Spatially resolved measurement of helium atom emission line spectrum in scrape-off layer of Heliotron J by near-infrared Stokes spectropolarimetry

1視線の観測のみで核融合プラズマ中のヘリウム近赤外輝線の発光分布を推定. 京都大学プレスリリース. 2022-09-26.For plasma spectroscopy, Stokes spectropolarimetry is used as a method to spatially invert the viewing-chord-integrated spectrum on the basis of the correspondence between the given magnetic field profile along the viewing chord and the Zeeman effect appearing on the spectrum. Its application to fusion-related toroidal plasmas is, however, limited owing to the low spatial resolution as a result of the difficulty in distinguishing between the Zeeman and Doppler effects. To resolve this issue, we increased the relative magnitude of the Zeeman effect by observing a near-infrared emission line on the basis of the greater wavelength dependence of the Zeeman effect than of the Doppler effect. By utilizing the increased Zeeman effect, we are able to invert the measured spectrum with a high spatial resolution by Monte Carlo particle transport simulation and by reproducing the measured spectra with the semiempirical adjustment of the recycling condition at the first walls. The inversion result revealed that when the momentum exchange collisions of atoms are negligible, the velocity distribution of core-fueling atoms is mainly determined by the initial distribution at the time of recycling. The inversion result was compared with that obtained using a two-point emission model used in previous studies. The latter approximately reflects the parameters of atoms near the emissivity peak

Recent Results from LHD Experiment with Emphasis on Relation to Theory from Experimentalist’s View

he Large Helical Device (LHD) has been extending an operational regime of net-current free plasmas towardsthe fusion relevant condition with taking advantage of a net current-free heliotron concept and employing a superconducting coil system. Heating capability has exceeded 10 MW and the central ion and electron temperatureshave reached 7 and 10 keV, respectively. The maximum value of β and pulse length have been extended to 3.2% and 150 s, respectively. Many encouraging physical findings have been obtained. Topics from recent experiments, which should be emphasized from the aspect of theoretical approaches, are reviewed. Those are (1) Prominent features in the inward shifted configuration, i.e., mitigation of an ideal interchange mode in the configuration with magnetic hill, and confinement improvement due to suppression of both anomalous and neoclassical transport, (2) Demonstration ofbifurcation of radial electric field and associated formation of an internal transport barrier, and (3) Dynamics of magnetic islands and clarification of the role of separatrix

ヘリカル プラズマチュウ ノ チュウセイ スイソ ゲンシ ノ ブンコウガクテキ ケンキュウ

京都大学0048新制・課程博士博士(エネルギー科学)甲第10981号エネ博第92号新制||エネ||25(附属図書館)UT51-2004-G828京都大学大学院エネルギー科学研究科エネルギー基礎科学専攻(主査)教授 近藤 克己, 教授 佐野 史道, 教授 前川 孝学位規則第4条第1項該当Doctor of Energy ScienceKyoto UniversityDA

Redeposition Characteristics of Heavy Hydrocarbon Molecules on a Divertor Plate * )

In this study, local redeposition characteristics of hydrocarbon molecules from the ethane family are investigated using Monte Carlo simulation. Information about redeposition characteristics is required to estimate tritium retention via redeposition with chemically eroded hydrocarbon molecules. For the condition of multiple reflections at divertor surface and a plasma density of 1.0 × 10 19 m −3 , the local redeposition characteristics for injection of ethane family (C 2 H 2 , C 2 H 4 , C 2 H 6 ) have been investigated for plasma temperatures ranging from 1 to 100 eV. The number of redeposited hydrocarbon molecules increases with plasma temperature because of the increase in impinging particle energy. The increase in sheath potential results in the increase in particle energy. For plasma temperatures lower than 5 eV, there is a sudden increase in the number of redeposited particles with plasma temperature because of the increase in the number of impinging molecular ions. Sheath field acceleration is the main mechanism that causes the ions to move to the divertor plate, and the exponential increase in the number of redeposited particles results from the increase in hydrocarbon break-up products in the sheath potential region

Studies of the Confinement and the Toroidal Current Control in Heliotron J

The plasma confinement properties of Heliotron J plasmas and the toroidal current are investigated. A plasma energy of 2.5 kJ has been achieved by 70 GHz-0.35 MW electron cyclotron heating (ECH). The energy confinement time is within the expected values as determined by the stellarator scaling law. In the high density region, however, better confinement plasmas are observed. The transition phenomena characterized by Hα signal drop are sometimes observed in such a region. The toroidal current generally affects plasma confinement since it generates a poloidal magnetic field. From this point of view, toroidal current control is studied in terms of field-component variation and electron cyclotron current drive. The zero current condition is found in the inner vertical field scan. Current control using the electron cyclotron wave is also demonstrated