Multispecies collisional effects on linear MHD stability of Wide Pedestal Quiescent H-mode DIII plasmas

We present full-extended linear MHD simulations of a Wide Pedestal QH (WPQH)-mode DIII-D plasma with the NIMROD code [1, 2] to address the role of ion multispecies collisionality on WPQH-modes. We show that 2-fluid and Finite Larmor Radius (2F/FLR) effects destabilize peeling-ballooning modes (PB) in the pedestal. Including carbon (C) to a pure deuterium (D) plasma has a stabilizing effect on the modes, due to the multispecies collisional effect on the electron collisionality that considers the interaction between electrons and ions, ultimately increasing the resistivity. When replacing C with tungsten (W), the multispecies collisional effects increase the resistivity further, as well as the stabilization effect. The resistivity impact on mode stability is reversed when 2F/FLR effects are ignored, as studied previously [3], proving the crucial role of multispecies collisional effects and 2F/FLR to address the stability of plasmas with significant impurity content. The results indicate that pure D plasmas are more prone to PB modes (potentially leading to ELMs), and that plasmas with W may be more prone to complete stabilization suppressing the edge instabilities that are key to regulating the pedestal. Work supported by US DOE under grants DE-SC0024592, DE-FC02-04ER54698, DE-AC02- 09CH11466 and DE-SC0022270.

References

[1] C.R. Sovinec et al., J. Comput. Phys. 195, 355 (2004).

[2] C.R. Sovinec et al., J. Comput. Phys. 229, 5803 (2010).

[3] D. Banerjee et al., Nucl. Fusion 57, 076005 (2017).