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The wide-angle view imaging system, in terms of a tangential view diagnostic with field of view (FOV) of 56.8° and a downward-looking diagnostic from the top of the machine with FOV of 94.7°, has been newly constructed for the first plasma of the HL-2M tokamak achieved in December 2020. Its mission in this stage is to monitor the plasma evolution during its startup, sustainment, and disruption in the visible spectral range as well as the plasma–wall interaction. For the latter ultrawide view diagnostic, nearly three-quarters of the divertor region and half the area of the inner wall are in the view range. Both the diagnostics are characterized by a similar optical structure, i.e., the light emission from the plasma is collected by a front-end lens and transferred through an imaging fiber bundle to the camera. This optical structure is suitable for application in the complex tokamak environment mainly because the fiber bundle is flexible. Photos of glow discharges are acquired prior to the first plasma for testing the FOVs in the vacuum vessel. The spatial resolution is ∼4mm for the tangential view diagnostic and ∼10mm for the downward-looking diagnostic. The temporal resolutions, ranging from 90 to 360 Hz by changing the region of interest or binning acquisition mode of the color camera, are applied to record the plasma evolutions and/or dust creation events during the first plasma campaign.

AbstractIn order to reconstruct the plasma current density, the Current Profile Fitting (CPF) code has been successfully developed on the HL-2A tokamak. A seven-channel motional Stark effect (MSE) diagnostic based on dual photoelastic modulators is installed to measure the pitch angle of the magnetic field, which can be used as an internal magnetic field constraint for the CPF code. Recently, the MSE polarimeter was upgraded with a real-time wavelength matching system to improve the signal-to-noise ratio. The magnetic field angle (γpitch) with a temporal resolution of 10 ms can be provided. In the CPF code, the plasma current density is described as a polynomial, and the Least-Squares method is used to determine the coefficients of the polynomial. The Finite Difference method and the Strongly Implicit Procedure method are used to solve the Grad-Shafranov equation. The code operation is stable. With the improved-quality MSE data, the CPF calculation result of shot 30782 suggests that the safety factor q profile is monotonic. The minimum q value is less than 1 on-axis during sawtooth oscillations in shot 30782. And, the position of the q = 1 surface is consistent with the sawtooth inversion radius measured by electron cyclotron emission and soft X-ray diagnostics.