Alcator C-Mod

Aaron Bader

Updated on July 7, 2006

There are many issues that may be problematic in a reactor-scale device such as ITER.  One of these, is the creation and inventory of dust particles. Large amounts of dust can cause adverse effects in plasma performance.  In a reactor device that uses tritium, tritiated particle density may exceed site limits, forcing termination of operation until the dust can be cleaned .

In order to prevent dust accumulation in the tokamak vessel, it is important to know what processes produce dust, and how dust is transported.  Much work has been done on theoretical modelling of dust transport.

The goal of my thesis is to study dust in tokamak plasmas.  We hope to gain time-resolved measurments of dust particles in localized regions.  We then hope to obtain evolution of dust clouds injected into the plasma and compare them to theoretical dust transport codes such as DUSTT.

Dust particles have been observed on the Thomson laser signal during Raman scattering calibrations.  This also occurred in the past when Rayleigh scattering was used.  Therefore, a diagnostic viewing the Thomson laser line (1064 nm) will be able to detect dust particles traversing through the laser. Other devices have used Thomson lasers to examine dust particles - , and dust particles are often observed on the C-Mod Thomson lasers during Raman Scattering calibrations.

It is conjectured that the Thomson laser is energetic enough that it ionizes a particle it interacts with, creating a small plasma.  It may be possible to obtain a spectrum of the particle, and determine what elements are present in the particle.

However, data obtained from the Thomson laser will not provide information regarding the evolution of the dust dynamics.  In order to obtain these data we will install a system which will inject dust into the plasma at a localized location.  A nearby location of the SOL will be illuminated by an expanded CW laser beam and will be viewed by a fast-framing CCD camera.