctuation can be originated from the narrow layer of the field penetration on the pedestal top. The forced magnetic island can emit the resonant drift wave of comparable sizes (relatively low-k) in the RMP ELM suppression phase, and it can result in the generation of stochastic higher wavenumber fluctuations coupled to tangled fields around the island. The analysis of the ion saturation current measurement around the major outer striking point on the divertor shows that it also becomes more stochastic as the stronger plasma response to the RMP field is expected.

Quasi-mode evolution in a stochastic magnetic field

“…Using this approach, the chaotic nature of the edge fluctuations in L-mode, H-mode, and I-mode has been identified [18][19][20]. However, as reported by Choi et al the rescaled Jensen-Shannon complexity of the temperature fluctuations Reprinted from [21], with the permission of AIP Publishing.…”

“…at the pedestal top in the RMP ELM suppression phase is reduced relative to that in the natural ELM-free phase and the RMP ELM mitigation phase [21]. This indicates that the edge plasma turbulence becomes more 'noisy' when ELM is suppressed by RMP.…”

“…Figure 1. Changes of the summed total bicoherence (a) and rescaled complexity (b) of the electron temperature fluctuation between the ELM mitigation and the initial suppression phases.Reprinted from[21], with the permission of AIP Publishing.…”

Effects of Stochastic Noises on Limit-Cycle Oscillations and Power Losses in Fusion Plasmas and Information Geometry

“…Some oscillations occurring in nature or a laboratory can be quite explosive, with the potential to cause undesirable damage to a system. An important example is quasi-periodic, limit-cycle oscillations in magnetically confined plasmas [ 11 ], such as edge-localised modes (ELMs) [ 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 ] and sawtooth oscillations [ 11 ]. Specifically, ELMs occur due to instabilities of pressure/current gradient at edge plasmas for a sufficiently high input power in the high-confinement mode (H-mode) regime (see, e.g., [ 22 , 23 , 24 , 25 ] and references therein) and take the form of sudden, quasi-periodic oscillations/bursts or more regular oscillations.…”

“…The former, bursty, large-amplitude (Type I) ELMs can damage the fusion device walls, and thus have stimulated various research efforts to suppress or mitigate such ELMs. The two main mechanisms invoke the injection of particle or magnetic field perturbations externally (e.g., resonant magnetic perturbations or a pellet injection in DIII-D, JET, ASDEX-U, EAST, KSTAR tokamaks [ 16 , 17 , 20 ]). In particular, the effect of magnetic perturbation requires attention even at a very small kinetic level [ 26 , 27 ].…”