Visualized Blow-off from Helium Irradiated Tungsten in Response to ELM-like Heat Load

Abstract

Laser-induced blow-off from a tungsten surface that was exposed to helium plasma is investigated experimentally in the divertor simulator NAGDIS-II. The pulse width of the laser is submillisecond and is similar to the duration of type-I edge localized modes in ITER. The temporal evolution of blow-off particles, which are visualized by the electron impact excitation in the surrounding plasma, is investigated by using filter spectroscopy. We demonstrate the effect of helium irradiation damages on the tungsten ejection behavior in response to a transient heat load.

Tungsten erosion under combined hydrogen/helium high heat flux loading

“…In the following we investigate two of these possible causes. The most obvious is the formation of a distorted surface layer, as shown in several experiments (see references [1][2][3][4][5][6][7][8][9][10][11]), which is investigated as a function of fluence and temperature in section 3.2.1. The second is the dependence of the sputtering yield on the crystal orientation.…”

“…The resulting morphology after irradiation with a H/He mixture is distinctly different form the morphology after irradiation with the pure species. The question how this morphology influences the erosion behaviour of tungsten has been addressed in linear plasma devices and also in tokamak edge plasmas [6,7,8].…”

Formation Condition of Fiberform Nanostructured Tungsten by Helium Plasma Exposure

“…author's e-mail: w-sakaguchi@ees.nagoya-u.ac.jp device [8]. Therefore, it is necessary to investigate the formation condition and the formation mechanism of the fiberform nanostructure.…”

Formation and mitigation of fiberform nanostructured tungsten by helium and sub-ms laser pulse irradiations

“…Figure 6(b) shows the laser pulse energy dependences of the emission intensity of tungsten neutral WI in response to the laser pulse. The emission was observed with a filter spectroscopy method by using an image-intensified fast CCD camera, and the details of the experimental setup are given in [16]. Interestingly, the emission was observed when the optical reflectivity was recovered.…”