Simultaneous Dual-Beam Implantation of Helium and Deuterium Ions in Tungsten Surfaces

摘要

One of the problems facing the fusion community is the particle fluxes that will impinge upon the plasma facing components (PFCs) such as the first wall and the divertor. Energetic helium (He) particles cause surface damage, microstructure development, and erosion. Tritium retention in the PFCs poses a safety hazard and must be limited. Tungsten is presently favored as the plasma-facing material for the divertor plates in the ITER reactor. While helium-only, deuterium-only (D, as a surrogate for tritium), and sequential helium-deuterium on tungsten implantation studies have been carried out over a broad range of energies and temperatures, simultaneous studies of He and D implantation are less common, particularly at energies over 1 keV.;A new dual ion beam experiment at the University of Wisconsin Inertial Electrostatic Confinement (UW-IEC) Laboratory has been designed and constructed to perform simultaneous dual-beam implantation studies: the Dual Advanced Ion Simultaneous Implantation Experiment (DAISIE). The work presented in this thesis focuses on helium and deuterium implantations in polycrystalline tungsten at energies of 30 keV, surface temperatures of 900 °C and 1100 °C, and incidence angles of 55° off normal. This experiment was based on electrostatic ion gun technology previously used to perform normal-incidence implantations by the UW-IEC laboratory. Single-beam, helium-only; dual-beam, helium-only; single-beam, deuterium-only; and simultaneous helium and deuterium implantations into tungsten were performed. Relative He and D implantation fluences of up to 6 x 1018 He cm--2 and 5.4 x 1019 D cm--2 were based on a 10% He-90% D fluence ratio.;Erosion yields were calculated from mass loss measurements, exceeding sputtering yield calculations by factors of 5 to 10 for He-only, D-only, and mixed He-D implantations. The surface morphologies induced by implantation were characterized using scanning electron microscopy, focused ion beam, and electron backscatter diffraction techniques to measure physical characteristics and trends with fluence and grain orientation. Surface morphologies created by He-only implantations were compared to previous implantation studies by the UW-IEC group at normal incidence, and similar morphologies and trends were identified. The orientation of the features was found to be highly dependent on the direction of the incident beam(s). Surface morphologies not previously identified by the UW-IEC group were created by D-only implantations at higher fluences, suggesting hydrogen embrittlement. Simultaneous implantation of He and D resulted in a superposition of the morphologies created by He-only and D-only implantation. Helium retention analysis was carried out using thermal desorption spectroscopy. The simultaneous implantation of He and D resulted in different trapping mechanisms for the implanted He compared to He-only implantation and an overall reduction in retained He in the samples. Another new experiment, the Ion Beam & Source Analyzer (IBSA) platform, was designed and constructed to perform experimental spatial and compositional analysis of the beams created by the ion guns for the first time since their development. Both the He and D beams were confirmed to have nearly-Gaussian profiles. The relative fractions of various D molecular ions created by the ion source were identified. Possible N and D2O impurities were identified within the He and D beams, respectively.