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

Abstract

The medium density plasma column (nz close to the exit of the cathode of a hollow cathode arc is highly ionised. with ion and electron temperatures T, ~0.5-1.5 eV and T, z 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 atom Ne, Ar and Kr. both in the ground state and in metastable states n*. Typical centre-line intensities for argon are I(0) = 2 x lo1* s-l sr-', T= 2 x lo4 K and I(0)n. =2 x 1014 s-' sr-'. T,. = 3 x lo4 K. 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 TZ 3000 K of the cathode tip. mW3)