Mass-spectrometric measurements of helium isotopes in structural materials of the Globus-M tokamak

•Helium-3 and tritium are generated by deuterium plasma of tokamak.•These gases diffuse into the bulk of structural materials of plant.•Gases extracted from hard samples are analyzed by means of mass spectrometer.•Quantities of helium isotopes and their ratios are determined.•These values give a possibility to estimate the rate of generation of 3He and 3T.

Nuclear synthesis reactions involving formation of protons and tritium nuclei or neutrons and helium-3 nuclei can proceed in deuterium plasma of tokamaks even at fairly low ion temperatures with practically the same probability. Therefore determination of an amount of any of these components forming in a known time provides the information on the rate of synthesis reactions. Measurement of small amounts of elementary particles (protons and neutrons) and calibration of instruments involve extremely complicated procedures and will not be treated here. We are going to discuss here the methods and difficulties associated with measurement of radioactive tritium and present briefly the technique employed for extraction and purification of gases from solid specimens, as well as the technique of mass-spectrometric measurements of helium isotopes by means of MI-9301 magnetic resonance mass spectrometer. The measured 3He/4He isotopic ratios and the extremely large amounts of 3He in samples suggested a conclusion that a significant part of the light isotope helium-3 revealed in construction materials is largely a product of nuclear synthesis proceeding in the deuterium plasma of the Globus-M spherical reactor. The same data enable to estimate of the rate of generation of helium-3 nuclei (and, hence, of tritium, neutrons and protons). We believe that such mass spectrometric measurements provide a possibility for a detailed study of the processes involving interaction of deuterium plasma with materials of the first wall, divertor and other elements of tokamaks.

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