Radiation-induced amorphization of quartz under a high fast-neutron fluence

Translated from Atomnaya Énergiya, Vol. 66, No. 3, pp. 204–205, March, 1989.     

Penetration of deuterium from plasma through a nickel membrane

Institute of Physical Chemistry, Russian Academy of Sciences. Translated from Atomnaya énergiya, Vol. 76, No. 2, pp. 145–148, February, 1994.     

Stimulation of deuterium combustion in a DT plasma by secondary particles

Engineering Materials Testing Laboratory.     

Production of defects in molybdenum by a deuterium glow discharge plasma

Conclusions Cathode bombardment of monocrystalline molybdenum surfaces oriented perpendicular to the [111] direction in a deuterium glow discharge plasma at a burning voltage of 500 V with a discharge current density of 4.5 mA/cm² and a temperature of 800°C leads to formation in the surface layer of edge and nearly edge loops with Burgers vectors b=a/2 111 lying in the {111} and {321} planes and the Burgers vectors b=a 100 lying in the {100}, {115}, and {117} planes. All loops with diameters >100 Å were injection loops. It is proposed that the smaller defects that can be seen in an electron microscope are also aggregates of interstitial atoms. The formation of dislocation loops with Burgers vectorsb=a 100 has been explained in terms of the large compressive stresses which arise in the surface layer of the foil during bombardment. The production of a large number of highly mobile interstitial atoms in the surface layer of a single crystal by the deuterium plasma and their subsequent diffusion to sinks probably play a dominant role in radiation-enhanced self- and heterogeneous diffusion.Translated from Atomnaya Énergiya, Vol. 48, No. 3, pp. 157–161, March, 1980.     

Flux and energy of deuterium incident on a limiter-like probe in PLT

Carbon samples were exposed to the plasma edge in the PLT tokamak at various distances from the plasma. The amount of deuterium retained was subsequently determined using nuclear reaction analysis. The deuterium retention was found to saturate with increasing exposure time. Values for the energies and fluxes of the deuterium incident on the samples were determined by comparing the observed retention behavior with a saturation model for the retention. The deuterium fluxes and energies were found to decrease from ø~4 × 10¹⁷ D/cm² s and kT~270 eV at the radius of the limiter to ø~0.8 × 10¹⁷ D/cm² s and kT~90 eV at the radius of the wall. At these energies the fraction of the incident deuterium directly reflected from carbon is predicted to be 30 to 40%. From the deuterium energies and fluxes, values for the power flux and erosion rates are estimated.     

Deuterium retention in sintered boron carbide exposed to a deuterium plasma

Depth profiles of deuterium up to a depth of 10 μm have been measured using the D(³He,p)⁴He nuclear reaction in a resonance-like technique after exposure of sintered boron carbide, B₄C, at elevated temperatures to a low energy (≈200 eV/D) and high ion flux (≈10²¹ m⁻² s⁻¹) D plasma. The proton yield was measured as a function of incident ³He energy and the D depth profile was obtained by deconvolution of the measured proton yields using the program SIMNRA. D atoms diffuse into the bulk at temperatures above 553 K, and accumulate up to a maximum concentration of about 0.2 at.%. At high fluences (?10²⁴ D/m²), the accumulation in the bulk plays a major role in the D retention. With increasing exposure temperature, the amount of D retained in B₄C increases and exceeds a value of 2 × 10²¹ D/m² at 923 K. The deuterium diffusivity in the sintered boron carbide is estimated to be D = 2.6 × 10⁻⁶exp{−(107 ± 10) kJ mol⁻¹/RT} m² s⁻¹.     

Saturation of deuterium retention in carbon a new calibration for plasma edge probes

Depth profiles were measured for deuterium implanted in carbon at 530, 1500, and 3000 eV. Measured profiles were in good agreement with profiles calculated using the TRIM code. Comparison between profiles for high and low fluence implants show a scaling of the local deuterium concentration with incident deuterium fluence up to a saturation concentration of 0.44 ± 0.08 D/C ratio. New measurements of retention versus fluence for monoenergetic deuterium implanted in carbon for incident energies from 300 to 1500 eV are in very good agreement with the retention behavior predicted by a saturation model using the observed depth profiles and saturation concentrations. The retention is calculated for deuterium with a Maxwellian velocity distribution to provide a new calibration for the determination of the energy and flux of deuterium incident on carbon probes exposed to the edge of magnetically confined plasmas. This new calibration gives deuterium energies and fluxes significantly different from those obtained using earlier calibrations. A simple analytic representation is also presented for retention of deuterium with a Maxwellian velocity distribution which provides a systematic approach for analyzing probe data.     

Surface morphology and deuterium retention in tungsten oxide layers exposed to low-energy, high flux D plasma

Surface morphology and deuterium retention in tungsten oxide layers (WO_3−z, z ? 0.25) grown on polycrystalline and recrystallized W substrates have been examined after exposure to a low-energy (38 eV/D), high flux (10²² D/m² s) D plasma to an ion fluence of 10²⁶ D/m² at various temperatures (up to ∼700 K). Characterization methods used were scanning electron microscopy, X-ray diffraction, Rutherford backscattering spectroscopy, and the D(³He,p)⁴He nuclear reaction analysis. During exposure to the D plasma at temperatures of 340-615 K, a partial reduction of the tungsten oxide takes place in the near-surface layer up to 0.3 μm in depth. Even at around room temperature, deuterium atoms diffuse several micrometers into the tungsten oxide. The high D concentration of about 0.1 D/W observed in the first micrometers below the surface at temperatures below 500 K can be related mainly to D atoms chemically bonded to O atoms. As the exposure temperature increases, the D concentration decreases, reaching about 2 × 10⁻⁴ D/W at 615 K. At plasma exposure temperatures of about 700 K, the oxide layer shrinks and loses a large fraction of oxygen.     

Stability of defects created by high fluence helium implantation in silicon

Stability of extended defects created by high fluence helium implantation (50 keV, 5 × 10¹⁶ cm⁻²) from room temperature to 800 °C has been studied using transmission electron microscopy. Our results clearly show that the cavities behave as good sinks for interstitial type defects generated during ion implantation, leading in some cases to the cavity dissolution. A three-dimensional “phase diagram” related to the formation and evolution of interstitial-type defects is also proposed. It is plotted in terms of quantity of damage, annealing time and implantation temperature.     

Development of a high energy pulsed plasma simulator for the study of liquid lithium trenches

To simulate detrimental events in a tokamak and provide a test-stand for a liquid-lithium infused trench (LiMIT) device [1], a pulsed plasma source utilizing a theta pinch in conjunction with a coaxial plasma accelerator has been developed. The plasma is characterized using a triple Langmuir probe, optical methods, and a calorimeter. Clear advantages have been observed with the application of a coaxial plasma accelerator as a pre-ionization source. The experimental results of the plasma gun in conjunction with the existing theta pinch show a significant improvement from the previous energy deposition by a factor of 14 or higher, resulting in a maximum energy and heat flux of 0.065 ± 0.002 MJ/m² and 0.43 ± 0.01 GW/m². A few ways to further increase the plasma heat flux for LiMIT experiments are discussed.     

Helium desorption in He implanted tungsten at low fluence and low energy

The behaviour of helium in polycrystalline ³He implanted tungsten at low energy (60 keV) and low fluence (2 × 10¹³ cm⁻²) has been studied as a function of post-implantation annealing temperature until 1873 K by means of Nuclear Reaction Analysis. Helium desorption has been observed only from ∼1500 K, suggesting a helium trapping at mono-vacancies. Only ∼75% of the implanted helium has been released after the annealing during 1 h at high temperature (1873 K); besides, the desorption rate decreased from 1673 K. The presence of a second type of helium trapping site is likely to explain this strong helium retention.     

Beryllium erosion induced by transient heat loads and subsequent reactions in a deuterium plasma

Pulsed laser irradiation (～0.1–4 MJ/m² at 1–10 ms) to a beryllium (Be) target has been performed under steady-state deuterium (D) plasma exposure in the linear divertor plasma simulator PISCES-B to investigate the response of Be to transient heat loads such as edge localized modes. Emission intensities from Be atoms and beryllium deuteride (BeD) molecules are observed in front of the Be target by using two fast framing cameras simultaneously; those exhibit similar time evolution to each other, but spatial profiles are different. While the Be I light emission peaks just in front of the target, the BeD emission peaks away from the target. This indicates that Be atoms are directly ejected from the surface, and BeD molecules are volumetrically formed in the plasma. It is also found that the time evolution of light emission can be qualitatively well reproduced by the evaporation flux of Be atoms, estimated from the calculated surface temperature. The Be surface is thought to be eroded as atoms due mainly to evaporation during laser irradiation.     

Damage produced in magnesium aluminate spinel by high energy heavy ions including fission products of fission energy: microstructure modifications

The radiation stability of spinel MgAl₂O₄ against the impact of beams of a fission product at fission energy (70 MeV iodine) and at different fluences was investigated using Transmission Electron Microscopy (TEM). Specimens prethinned before irradiation were analysed by TEM and irradiated bulk specimens were investigated using cross-sectional TEM. Tracks were observed in pre-thinned specimens. Partial amorphisation was observed for the irradiation at the highest fluence. Recrystalization of the amorphous region, induced by the microscope electron beam was observed. A threshold value of 6 keV nm⁻¹ was determined for the amorphization of spinel under the above mentioned irradiation conditions. Moreover, profile measurements of the irradiated areas confirmed the large swelling values for this material when irradiated with fission products of fission energy. A thermal spike model was used to calculate the damage threshold for spinel using experimentally measured heavy-ion track radii, including results for other ions of up to very high energies. These accelerator-based fission product irradiations revealed an unexpected poor radiation stability, in contrast to the known good behaviour of the spinel against neutron or alpha particle damage.     

Hydrogen incorporation in tungsten deposits growing by deuterium plasma sputtering

Tungsten deposits were produced by sputtering method using hydrogen isotope RF plasma, and the density and the incorporated components in the deposits were investigated. The density changed in the range from 14.2 g/cm³ to 6.1 g/cm³, and hydrogen isotope retention changed in the range from 0.25 to 0.05 as (H + D)/W by the difference of deposition conditions. Both the density and hydrogen isotope retention tended to decrease with an increase of pressure. Even though a deuterium gas was used for producing tungsten deposits, not only deuterium but also hydrogen, oxygen and water vapor were incorporated in the deposits. It is considered that the incorporation of these components originated in water vapor unintentionally existing in the vacuum chamber.     

Study of deuterium retention on lithiated tungsten exposed to high-flux deuterium plasma using laser-induced breakdown spectroscopy

Tungsten is under consideration for use as a plasma-facing material in the divertor region of ITER. Lithiation can significantly improve plasma performance in long-pulse tokamaks like EAST. The investigation of lithiated tungsten is important for understanding the lithium conditioning effects for EAST, where tungsten will be used as a plasma-facing material. In this paper, a few important issues of lithiated tungsten interacting with high-flux deuterium plasma have been studied, such as the effect of lithiation on deuterium retention, the profile of elemental distribution, and the chemical state of lithiated tungsten. Deuterium retention inside both pure and lithiated tungsten has been investigated for the first time in the linear plasma simulator Magnum-PSI by in-situ laser induced breakdown spectroscopy (LIBS). The results indicate that, after deuterium plasma exposure, deuterium retention could be saturated in the lithiation layer, and the lithium in the lithiated layer is chemically bound with deuterium. Moreover, the lithiation can inhibit the blistering on the tungsten surface. These results can be valuable for the application of LIBS as a diagnostic technique for plasma-facing components of tokamaks.