Speaker
Dr
Kiyong Lee
(National Fusion Research Institute)
Description
Having very fine spatial resolution of 63 measurable points along a 25-mm line, the high-resolution Thomson scattering system has been tested with several trial runs. The system uses a frequency doubled (532 nm) Nd:YAG laser with 0.25 J/pulse at 20 Hz. The scattered light is collected and sent to a triple-grating spectrometer (1800 grooves/mm) via optical fibers. The main purpose of using three gratings is to eliminate unwanted stray-light, where the central portion of the spectrum is mostly eliminated by a mask (thin block). Further reduction of stray-light is accomplished by rejection of n=2 components through multiple gratings. The final image is amplified and recorded by an ICCD camera (QE$\sim$50%). Due to relatively low optical transmission, accumulation of many images is necessary to produce interpretive data. Maximum likelihood estimation is used to find best fitting parameters T$_e$ and n$_e$ with experimental data. In addition, a feature of acquiring plasma background light with scattered shots during a single sequence of image collection is incorporate into the controls. The ICCD camera capture images at 40 Hz while the laser is operated at 20 Hz. In such a way, obtained images intervene between background and scattered shots. After a few trial runs, we have located several problems with the system. Upon tackling each problem, the signal-to-noise ratio still turns out to be rather low than expected. This led us to believe, there is a major transmission lose within the spectrometer. Turns out that the intermediate slit opening was not wide enough. Presently, the triple-grating spectrometer is undergoing a full optical re-alignment. After re-calibration of the Thomson scattering system, we anticipate improved data for the next set of plasma shots.
Primary author
Dr
Kiyong Lee
(National Fusion Research Institute)
Co-authors
Dr
Ji Hoon Kim
(National Fusion Research Institute)
Mr
Kang Il Lee
(National Fusion Research Institute)
Dr
Taihyeop Lho
(National Fusion Research Institute)
