Browsing by Author "Corr, CS"
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- ItemDeuterium retention and near-surface modification of ion-irradiated diamond exposed to fusion-relevant plasma(IOP Science, 2014-04-01) Deslandes, A; Guenette, MC; Corr, CS; Karatchevtseva, I; Thomsen, L; Lumpkin, GR; Riley, DPChemical vapour deposited diamond was irradiated with 5 MeV carbon ions to simulate the damage caused by collision cascades from neutron irradiation in a fusion environment. Ion-irradiated samples were then exposed to a deuterium plasma in MAGPIE with ion flux of ~1.3 × 1021 ions m−2 s−1. Raman and near edge x-ray absorption fine structure (NEXAFS) spectroscopy were used to characterize the degree of disorder and sp2-bonding induced by the ion irradiation. The signals of sp2-bonded and disordered carbon were observed to decrease after exposure to the deuterium plasma, although sharp Raman peaks indicative of vacancy and interstitial defects induced by the MeV ions were less affected. Recovery of a diamond-like surface after plasma exposure was evident in the NEXAFS spectra. Elastic recoil detection analysis showed that the ion-damaged diamond retained more deuterium than diamond exposed only to deuterium plasma. For the case of unirradiated samples, diamond retained more deuterium than graphite. However, for the case of the ion-irradiated samples, diamond exhibited less deuterium retention than graphite. © 2014, IAEA Vienna.
- ItemHigh water diffusivity in low hydration plasma-polymerised proton exchange membranes(Trans Tech Publications, 2010-08-02) Peterson, VK; Corr, CS; Kearley, GJ; Boswell, RW; Izaola, ZThis paper compares proton diffusion through plasma-polymerised proton-exchange membranes (PEMs) produced using traditional wet-chemical methods (Nafion®) and those produced using plasma-polymerisation. Using quasielastic neutron scattering and a simple model of proton motion we find the measured diffusion-rate of protons in the plasma-polymerised material and Nafion® is the same (within 1 standard error) even though the plasma-polymerised membrane has 80% less water than the Nafion®. We attribute this result to the highly cross-linked structure of the plasma-polymerised membrane.
- ItemInfluence of plasma impurities on the effective performance of fusion relevant materials(Australian Institute of Physics, 2014-02-04) Riley, RP; Guenette, MC; Deslandes, A; Middleburgh, SC; Lumpkin, GR; Thomsen, L; Corr, CSThe development of a sustainable source of power derived from fusion energy is presently constrained by the limited number of materials capable of operating under such extreme conditions. Plasma facing components within magnetically confined fusion reactors must withstand extremes of temperature and loads, while maintaining a high tolerance to radiation damage from energetic particles or neutrons. More specifically, factors of sputtering yield, thermal conduction, electrical conduction and retention of fuel can all degrade the performance of the reactor and hence detrimentally lower the efficiency. In aiming to improve our understanding of materials capable of operating within the fusion environment, it is essential to establish how present generation materials become degraded. Use of ion beam accelerators and linear plasma devices simulate the respective impact of energetic neutron damage (14.1 MeV) and plasma erosion (H+, D+, He+) within a magnetically confined fusion environment. Methods of characterising changes in the local structure and chemistry of surface and near surface regions of fusion relevant materials quantify material degradation resulting from the uptake of plasma impurities. While complementary density functional theory (DFT) simulations have identified possible mechanisms for degradation of material performance. An overview of material evaluation methods will also be presented.
- ItemInitial damage processes for diamond film exposure to hydrogen plasma(Elsevier Science, 2013-12-01) Deslandes, A; Guenette, MC; Samuell, CM; Karatchevtseva, I; Ionescu, M; Cohen, DD; Blackwell, B; Corr, CS; Riley, DPDiamond is considered to be a possible alternative to other carbon based materials as a plasma facing material in nuclear fusion devices due to its high thermal conductivity and resistance to chemical erosion. In this work CVD diamond films were exposed to hydrogen plasma in the MAGnetized Plasma Interaction Experiment (MAGPIE): a linear plasma device at the Australian National University which simulates plasma conditions relevant to nuclear fusion. Various negative sample stage biases of magnitude less than 500 V were applied to control the energies of impinging ions. Characterisation results from SEM, Raman spectroscopy and ERDA are presented. No measureable quantity of hydrogen retention was observed, this is either due to no incorporation of hydrogen into the diamond structure or due to initial incorporation as a hydrocarbon followed by subsequent etching back into the plasma. A model is presented for the initial stages of diamond erosion in fusion relevant hydrogen plasma that involves chemical erosion of non-diamond material from the surface by hydrogen radicals and damage to the subsurface region from energetic hydrogen ions. These results show that the initial damage processes in this plasma regime are comparable to previous studies of the fundamental processes as reported for less extreme plasma such as in the development of diamond films. © 2013, Elsevier Ltd.
- ItemIon irradiated graphite exposed to fusion-relevant deuterium plasma(Elsevier, 2014-12-01) Deslandes, A; Guenette, MC; Corr, CS; Karatchevtseva, I; Thomsen, L; Ionescu, M; Lumpkin, GR; Riley, DPGraphite samples were irradiated with 5 MeV 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 × 1024 ions m−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. © 2014, Elsevier B.V.
- ItemNEXAFS spectroscopy of CVD diamond films exposed to fusion, relevant hydrogen plasma(Elsevier, 2013-04-01) Guenette, MC; Deslandes, A; Samuell, CM; Tadich, A; Thomsen, L; Cowie, BCC; Corr, CS; Riley, DPA series of CVD diamond films have been exposed to hydrogen plasma in the linear magnetized plasma device, MAGPIE, with various applied sample stage biases between 0 V (no applied bias) to − 500 V. The plasma-induced damage to the surface structure of the diamond films has been investigated by Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy in both the Auger electron yield (AEY) and total fluorescence yield (TFY) modes. The key diamond NEXAFS spectral features (diamond core exciton and second absolute band gap) are found to be diminished following plasma exposure as measured in the surface sensitive, AEY spectra, whilst these features remain unchanged relative to an unexposed diamond reference film as measured using the bulk sensitive, TFY spectra. These results, in conjunction with SRIM simulations, show definitively that the damage to the surface of the diamond films is restricted to the scale of the penetration depth of the H ions and no damage is induced at greater depths. The power and sensitivity of NEXAFS spectroscopy in assessing damage to the surface of diamond from fusion-relevant plasma-surface interactions are demonstrated. © 2013, Elsevier B.V.
- ItemSuperfast proton diffusion achieved in a plasma-polymerized fuel-cell membrane(American Chemical Society, 2013-03-07) Peterson, VK; Corr, CS; Boswell, RW; Izaola, Z; Kearley, GJWe measure superfast proton diffusion in a proton-exchange membrane (PEM) produced by plasma polymerization. The proton self-diffusion is measured in water-saturated PEMs from the proton autocorrelation function obtained from quasielastic neutron scattering (QENS). 41(3)% of protons in the plasma-produced membrane diffuse at a rate that is an order of magnitude faster than that measured in the commercially available membrane, Nafion, and this is achieved in low hydration conditions. Both molecular dynamic simulations and experimental results are consistent with an assisted superfast diffusion process that may open the way to more powerful fuel cells. © 2013, American Chemical Society.