The role of aspect ratio and beta in H-mode confinement scalings

The addition of high power, low aspect ratio data from the NSTX and MAST experiments has motivated a new investigation of the effect of aspect ratio on confinement scaling. Various statistical methods, including those that incorporate estimates of measurement error, have been applied to datasets constrained by the standard set of criteria in addition to the range of κ and M_eff appropriate to ITER operation. Development of scalings using engineering parameters as predictor variables results in ε-scaling coefficients that range from 0.38 to 1.29; the transformation of these scalings to physics variables results in an unfavourable dependence of Bτ on β, but a favourable dependence on ε. Because the low aspect ratio devices operate at low B_T and therefore high β_T, a strong correlation exists between ε and β, and this makes scalings based on physics variables imprecise.