Evidence of a nonlinear transition from mitigation to suppression of the edge localized mode (ELM) by using resonant magnetic perturbations (RMPs) in the EAST tokamak is presented. This is the first demonstration of ELM suppression with RMPs in slowly rotating plasmas with dominant radio-frequency wave heating. Changes of edge magnetic topology after the transition are indicated by a gradual phase shift in the plasma response field from a linear magneto hydro dynamics modeling result to a vacuum one and a sudden increase of three-dimensional particle flux to the divertor. The transition threshold depends on the spectrum of RMPs and plasma rotation as well as perturbation amplitude. This means that edge topological changes resulting from nonlinear plasma response plays a key role in the suppression of ELM with RMPs. DOI: 10.1103/PhysRevLett.117.115001 Magnetic reconnection and the resultant topological change play an important role in plasma dynamics in both laboratory and space plasma physics research. The formation of an edge stochastic magnetic field caused by resonant magnetic perturbations (RMPs) is believed to be the reason for the suppression of periodic crash events near the plasma edge known as the edge localized mode (ELM) observed in the DIII-D tokamak [1]. The ELM causes transient heat loads to the plasma facing components and may degrade them on the next generation fusion device like ITER [2]. The reduction of free energy in the edge pressure gradient and current because of field stochasticity moves the plasma into a stable regime against the ELM [3]. This successful experiment motivated ELM control using RMPs in many other tokamaks [4][5][6][7]. However, the plasma response effect usually shields the external applied RMPs and may significantly reduce the magnetic field stochasticity [8][9][10][11], which makes this mechanism questionable. Different from topological change, the linear peelinglike magneto hydro dynamics (MHD) response has been found to play an important role in ELM control [12][13][14]. Nonlinear plasma response has been observed in the JET totamak [15]. The possible formation of a magnetic island near the plasma edge [16] with a toroidal Fourier mode number n ¼ 1 during ELM suppression by using n ¼ 2 RMP has been recently observed on DIII-D [17]. However, the key difference between ELM suppression and mitigation and the different roles of linear and nonlinear plasma response on ELM suppression are still not clear.In this Letter, we report the first observation of full ELM suppression using low n RMPs in slowly rotating plasmas with dominant radio-frequency (rf) wave heating, which is potentially important for the application of this method for a future fusion device. This is the first observation of full ELM suppression using RMPs in the medium plasma collisionality regime in EAST, and it expands beyond the previous observations of ELM suppression on DIII-D [1,3] and KSTAR [7]. It is found that not only the formation of a magnetic island near the edge [17] but also a critical leve...

[1] A marine Permian-Triassic boundary (PTB) section at Nhi Tao, Vietnam, contains a series of at least 9 pyritic horizons characterized by concurrent decreases in pyrite S-(d 34 S py ) and carbonate C-isotopic compositions (d 13 C carb ). The first and largest of the events that precipitated these pyritic horizons was coincident with the Late Permian mass extinction, while subsequent events were generally smaller and occurred at quasiperiodic intervals of $20 to 30 ka. A near complete lack of organic carbon to drive bacterial sulfate reduction in sediment pore waters, among other considerations, argues against a diagenetic control for these relationships. Rather, the covariant patterns documented herein are most easily explained as the product of recurrent upwelling of anoxic deep-ocean waters containing 34 S-depleted hydrogen sulfide and 13 C-depleted dissolved inorganic carbon. The sulfide d 34S record of the study section represents a mixture of a small amount of isotopically heavy authigenic pyrite (formed via in situ bacterial sulfate reduction) with a generally larger quantity of isotopically light syngenetic pyrite precipitated within the water column during upwelling episodes. Although upwelling of toxic deepwaters has been invoked in earlier studies as a mechanism for the Late Permian marine mass extinction, this is the first study to (1) document patterns of pyrite-d 13 C carb covariation that strongly support upwelling as a major process at the PTB and (2) provide evidence of multiple, quasiperiodic upwelling events that may reflect reinvigoration of global-ocean overturn following a prolonged interval of Late Permian deep-ocean stagnation.Components: 5322 words, 5 figures.

Fe speciation and S-isotope of pyrite data from the terminal Proterozoic Sheepbed Formation in Canada and Doushantuo Formation in China reveal that ocean deep waters were anoxic after the global glaciations (snowball Earth) ending 635 million years ago, but that marine sulfate concentrations and inferentially atmospheric oxygen levels were higher than before the glaciations. This supports a long-postulated link between oxygen levels and the emergence of eumetazoa. Subsequent ventilation of the deep ocean, inferred from shifts in Fe speciation in Newfoundland (previously published data) and western Canada (this report), paved the way for Ediacaran macrobiota to colonize the deep seafloors.atmospheric oxygen ͉ iron speciation ͉ sulfur isotopes ͉ Sheepbed Formation ͉ Doushantuo Formation A pair of global glaciations (1) between 725 and 635 million years ago (Cryogenian Period) was followed by the appearance and diversification of (mainly nonskeletal) multicellular animals in the Ediacaran Period from 635 to 541 million years ago (2-7). The oldest animal fossils include diapause egg and embryo cysts (Tianzhushania spinosa) from the lower Doushantuo Formation (Ϸ632 Ma) in South China (8) and lipid biomarkers (24-isopropylcholestane) diagnostic of marine demosponges in late Cryogenian and early Ediacaran strata of Oman (9). In contrast, colonization of the deep seafloor (below the euphotic zone) by large soft-bodied organisms was delayed until mid-Ediacaran time Ϸ579 Ma (10-14).

Global fossil data show that profound biodiversity loss preceded the final catastrophe that killed nearly 90% marine species on a global scale at the end of the Permian. Many hypotheses have been proposed to explain this extinction and yet still remain greatly debated. Here, we report analyses of all four sulphur isotopes (32S, 33S, 34S and 36S) for pyrites in sedimentary rocks from the Meishan section in South China. We observe a sulphur isotope signal (negative δ34S with negative Δ33S) that may have resulted from limitation of sulphate supply, which may be linked to a near shutdown of bioturbation during shoaling of anoxic water. These results indicate that episodic shoaling of anoxic water may have contributed to the profound biodiversity crisis before the final catastrophe. Our data suggest a prolonged deterioration of oceanic environments during the Late Permian mass extinction.