Design and operation of a stable intense high-temperature arc-discharge source of hydrogen atoms and metastable trihydrogen molecules

We report a design for a stable intense beam source of hyperthermal hydrogen atoms. The basis for the design is an arc heater used first by Knuth for the generation of high-translational energy He-Ar beams. In the case of hydrogen atom generation this source is very unstable due to the corresponding higher temperatures which are generated by the plasma discharge. We have substantially eliminated these difficulties by the insertion of discharge-localizing insulators and the use of a tungsten nozzle mounted in the center of a 1-kG electromagnet. This source generates exceptionally high hydrogen atom beam intensities of ∼10²² atoms s^-1 sr^-1 with translational energy distribution functions which extend to 18 eV and whose peak occurs at energies as high as 13 eV. In addition metastable H₃ molecules having an intensity between 10²⁰ and 10²¹ molecules s^-1 sr^-1 are formed.