Energy confinement comparison of Ohmically heated stellarators to tokamaks

Abstract

An empirical scaling prescribes that the energy confine ment time in ohmically heated stellarators and tokamaks is pro portional to the internal energy of the plasma and the minor radios, anl inversely proportional to the current density. A thermal-conduction energy transport model, based on a heuristic assumption that the effective momentum transfer in the racial direction is proportional to the classical parallel momentum transfer which results in ohmic heating, is used to explain this scaling.

Transport of electron energy in Ohmically heated tokamaks

“…It has been predicted theoretically that a fast-electron beam carrying a continuous current is produced at the tail of the velocity space by quasi-linear Landau damping of lower hybrid waves (LHW) [ 1 ]. The anisotropic fast-electron beam is, however, subject to the HF instability due to the anomalous Doppler effect, which gives rise to beam pitch-angle scattering of the electrons and results in a relaxation oscillation [6][7][8][9][10][11].…”

“…V ~ A 2 and r E e ~ a 4 /R s / 3 [4,6] or V ~ A and T Ee ~ a 7/3 [7,8] (see also Ref. [9] for both tokamaks and stellarators). Alternative, rather different, parametric dependences on a and R have also been proposed for the same devices and other existing tokamaks (D-III, DIVA, ISX, PULS, ST, T-l 1,. .…”