Latest Development of Surface Conservation Materials in Sources of Negative Hydrogen Ion

The latest advance of negative hydrogen ions (H^-) generation, for Negative Beam Injection (NBI) of fusion reactor, was tentatively reviewed. The discussions with specific examples focused on:i) the source structures and H^--ion generation modes, including the charge exchange generation, surface plasma generation (SPG) and volume generation (VG), and their strengths and weaknesses; ii) the advanced H^--ion surface conversion materials for SPG and VG, including but not limited to the Cs-coating, B-doped poly-diamond films, highly oriented pyrolytic graphite, LaB₆, and surface caesiated Mo-, W-, Ni-, Cu-substrates; and iii) the existing problems and possible solutions, for example, the complicated structure and short service life of LaB₆ hot cathode. Moreover, the extensively research subjects and development trends of the promising H^--ion surface conversion materials, particularly caesiated metals and mono-diamond coatings, were briefly discussed in a thought provoking way.