Hydrogen Isotope Trapping in Tungsten During Cyclic Irradiation by Deuterium and Hydrogen Ions in Oxygen-containing Atmo
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ATERIALS AND TECHNOLOGY FOR NEW SOURCES OF ENERGY
Hydrogen Isotope Trapping in Tungsten During Cyclic Irradiation by Deuterium and Hydrogen Ions in Oxygen-containing Atmosphere1 L. B. Begrambekova, S. S. Dovganyuka, A. E. Evsina, and A. S. Kaplevskya,* a
National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), Moscow, 115409 Russia *e-mail: [email protected] Received October 29, 2018; revised December 11, 2018; accepted December 24, 2018
Abstract—An investigation on mechanisms of hydrogen and deuterium trapping in tungsten during irradiation by hydrogen ion plasma with oxygen impurity using the methods of thermal desorption spectrometry (TDS) and secondary ion mass spectrometry (SIMS) is presented in this paper. It was shown that almost 40% of trapped particles were retained in the surface oxide layer after first implantation of deuterium. Subsequent irradiation by hydrogen plasma with oxygen impurity lead to the increase of oxygen concentration and hydrogen trapping in the oxide layer and tungsten bulk. In the next cycle, which started with deuterium implantation, oxygen concentration in the oxide layer decreased and some hydrogen was removed from tungsten. Then an increase of hydrogen and oxygen concentration in the sample repeated during irradiation with ions of (H2 + 1 at. % O2) plasma. The same sequence of processes was observed during subsequent irradiation cycles. Keywords: plasma, oxygen impurity, tungsten, trapping, desorption DOI: 10.1134/S1063778818120025
1. INTRODUCTION Tungsten is used as a material for divertors of modern tokamaks, and it will be implemented in this fashion in ITER. During the operation of the reactor, deuterium and tritium plasma will interact with the first wall and the divertor, which will result in accumulation of hydrogen isotope atoms inside the material, including radioactive tritium. Tritium trapping by plasma-facing elements is limited by the amount of 700 g. [1], which is why the development of a method for low-temperature tungsten degassing is of utmost interest. Currently, intensive research is underway in this direction [2–8]. It was shown in the works [9, 10] that barrier properties of the oxide layers on metal surfaces (stainless steel, tungsten, aluminum) relative to hydrogen isotope diffusion change under irradiation with hydrogen isotope atoms and ions of hydrogen plasma with oxygen impurity. When this happens the intensive penetration of hydrogen isotopes through the surface (phenomenon of Active Surface Penetration—ASP) under considerably low temperature (room temperature for stainless steel) [9]. In work [11] it was shown that periodic irradiation of tungsten by low energy H2 + 1 at. % O2 plasma ions allows keeping the concentration of trapped deuterium in tungsten at relatively low levels (Fig. 1). This result allowed proposing such periodic irradiation by 1 The article is published in the original.
low temperature plasma with oxygen impurity as a method of prevention of tritium accumulation in tungsten and other plasma-fac
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