Effective beam stopping/excitation coefficients
The data sets are collections of beam stopping coefficients, given the mnemonic BMS. They are effective ionisation coefficients, including charge transfer losses, which leave the beam atoms ionised. The ionisation is due to collisions with ions in the plasma and free electrons, with the former more efficient at typical neutral heating beam energies. The ionisation losses are strongly influenced by the stepwise process and so the beam stopping coefficients are obtained from a collisional–radiative model. ADF21 is a derived data format. The stopping coefficients depend on the particular mixture of impurity ions present in the plasma. They are strongly parametrically dependent on the beam energy and the plasma ion densities and more weakly on plasma temperature. Data sets are for a single impurity (assumed fully ionised with their associated free electrons under charge conservation). A reference parameter set is specified and coefficient data are tabulated as an array in beam energy and density and as a vector in temperature, centred on the reference values. Stopping by a mixed impurity plasma is assembled as a linear combination of pure species stopping coefficients. It is recommended that the detailed prescription and use be examined with care. Conventionally beam stopping is related to the electron density, even though it is the ions which are the main influence, and that is what is done with ADF21. See Anderson et al (2000) for more detail. ADF21 spans both hydrogen and helium with sub-directories for the different beam species and for different reference conditions (fast and and slow beams). The helium is treated as a metastable-resolved atom (ground and two metastables) and so it has further sub-directories for different GCR loss and cross-coupling coefficients.