Abstract
An Electron Cyclotron Emission Imaging (ECEI) diagnostic system for the WEST tokamak has been developed under the UNIST-WEST collaboration. This diagnostic system is designed to overcome accessibility and thermomechanical constraints for long pulse operation. The first O-mode channel will be installed in the first trimester of 2019 to probe the low field side (LFS) of the WEST plasma. Two large metallic reflective mirrors are installed inside the duct which is being used for maintenance access. They are suspended on a rail to facilitate mirror manipulation. The ex-vessel optical system (lens, detection array, etc.) is housed in a compact optical enclosure that fits in a tight free space between the port flange and tokamak access lobby. The design emphasized reproducibility of the precise alignment between in-vessel mirrors and optical enclosure since the both elements must be removed during shutdown period for maintenance access. The overall optical system was fully tested at UNIST last year. The test results demonstrated that the imaging optics can full access at any radial position on the LFS. The 2D beam pattern measurements were consistent with the design values.
Highlights
WEST (Tungsten (W) Environment in Steady-state Tokamak) is transformation of the Tore Supra tokamak plasma in an X-point divertor configuration
This paper describes innovative approaches to integrate the Electron Cyclotron Emission Imaging (ECEI) optics on WEST
The WEST diagnostic relies on the ECEI principles, introduction of the large reflective optics to be positioned inside the manaccess port, which induce new constraints on the optics design compared to standard ECEI
Summary
WEST (Tungsten (W) Environment in Steady-state Tokamak) is transformation of the Tore Supra tokamak plasma in an X-point divertor configuration. Electron Cyclotron Emission imaging (ECEI) diagnostic system, first developed in the 90's, images the temperature fluctuations [2,3] It has proven extremely powerful for understanding the physics of sawtooth crash [4,5], the structure of ELMs [6] or fast particles induced instabilities [7]. The WEST diagnostic relies on the ECEI principles, introduction of the large reflective optics to be positioned inside the manaccess port, which induce new constraints on the optics design compared to standard ECEI. The solution of both the in-vessel mirrors and compact ex-vessel optics was proposed to overcome the constraints in WEST will be described in part 2. The article concludes that the ECEI implantation on large steady-state tokamaks is challenging, innovative solutions can overcome the integration issues to get the unrivalled information provided by 2D images of temperature fluctuations
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