Hydrogen ion beam transport in an energy range lower than 50 eV: Ion beam species

Low energy beam transport in the energy range below 50 eV is studied using a compact ion source with a high temperature tungsten cathode that can be put into a vacuum system. A 2.6 cm diameter, 5.2 cm long compact ion source successfully produced more than 2.4 nA beam of H₂ ⁺ ions at 50 eV beam energy. The source also supplied a stable beam of H₃ ⁺ ions at 2.5 eV energy with more than 100 pA mass-separated current. The inside wall of the ion source was covered by thin sheets of titanium, nickel, and molybdenum to see if the species composition of the ion beam can be controlled by changing the ion source wall material. Usually, the H₂ ⁺ ion peak was the highest in the mass spectrum, and the H₂ ⁺ ion ratio (H₂ ⁺/H_n ⁺) was measured for a source operation with hydrogen gas. The ion species ratio drifted against time, and Mo showed the most stable ion ratio.