Deuterium behavior in pristine and pre-damaged tungsten under plasma exposure at a rising or declining temperature

Temperature is an important factor affecting the behavior of deuterium in plasma-facing material. This paper focuses on the effect of variable temperature on deuterium behavior in tungsten. Deuterium plasma exposures were conducted for the pristine and pre-damaged tungsten at two variable temperatures: one is rising from 323 K to 723 K (named TR exposure), and the other is declining from 723 K to 323 K (named TD exposure). Statistical results of surface blisters show that the TD exposure favors the nucleation of small intergranular and intragranular blisters, while the TR exposure favors the formation of large intergranular and intragranular blisters. Thermal desorption spectra results demonstrate that total deuterium retention is reduced, and the defects could evolve into higher-energy deuterium traps in the TR exposure compared to the TD exposure. Comparing the pristine and damaged tungsten revealed that the pre-damage suppressed the formation of intragranular blisters, accelerated the intergranular blisters, and enhanced deuterium retention in both the TR and TD exposures. Nevertheless, the aggravating effect of pre-damage is more pronounced in the TR exposure, while the suppressive effect on intragranular blisters is alleviated in the TD exposure. Furthermore, the evolution result of pre-damage defects in the TR exposure is more pronounced than that of the pristine one. The above results reveal significant differences in the deuterium behavior and defect evolution in tungsten under the TR and TD exposures, demonstrating the inconstant temperature effect on deuterium behavior.