31 / 2021-04-09 19:54:26

Heavy impurity transport in the presence of 3D MHD ideal saturated modes, rotation and ambipolar electric field

MHD,Heavy Impurity Transport,3D flows,Internal Kink,EHO

Early plasma termination is often observed in hybrid scenarios due to tungsten

accumulation events following large living MHD perturbations. This situation is currently

observed in JET and ASDEX-U, and similar behaviour may be of concern for future

tokamaks featuring tungsten plasma facing components like ITER and EU-DEMO. The

effects of background rotation profiles and 3D MHD equilibria on the transport of heavy

impurities have been investigated previously [1]. The VENUS-LEVIS code has been used

to follow heavy impurities in the presence of a 1/1 kink saturated 3D MHD equilibrium

and strong toroidal rotation [1]. This approach has recently been improved by

considering the effect of the background species’ heat flux as well as the effect of an

ambipolar radial electric field set by neoclassical toroidal viscosity (NTV) in the presence

of 3D perturbations in the low collisionality (1/ν) regime of the main ions [2]. The heat

flux effect is included using a recently developed neoclassical collision operator. NTV

effects are introduced by building on flow theory for general 3D magnetic configurations

[3]. The self-consistent background plasma configuration obtained in this way is then

used to follow heavy impurities with VENUS-LEVIS making use of the guiding centre

theory in [4] which allows for strong flows. The effect of the radial electric field

generated by ions and electrons in 3D stellarator configurations has been seen to be

important for impurity transport in the presence of impurity density asymmetries due

to helically trapped ions [5]. Nevertheless, the presence of saturated 3D MHD

perturbations in tokamaks like JET and ASDEX-U is a fundamentally different problem

due to strong flows which are inhibited in stellarator geometry. A numerical study

performed with VENUS-LEVIS shows that the synergy between centrifugal forces and

the NTV induced electric field has an important impact on heavy impurity transport in

the presence of a 1/1 internal kinked JET-like equilibrium [2]. In this work we also discuss

how heavy impurities behave in the presence of EHO perturbations which are generated

in ELM free QH-modes of relevance for EU-DEMO operation.

References:

[1] M. Raghunathan, et al., Plasma Physics and Controlled Fusion 59, 124002 (2017)

[2] E. Neto, et al., “Heavy Impurity transport in the presence of 3D MHD ideal perturbations, rotation

and NTV”, Theory of Fusion Plasmas Joint Varenna-Lausanne International Workshop (Lausanne,

Switzerland), P-17 (2020) (and submitted to PPCF 2021)

[3] P. Helander, et al., Journal of Plasma Physics 83, 905830206 (2017)

[4] A. J. Brizard, Physics of Plasmas 2, 459 (1995)

[5] I. Calvo, et al., Nuclear Fusion 58, 124005 (2018)