Adhesion measurements for tungsten dust deposited on tungsten surfaces

摘要

Highlights ? Experimental determination of the pull-off force for W dust adhered to W surfaces. ? Pull-off force is in strong agreement with the Van der Waals expression. ? Pull-off force is two orders of magnitude less than contact mechanics predictions. ? This discrepancy stems from the effect of nano-scale roughness for stiff materials. Abstract The first experimental determination of the pull-off force for tungsten dust adhered to tungsten surfaces is reported. Dust deposition is conducted with gas dynamics methods in a manner that mimics sticking as it occurs in the tokamak environment. Adhesion measurements are carried out with the electrostatic detachment method. The adhesion strength is systematically characterized for spherical micron dust of different sizes and planar surfaces of varying roughness. The experimental pull-off force is nearly two orders of magnitude smaller than the predictions of contact mechanics models, but in strong agreement with the Van der Waals formula. A theoretical interpretation is provided that invokes the effects of nanometer-scale surface roughness for stiff materials such as tungsten.