High speed vacuum ultraviolet telescope system for edge fluctuation measurement in the large helical device

Wang

et al. 2018

Plasma Sci. Technol.

A high-speed vacuum ultraviolet (VUV) imaging telescope system has been developed to measure the edge plasma emission (including the pedestal region) in the Experimental Advanced Superconducting Tokamak (EAST). The key optics of the high-speed VUV imaging system consists of three parts: an inverse Schwarzschild-type telescope, a micro-channel plate (MCP) and a visible imaging high-speed camera. The VUV imaging system has been operated routinely in the 2016 EAST experiment campaign. The dynamics of the two-dimensional (2D) images of magnetohydrodynamic (MHD) instabilities, such as edge localized modes (ELMs), tearing-like modes and disruptions, have been observed using this system. The related VUV images are presented in this paper, and it indicates the VUV imaging system is a potential tool which can be applied successfully in various plasma conditions.

Section: Methodsmentioning

confidence: 99%

“…A tangentially viewing VUV imaging system was developed in the Large Helical Device (LHD) in 2008 [9], and it was upgraded in 2010 [10]. The 2D structure of the m/n=1/1 (m is the poloidal mode number and n is the toroidal mode number) interchange mode in LHD plasma has been obtained using this system.…”

Section: Introductionmentioning

confidence: 99%

Two-dimensional vacuum ultraviolet images in different MHD events on the EAST tokamak

Gao

Wang

et al. 2018

Plasma Sci. Technol.

“…The synthetic image, I, is made according to the formula I = GE, where E is the 2D emissivity profile and the G denotes the geometry matrix. Each element Gij describes the contribution to the ith pixel from the jth grid of the discretized target plane [10,13]. Assuming the emissivity along the magnetic field line is constant, the geometry matrix is constructed by projecting each sight line onto the target plane along magnetic field lines (details can be found in references [10,13]).…”

Section: Synthetic Image From the Simulationmentioning

confidence: 99%

“…Each element Gij describes the contribution to the ith pixel from the jth grid of the discretized target plane [10,13]. Assuming the emissivity along the magnetic field line is constant, the geometry matrix is constructed by projecting each sight line onto the target plane along magnetic field lines (details can be found in references [10,13]). Since the projection is based on the equilibrium from EFIT (the whole poloidal cross-section is divided into 129 × 129 points), the spatial resolution (especially in the radial direction) is much poorer compared to that in the BOUT++, and this may cause uncertainties in the production of synthetic images.…”

Section: Synthetic Image From the Simulationmentioning

confidence: 99%

“…The filament structure induced by the ELM has been observed via varied diagnostics in a wide range of tokamaks [1][2][3][4]. The filaments along the magnetic field line have a certain toroidal and poloidal mode number and move outwards via the E × B drift, as (n = 4-2 transition) [10][11][12][13]. The poloidal width of the filaments (hereinafter referred as filament width), which is defined as the shortest distance of the two edges (i.e., binormal direction) of the filament structure, are found in proportional to the heating power and ELM size [12].…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Study on filament width of type-I ELM in EAST using VUV imaging system and simulation

Tang²,

Shi³

et al. 2022

Nucl. Fusion

The poloidal width of the filaments induced by the Type-I edge localized mode has power dependence in EAST. The poloidal widths of the filaments observed by the high-speed vacuum ultraviolet (VUV) imaging system are proportional to the heating power and the ELM size. To understand this power dependence, the BOUT++ nonlinear simulations have been performed with the reconstructed equilibriums from the experimental measurements in this paper. The synthetic filament structures from BOUT++ nonlinear simulation match the experimental observations by the VUV imaging system. The BOUT++ nonlinear simulations also reproduce the power dependence of the filament widths and the ELM size. The filament width and the ELM size are inversely proportional to the toroidal mode number. The low-n mode has a broader radial and poloidal structure, which causes the larger filament width and ELM size. In the high input power case, the mode spectrum shifts to low-n, a result of increasing peeling drive. Besides, we found the β_p in a higher input power case leads to a broader pedestal, expanding the radial mode structure of the Peeling-Ballooning mode.

Upgrade of the tangentially viewing vacuum ultraviolet (VUV) telescope system for 2D fluctuation measurement in the large helical device

Wang

Review of Scientific Instruments

Gao

et al. 2016

A high-speed tangentially viewing vacuum ultraviolet (VUV) telescope system, using an inverse Schwarzschild-type optic system was developed to study fluctuations in the Large Helical Device (LHD). However, for the original system, the sampling rate was restricted to below 2000 Hz due to the low signal to noise (S/N) ratio in the experiment. In order to improve the S/N ratio, upgrade of the system was made. With this upgraded optical system, the maximum framing rate is improved to 6000 fps with a similar spatial resolution. Rotation of the m = 2 structure caused by the magnetohydrodynamic (MHD) instability is measured by the upgraded system. The spatial structure of the image is consistent with the synthetic image assuming the interchange mode type displacement of the flux surfaces.