The divertor of a tokamak reactor is a key component for the control and exhaust of helium ash, impurity particles and plasma heat from the core plasma, essential to sustain a high performance steady-state tokamak plasma (continuous tokamak operation). It is quite important to fully understand microscopic physical processes occurring in the high density, low temperature plasmas near the divertor region, such various processes as recycling and radiation as well as the complicated behavior of atoms and electrons and their reactions.
In JT-60 we have fabricated a visible spectroscopic system with high wavelength resolution (wavelength/difference of adjacent wavelengths ~120,000), roughly 50 times as high as a standard spectrometer) and high spatial resolution (10 mm). We have made detailed measurements of the structure of spectral lines and their spatial variations of light emitted from deuterium atoms and molecules in the divertor region plasmas and studied various radiation processes. We have also made detailed studies of the various behaviors of atoms and molecules in divertor plasmas with temperatures less than several hundred thousand degrees, by comparing the experimental results obtained above with those of computer simulations (Fig. 2-6). Figure 2-7 shows the comparison of the measured results of profiles of Dalpha spectral lines emitted from deuterium atoms in the plasma near the divertor plate with those of a model calculation. As shown in the figure these two results are in good agreement, and from this we can estimate the composition of the Dalpha spectral lines together with the ratio of each component. They are components attributed to dissociative excitation and electron collisional excitation of the atoms produced by dissociation of deuterium molecules and molecular ions, and to electron collisional excitation of the atoms produced by reflection at the surface of the divertor plates and first walls and by charge exchange reactions between deuterium ions and atoms. This analysis has shown that the behavior of molecules has an important role in the particle recycling processes in the divertor plasma. |
