EFFECT OF TEMPERATURE-GRADIENT ON PLASMA SHEATH

In the plasma sheath the electron current is severely limited by a ret arding electrostatic potential, which implies that only fast plasma el ectrons reach the material surface. These fast electrons have a much l onger mean free path than thermal electrons and consequently their las t collision will have occurred well away from the surface. If the temp erature gradient is such that the temperature at these last collisions is different from that at the surface, the sheath potential will be m odified. This effect can lead to large modifications of the sheath pot ential and possibly also to substantial errors in the interpretation o f probe signals.