Turbulence simulations of drift-Alfvén wave effects on edge-localized modes and divertor target heat flux width

Abstract A series of BOUT++ turbulence simulations are performed for two Pre-Fusion Power Operation (PFPO-1,2) phases of the ITER Research Plan proclaimed in 2019. Linear simulation results show that PFPO-1 is unstable to peeling–ballooning modes (PBs), while PFPO-2 is unstable to the coupling of PB and drift-Alfvén wave (DAW) instabilities. The linear results are qualitatively consistent with the dispersion relation of DAWs. To study the influence of DAWs on the edge-localized mode (ELM) crash, PFPO-2 is adopted in this section. Unlike the grassy ELM in Li et al (2022 Nucl. Fusion 62 096030), nonlinear simulations show that the ELM size of PFPO-2 is almost one-third of that of the grassy ELM, representing a distinct small ELM. However, simulations then show that if the PB instability is removed, the fluctuation amplitude drops by an order of magnitude and the ELM crash disappears, which is in accordance with the theory in Xu et al (2010 Phys. Rev. Lett. 105 175005) and the results in Li et al (2022 Nucl. Fusion 62 096030), confirming that PB instability is a necessary condition for an ELM crash. Furthermore, removing the DAW drive also suppresses ELM crashes, implying that PB instability is necessary but insufficient for the PFPO-2 ELM and that DAWs can amplify PB-driven turbulence. In addition, by integrating the results of both PFPO phases by BOUT++ turbulence analysis with the heat flux width ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:msub> <mml:mi>λ</mml:mi> <mml:mi>q</mml:mi> </mml:msub> </mml:mrow> </mml:mrow> </mml:math> ) and electron thermal diffusivity ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:msub> <mml:mi>χ</mml:mi> <mml:mrow> <mml:mtext>e</mml:mtext> </mml:mrow> </mml:msub> </mml:mrow> </mml:mrow> </mml:math> ), these simulations establish a predictive framework for heat flux width and its dominant mechanisms, thereby providing a comprehensive scheme for the prediction of the heat flux width. Moreover, simulations indicate that DAW driving can increase the transport coefficient by enhancing the turbulent transport, leading to a broadened heat flux width once the transport coefficient exceeds its critical value.