Molybdenum limiters for Extrap-T2 upgrade: surface properties and high heat flux testing

A vacuum vessel, a conductive copper shell and plasma-facing components of the Extrap-T2 device, a medium size reversed field pinch, are under major r ebuild. The new machine is equipped with an array of 180 molybdenum limiter s, which will be exposed to power loads of about 30 MW m(-2), but higher lo ads can not be excluded. Prior to the limiters' installation in the vessel, they were tested under high heat loads in the JUDITH electron beam facilit y in order to assess the possible damage to the surface and to the bulk of the material. A test limiter was irradiated with a beam of increasing power density from 15 to 1500 MW m(-2). Surface characterization was performed b efore and after the irradiation using electron and optical microscopy, ener gy dispersive X-ray spectroscopy, enhanced proton scattering and laser prof ilometry. Metallography studies were performed for the irradiated areas. Th e irradiation induced the change in surface morphology, e.g. surface meltin g and re-crystallization of grains, only following the 10 ms long pulses wi th the absorbed power density approaching 1500 MW m(-2). (C) 2000 Elsevier Science B.V. All rights reserved.