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Abstract

Using a hot wire (emitter) in the axis of a cylindrical glass vessel containing cesium vapour a plasma was formed by contact ionization. The plasma diffuses to the walls where it recombines. Plasma density, electron temperature (respectively the energy distribution function of the electrons), and the space potential were measured by probes in different distances from the emitter. Perturbations of the plasma by the current in the directly heated emitter are eliminated by using a pulsed current and a sampling method for the probe measurements. At vapour pressures exceeding 10−3Torr the plasma follows the equilibrium theory. At low pressures when an ion sheath at the emitter is present nonmaxwellian electron distribution functions occur. The perturbations of the plasma by the probe are thoroughly discussed.