Experimental study of non-inductive current in Heliotron J

It is important to control non-inductive current for generation and steady-state operation of highperformance plasmas in toroidal fusion devices. Helical devices allow dynamic control of non-inductivecurrent through a wide variety of magnetic configurations. The reversal of non-inductive current consisting of bootstrap current and electron cyclotron driven current in electron cyclotron heating plasmas has been observed in a specific configuration at low density in Heliotron J device. By analyzing thenon-inductive current for normal and reversed magnetic fields, we present experimental evidence for the reversal of bootstrap current. Our experiments and calculations suggest that the reversal is caused bya positive radial electric field of about 10 kV/m. Moreover, we show that the typical electron cyclotron current drive efficiency in Heliotron J plasma is about 1.0 × 1017 AW?1m?2, which is comparable to other helical devices. We have found that the value is about 10 times lower than that of tokamak devices. This might be due to an enhanced Ohkawa effect by trapped particles

Effects of the resonance modification by electron cyclotron current drive on the linear and nonlinear dynamics of energetic particle driven magnetohydrodynamics modes in Heliotron J

ORCID　0000-0001-7332-037XThis study investigates the effects of electron cyclotron current drive (ECCD) on the linear and nonlinear dynamics of energetic-particle (EP)-driven magnetohydrodynamics (MHD) instability (mode) in Heliotron J (HJ), using MEGA, a nonlinear hybrid EP-MHD simulation code. The effects of ECCD are included through the modification of the equilibrium magnetic field. Five MHD equilibria with plasma currents (Ip) of −2.00, −1.00, 0.00, 0.50, and 1.00 kA are considered, where negative and positive Ip represent counter and co-ECCD, respectively. To account for the EP finite charge-exchange loss observed in HJ, a bump-on-tail velocity distribution is assumed for EP. The study finds that the stabilization trends in terms of the linear growth rate (γω−1A ) are qualitatively similar to the FAR3D linear simulation and experimental results. In addition to the enhancements of the local magnetic shear and continuum damping by ECCD as proposed in previous studies, the study suggests that changes in the linear EP and shear Alfvén wave resonance are another important factor, especially for the n/m = 1/2 mode. The study shows that in the currentless equilibrium, the high-velocity toroidicity-induced resonance between the n/m = 1/2 mode and the co-passing EP (L = −1) has the highest EPjournal articl

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

Response of a core coherent density oscillation on electron cyclotron resonance heating in Heliotron J plasma

We report properties of a coherent density oscillation observed in the core region and its response to electron cyclotron resonance heating (ECH) in Heliotron J plasma. The measurement was performed using a multi-channel beam emission spectroscopy system. The density oscillation is observed in a radial region between the core and the half radius. The poloidal mode number is found to be 1 (or 2). By modulating the ECH power with 100 Hz, repetition of formation and deformation of a strong electron temperature gradient, which is likely ascribed to be an electron internal transport barrier, is realized. Amplitude and rotation frequency of the coherent density oscillation sitting at the strong electron temperature gradient location are modulated by the ECH, while the poloidal mode structure remains almost unchanged. The change in the rotation velocity in the laboratory frame is derived. Assuming that the change of the rotation velocity is given by the background E × B velocity, a possible time evolution of the radial electric field was deduced

H・ベルの初期の短篇小説

「私がこれまでに書いたものは――合間に書いた比較的ささやかなもの，論文，批評も合めて――すべて一つの続きである。」とベルが言明したのは1971年，ノーベル賞受賞の前年である。これはとりたてて意外な発言とは思えない。一般に，時代の結節点となり得るような社会的，歴史的事件は，それに参加したか否かという個人の次元を超えて，ある世代の原風景というべき，特有な精神の形成を行うものであって，ベルの場合，根強い人気の秘密がこの共通体験にあるとは充分考えられるからである。そうしてベルが，それは「ある根本的な主題の絶えざるヴァリエーション」であり，「書き加え」であるとつけ加える時，そこに一つの軌跡を描き出すのはそれほど困難には見えない。しかし他方で，体験は一世代への拡がりを持つと同時に，元来個人的，意識的思想形成の前提であり，それぞれに時間の侵蝕を受け，風化，あるいは変質してゆくことを考慮するならば，恐らく上の発言に籠められている苦渋，困難が予想されてくるし，その軌跡が単純である筈はなく，この作家の体験がその後の歴史の変化する状勢に対しても常に開かれ，それに基いて，きわめて現代的な世界を呈示し続けて来たことに思い当る。その作品世界は，恒常性を堅持する側面と折々の瞬間に向けられた側面との対立，緊張関係のうちに構築されて来たのである。このような展開の跡を辿るためには，むろんまず初期作品の検討から出発しなければなるまい。本論はそのささやかな試みである