Measurements of the average energy of carbon atoms released from breakup of methane in the main SOL of DIII-D compared with DIVIMP code modeling

13CH4 , 12CD4 or 12CH4 gases were puffed into the crown (top) of lower single-null divertor plasmas in DIII-D using toroidally symmetric injection, constituting a particularly simple experiment to interpret. The resulting CI (9094.83 Å) wavelength profiles were measured with a high resolution spectrometer. For a wide variety of plasma conditions, the shape of the profile was nearly constant, and could be approximately represented by a shifted gaussian distribution, corresponding to a temperature of the C-atoms of <1 eV. DIVIMP code analysis reported here, based on the recent Janev–Reiter database/model for methane breakup, has produced sufficiently close matches to these experimental CI profiles, to provide reasonable confidence that the controlling processes have been included.