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TJ-II: Influence of magnetic configuration on filament dynamics: Difference between revisions
TJ-II: Influence of magnetic configuration on filament dynamics (view source)
Revision as of 09:51, 10 December 2020
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== Description of the activity == | == Description of the activity == | ||
SOL transport in tokamaks is generally thought to be dominated by the macroscopic convective cells usually known as “filaments” or “blobs”. These filaments propagate ballistically in the radial direction due to the ExB velocity associated to the dipole generated around a pressure oscillation in the presence of a magnetic field featuring curvature (IC instability) <ref> S. I. Krasheninnikov, D. A. D'Ippolito and J. R. Myra, J. Plasma Phys. 74 (2008) 679717 </ref>. Depending on several characteristics of the SOL, filaments may be in a number of propagation regimes <ref> P. Manz, D. Carralero, G. Birkenmeier et al., Physics of Plasmas 20 (2013) 102307</ref>, which affect their size, frequency, speed, amplitude and eventually the magnitude of the transport associated to them. | |||
In tokamaks, a substantial amount of work has been done to validate experimentally these simple filament models and to measure the transport associated to them <ref> D’Ippolito D.A., Myra J.R. and Zweben S.J., Phys.Plasmas 18 (2011) 060501,4</ref><ref>D. Carralero, P. Manz, L. Aho-Mantila, et al. Phys. Rev. Lett. 115 (2015) 215002</ref>. However, substantially less studies in stellarators are found in the literature, leaving the open question of how does the complex geometry of a non-axially symmetric SOL influence these structures. Recently, a first filament characterization has been carried out in the novel optimized stellarator Wendelstein 7-X, in which filaments feature sizes comparable to those found in tokamaks, but substantially lower speeds and transport <ref>C. Killer, B. Shanahan, O. Grulke et al., Plasma Phys. Control. Fusion 62 (2020) 085003</ref>. This result has been explained invoking the reduced curvature drive associated to the large aspect ratio of W7-X with respect to a tokamak. However, this effect remains largely intertwined with the complex geometry of the stellarator, involving islands, and long connection lengths which cause filaments to alternate many regions of good and bad curvature along the parallel direction. | |||
TJ-II is equipped with a dual system of multi-probes arrays placed at two different toroidal and poloidal locations [probes B and D] [<ref>T. Kobayashi, U. Losada, B. Liu et al., Nuclear Fusion 59, 044006 (2019)</ref>]. While | In this context, the stellarator TJ-II provides a very appropriated experimental setup to test this hypothesis. While it shares with W-7X a fully 3D SOL, it differs from it in two relevant aspects: in the first place, due to its heliac configuration and smaller size, there are regions in it with substantial curvature, closer to that found in a tokamak. Since it is equipped with a dual system of multi-probes arrays placed at two different toroidal and poloidal locations, it is posible to measure filaments in regions with different curvatures (probe B lies in a neutral to favorable curvature probe D is in an unfavorable negative curvature zone). In the second place, it does not typically feature a rational close to the edge for a typical operation setting, although one can be intruduced by selecting the right magnetic configuration. By this means, it would be posible to disentangle the effects of curvature and SOL islands on filaments. | ||
While some | |||
TJ-II is [probes B and D] [<ref>T. Kobayashi, U. Losada, B. Liu et al., Nuclear Fusion 59, 044006 (2019)</ref>]. While . This makes TJ-II a unique device to explore (simultaneously) the influence of magnetic curvature on blob dynamics. | |||
The goal of this research proposal is: | The goal of this research proposal is: | ||