Temperature Dependence of Deuterium and Helium Accumulation in W and Ta Coatings during D + - or He + -Ion Irradiation
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ature Dependence of Deuterium and Helium Accumulation in W and Ta Coatings during D+- or He+-Ion Irradiation V. V. Bobkova, *, L. P. Tishchenkoa, **, Yu. I. Kovtunenkoa, A. B. Tsapenkoa, A. A. Skrypnika, and L. A. Gamayunovaa a
Karazin Kharkiv National University, Kharkiv, 61022 Ukraine *e-mail: [email protected] **e-mail: [email protected]
Received December 16, 2019; revised January 4, 2020; accepted January 17, 2020
Abstract—Thermal desorption spectrometry (TDS) is used to study the processes of the accumulation and thermal release of deuterium and helium in tungsten and tantalum coatings of three-layer composites consisting of a stainless-steel substrate and an intermediate titanium layer, depending on the temperature of the samples upon 20-keV D2+ - or He+-ion irradiation. The sample temperature range 290–870 K affects the TDS spectra of these gases. With an increase in the sample temperature the deuterium and helium concentrations and capture coefficients decrease in coatings of both types. The mechanisms of deuterium and helium accumulation and thermal desorption as well as the formation of crystal lattice defects are proposed. Deuterium and helium are captured by radiation-induced defects of the vacancy type, forming gas–vacancy complexes. An increase in the sample temperature during D2+ - or He+-ion irradiation enhances the thermal desorption of implanted gases caused by the dissociation of gas–vacancy complexes, the migration of gas particles through lattice interstices to the surface, and deuterium recombination into a D2 molecule and its release to free space. Keywords: radiation-induced defects, deuterium, helium, ion implantation, thermal desorption, tantalum and tungsten coatings on a stainless-steel substrate DOI: 10.1134/S1027451020050031
INTRODUCTION Tungsten and tantalum are considered in [1–5] as materials that may be used in the protective coatings of plasma-facing components in thermonuclear reactors with magnetic [1, 3–5] and inertial plasma confinement [2]. They are proposed to be utilized as both separate materials (W [1, 3, 5] and Ta [2, 3]) and in the composition of tungsten-tantalum composites [4] (with 10 and 20 at % Ta fibers in a W matrix) and WTa5 alloys [5] (with 5 wt % Ta). In [1, 2] it is noted that one of the ways of preparing protective coatings for plasma-facing elements of constructions could be the plasma sputtering of tungsten or tantalum onto them. One of the advantages of using Ta and W is the negligible accumulation of hydrogen isotopes in them, and consequently, the insignificant accumulation of radioactive tritium upon the action of plasma fluxes. This problem has been extensively investigated [1–9] to enhance the radiation stability of the proposed materials and to obtain novel materials with improved parameters. We previously performed a comprehensive study of the formation of radiation defects in the crystal lattice, the capture, retention, and thermal
desorption of deuterium and helium ion-implanted into tungsten [6–9] and tantalum [10] coatings at room temperature.
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