High-quality graphene as a coating for polycrystalline tungsten in low-energy helium and deuterium plasma exposures

Abstract

• Graphene acts as a sputter shield against low energy helium and deuterium plasmas. • High ion fluences can limit the functional range for graphene coatings. • Tungsten fuzz growth can be slowed down by coating polished surfaces with graphene. In the presence of irradiation by energetic ions, plasma facing components (PFCs) tend to develop surface morphologies that lead to mass loss of the wall material, potentially diminishing their lifetime and plasma performance. We explore the performance of graphene as a coating for plasma facing components to protect against sputtering due to low-energy ions. We show that graphene can slow changes in surface morphology of tungsten subjected to energetic-helium and deuterium ion bombardment over a wide range of energies, as tested in the PISCES-A facility at UC-San Diego. We exposed tungsten samples half-coated with graphene in the PISCES-A facility, at energies of 40 and 140 eV and fluences ranging from 1 × 10 24 - 3.6 × 10 25 ions/m 2 . We found that tungsten “fuzz” growth at high fluences (10 24 –10 25 He-D/m 2 ) can be reduced by approximately 30%. At the lower fluence and energy, no fuzz formed. Using scanning electron microscopy and focused-ion beam machining, we investigate these changes in surface morphology. Deuterium results do not show the graphene defect production to be as energy or fluence dependent as helium bombardment. We determine damage to and the lifetime of the graphene membrane with Raman spectroscopy for vacuum components subjected to such extreme environmental conditions.