Ionisation per photon coefficients
The data sets are collections of ionisation per photon quantities, given the mnemonic SXB. Its reciprocal is called the `photon efficiency'. An SXB is a quantity given for a specific spectrum line of an ion. It is useful in analysis of a spectrum line from an ionisation stage of an element, which is inflowing into a plasma from a surface, when the ionisation stage `burns-through' fully to higher ionisation stages along the line of sight. Then the line-of-sight integrated intensity may be directly related to the influx of the element. The theory and application are described in Behringer \etal (1989). ADF13 is a derived data format with SXB calculated from a collisional–radiative model. It is closely related to the SCD sub-class of format ADF11 and to the excitation \pecs\ of format ADF15 — being essentially the ratio of the two. The collisional–radiative calculation is most appropriately carried out in the metastable-resolved GCR picture, with as many spectrum lines being needed to deduce the element influx as there are significant metastable populations in the analysed ion. The interpretation is a little subtle and it would be worthwhile to consult the reference above. There is an indexed block in the data set for each spectrum line (and for each metastable in the metastable-resolved case), with the tabulation an array in electron temperature and electron density. Sub-directories of ADF13 are according to iso-electronic sequence, with most available data being for light elements. The use of SXB has been particularly popular with visible wavelength lines, due to ease of observation and intensity calibration, but the data sets extend to short wavelength lines also.