Neutron Activation System for ITER Tokamak

Neutron activation system (NAS) is currently designed for ITER and will be procured by the Korean DA. The main purpose of this diagnostic is to evaluate the integrated fusion power and cross-check with other neutron diagnostic, whose sensitivity can vary over time. Total neutron production rate shall be measured from all over the plasma, regardless of the position or profile of the neutron source. Therefore, it is required to minimize material and its density variation across the field of view between the plasma and the irradiation end

High detection efficiency scintillating fiber detector for time-resolved measurement of triton burnup 14 MeV neutron in deuterium plasma experiment

The behavior of the 1 MeV triton has been studied in order to understand the alpha particle confinement property in the deuterium operation of toroidal fusion devices. To obtain time evolution of the deuterium-tritium (D-T) neutron emission rate where the secondary DT neutron emission rate is approximately 1012 n/s, we designed two high detection efficiency scintillating fiber (Sci-Fi) detectors: a 1 mm-diameter scintillation fiber-based detector Sci-Fi1 and a 2 mm-diameter scintillation fiber-based detector Sci-Fi2. The test in an accelerator-based neutron generator was performed. The result shows that the directionality of each detector is 15° and 25°, respectively. It is found that detection efficiency for DT neutrons is around 0.23 counts/n cm2 for the Sci-Fi1 detector and is around 1.0 counts/n cm2 for the Sci-Fi2 detector

Time dependent neutron emission rate analysis for neutral-beam-heated deuterium plasmas in a helical system and tokamaks

A neutron emission rate analysis code called FBURN, based on the classical energetic ion confinement assumption with radial diffusion, is developed for the time-dependent analysis of the total neutron emission rate (Sn) in neutral beam (NB) heated deuterium plasmas. The time trend of Sn evaluated by FBURN shows good agreement with the Sn measured by the neutron flux monitor on the deuterium operation of the Large Helical Device. The dependence of Sn on line-averaged electron density (ne_avg) has a peak at ne_avg of around 2.5 × 1019 m−3 in both experiment and calculation. Here, the absolute value of Sn evaluated by calculation agrees with that obtained in experiments within a factor of two. A time trend analysis of Sn in an electron cyclotron heated plasma with a short pulse NB injection is performed. The analysis shows that the diffusion coefficient of co-going transit beam ions is 0.2 to 0.3 m2 s−1. In addition, the diffusion coefficient of helically trapped beam ions decreases from 5 to 3 m2 s−1 with the inward shift of the magnetic axis position. Time-resolved analysis of the triton burnup experiment shows that the diffusion coefficient of tritons is around 0.15 m2 s−1. It is found that the diffusion coefficients of the beam and tritons are of a similar value as obtained in JT-60U. The trend of the triton burnup ratio on the ne_avg calculated by the FBURN agrees with the experiments. The results suggest that the decrease of the triton burnup ratio with the increase of ne_avg is due to the shorter slowing down time of tritons by the decrease of the electron temperature, and the increase of the triton burnup ratio with the increase of ne_avg is due to the diffusion of tritons. Time trend analysis of Sn in the Korea Superconducting Tokamak Advanced Research and the Experimental Advanced Superconducting Tokamak plasmas with a short pulse NB injection is performed. The time trend of Sn is successfully reproduced by FBURN

Design of ITER divertor VUV spectrometer and prototype test at KSTAR tokamak

Design and development of the ITER divertor VUV spectrometer have been performed from the year 1998, and it is planned to be installed in the year 2027. Currently, the design of the ITER divertor VUV spectrometer is in the phase of detail design. It is optimized for monitoring of chord-integrated VUV signals from divertor plasmas, chosen to contain representative lines emission from the tungsten as the divertor material, and other impurities. Impurity emission from overall divertor plasmas is collimated through the relay optics onto the entrance slit of a VUV spectrometer with working wavelength range of 14.6–32 nm. To validate the design of the ITER divertor VUV spectrometer, two sets of VUV spectrometers have been developed and tested at KSTAR tokamak. One set of spectrometer without the field mirror employs a survey spectrometer with the wavelength ranging from 14.6 nm to 32 nm, and it provides the same optical specification as the spectrometer part of the ITER divertor VUV spectrometer system. The other spectrometer with the wavelength range of 5–25 nm consists of a commercial spectrometer with a concave grating, and the relay mirrors with the same geometry as the relay mirrors of the ITER divertor VUV spectrometer. From test of these prototypes, alignment method using backward laser illumination could be verified. To validate the feasibility of tungsten emission measurement, furthermore, the tungsten powder was injected in KSTAR plasmas, and the preliminary result could be obtained successfully with regard to the evaluation of photon throughpu

Design of ITER divertor VUV spectrometer and prototype test at KSTAR tokamak

Design and development of the ITER divertor VUV spectrometer have been performed from the year 1998, and it is planned to be installed in the year 2027. Currently, the design of the ITER divertor VUV spectrometer is in the phase of detail design. It is optimized for monitoring of chord-integrated VUV signals from divertor plasmas, chosen to contain representative lines emission from the tungsten as the divertor material, and other impurities. Impurity emission from overall divertor plasmas is collimated through the relay optics onto the entrance slit of a VUV spectrometer with working wavelength range of 14.6–32 nm. To validate the design of the ITER divertor VUV spectrometer, two sets of VUV spectrometers have been developed and tested at KSTAR tokamak. One set of spectrometer without the field mirror employs a survey spectrometer with the wavelength ranging from 14.6 nm to 32 nm, and it provides the same optical specification as the spectrometer part of the ITER divertor VUV spectrometer system. The other spectrometer with the wavelength range of 5–25 nm consists of a commercial spectrometer with a concave grating, and the relay mirrors with the same geometry as the relay mirrors of the ITER divertor VUV spectrometer. From test of these prototypes, alignment method using backward laser illumination could be verified. To validate the feasibility of tungsten emission measurement, furthermore, the tungsten powder was injected in KSTAR plasmas, and the preliminary result could be obtained successfully with regard to the evaluation of photon throughpu