Tritium concentration in tungsten surface exposed to low-energy, high-flux D plasma

The limits on tritium inventory in the vacuum vessel and the need for prevention of impurity ingress into plasma make plasma-surface interaction on tungsten an important issue. It is well known that plasma exposure on tungsten makes some kinds of blisters on the surface and increases the hydrogen inventory. O n the other hands, there is a possibility that plasma exposure would change the characteristic of surface and surface region in tungsten and cause the increase of tritium inventory. To understand the change of tritium inventory in the surface region and surface in tungsten by plasma exposure, tritium concentration in tungsten exposure by low-energy (3 8eV), high-flux D plasma with was examined with BIXS after thermal exposure of tritium gas. D plasma exposure was carried out at specimen temperature around 495 and 550K. After that, specimens were exposed to gaseous tritium diluted with deuterium at 473K for 3 hours. The tritium concentration was measured with BIXS. The tritium concentration in surface and surface region was found to be increased by plasma exposure. And its concentration of tungsten exposed at 495K was estimated to be twice higher than that of as-received tungsten

Modification of optical properties of tungsten exposed to low-energy, high flux deuterium plasma ions

Anomalous change of optical properties of recrystallized W caused by exposure to D plasma ions at sample temperature of ~535 K was studied by ellipsometry and reflectometry. There is a qualitative difference between the samples reflectivity values measured directly and calculated using ellipsometric data. A physical model of the phenomenon is suggested. It is shown that on the W surface exposed at ~535 К two processes take place 1) blistering and 2) modification of electron structure in the upper-most layer.Методами еліпсометрії та рефлектометрії виявлено аномальне змінення оптичних властивостей рекристалізованого W внаслідок бомбардування іонами D при температурі ~535 К. Існує принципова різниця між значеннями коефіцієнту відбиття, що отримано рефлектометрією та розраховано за даними еліпсометрії. Запропоновано фізичну модель виявленого ефекту. Показано, що на поверхні W, що опромінено при 535 К, мають місце два процеси: 1) блістерінг и 2) модифікація електронної структури поверхневого шару.Методами эллипсометрии и рефлектометрии обнаружено аномальное изменение оптических свойств рекристаллизованного W в результате бомбардировки ионами D при температуре ~535 К. Имеет место принципиальное отличие между значениями коэффициента отражения, измеренными рефлектометрией и рассчитанными по данным эллипсометрии. Предложена физическая модель обнаруженного эффекта. Показано, что на поверхности W, облученного при 535 К, имеют место два процесса: 1) блистеринг и 2) модификация электронной структуры поверхностного слоя

Deuterium release from deuterium plasma-exposed neutron-irradiated and non-neutron-irradiated tungsten samples during annealing

We examine the effect of neutron irradiation on the release of deuterium from tungsten at 573 K to understand the efficiency of tritium removal by baking out at moderate temperatures. Tungsten samples, undamaged and neutron-irradiated to a damage level of approximately 0.016 displacements per atom, are exposed to low-energy (108 eV), high-flux (3.0 × 1021 to 9.4 × 1021 m−2 s−1) deuterium plasma at temperatures ranging from 573 to 773 K to an ion fluence of 1.1 × 1025 m−2. At each exposure temperature, two undamaged and two neutron-irradiated tungsten samples are exposed to plasma. The deuterium content in the tungsten samples is measured by thermal desorption spectrometry soon after the plasma exposure and after post-plasma annealing at 573 K for 30 h. It is found that: (i) the deuterium retention in the neutron-irradiated tungsten samples is significantly higher than that in the undamaged tungsten samples; (ii) annealing at 573 K of undamaged tungsten samples pre-exposed to deuterium plasma at 573–773 K leads to an almost complete (60%–99%) release of deuterium from the samples; (iii) annealing at 573 K of neutron-irradiated tungsten samples pre-exposed to deuterium plasma at 573–773 K leads to a significant (8%–20%) release of deuterium from the samples

Deuterium retention in reduced activation ferritic/martensitic steel EUROFER97 exposed to low-energy deuterium plasma

EUROFER97 steel samples were exposed to deuterium plasma in the linear plasma device PISCES-A with the ion energies of 90 and 140 eV at exposure temperatures between 360 and 773 K to deuterium ion fluences between 3.8 × 1023 and 6.3 × 1025 m−2. RBS analysis of these plasma-exposed samples showed that the uppermost surface layers were enriched with tungsten and tantalum. Deuterium depth profiles in the plasma-exposed samples were examined using the energy-scanning NRA technique allowing measurements of the deuterium depth profiles at depths of up to about 9 μm. With an increase in the exposure temperature from 360 to 773 K, the deuterium retention in the 1 µm thick sub-surface layer decreased almost monotonically from about 1 × 1019 D/m2 to 5 × 1017 D/m2. The deuterium concentration at a depth of 8 μm demonstrated a different temperature dependence - with an increase in the exposure temperature from 360 to 500 K, the deuterium concentration significantly decreased from about 4 × 10−3 to (4 ± 3) × 10−5 at.%. With a further increase in the temperature up to 773 K, the deuterium concentration at a depth of 8 μm became equal to or less than 5 × 10−5 at.%