Abstract
The vacuum ultraviolet (VUV) spectroscopy system on the Joint Texas Experimental Tokamak has been upgraded to achieve fast acquisition for the study of impurity transport in transient modulated experiments. In this upgrade, the previous high-energy charge-coupled device detector was replaced by a microchannel plate with a CsI-coated photocathode and P43 phosphor to transform the VUV light to visible light, which is then acquired by a high-speed electron-multiplying charge-coupled device. Two-stage focusing was achieved using a reference slit plate illuminated successively by a green light source and the Lyman series hydrogen spectral lines from the vacuum-conditioning plasma. The spatial resolution was evaluated as ∼4mm based on the level of image blurring from the alignment plate. A response time of ∼2ms was obtained with the ten-vertical-track setup.
Highlights
Spectroscopy diagnostics, as one of the most fundamental diagnostic systems on tokamaks, has long been used in the study of impurity behaviors
The previous high-energy charge-coupled device detector was replaced by a microchannel plate with a CsI-coated photocathode and P43 phosphor to transform the VUV light to visible light, which is acquired by a high-speed electron-multiplying charge-coupled device
The spatial resolution was evaluated as ∼4 mm based on the level of image blurring from the alignment plate
Summary
Spectroscopy diagnostics, as one of the most fundamental diagnostic systems on tokamaks, has long been used in the study of impurity behaviors. As a typical J-TEXT discharge can last for 800 ms with the particle confinement time ranging from 10 to 20 ms, the previous system cannot resolve the impurity evolution in the transient modulated experiments on the J-TEXT, such as those studies using external resonant magnetic perturbation (RMP) and electrode biasing. It raises the requirements of operating the VUV system at a high-time response of about 5 ms.
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