Design and Characterization of a Dust Injector for Future Studies of Tungsten Dust in the STOR-M Plasma

Abstract

Dust generation from Plasma Facing Components (PFC) is a problem for tokamaks as they approach suitable reactor conditions. Tungsten dust is especially detrimental in the core, due to associated high Z bremsstrahlung power losses. As Tungsten is a primary candidate for PFC materials in large projects such as ITER, this remains a pressing issue. In order to better understand dust dynamics in tokamaks, a dust injection experiment is proposed for the Saskatchewan Torus-Modified (STOR-M). This experiment will utilize calibrated, spherical tungsten micro-particles. A known mass of these tungsten micro-particles are to be injected into STOR-M with control over the position of the dust plume. This will enable future observation and study of dust dynamics within STOR-M. In preparation for this experiment, a new dust injector has been designed, based on the fast gas valve for the University of Saskatchewan Compact Torus Injector. An experimental test apparatus was developed to characterize the dust injector. In the experiment, nitrogen gas and dust particles are injected into the test vacuum chamber under various dust injector parameters. Vacuum chamber pressures range from 10−4 - 10−5 Torr, which is within the operation range of STOR-M. These particles are then imaged with a high-speed camera via laser light scattering. Collected 12-bit raw image data was then processed and analysed. This analysis fully characterizes the dust injector in terms of the time evolution of the injector dust plume, amount of gas injected and injected dust mass.