On the node in the current density profile during current peaking in a sawtooth oscillation

The measured location of current node in sawtooth oscillation, rn, by Soltwisch et al. can be explained by employing the principle of minimum energy dissipation and current conservation within the q=1 surface (at r1). djφ/dq0=0 requires rn/r1=[q0/(1+q0)]1/2.