Energy confinement comparison of ohmically heated stellarators to tokamaks

An empirical scaling prescribes that the energy confinement time in ohmically heated stellarators and tokamaks is proportional to the internal energy of the plasma and the minor radius and inversely proportional to the current density. A thermal-conduction energy transport model, based on the heuristic assumption that the effective momentum transfer in the radial direction is proportional to the classical parallel momentum transfer which can be related to the driving ohmic-heating voltage and current, is used to explain this scaling.