Details are given for an electrodeless hydrogen discharge tube excited in a microwave cavity. The tube is extremely simple in construction. The hydrogen is stored as UH3. The excitation is efficient, and the spectrum is obtained with great strength and purity. Discharge conditions can be held constant much better than in the conventional tubes.
G. H. DIEKE and S. P. CUNNINGHAM, "A New Type of Hydrogen Discharge Tube," J. Opt. Soc. Am. 42, 187-189 (1952)