Divertor scaling laws for tokamaks

The breakdown of two body scaling laws is illustrated by using the two dimensional plasma code UEDGE coupled to an advanced Navier-Stokes neutrals transport package to model attached and detached regimes in a simplified geometry. Two body similarity scalings are used as benchmarks for runs retaining non-two body modifications due to the effects of (i) multi-step processes altering ionization and radiation via the excited states of atomic hydrogen and (ii) three body recombination. Preliminary investigations indicate that two body scaling interpretations of experimental data fail due to (i) multi-step processes when a significant region of the plasma exceeds a plasma density of 10(19) m(-3) or (ii) three body recombination when there is a significant region in which the temperature is less than or equal to 1 eV while the plasma density is greater than or equal to 10(20) m(-3). These studies demonstrate that two body scaling arguments are often inappropriate in the divertor and the first results for alternate scalings are presented.