Structural evolution of tungsten surface exposed to sequential low-energy helium ion irradiation and transient heat loading

Sinclair, G.; Diwakar, P. K.; Tripathi, J. K.; Hassanein, A.; Linke, J.; Wirtz, Marius

doi:10.1016/j.nme.2017.03.003

Journal Article

FZJ-2018-02222

Structural evolution of tungsten surface exposed to sequential low-energy helium ion irradiation and transient heat loading

Sinclair, G. (Corresponding author) ; Tripathi, J. K. ; Diwakar, P. K. ; Linke, J.FZJ* ; Hassanein, A. ; Wirtz, M.FZJ*

2017
Elsevier Amsterdam [u.a.]

Nuclear materials and energy 12, 405 - 411 (2017) [10.1016/j.nme.2017.03.003]

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Please use a persistent id in citations: http://hdl.handle.net/2128/17952 doi:10.1016/j.nme.2017.03.003

Abstract: Structural damage due to high flux particle irradiation can result in significant changes to the thermal strength of the plasma facing component surface (PFC) during off-normal events in a tokamak. Low-energy He+ ion irradiation of tungsten (W), which is currently the leading candidate material for future PFCs, can result in the development of a fiber form nanostructure, known as “fuzz”. In the current study, mirror-finished W foils were exposed to 100 eV He+ ion irradiation at a fluence of 2.6 × 1024 ions m−2 and a temperature of 1200 K. Then, samples were exposed to two different types of pulsed heat loading meant to replicate type-I edge-localized mode (ELM) heating at varying energy densities and base temperatures. Millisecond (ms) laser exposure done at 1200 K revealed a reduction in fuzz density with increasing energy density due to the conglomeration and local melting of W fibers. At higher energy densities (∼ 1.5 MJ m−2), RT exposures resulted in surface cracking, while 1200 K exposures resulted in surface roughening, demonstrating the role of base temperature on the crack formation in W. Electron beam heating presented similar trends in surface morphology evolution; a higher penetration depth led to reduced melt motion and plasticity. In situ mass loss measurements obtained via a quartz crystal microbalance (QCM) found an exponential increase in particle emission for RT exposures, while the prevalence of melting from 1200 K exposures yielded no observable trend.

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