Tokamak fusion reactors are now at the stage of solving engineering problems. The technical design of an international fusion reactor is under development [1], and the operating installations JAE (Great Britain) and TSTA (USA) are being modified for operation with D-T fuel (plasma gas) [2, 3]. Monitoring of the isotopic composition and the impurity content of D-T fuel is necessary during the preparation, purification, recovery, and storage of the fuel gas and its components. Many scientific centers are devoting a great deal of attention to the development and construction of the required instruments and methods of analysis. Some requirements for monitoring the composition of fuel gas were formulated in [4, 5]. The mass-spectrometric method is most suitable. This method makes it possible to solve simultaneously the problems of isotopic and chemical analyses.It is of interest to summarize information on foreign and domestic designs of specialized mass spectrometers intended for isotopic and chemical analyses of fuel gas at different stages of preparation and recovery of the gas.Characteristics of Mass-Spectrometric Analysis of Hydrogen-Helium Mixtures. In the general case the fuel gas contains three hydrogen isotopes (protium, deuterium, and tritium) and two helium isotopes (3,4He) as well as impurity gases (nitrogen, oxygen, argon, carbon and nitrogen monoxide and dioxide, hydrocarbons, containing all isotopes of hydrogen, and others). The specific nature of the analysis of hydrogen-helium mixtures by the mass-spectrometric methods [6][7][8] is determined by the following:hydrogen isotopes can be in a nonequilibrium state, and one of them (tritium) is/3-active; the isotopic and chemical compositions of the mixture must be determined simultaneously; the measured isotopic ratio is less than 104; the significant difference of the masses of the hydrogen isotopes suggests the possibility of significant discrimination of ions by mass in the ion source, in injection and ion-current detection systems, and so on; and, the fixed relative measurement error does not exceed 0.1-0.5 % in a wide range of content of hydrogen isotopes. In order to meet these requirements a mass spectrometer must have high technical parameters and certain structural features. Thus, determination of the isotopic composition of a hydrogen-helium mixture in the case when the hydrogen isotopes are in a nonequilibrium state is possible if the mass spectrometer has a resolution of not less than 3000 (at 10% of the maximum). In this case, all multiplets of singly-charged ions, except for the 3He+ -T + doublet, are separated in the mass spectrum; separation of the doublet requires a resolution of not less than 150.103. Chemical analysis (determination of impurity gases) with identification of the main components is also possible only with a resolution of not less than 25-103 . The lack of mass discrimination of ions, satisfaction of the error requirements, and the required ion ratio are achieved with a special construction of the ion source, formation of a...
