Surface modification of molten W exposed to high heat flux helium neutral beams

Abstract

High heat flux tests with central heat flux of 10.5 MW/m 2 using helium neutral beams have been carried out on rolled tungsten. The energy of helium particles is 33 keV and the particle flux is 2×10 21 m -2 s -1 . An 80×65×3 mm 3 rolled tungsten plate is firstly exposed to a 4.6 s pulse resulting in partially molten surfaces. Thereafter the tungsten plate is irradiated by several helium pulses with fluences of 1.2-2.5×10 22 /m 2 and peak temperatures from 1450 to 2590 °C . The experiments show that: (1) helium-induced surface modification of the resolidified tungsten surface is very different from that of the non-molten surface; (2) the surface morphology of molten surface is closely related to the orientation of the resolidified grain; (3) the evolution of surface modifications, for both of the molten and non-molten tungsten surfaces, 2 indicates a strong dependence on the surface temperature and local helium fluence.

Effects of temperature on surface modification of W exposed to He particles

“…1 summarizes the results reported in Ref. [2], [5] and [7], and shows the observed relationship between surface modification, fluence and peak surface temperature. The mechanism for the formation of these surface morphologies is, however, not fully understood, especially the effects of temperature dependence.…”

“…The mechanism for the formation of these surface morphologies is, however, not fully understood, especially the effects of temperature dependence. In addition, some studies have found an orientation dependence for He-induced damage [3,5,8]. This is interesting as it may provide a way to optimize the plasma facing material by control of the crystallographic texture.…”

“…During such usage it will be exposed to both particle irradiation and high heat flux loads. Particle irradiation from the fusion plasma, especially helium (He) bombardment, is expected to lead to performance degradation of W components due to the development of significant changes in surface morphology, such as the formation of blisters, holes, fiber-form nanostructures and coral-like structures [2][3][4][5][6][7]. In addition, synergistic effects between heat loading and particle irradiation can accelerate such surface damage [2].…”

“…In addition, synergistic effects between heat loading and particle irradiation can accelerate such surface damage [2]. The performance of W under the combined action of both heat and a particle flux has therefore been studied keenly in recent years [2,5]. In fusion devices during steady-state heat flux conditions active cooling of the plasma facing components ensures that the surface temperature is kept at a relatively low level.…”

Heat load and deuterium plasma effects on SPS and WSP tungsten

“…The saturation of helium atoms leads to the formation of bubbles as well. Depending on the irradiation conditions, bubbles ranging from several tens of nanometers up to micron in size can develop in the material [9,10]. Moreover, with increasing temperature (above 700°C) and fl uence approximately 10 25 m -2 a nanostructure called helium/tungsten 'fuzz' starts to develop [11].…”