Electron heat conduction in the solar transition region: Validity of the classical description

We have studied the transport of energy in the solar transition region, wit h the aim of finding out whether classical transport theory is applicable i n this region. We use a test particle approximation, where test electrons m ove in a prescribed, background Maxwellian electron-proton plasma. This app roximation is validated by comparing with the Spitzer-Harm result in the co llision-dominated limit, where the Spitzer-Harm result should be valid. We find that the test particle approximation yields velocity distribution func tions in good agreement with Spitzer and Harm, and the test particle energy flux is only 25% lower than the correct result. Then, applying the model t o conditions believed to be found in the solar transition region, we obtain essentially the same good agreement with the classical result, showing tha t classical transport theory is sufficient to describe heat transport in th e solar transition region. When the transition region pressure (density) is reduced to unrealistically low values, while the temperature profile is ke pt unchanged, a significant fraction of the energy flux is carried by nonth ermal electrons from the corona. But the total energy flux is never larger than the classical Spitzer-Harm value. The heat flux is independent of dens ity at high densities (the classical result), and decreases monotonically a s the transition region pressure is reduced.