New Steady-State Quiescent High-Confinement Plasma in an Experimental Advanced Superconducting Tokamak

J. S. Hu, Z. Sun, H. Y. Guo, J. G. Li, B. N. Wan, H. Q. Wang, S. Y. Ding, G. S. Xu, Y. F. Liang, D. K. Mansfield, R. Maingi, X. L. Zou, L. Wang, J. Ren, G. Z. Zuo, L. Zhang, Y. M. Duan, T. H. Shi, L. Q. Hu, and East team

Phys. Rev. Lett. 114, 055001 – Published 3 February 2015; Erratum Phys. Rev. Lett. 115, 169901 (2015)

Abstract

A critical challenge facing the basic long-pulse high-confinement operation scenario ( $H$ mode) for ITER is to control a magnetohydrodynamic (MHD) instability, known as the edge localized mode (ELM), which leads to cyclical high peak heat and particle fluxes at the plasma facing components. A breakthrough is made in the Experimental Advanced Superconducting Tokamak in achieving a new steady-state $H$ mode without the presence of ELMs for a duration exceeding hundreds of energy confinement times, by using a novel technique of continuous real-time injection of a lithium (Li) aerosol into the edge plasma. The steady-state ELM-free $H$ mode is accompanied by a strong edge coherent MHD mode (ECM) at a frequency of 35–40 kHz with a poloidal wavelength of 10.2 cm in the ion diamagnetic drift direction, providing continuous heat and particle exhaust, thus preventing the transient heat deposition on plasma facing components and impurity accumulation in the confined plasma. It is truly remarkable that Li injection appears to promote the growth of the ECM, owing to the increase in Li concentration and hence collisionality at the edge, as predicted by GYRO simulations. This new steady-state ELM-free $H$ -mode regime, enabled by real-time Li injection, may open a new avenue for next-step fusion development.

Received 19 August 2014

DOI:https://doi.org/10.1103/PhysRevLett.114.055001

Erratum

Erratum: New Steady-State Quiescent High-Confinement Plasma in an Experimental Advanced Superconducting Tokamak [Phys. Rev. Lett. 114, 055001 (2015)]

J. S. Hu, Z. Sun, H. Y. Guo, J. G. Li, B. N. Wan, H. Q. Wang, S. Y. Ding, G. S. Xu, Y. F. Liang, D. K. Mansfield, R. Maingi, X. L. Zou, L. Wang, J. Ren, G. Z. Zuo, L. Zhang, Y. M. Duan, T. H. Shi, L. Q. Hu, and EAST team

Phys. Rev. Lett. 115, 169901 (2015)

Authors & Affiliations

J. S. Hu^1,*, Z. Sun¹, H. Y. Guo^1,2, J. G. Li¹, B. N. Wan¹, H. Q. Wang¹, S. Y. Ding¹, G. S. Xu¹, Y. F. Liang^1,3, D. K. Mansfield⁴, R. Maingi⁴, X. L. Zou⁵, L. Wang¹, J. Ren¹, G. Z. Zuo¹, L. Zhang¹, Y. M. Duan¹, T. H. Shi¹, L. Q. Hu¹, and East team

¹Institute of Plasma Physics, Chinese Academy of Sciences, Hefei, Anhui 230031, China
²General Atomics, P.O. Box 85608, San Diego, California 92186-5608, USA
³Forschungszentrum Jülich GmbH, Association EURATOM-FZ, Jülich D-52425, Germany
⁴Princeton University Plasma Physics Laboratory, Princeton, New Jersey 08543, USA
⁵CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France

^*Corresponding author. hujs@ipp.ac.cn

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Vol. 114, Iss. 5 — 6 February 2015

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Images

Figure 1
Left: a magnetic flux plot typical of the double-null discharges (e.g., No. 41079) studied in this work with the location of the Li aerosol injector indicated. Right: a sequence of true color images beginning at the time of Li aerosol injection started at $\sim 4.9 s$ , viewed at a location 90 deg toroidally separated from the injection point. The green color shows 5485 Å Li-II emission from singly-ionized Li, demonstrating that relatively uniform Li emission can be achieved about 1 sec after the start of the Li aerosol injection. It is interesting to note the initial absence of Li-II emission, even though the EAST PFCs were covered with 500 g of evaporated Li accumulated before the start of this Li aerosol injection experiment.
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Figure 2
Demonstration of reproducible long-pulse ELM-free $H$ modes with real-time Li injection. Data shown are the evolution of $D α$ emission at the lower divertor target in various $H$ -mode plasmas with and without Li aerosol injection. ELMs are manifested as spikes in the $D α$ emission.
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Figure 3
Comparison of two long-pulse $H$ -mode discharges with and without real-time Li injection (double null divertor configuration, $P_{LHW} = 1.4 WM$ , $P_{ICRF} = 0.7 WM$ ). Shown are the (a) Li-II line radiation emission integrated across the main plasma at midplane, (b) line average density, (c) H98( $y$ , 2) confinement enhancement factor, (d) LHW and ICRF heating power, (e) C-III line radiation, (f) core radiation from ultraviolet photodiodes with a wavelength range of 0.2–1240 nm, (g) edge radiation, (h) MHD signals measured by the low-sampling-frequency Mirnov coil (50 kHz) at midplane on the high field side, (i) divertor heat flux measured by Langmuir probes embedded in the lower outboard divertor target, and (j) $D α$ at the lower outboard divertor. Panels (k) and (l) show an expanded time base of the $D α$ emission and heat flux at the lower outboard divertor, the latter obtained from Langmuir probe data.
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Figure 4
The magnetic fluctuation time-frequency spectrum with two active edge coherent modes at 35–40 kHz in $H$ -mode plasmas with $q_{95} = 7.4$ using real-time Li aerosol injection. Shown are the (a) phase spectrum, obtained from two high-sampling-frequency (250 kHz) Mirnov magnetic pickup probes near the midplane on the outboard side (the poloidal distance is 63 cm; the intensity scale from $- 1$ to 1 means the poloidal phase from $2 n π - π$ to $2 n π + π$ ), (b) power intensity spectrum, obtained from one of the above probes, and (c) phase and power intensity versus frequency at 20 s during the shots.
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