Irradiation Stability of Nano-Columnar Tungsten Under Fusion-Relevant Ion Bombardment

Abstract

Plasma facing components (PFCs) in magnetic confinement fusion devices are exposed to very high thermal loads and particles fluxes during op- eration. Currently built and planned fusion reac- tors predominantly use tungsten (W) as the ma- terial of choice for their PFCs [1]. This choice is driven by tungsten’s beneficial properties, in- cluding a high melting point, excellent thermal conductivity and low fuel retention [2]. How- ever, at high temperatures (→ 800 K) and high helium fluxes, a porous nano-structure starts to form on its surface. This so called ”W-fuzz” is brittle, non-reflective and facilitates unipolar arc- ing, leading to a quicker degradation of PFCs [3]. It was shown that nano-structured surfaces, e.g. nano-foam or nano-columns, reduce the growth rate of W-fuzz and have a reduced sputter yield at high angles of incidence towards the surface normal [4, 5]. References [1] P. Barabaschi et al. Fusion Engineering and Design 215 (2025) [2] M. Kaufmann et al. Fusion Engineering and Design 82 5 (2007) [3] M. J. Baldwin et al. Nuclear Fusion 48 3 (2008) [4] W. Qin et al. Acta Materialia 153 (2018) [5] A. Lopez-Cazalilla et al. Physical Review Materials 6 7 (2022) [6] C. Cupak et al. Physical Review Materials 6 7 (2023) [7] R. Gonza ́lez-Arrabal et al. Nuclear Materi- als and Energy 40 (2024) [8] R. Arredondo et al. Nuclear Materials and Energy 18 (2019) Cupak et al. simulated the erosion of such a nano-columnar tungsten (NCW) surface under prolonged ion irradiation [6]. This gave a first estimate at the irradiation stability of such a structure in a fusion reactor. We investigated the NCW stability experimentally through ero- sion with a 2 keV Ar+ ion beam and simultane- ously measured the sputter yield via the means of a highly sensitive Quartz-Crystal-Microbalance (QCM). To enable the QCM measurement, the thin NCW layer was deposited directly onto a quartz resonator by magnetron sputter deposi- tion [7]. Erosion was conducted in three steps to enable investigation of surface topography changes, which significantly impact the sput- ter yield, via atomic force and scanning elec- tron microscopy in between. For a qualitative analysis of the experimental data, accompanying