Recombination of Alkali Plasma Ions on Hot Tungsten Surfaces

The rate of surface recombination of cesium and potassium plasma ions on the hot tungsten end plates of a Q machine has been measured with a Langmuir-Taylor detector. Good agreement of the measurements with the equilibrium theory of electrostatic confinement is found under conditions in which the plasma potential is not highly negative or positive (|V|<2kT/e). Corrections to the equilibrium theory for ion heating (highly negative plasma) and ion drifts (highly positive plasma) bring theory into good agreement with experiment over a range in density of 2 ×{} 10⁹ to 2 ×{} 10¹² cm^-3.