Bulletin of the American Physical Society
55th Annual Meeting of the APS Division of Plasma Physics
Volume 58, Number 16
Monday–Friday, November 11–15, 2013; Denver, Colorado
Session JM9: Mini-Conference: Plasma Material Interactions Involving Helium (SciDAC and Beyond) I |
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Chair: David Ruzic and Jean Paul Allain, University of Illinois Room: Governor's Square 16 |
Tuesday, November 12, 2013 2:00PM - 2:20PM |
JM9.00001: Modeling Plasma Surface Interactions in Tungsten through High-Performance Computing Brian D. Wirth The plasma facing components of future tokamak-based fusion power plants arguably represent the single greatest materials engineering challenge of all time. Fortunately, recent innovations in computational modeling, increasingly powerful high performance computing platforms and improved experimental characterization tools provide the opportunity to develop self-consistent, experimentally validated models of materials performance in the fusion energy environment. This presentation will describe the challenges of modeling plasma facing components in a fusion materials environment, opportunities to utilize high performance computing and then focus on recent progress to investigate the surface evolution of tungsten exposed to low-energy He/H plasmas. These results identify the mechanisms of tungsten surface morphology changes during 100 eV He plasma exposure as a function of temperature and initial tungsten microstructure. The results demonstrate that He clusters create self-interstitial defect clusters in W by a trap mutation process, followed by the migration of these defects to the surface that forms adatom layers on the tungsten surface. As the helium clusters grow into nanometer bubbles, their proximity to the surface and extremely high gas pressures leads to rupture the surface. Helium bubble bursting induces additional surface damage and tungsten mass loss. [Preview Abstract] |
Tuesday, November 12, 2013 2:20PM - 2:40PM |
JM9.00002: Plasma-surface interactions on extreme grain-refined tungsten tested under multi-scale fusion reactor conditions Jean Paul Allain, Osman El-Atwani, Jonathan Hinks, Sean Gonderman, Anton Neff, Thomas Morgan, Kirill Bystrov, Greg de Temmerman Tungsten is being considered as one of the top material candidates for divertor and first-wall components of future plasma-burning magnetic fusion reactors. Future operation demands reliable performance under extreme environmental conditions including: multi-scale variables including: particle flux (e.g. 10$^{17}$-10$^{24}$ /m$^2$/sec), fluence (e.g. 10$^{19}$-10$^{28}$ m$^{-2}$), temperature (200-1500 C), incident particle energies (5-1000 eV/amu) and heat fluxes (10-50 MWm$^{-2}$). Recent studies have observed complex surface morphology evolved when exposed to He and D/He plasmas. Extreme grain-refined tungsten is investigated as a plasma-facing component material with possible radiation-resistant properties. A systematic study ranging from early-stage He irradiation conditions to fusion reactor-level plasmas has been conducted. Early-stage studies include \textit{in-situ} TEM analysis of He-irradiated nanostructured tungsten. Simulated conditions in future fusion plasma-burning devices are replicated using Pilot-PSI plasmas at DIFFER. Results shed light on critical gaps in our understanding of the surface response and nano-to-microstructural deformation behavior motivating pathways for improved theoretical and computational modeling strategies. [Preview Abstract] |
Tuesday, November 12, 2013 2:40PM - 3:00PM |
JM9.00003: Impact and effects of simultaneous MeV-ion irradiation and helium plasma exposure to the formation of tungsten nano-tendrils Graham Wright, Leigh Ann Kesler, Dennis Whyte The extrusion of nano-tendrils from high temperature (\textgreater 1000 K) tungsten (W) targets exposed to helium (He) plasma ions remains a concern for future fusion reactors. Previous work on the Alcator C-Mod tokamak has demonstrated it is possible to form these structures in a tokamak environment. However, one area where Alcator C-Mod and a fusion reactor differ is total neutron flux at the wall and the displacement damage these neutrons produce in the plasma-facing materials. This dsiplacement damage may affect the size and number He bubbles precipitating in the W target, which is a key factor in the formation and growth of the nano-tendrils. The DIONISOS experiment directly measures the impact of the displacement damage by simultaneously bombarding high temperature W targets with MeV-range ions (to simulate the displacement damage caused by neutron flux) and high flux of He plasma ions. Different combinations of irradiating ion species and W target temperatures are used to vary the different processes and rates that are involved such as He trapping rate, vacancy production and annealing rates, and nano-tendril growth rate. The nano-tendril growth is characterized by SEM imaging and focused ion beam (FIB) cross-sectioning and compared to nano-tendril formation without the presence of the irradiating ion beam. [Preview Abstract] |
Tuesday, November 12, 2013 3:00PM - 3:20PM |
JM9.00004: Experimental Validation Plan for the Xolotl Plasma-Facing Component Simulator Using Tokamak Sample Exposures V.S. Chan, C.P.C. Wong, A.G. McLean, G.N. Luo, B.D. Wirth The Xolotl code under development by PSI-SciDAC will enhance predictive modeling capability of plasma-facing materials under burning plasma conditions. The availability and application of experimental data to compare to code-calculated observables are key requirements to validate the breadth and content of physics included in the model and ultimately gain confidence in its results. A dedicated effort has been in progress to collect and organize a)~a database of relevant experiments and their publications as previously carried out at sample exposure facilities in US and Asian tokamaks (e.g., DIII-D DiMES, and EAST MAPES), b)~diagnostic and surface analysis capabilities available at each device, and c)~requirements for future experiments with code validation in mind. The content of this evolving database will serve as a significant resource for the plasma-material interaction (PMI) community. [Preview Abstract] |
Tuesday, November 12, 2013 3:20PM - 3:40PM |
JM9.00005: Discussion on Experimental Validation |
Tuesday, November 12, 2013 3:40PM - 4:00PM |
JM9.00006: Kinetic modeling of sheath/presheath of a magnetized plasma Xianzhu Tang, Zehua Guo, Ying Wang, Gian Luca Delzanno, John Canik An initial plan for the PSI SciDAC project is to use the experimental results from linear devices to develop and validate a predictive modeling capability of redeposition. This involves fluid modeling of the PISCES plasma by SOLPS, and kinetic modeling of the sheath/presheath by VPIC. Here we describe the kinetic modeling results of the sheath/presheath in a PISCES plasma, with an emphasis on the fluid moments at the sheath entrance that serve as the boundary condition for the SOLPS code. These include the plasma flow, and the electron and ion energy fluxes, which are typically modeled by energy transmission coefficient in fluid codes. A comparison of the sheath with magnetic field normal and oblique to the wall will also be given, along with the different behavior of prompt redeposition in these two cases. {\em Work supported by OFES and OASCR} [Preview Abstract] |
Tuesday, November 12, 2013 4:00PM - 4:20PM |
JM9.00007: Fluid and kinetic plasma modeling of redeposition regimes J.M. Canik, X. Tang Strong redeposition of eroded material from plasma-facing components (PFC) is required in a fusion reactor to ensure long PFC lifetimes. Reaching redeposition regimes depends on the plasma conditions near the PFC surface, as well as the surface material itself. Here we present plasma modeling of experiments performed at the PISCES device studying the erosion properties of Be surfaces that have been produced via seeding to simulate the redeposition process [Doerner, Nucl. Fusion \textbf{52} (2012) 13033]. Initial modeling has utilized the SOLPS code [Schneider, Contrib. Plasma Phys. \textbf{46} (2006) 3], which treats the plasma as a fluid, and can simulate the long-range transport of eroded impurities. To treat the effect of the magnetic sheath near the surface, which can dominate the prompt redeposition characteristics of heavy PFC materials including W, requires a kinetic plasma simulation, and is being addressed using the VPIC code [Bowers, Phys. Plasmas \textbf{15} (2008) 055703]. Results from the fluid plasma modeling will be presented, and the coupling of the VPIC and SOLPS codes will be discussed. [Preview Abstract] |
Tuesday, November 12, 2013 4:20PM - 4:40PM |
JM9.00008: ABSTRACT WITHDRAWN |
Tuesday, November 12, 2013 4:40PM - 5:00PM |
JM9.00009: MAPES Plans at EAST Guang-Nan Luo The Material and Plasma Evaluation System (MAPES) has been successfully built up at the H section of EAST tokamak, consisting of a mid-plane material probe with both active cooling and heating, and multiple diagnostics of sample and boundary plasma. Samples or PFC mock-ups with a weight less than 20 kg and a diameter less than 500 mm can be inserted into the main scrape-off layer plasma from the low field side of EAST. Local background plasma could be characterized by Langmuir probes and thermocouples embedded in the samples, visible and infrared cameras are set at M and D sections. During the 2012 EAST campaign, MAPES has been used to address a variety of PMI issues relevant to ITER. In 2014, several new optical systems will be constructed. A WI emission spectroscopy system and an IR imaging system are being developed and dedicated to the monitoring of the W influx profile and temperature distribution. A set of lens will also be set at H upper port to collect the visible emission light from the lower divertor. The laser induced breakdown spectroscopy (LIBS) is planned to be installed to detect the first wall surface composition at the high field side. In the next EAST campaign, more experiment proposals have been accepted and are being prepared. EAST-MAPES is oriented towards a bridge for international collaborations and is playing an active role in supporting PWI-related researches under tokamak plasma environment. [Preview Abstract] |
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