Institute of High Energy Physics

Abstract Tungsten has demonstrated a competitive figure of merit in its application to plasma-facing components (PFCs) of fusion reactors. During service, the material is exposed to high temperatures and high-level displacement damage. A common interest is fostered in the nuclear materials community to address the issue of defect evolution at operating temperatures, and how they recover throughout service. During maintenance, the application of in situ thermal repair technologies is tempting, featuring attractive efficiency in defect removal via an optimal selection of post-irradiation annealing (PIA) parameters. In previous studies, we examined the role of PIA temperature, PIA duration, and initial defect concentration on defect evolution, and redefined the damage recovery stages for tungsten, but this was done from a room-temperature heavy-ion irradiation perspective; see Wang et al (2023 J. Nucl. Mater. 581 154454), Wang et al (2024 Acta Mater. 273 119942). In this study, the scope is expanded to displacement damage saturation induced by heavy-ions at high temperatures, relevant to the service conditions of tungsten-based PFCs. The damage microstructure evolution in response to varied irradiation temperatures ( T Irr ) and PIA temperatures ( T PIA ) was assessed via transmission electron microscopy and Doppler broadening positron annihilation spectroscopy. Irradiation hardening was evaluated via nano-indentation. A scientific framework is proposed to guide thermal healing of displacement damage in tungsten via PIA treatment. It was ineffective when T PIA ⩽ T Irr . An adverse effect of PIA-induced secondary hardening occurred when T PIA (stage III) > T Irr (stage III). The optimal PIA scheme was confirmed when T PIA (stage IV) > T Irr (stages III–IV), eluding PIA-induced secondary hardening and minimizing PIA-enhanced recrystallization.

Abstract It is widely believed that stellar-mass black holes (sMBHs) exist within the accretion disks of active galactic nuclei (AGN), forming a distinct population termed “accretion-modified star” (AMS). Gas from the dense disk accretes onto these AMSs, dissipating substantial gravitational energy through a minidisk around the sMBHs, which drives powerful outflows that interact with the surrounding disk gas. In this study, we investigate two scenarios for AMS accretion: episodic Bondi explosions with hyper-Eddington accretion (Scenario A) and steady Eddington accretion (Scenario B). These outflows generate turbulence, facilitating outward angular momentum transport in the AGN disk via shock interactions and angular momentum exchange. We explore a broad parameter space, spanning the central supermassive black hole (SMBH) mass ( M p ), dimensionless accretion rate ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mover> <mml:mrow> <mml:mi mathvariant="script">M</mml:mi> </mml:mrow> <mml:mo>˙</mml:mo> </mml:mover> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">p</mml:mi> </mml:mrow> </mml:msub> </mml:math> ), sMBH mass function, and spatial distribution to calculate the effective viscosity parameter α AMS . Our analysis reveals the scaling relations <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>α</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">AMS</mml:mi> </mml:mrow> </mml:msub> <mml:mo>∝</mml:mo> <mml:mi>ζ</mml:mi> <mml:msubsup> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">p</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msubsup> <mml:msub> <mml:mrow> <mml:mover accent="true"> <mml:mrow> <mml:mi mathvariant="script">M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>̇</mml:mo> </mml:mrow> </mml:mover> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">p</mml:mi> </mml:mrow> </mml:msub> </mml:math> for Scenario A and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>α</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">AMS</mml:mi> </mml:mrow> </mml:msub> <mml:mo>∝</mml:mo> <mml:mi>ζ</mml:mi> <mml:msubsup> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">p</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>1.5</mml:mn> </mml:mrow> </mml:msubsup> <mml:msubsup> <mml:mrow> <mml:mover accent="true"> <mml:mrow> <mml:mi mathvariant="script">M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>̇</mml:mo> </mml:mrow> </mml:mover> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">p</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0.1</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> for Scenario B, where ζ denotes the ratio of the total sMBH mass to the SMBH disk mass. For ζ = 0.01 and M p = 10 8 M ⊙ , α AMS ranges from ∼3 × 10 −4 to 0.01 (Scenario A) and ∼3 × 10 −3 to 0.04 (Scenario B) from the inner to outer disk regions. These results demonstrate that AMS feedback provides an efficient mechanism for angular momentum transport in AGN disks.