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

Hu, Jiansheng; Sun, Zhuo; Guo, H.Y.; Li, J. G.; Wan, Baonian; Wang, H. Q.; Ding, Siye; Xu, G. S.; Liang, Y.; Mansfield, D. K.; Maingi, R.; Zou, X. L.; Wang, L.; Ren, Jin; Zuo, Guizhong; Zhang, L.; Duan, Yanmin; Shi, Tonghui; Hu, Liqun; Team, East

doi:10.1103/physrevlett.114.055001

Cited by 97 publications

(92 citation statements)

References 29 publications

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“…We have concentrated our efforts in the domain where J BS at the edge is large, which tends to coincide with the region where low n = 1 structures dominate (corresponding to the upper half of the graph in figure 8). In our opinion, these structures constitute a very realistic model for the OM observed on JET (Solano 2010) and the EHO detected on DIII-D and other tokamaks (Burrell et al 2005;Suttrop et al 2005;Hu et al 2015). A detailed analysis of the equilibrium state for large edge J BS indicates that a parallel helical current density ribbon forms just outside the q = 3 rational surface with a radial extent that aligns with the vanishing magnetic shear region associated with the flat spot in the q-profile caused by the bootstrap current.…”

Section: Discussionmentioning

confidence: 99%

“…We interpret these deformations as indicative of the development of an external kink/peeling mode that saturates at finite amplitude. The distortions observed are symptomatic of the edge harmonic oscillation (EHO) (Burrell et al 2005) first reported on DIII-D, but subsequently observed on many other machines (Suttrop et al 2005;Hu et al 2015), and the outer mode (OM) measured on JET (Solano et al 2010). The shape of the last closed magnetic flux surface on TCV at four different cross-sections projected onto a single toroidal plane for β N = 1, 1.49, 1.99 and 2.47 are presented in figure 4.…”

Section: -D Equilibrium Numerical Simulations: Nonlinearly Stable Stmentioning

confidence: 99%

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A 3-D MHD equilibrium description of nonlinearly saturated ideal external kink/peeling structures in tokamaks

et al. 2015

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Novel free boundary magnetohydrodynamic equilibrium states with spontaneous three-dimensional (3-D) deformations of the plasma-vacuum interface are computed. The structures obtained look like saturated ideal external kink/peeling modes. Large edge pressure gradients yield toroidal mode number n = 1 distortions when the edge bootstrap current is large and higher n corrugations when this current is small. Linear ideal MHD stability analyses confirm the nonlinear saturated ideal kink equilibrium states produced and we can identify the Pfirsch-Schlüter current as the main linear instability driving mechanism when the edge pressure gradient is large. The dominant non-axisymmetric component of this Pfirsch-Schlüter current drives a near resonant helical parallel current density ribbon that aligns with the near vanishing magnetic shear region caused by the edge bootstrap current. This current ribbon is a manifestation of the outer mode previously found on JET (Solano 2010). We claim that the equilibrium corrugations describe structures that are commonly observed in quiescent H-mode tokamak discharges.

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Section: Discussionmentioning

confidence: 99%

Section: -D Equilibrium Numerical Simulations: Nonlinearly Stable Stmentioning

confidence: 99%

A 3-D MHD equilibrium description of nonlinearly saturated ideal external kink/peeling structures in tokamaks

et al. 2015

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“…Finally, a scenario was developed on EAST [49] which seems to be a combination of the above two scenarios. When lithium is injected into a discharge, an pre-existing edge coherent mode (ECM), thought to be a TEM, is further excited and results in a stable ELM-free scenario.…”

Section: Low-z Impurity Injectionmentioning

confidence: 99%

Impact of impurity seeding and divertor conditions on transitions, pedestal structure and ELMs

Dunne

2016

Nucl. Fusion

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Future devices will require a high scrape-off later (SOL) density and impurity seeding to avoid high-Z sputtering. However, these operational parameters are not included in present-day scaling laws, making extrapolations to larger devices difficult. As such, understanding the physics of such effects is vital in order to design the operational scenarios most favorable to high fusion gain. This review presents the favorable lowering of L-H transition power by changing to metal walled devices and sumarises the effects currently thought to be responsible for how SOL geometry can play a role in determining this threshold. Experimental observations on changes to the pedestal structure with main ion fuelling and low-, medium-, and high-Z impurity seeding are presented. These results, from several devices, show that main ion fuelling or high density operation can result in a lower pedestal top pressure, and hence reduced stored energy, while impurity seeding can recover this lost pressure. Particular focus is given to nitrogen seeded discharges and the recovery of pedestal parameters (notably high T e,ped ) in JET and AUG since the changeover to metal walls in these devices. Lithium seeding is also emerging as a strong actuator in pedestal dynamics, with results ranging from a prolonged inter-ELM period to completely ELM-free scenarios on different devices. ELM dynamics are also presented in each section, with nitrogen seeding offering a probe into the structure of the ELM and demonstrating the difference between the initial ELM crash, likely due to a sharp MHD event, and a prolonged second phase, the origin of which remains unkown. Finally, modelling of the pedestal in impurity seeded scenarios reveals a common effect in the position of the density profile. Either through mode excitation near to the separatrix or an altered fuelling profile, seeding of impurities results in an inward shift of the density profile. This inward shift improves MHD stability, allowing access to regions of higher pressure gradient and current density, and, hence, offering a promising operational scenario for future devices.

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“…As another Li wall conditioning method, the real-time Li aerosol injection technique is also developed on EAST and actively supports the achievement of long-pulse ELMfree H modes [26,27]. The edge impurity levels and particle recycling can be reduced by real-time Li injection, thus improving plasma performances.…”

Section: Control Of W Sputtering Sourcementioning

confidence: 99%

Plasma–tungsten interactions in experimental advanced superconducting tokamak (EAST)

et al. 2019

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Tungsten (W) is used as the armor material of the International Thermonuclear Experimental Reactor (ITER) divertor and is regarded as the potential first wall material of future fusion reactors. One of the key challenges for the successful application of W in fusion devices is effective control of W at an extremely low concentration in plasma. Understanding and control of W erosion are not only a prerequisite for W impurity control, but also vital concerns to plasma-facing component (PFC) lifetime. Since the application of ITER-like water-cooled full W divertor in EAST in 2014, great efforts were made to investigate W erosion by experiment and simulation. A spectroscopic system was developed to provide a real-time measurement of W sputtering source. Both experiment and simulation results indicate that carbon (C) is the dominant impurity causing W sputtering in L-mode plasmas, which comes from the erosion of C plasma-facing material (PFM) in the lower divertor and the main chamber limiters. The mixture layer on the surface of W PFCs formed through redeposition or the wall coating can effectively suppress W erosion. Increasing the plasma density and radiation can reduce incident ion energy, thus alleviating W sputtering. In H-mode plasmas, control of edge localized mode (ELM) via resonant magnetic perturbation (RMP) proves to be capable of suppressing intra-ELM W erosion. The experiences and lessons from the EAST W divertor are beneficial to the design, manufacturing and operation of ITER and beyond.

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

Cited by 97 publications

References 29 publications

A 3-D MHD equilibrium description of nonlinearly saturated ideal external kink/peeling structures in tokamaks

A 3-D MHD equilibrium description of nonlinearly saturated ideal external kink/peeling structures in tokamaks

Impact of impurity seeding and divertor conditions on transitions, pedestal structure and ELMs

Plasma–tungsten interactions in experimental advanced superconducting tokamak (EAST)

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