As the finalization of the hydrogen experiment towards the deuterium phase, the exploration of the best performance of the hydrogen plasma was intensively performed in the Large Helical Device (LHD). High ion and electron temperatures, Ti, Te, of more than 6 keV were simultaneously achieved by superimposing the high power electron cyclotron resonance heating (ECH) on the neutral beam injection (NBI) heated plasma. Although flattening of the ion temperature profile in the core region was observed during the discharges, one could avoid the degradation by increasing the electron density. Another key parameter to present plasma performance is an averaged beta value . The high regime around 4 % was extended to an order of magnitude lower than the earlier collisional regime. Impurity behaviour in hydrogen discharges with NBI heating was also classified with the wide range of edge plasma parameters. Existence of no impurity accumulation regime where the high performance plasma is maintained with high power heating > 10 MW was identified. Wide parameter scan experiments suggest that the toroidal rotation and the turbulence are the candidates for expelling impurities from the core region.
Thomson scattering (TS) is a proven diagnostic technique that will be implemented in ITER in three independent systems. The Edge TS will measure electron temperature T e and electron density n e profiles at high resolution in the region with r/a>0.8 (with a the minor radius). The Core TS will cover the region r/a<0.85 and shall be able to measure electron temperatures up to 40 keV. The Divertor TS will observe a segment of the divertor plasma more than 700 mm long and is designed to detect T e as low as 0.3 eV.The Edge and Core systems are primary contributors to T e and n e profiles. Both are installed in equatorial port 10 and very close together with the toroidal distance between the two laser beams of less than 600 mm at the first wall (∼ 6 • toroidal separation), a characteristic that should allow to reliably match the two profiles in the region 0.8 < r/a < 0.85.Today almost every existing fusion machine has one or more TS systems installed, therefore substantial experience has been accumulated worldwide on practical methods for the optimization of the technique. However the ITER environment is imposing specific loads (e.g. gamma and neutron radiation, temperatures, disruption-induced stresses) and also access and reliability constraints that require new designs for many of the sub-systems.The challenges and the proposed solutions for all three TS systems are presented. K : Plasma diagnostics -interferometry, spectroscopy and imaging; Plasma diagnosticscharged-particle spectroscopy 1Corresponding author.
This paper includes discussions of spatial resolution and accuracy of the edge Thomson scattering system in ITER (ITER ETS). In the present design, the dominant factor for spatial resolution degradation relative to the scattering length is aberrations of the collection optics. A scattering length of approximately 4 mm is acceptable to obtain a spatial resolution of 5 mm. Statistical errors were evaluated according to measurement accuracy. Since the background light during ITER plasma discharge is much stronger than the Thomson scattering, the laser pulse duration is one of the most crucial specifications to obtain accurate measurements. The impact of fast sampling relative to current integration was also investigated. It is expected that the measurement accuracy improves when the waveform of the scattered light is sampled directly particularly for low density measurement.
A prototype YAG laser system for the edge Thomson scattering system in ITER has been newly developed. Performance of the laser amplifier was improved by using flow tubes made of samarium-doped glass; the small signal gain reached 20 at its maximum. As a result, an output energy of 7.66 J at 100 Hz was successfully achieved, and the performance exceeded the target performance (5 J, 100 Hz).
Anisotropic electron temperature can be measured by utilizing two Thomson scattering spectra from different scattering angles. The ideal conditions for measurement are as follows: the sum of the two scattering angles is 180°, and the magnetic field is parallel to the bisector of the angle formed by the direction of laser propagation and the line of sight or is perpendicular to this bisector. When these conditions are satisfied, one of the spectra predominantly reflects the parallel electron temperature, and the other spectrum predominantly reflects the perpendicular electron temperature. A deviation in the direction of magnetic field of the order of approximately a few tens of degrees from the ideal direction is acceptable in terms of the deviation obtained by both rotating parallel to and tilting from the scattering plane.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.