1. Hall D, Helmer JC, Jepsen RL. U.S. patent No. 2, 993, 638, “Electrical vacuum pump apparatus and method”, filed 7/24/57, awarded 7/25/61.
2. Electrical Characteristics of a Penning Discharge
3. Magnetically Confined Cold‐Cathode Gas Discharges at Low Pressures
4. Jepsen RL, Trans. 4th Int Vac Cong (The Institute of Physics and the Physical Society, London, 1969); 1968. p. 317.