On the Field Focusing Effect at the Tungsten Fuzzy Nanostructures Formed by Helium Plasmas

Abstract

Tungsten fuzzy nanostructures commonly form on the plasma-facing walls of magnetic-confinement nuclear fusion reactors, induced by the helium plasma irradiation. We calculate the field enhancement factors at the fuzz tips of tungsten, molybdenum, and tantalum, quantitatively representing the degree of field focusing, based on the classical electromagnetic field theory under the quasistatic approximation, for a model system comprising a subwavelength-scale prolate metal hemispheroid protruding from a conducting plane. Field enhancement factors of 2.4 × 10³, 5.4 × 10⁶, and 2.3 × 10¹⁰ for the spheroidal aspect ratio of 10, 100, and 1000, respectively, are observed in the gigahertz regime for the incident electric field parallel to the fuzz, i.e., normal to the reactor wall. Such a potential large field focusing effect may be worth accounting for in the designing and operation of fusion reactors.