Dust dynamics and radiation in fusion plasmas

Abstract

Summary form only given. Dust is commonly found in current magnetic fusion devices. In reactors like ITER dust can pose safety hazards and impact plasma performance. However, the properties, generation rate, dynamics, and role of dust in fusion plasmas are still not well understood. In this work we simulate dynamics of dust particles in tokamaks with the dust transport, DUSTT, code and analyze the visibility of dust particles of different sizes in fusion plasmas by modern fast framing cameras. Using the DUSTT code, the dust density, radius and velocity distributions at different locations in the edge plasma are simulated and evaluated against the available experimental data. We compare the simulated dust trajectories with ones experimentally measured on NSTX with the fast camera imaging technique. The imaging is possible because dust heating and ablation by plasma creates two sources of radiation: thermal radiation from the heated dust particle and radiation from the ablation cloud interacting with the surrounding plasma. The analysis of spectral characteristics of the radiation can provide information as on dust (size, temperature, composition), as well as on dust-plasma interaction processes (ablation dynamics, local plasma parameters). We calculated the intensity of both the thermal radiation from a carbon dust particle and the radiation from the ablation cloud surrounding it for various plasma parameters. This allows to estimate minimal size of the visible dust and the ablation cloud characteristics in different tokamak plasma regions. We have also analyzed dust radius distribution resulting from laser scattering measurements on DIII-D taking into account non-Rayleigh regimes of light scattering as well as dust evaporation due to heating by laser radiation.