Dynamics of Plasma-Surface Interactions using In-situ Ion Beam Analysis

Abstract

SummaryThe overall goal of this proposal was to develop an innovative experimental facility that would allow for the measurement of real-time response of a material surface to plasma bombardment by employing in-situ high-energy ion beam analysis. This facility was successfully developed and deployed at U. Wisconsin-Madison and was named DIONISOS (Dynamics of IONic Implantation & Sputtering on Surfaces).There were several major highlights to the DIONISOS research which we will briefly highlight below. The full technical details of the DIONISOS development, deployment and research results are contained in the Appendices which contain several peer-reviewed publications and a PhD thesis devoted to DIONISOS. The DIONISOS results on deuterium retention in molybdenum were chosen as an invited talk at the 2008 International Conference on Plasma-Surface Interactions in Toledo, Spain. Design HighlightsThe DIONISOS design activity was significant. For the first time ever, a high power magnetized plasma environment was combine with high-energy ion beams from an accelerator. This posed several unique challenges that were overcome in the first 1.5 years of design and implementation.1. The 1.7 MV tandem ion accelerator was refurbished and commissioned. The accelerator was re-assembled and installed at UW-Madison after being shipped from Bell Labs in New Jersey, from where it was purchased 2. A dedicated plasma exposure chamber was designed which featured several innovations ( Fig. 1 5. Innovative charged-particle detectors for ion beam analysis that included active cooling and particle shielding from the nearby plasma. This allowed in-situ surface analysis when the plasma was bombarding the target samples.6. Remotely controlled beam-steering and rastering across the sample face using upstream electrostatic deflectors and strong differential pumping.7. Plasma diagnostics including a scanning langmuir probe and infrared thermography of the target.In summary, the design was successful at integrating a high flux plasma exposure chamber with real-time in-situ ion beam surface analysis for the first time. Fig. 2 Photos of the DIONISOS target chamber a) Rotatable target assembly with active heating/cooling and electrical biasing. Overlays shows how the ~mm diameter ion beam can be scanned across the plasma profile. B) Deuterium helicon plasma incident on a molybdenum target. Research HighlightsThe latter half of the research grant activity focused on deuterium fuel retention in refractory metals. In future burning plasma devices like ITER, tritium fuel retention is a serious safety concern; and tritium fuel economy is a concern for eventual fusion reactors breeding their own tritium. At the same time, refractory metals such as molybdenum and tungsten are leading candidates as PFC materials because of their erosion resistance. We used the unique scientific measurement tools of DIONISOS to explore the dynamic interaction of a deuterium plasma with the metals to illuminate fundamental process of importance. Further motivation was provid...