Empirical study of gradient lengths ratio η_e in edge plasma region in the near SOL region in ASDEX Upgrade tokamak

Empirical study of gradient lengths ratio η_e in edge plasma region in the near SOL region in ASDEX Upgrade tokamak

Empirical study of gradient lengths ratio η_e in edge plasma region in the near SOL region in ASDEX Upgrade tokamak 150 150 UKAEA Opendata
UKAEA-CCFE-PR(21)08

Empirical study of gradient lengths ratio η_e in edge plasma region in the near SOL region in ASDEX Upgrade tokamak

A survey of the correlation between temperature and density gradient lengths ( and ) has been performed for the near SOL regions in the ASDEX Upgrade tokamak. In common with previous studies, the near SOL temperature and density gradient length ratio, , is found to be close to unity across a wide range of plasmas. However, it is found that it is possible for both the temperature and density gradients to vary separately without varying the other greatly. The empirical results show that the correlation between temperature and density profiles in the near SOL is related to the divertor regimes. In the linear/sheath limited regime, the density and temperature profiles are correlated as , giving . In the high recycling/ conduction limited regimes, which is the most common case for ASDEX Upgrade plasma, and are correlated due to a common dependence on or, equally, . A weak dependence of on separatrix temperature is observed in this regime. Since the separatrix temperature depends only weakly on the power density flowing through the SOL and the variation is very small, a small variation of is observed. For ASDEX Upgrade, it lies between 1 and 2 for most of discharges in the conduction limited regime. In the detached regime, convection could be important for the cross field particle transport and filaments appear, may trigger a regime transition leading to strongly enhanced perpendicular particle fluxes, resulting in a very flat density profiles while temperature profile remain unaffected, resulting in very high , for ASDEX Upgrade, up to 6.

Collection:
Journals
Journal:
Plasma Physics and Controlled Fusion
Publisher:
IOP (Institute of Physics)
Published date:
06/03/2021