A hollow cathode arc as a high intensity beam source for ground state and metastable noble gas atoms in the eV translational energy range

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Abstract
The medium density plasma column (n approximately=1022 m-3) close to the exit of the cathode of a hollow cathode arc is highly ionised, with ion and electron temperatures Ti approximately=0.5-1.5 eV and Te approximately=3 eV, respectively. By sampling this plasma with an orifice in the end anode (at a floating potential) a high intensity beam with a broad velocity distribution is obtained for the noble gas atoms Ne, Ar and Kr, both in the ground state and in metastable states n*. Typical centre-line intensities for argon are I(0)=2*1018 s-1 sr-1, T=2*104K and I(0)n*=2*1014 s-1 sr-1, Tn*=3*104K. These values are in good agreement with model calculations of the process of molecular beam sampling, which are discussed in this paper. The source is of a simple design and easy to operate. The life time of the tungsten (or tantalum) hollow cathode is typically 40 h for argon and krypton. The shortest life time is for neon with a tungsten cathode, due to the high operating temperature T approximately=3000K of the cathode tip.