Correlation between negative hydrogen ion production and work function of plasma grid surface in a cesium-introduced volume-production-type negative hydrogen ion source

• Published in: Japanese Journal of Applied Physics 1996-03, Vol.35 (3), p.1894-1900
• Main Authors: SHINTO, K, OKUMURA, Y, ANDO, T, WADA, M, TSUDA, H, INOUE, T, MIYAMOTO, K, NAGASE, A
• Format: Article
• Language: English
• Subjects: Exact sciences and technology; Experimental methods and instrumentation for elementary-particle and nuclear physics; Ion sources: positive and negative; Magnetic confinement and equilibrium; Nuclear physics; Particle sources and targets; Physics; Physics of gases, plasmas and electric discharges; Physics of plasmas and electric discharges; Plasma heating (beam injection, radio-frequency and microwave, ohmic, icr, ecr and current drive heating); Plasma production and heating; Tokamaks
• ISSN: 0021-4922; 1347-4065
• DOI: 10.1143/jjap.35.1894

The correlation between the work function of a plasma grid surface in a Cs-introduced volume-production-type negative hydrogen ion ( H - ) source and the extracted H - current has been investigated experimentally. The quantum efficiency of a Cs/Mo surface has been measured as a function of the photon energy in a high-vacuum test chamber, and a relationship between the photoelectric work function and the quantum efficiencies at the wavelengths of an Ar + laser has been obtained. Using this relationship, the work function of the plasma grid surface has been determined by measuring quantum efficiency using an Ar + laser. When the increment of the H - current is plotted against the measured work function, an exponential dependence on the decrease of the work function is observed. The experimental result cannot be explained by a theoretical H - formation model when one assumes that H - are produced from H atoms leaving from the surface with the energy corresponding to the temperature of H atoms in the plasma. When H - are produced with the kinetic energy substantially larger than thermal energy, the theoretical result shows good agreement with the experimental result.