Abstract
In type I ELMy H-mode experiment, Edge localized mode (ELM) filaments are clearly captured by the high-speed vacuum ultraviolet imaging (VUVI) system which is developed on the Experimental Advanced Superconducting Tokamak. To analyze the ELM filament structures, the so-called singular value decomposition is performed on the imaging data to extract the key fluctuating components. In this work, the filament structure is characterized by the pitch angle and poloidal width. In a single ELM crash, it is found that the poloidal width increases (decreases) in the rise (decay) phase of the VUVI intensity induced by ELM crash. The pitch angle derived from the VUVI data agrees well with that calculated by the Equilibrium FITting code, indicating the filaments are aligned with the field lines. The poloidal velocity shows no obvious change during the rise and decay phases in an ELM crash. In addition, both the poloidal width and the poloidal velocity of the filament increase with the heating power. Since the filament structures are extracted from the line-integrated imaging data, all these results are obtained on the condition that the ELMs are confined to a narrow layer in the plasma.
Highlights
The high confinement mode operation (H-mode) was firstly discovered on ASDEX in 1982.1 Edge localized modes (ELMs) are routinely observed in different magnetic fusion devices in ELMy H-mode discharges.2–4 They are often triggered by the magnetohydrodynamic (MHD) instabilities, due to the steep pressure gradient and bootstrap current at the pedestal region.5 These unstable modes give rise to plasma filaments that burst radially outward, moving across the so-called last closed flux surface (LCFS) into the scrape-off layer (SOL)
The filament characteristics are analyzed based on the imaging data captured by the vacuum ultraviolet imaging (VUVI) system in type I ELMy H-mode on the Experimental Advanced Superconducting Tokamak (EAST) tokamak
Multi-filament structures are observed during the ELM crash
Summary
The high confinement mode operation (H-mode) was firstly discovered on ASDEX in 1982.1 Edge localized modes (ELMs) are routinely observed in different magnetic fusion devices in ELMy H-mode discharges. They are often triggered by the magnetohydrodynamic (MHD) instabilities, due to the steep pressure gradient and bootstrap current at the pedestal region. These unstable modes give rise to plasma filaments that burst radially outward, moving across the so-called last closed flux surface (LCFS) into the scrape-off layer (SOL). The high confinement mode operation (H-mode) was firstly discovered on ASDEX in 1982.1 Edge localized modes (ELMs) are routinely observed in different magnetic fusion devices in ELMy H-mode discharges.2–4 They are often triggered by the magnetohydrodynamic (MHD) instabilities, due to the steep pressure gradient and bootstrap current at the pedestal region.. There are several 2D imaging diagnostics developed for edge plasma studies including the filamentary structure on EAST, such as the fast visible charge-coupled device (CCD) system, gas puffing imaging (GPI) system and beam emission spectroscopy (BES).14–16 These diagnostics mainly focus on the pedestal bottom and the SOL region. A high-speed vacuum ultraviolet imaging (VUVI) system is developed, which aims to study the coherent structure at the pedestal region.19 It selectively measures emissions with a wavelength of 13.5 nm, which are mainly expected to be contributed from the pedestal region in typical H-mode discharges in EAST experiment.
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