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TJ-II: Density limit and ZFs in TJ-II: Difference between revisions
TJ-II: Density limit and ZFs in TJ-II (view source)
Revision as of 11:48, 20 January 2020
, 20 January 2020→Description of the activity
(Created page with "== Experimental campaign == 2020 Spring == Proposal title == '''TJ-II: Density limit and ZFs in TJ-II''' == Name and affiliation of proponent == Ulises Losada, Daniel Ferná...") |
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Density limit is manifested in tokamaks, stellarators and RFPs. In stellarator the density limit is related to radiation collapse mechanisms <ref>M. Hirsch et al., PPCF 2007)</ref> whereas in tokamaks edge transport can play an important role <ref>M. Greenwald Plasma Phys. Control. Fusion 44 (2002) R27</ref>. | Density limit is manifested in tokamaks, stellarators and RFPs. In stellarator the density limit is related to radiation collapse mechanisms <ref>M. Hirsch et al., PPCF 2007)</ref> whereas in tokamaks edge transport can play an important role <ref>M. Greenwald Plasma Phys. Control. Fusion 44 (2002) R27</ref>. | ||
LRC in floating potential fluctuations has been investigated in the proximity of the density-limit in the NBI plasma scenarios in TJ-II | LRC in floating potential fluctuations has been investigated in the proximity of the density-limit in the NBI plasma scenarios in TJ-II. The density limit decreases with the magnetic field (B = 0.7 – 1 T) in qualitative agreement with the empirical stellarator scaling law for density limit [5]. At low densities the LRCs, measured at rho ≈ 0.9 for frequencies below 20 kHz, are quite large (≈ 0.8) and vary only slightly with increasing density. When approaching the density-limit the amplitude of LRC reduces rapidly with increasing plasma density, in agreement with previous results <ref>Y. Xu et al Nucl. Fusion 51 (2011) 063020</ref>. The reduction in the LRC as approaching the density limit is accompanied by a reduction in edge mean radial electric field and the level of plasma turbulence. Results point to the role of collisionality, mean E × B flows and level of turbulence on the amplitude of zonal flows in the proximity of the density limit. | ||
TJ-II findings suggest that at a threshold radiation value for the density limit the degradation of confinement would be partially due to the damping of Zonal Flows as recently pointed out <ref>R. J. Hajjar et al., Physics of Plasmas 25 (2018) 062306</ref>. If this is the case, density limit in stellarators would depend on the transport optimization criteria, a prediction that could be validated experimentally. | TJ-II findings suggest that at a threshold radiation value for the density limit the degradation of confinement would be partially due to the damping of Zonal Flows as recently pointed out <ref>R. J. Hajjar et al., Physics of Plasmas 25 (2018) 062306</ref>. If this is the case, density limit in stellarators would depend on the transport optimization criteria, a prediction that could be validated experimentally. | ||
== International or National funding project or entity == | == International or National funding project or entity == | ||