the median diameter of dust grains found in fusion devices is in the range of 1–10 μm
[15]. The size distribution is often estimated from the dust collected from fusion
devices during the ventilation events. However, the result can depend on both the
collection method and counting. For example, counting with an optical microscope
gives a log-normal distribution of dust particles [19], whereas counting with scanning (SEM) and transmission (TEM) electron microscopes reveals the presence of a
large amount of sub-micron particles [20, 21]. As a result, the size distribution of the
dust particles of small diameter in the LHD device appears to be far from the
Fig. 5.3 Dust particles of different shapes and sizes collected from fusion devices. (Reproduced
with permission from [19], © Elseiver 2002)
Fig. 5.4 Size distribution of
the dust particles found in
LHD. (Reproduced with
permission from [20],
© JSPF 2009)
5.1 Experimental Study of Dust in Magnetic Fusion Devices
91