Linking the two-field dynamics of plasma edge turbulence with the one-field balanced model through systematic unstable forcing at low resistivity

Abstract

After the original contributions of Hasegawa and Wakatani (HW), basic two-field models such as the modified and balanced Hasegawa-Wakatani (BHW) models improve the understanding of plasma edge turbulence. The recent two-field flux-BHW model provides an improved treatment for the balanced electron dynamics on magnetic flux surfaces. The Hasegawa-Mima (HM) model offers another simplified one-field characterization of the zonal flow–drift wave interaction mechanism. A major restriction in the original HM model is the lack of intrinsic instability which is essential to maintain drift wave turbulence and plasma transport. We overcome this limitation by linking this model with the two-field HW equations with drift instability while keeping the simplicity in the one-field balanced formulation. A systematically derived unstable forcing is introduced to the modified HM model mimicking the role of the inherent instability near the low resistivity limit, where the unstable branch of the HW solution gradually becomes aligned with the HM potential vorticity. Detailed numerical experiments are performed to test the skill in the one-field model with unstable forcing. It is shown with qualitative and quantitative agreement that the one-field modified HM model is able to replicate the typical drift wave and zonal flow interacting procedure under a more analytically tractable framework. The insight gained from the simple model analysis can also offer guidelines for the development of model reduction methods for more complicated systems.