Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing  

Spatially resolved rotational temperature of ground state hydrogen molecules desorbed from plasma-facing surface was measured in QUEST, LTX-β, and DIII-D tokamaks, and the increases of the rotational temperature with the surface temperature and due to collisional-radiative processes in the plasmas were evaluated. The increase due to collisional-radiative processes was calculated by solving rate equations considering electron and proton collisional excitation and deexcitation and spontaneous emission. The calculation results suggest a high sensitivity for the rotational temperature to electron and proton densities, but a negligible sensitivity to the electron, proton, and surface temperatures. In the three tokamaks with different plasma parameters and plasma-facing surface materials, the spatial profile of the rotational temperature was estimated using Fulcher-α emission lines (600–608 nm). In QUEST, the spatial profile of the rotational temperature was estimated from spatially resolved spectra. In the other tokamaks, the rotational temperature was evaluated assuming a single point emission with a location determined from the Fulcher-α emission profile as measured with a filtered camera. In metal-walled devices QUEST and LTX-β, the rotational temperature increased with the surface temperature, and the calculated collisional-radiative increase is consistent with measured increase assuming that the rotational temperature at the surface is approximately 500–600 K higher than the surface temperature. In DIII-D with carbon walls, a larger collisional-radiative increase than the other tokamaks was observed because of the higher density leading to a large difference from the calculated increase compared to the other smaller tokamaks. Measurement of the Fulcher-α emission profile with higher spatial resolution in DIII-D may reduce the difference and reveal the effect of the surface temperature on the rotational temperature. These results show the increases in the rotational temperature with the surface temperature and due to the collisional-radiative processes.

DOI： 10.1088/1741-4326/acd4d1

Web of Science

Scopus

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Plasma Science and Nuclear Fusion Research  

<p>A design study of a line integrated Thomson scattering (TS) system with a complete backscattering configuration has been performed to clarify practical problems. Installation on the TST-2 spherical tokamak was assumed, and an optical system design with ready-made components, are adopted. Some practical aspects, such as aberration, masking effect of the laser combining mirror, misalignment are investigated by ray tracing calculations. The performance of density profile reconstruction was also investigated. It was found that a tangential-multi-chord measurement configuration on the midplane shows a good effective localization, and error enhancement in the reconstruction is small. In addition, the efficiency of the system is about an order of magnitude larger than the present conventional TS system in TST-2. The attractiveness of the line integrated TS measurements was demonstrated.</p>

DOI： 10.1585/pfr.18.2402025

Web of Science

Scopus

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Plasma Science and Nuclear Fusion Research  

<p>The Thomson scattering control system has been modified to measure the time evolution of the electron density and temperature profiles during long duration discharges in the QUEST spherical tokamak. The system consists of a signal generator and a control circuit. The former accepts a QUEST main trigger and provides multiple triggers, each of which starts a short-term (e.g. 15 s) measurement. The latter provides triggers to synchronize the oscilloscope and laser oscillation during a short-term measurement. The system was used in 1000 s long duration discharges in QUEST, and the temporal evolutions of density and temperature profiles were obtained successfully. It was found the profiles are stationary after about 300 s.</p>

DOI： 10.1585/pfr.18.1405012

Web of Science

Scopus

CiNii Research