| Three devices at the University of Wisconsin-Madison Inertial Electrostatic Confinement (UW IEC) laboratory were used to implant W and W alloys with helium ions at high temperatures. These devices were HOMER, HELIOS, and the Materials Irradiation Experiment (MITE-E). The research presented in this thesis will focus on the experiments carried out utilizing the MITE-E.;Early UW work in HOMER and HELIOS on silicon carbide, carbon velvet, W-coated carbon velvet, fine-grain W, nano-grain W, W needles, and single- and polycrystalline W showed that these materials were not resistant to He+ implantation above ∼800 °C. Unalloyed W developed a "coral-like" surface morphology after He+ implantation, but appeared to be the most robust material investigated.;The MITE-E used an ion gun technology to implant tungsten with 30 keV He+. Tungsten specimens were implanted at 900 °C to total average fluences of 6x1016 -- 6x1018 He +/cm2. Other specimens were implanted to a total average fluence of 5x1018 He+/cm2 at temperatures between 500 and 900 °C. Micrographs of the implanted W specimens revealed the development of three distinct surface morphologies. These morphologies are classified as "blistering", "pitting", and "orientated ridges".;Preferential sputtering of the W by the energetic He+ appears to be responsible for pitting and orientated ridges which developed at high fluences (1019 He+/cm2) in the MITE-E. While the orientated ridges were the dominant morphology on the W surface above 700 °C, the pitting was prevalent below 700 °C. The blister morphology was observed at all of the examined temperatures at fluences ≥5x1017 He+/cm2 but disappeared above fluences of 1019 He+/cm 2.;The "coral-like" surface morphology on W inherent to He + implantation experiments in HOMER and HELIOS developed from a combination of sources: multiangular ion incidence, ion energy spread (softening), and electron field emission from nano-scale surface features induced by He + implantation. The HOMER and HELIOS devices were found to be better suited for simulation of magnetic fusion environments with off-normal particle incidences, and the MITE-E was found to be more suited for simulating the normal particle incidence of inertial fusion environments. |
