Experimental study of classical heat transport in a magnetized plasma

A systematic study is made of the axial and transverse heat transport that arises when a microscopic temperature filament is generated, under controlled conditions, in a magnetized plasma of large dimensions. For early times and relatively small temperature gradients the study conclusively demonstrates the two-dimensional pattern characteristic of the classical theory based on Coulomb collisions. The full nonlinear dependence of the transverse and axial electron heat conductivities is sampled through temperature changes in the range δTe/Te∼1–10. The dependence on the confining magnetic field is explored over a factor of 3 (∼ factor of 10 in transverse conductivity). It is found that under quiescent conditions, the observed behavior agrees with classical theory within the experimental uncertainties. However, over long times and/or for steep temperature gradients, fluctuations develop spontaneously and cause a significant departure from the predictions of the classical theory.