Deuterium In Graphite Research Articles

Ion irradiated graphite exposed to fusion-relevant deuterium plasma

Graphite samples were irradiated with 5MeV carbon ions to simulate the damage caused by collision cascades from neutron irradiation in a fusion environment. The ion irradiated graphite samples were then exposed to a deuterium plasma in the linear plasma device, MAGPIE, for a total ion fluence of ∼1×1024ionsm−2. Raman and near edge X-ray absorption fine structure (NEXAFS) spectroscopy were used to characterize modifications to the graphitic structure. Ion irradiation was observed to decrease the graphitic content and induce disorder in the graphite. Subsequent plasma exposure decreased the graphitic content further. Structural and surface chemistry changes were observed to be greatest for the sample irradiated with the greatest fluence of MeV ions. D retention was measured using elastic recoil detection analysis and showed that ion irradiation increased the amount of retained deuterium in graphite by a factor of four.

Thermal desorption of hydrogen from carbon and graphite at elevated temperatures

Abstract Thermal desorption spectrometry (TDS) has been investigated to obtain fundamental information of hydrogen behavior in graphite and CFC especially at high temperatures. Thirteen brands of graphite and CFC materials charged with deuterium gas are tested up to the temperature of 1720 K with a heating rate of 0.1 K/s. TDS spectra have at least four peaks at 600–700 K, around 900 K, 1300–1450 K and 1600–1650 K. The change of TDS spectra is measured for the samples, which are charged with deuterium at 1273 K under a different pressure in the range of 83 Pa to 79 kPa. Physical and chemical states of deuterium in graphite and mechanisms of desorption are discussed.

In-situ ion beam analysis and dynamic studies of deuterium retention in graphite exposed to a high flux magnetron plasma

A new compact plasma simulator device has been mounted on line at the Van de Graaff accelerator and successfully used for deposition experiments of deuterium atoms with the mean ion energy of 120–140 eV. Deuterium retention in graphite exposed to a magnetron plasma at flux densities above 10 17 D cm −2 s −1 has been studied by nuclear reaction analysis. A dynamic retention of about 1 × 10 16 D/ cm 2 has been identified in the discharge with a current density exceeding 16 mA/cm 2. This dynamic inventory is released within 60 ms after the discharge has been stopped. The interpretation is based on trapping, detrapping and diffusion of deuterium in graphite.

Trapping and reflection coefficients for deuterium in graphite at low energy and oblique incidence

Trapping and particle reflection coefficients for 33–500 eV D on graphite have been measured for angles of incidence 0° ≤ α ≤ 75° by determining the areal density of implanted D as a function of the implanted fluence using the D(3He, p)α nuclear reaction. The experimental data are compared to computer calculations with the TRIM.SP-program. The particle reflection coefficients obtained from a smooth and a rough surface are compared. Surface roughness accounts for a strong decrease of particle reflection at oblique incidence and low energies.

Calibration of a basic secondary ion mass spectrometer, by means of elastic recoil detection, for hydrogen isotopes implanted into graphite

AbstractA secondary ion mass spectrometer equipped with a low‐resolution argon ion source and a small quadrupole ion mass analyser was calibrated for moderate to high concentrations of hydrogen and deuterium in graphite. The polished graphite samples were implanted with hydrogen isotope ions of 1 or 2 KeV energy. The depth profiles of the implanted hydrogen were determined by means of elastic recoil detection (ERD) and compared with those obtained by SIMS. Linear correlations were found between the peak D+/C+ or CH+/C+ ratio and the maximum D or H concentration determined by ERD, as well as between the integral of the SIMS profile curves and the total quantity of hydrogen isotope.

Chemical release of implanted deuterium in graphite

Graphite is extensively being used in present‐day fusion devices and has been selected as the reference material for plasma‐facing components in the international thermonuclear experimental reactor, ITER. Graphite’s major advantages are associated with its low Z and excellent thermomechanical properties. Its drawbacks include susceptibility to erosion and large capacity for H retention under hydrogen plasma exposure. H‐retention affects fuel recycling and also presents a potential environmental risk when operating with tritium, during vacuum vessel maintenance and accidental vacuum loss. The objective of the present study was to investigate the removal of energetically implanted deuterium from pyrolytic graphite via chemical reaction with atmospheric gases (N2, O2, and H2O) for different graphite temperatures. N2 exposure at 300–570 K appeared to be ineffective for the removal of implanted D. Oxygen exposure, on the other hand, was most effective in removing the implanted D from graphite, most likely by t...

Dynamic inventory of implanted deuterium in graphite at 116–223 K

Abstract We have measured the time dependence of deuterium re-emission from graphite during and after implantation with 18 keV D+3 in the temperature range 116 ⩽ T ⩽ 223 K. In all cases the implantation was continued until stationary conditions were established. After stopping the beam, 5–10% of the total inventory was released with a time constant decreasing with increasing temperature. In this temperature range the release is tentatively described by an activated diffusion process with an activation energy of 0.03 ± 0.01 eV. It is suggested that the dynamic fraction consists of molecular deuterium which is formed by local recombination during implantation.

Temperature dependence of ion-induced detrapping of deuterium in graphite

We have extended our previous work on the release of deuterium from saturated near-surface layers of graphite by keV proton bombardment [B.M.U. Scherzer et al., Nucl. Instr. and Meth., to be published] t^ the temperature range 93 K ≤ T ≤ 573 K. The saturated deuterium layers were produced by 300 eV D + implantation. Retention and reemission of D has been measured for proton fluences up to 3 × 10 18 cm −2. The results suggest two different mechanisms to contribute to the release, one being due to detrapping of bound D by protons penetrating the deuterium layer, the other being due to deposition of protons in the deuterium layer up to saturation. The importance of the second mechanism compared to the first one increases with decreasing temperature. The results have been compared to model calculations taking into account detrapping by nuclear collisions, local retrapping and molecular recombination. This simple model is not suitable to describe the detailed release behaviour probably due to the presence of different types of traps and possibly to an inhomogeneity of structure with depth in the implanted films.

Hydrogen-ion-induced detrapping of implanted deuterium in graphite

The release of saturated 300 eV D + implants in graphite by 6–30 keV H + bombardment has been measured at temperatures between 295 and 473 K and fluences up to more than 3 × 10 18 H +-ions/cm 2. The decrease of retained D is found to be slower than exponential. Release rates decrease with increasing energy indicating that detrapping is primarily due to atomic collisons. A faster release is observed at higher target temperatures during H + bombardment and some enhancement persists if the target is annealed after deuterium implantation. The release of low energy implants by high energy ions cannot be described by the local mixing model. Instead, a model accounting for local molecular recombination and detrapping gives qualitative agreement with experimental dependence on H + energy. It cannot, however, explain the temperature dependence.

Trapping and reflection coefficients for deuterium in graphite at oblique incidence

Trapping and particle reflection coefficients for 0.4–10keVD on graphite have been measured for angles of incidence 0≦α≦85° by determining the areal density of implanted D as a function of the implanted fluence. The experimental data are compared to computer calculations with the TRIM-program. The agreement between measurement and calculation is good.