Bulletin of the American Physical Society
57th Annual Meeting of the APS Division of Plasma Physics
Volume 60, Number 19
Monday–Friday, November 16–20, 2015; Savannah, Georgia
Session NO6: Plasma-Material Interactions & Boundary |
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Chair: Tom Rognlien, Lawrence Livermore National Laboratory Room: 201/202 |
Wednesday, November 18, 2015 9:30AM - 9:42AM |
NO6.00001: Status of the Hybrid Illinois Device for Research and Application (HIDRA) Daniel Andruczyk, Peter Fiflis, Jean Paul Allain, Davide Curreli, David Ruzic HIDRA is currently being assembled at CPMI at the University of Illinois [1]. It's a 5 period, medium sized classical stellarator using a $l=$2, $m=$5 configuration with $R=$0.72 m, $r=$0.19 m. Initial operation will have 26 kW of magnetron power and with OXB heating is expected to reach densities of $n_{e}=$1x10$^{18}$ m$^{-3}$ and temperatures $T_{e}=$20 eV. The focus of HIDRA will be PMI research and PFC development. In fact HIDRA will be the first toroidal device dedicated to the development of new PMI experiments in fusion environments. The expertise of CPMI with in-situ diagnostics, such as MAPP, will open up new opportunities for innovative material testing and play a leading role in the development of future PFC solutions, e.g. innovative liquid metal divertor designs such as LiMIT. HIDRA will also play an important role in helping to validate computational modeling of edge plasmas and plasma surface interactions. Currently HIDRA is still being assembled with first vacuum expected in the summer 2015 and the first plasma to be in Fall 2015. This paper will present some of the initial measurements of HIDRA as it comes on line, discuss, challenges encountered and talk about future plans for research on HIDRA at UIUC. \\[4pt] [1] D. Andruczyk, et al., 2015 Fusion Sci. Technol., (accepted). [Preview Abstract] |
Wednesday, November 18, 2015 9:42AM - 9:54AM |
NO6.00002: A Vlasov-BCA analysis on the wall erosion of a beryllium wall exposed to a high-density Helium plasma Shane Keniley, Davide Curreli Understanding the effects of plasma-material interactions on the wall of fusion reactors will help characterize the durability and performance of plasma facing components over time. It can provide insight into how impurities injected into the plasma from the wall can affect plasma performance. To this end, we perform a numerical characterization of the gross and net erosion of a Beryllium wall exposed to a Helium plasma by using a Vlasov description of the plasma phase coupled to a Binary Collision Approximation model (Fractal-TRIDYN) of the material under plasma irradiation. Both the plasma ions and the impurities are treated as Vlasov kinetic species, allowing high resolution even at very disparate density ratios of the main species over the impurities. From the moments of the distribution, all the relevant fluid quantities are obtained, including densities, particle fluxes, drift velocities, and energy fluxes.~From our model we can provide a measure, intended as magnitude and uncertainty, of net erosion. The effects of the impurity release on the plasma sheath stability and structure is preliminarily explored.~ [Preview Abstract] |
Wednesday, November 18, 2015 9:54AM - 10:06AM |
NO6.00003: Kinetic Characterization using hybrid Particle-in-Cells of the Impurity Release and Wall Erosion of Metal Samples Exposed to a DIII-D Divertor Plasma Rinat Khaziev, Davide Curreli We present a numerical characterization of the wall erosion and impurity release of high-Z metal samples (Mo and W) exposed to a DIII-D plasma using coupled Particle-in-Cell and Binary Collision Approximation codes. The hPIC code was used together with the BCA code TRIDYN to provide a self-consistent treatment of the ion dynamics inside a magnetized plasma sheath. The simulations have been run for the typical plasma conditions encountered at the divertor of DIII-D, $n_e\approx10^{19} \mathrm{m^{-3}}$ $T_e \approx 2-20$ eV, magnetic angle $1.5$ deg. The calculated ion energy-angle distributions (IEAD) at the material wall are fed as an input to TRIDYN, to determine the flux and the distribution of the sputtered material. We present the gross erosion rate and an estimate of the net erosion of the divertor material as function of the relevant plasma parameters, and we highlight the kinetic effects of the erosion process. [Preview Abstract] |
Wednesday, November 18, 2015 10:06AM - 10:18AM |
NO6.00004: Secondary Electron Emission of Li and Li Compounds Angela Capece, Marlene Patino, Yevgeny Raitses, Bruce Koel Secondary electron emission (SEE) results from bombardment by charged particles and can adversely affect plasma stability and alter the plasma-wall interactions in tokamaks and other plasma devices. We present measurements of the SEE yield and the electron energy distribution function for Li and Li compounds using a retarding field analyzer in ultrahigh vacuum. These results are important for proper modeling of the edge plasma in the divertor region of tokamaks using Li coatings. Previous studies\footnote{H. Bruining and J. H. De Boer, Physica 5 (1938) 17.}$^{,}$\footnote{E. Oyarzabal et al., J. Nucl. Mater. 452 (2014) 37.} have reported Li yields for energies up to 900 eV and have shown that yield values are sensitive to surface composition and can vary by as much as an order of magnitude for some energies. We extend our measurements to provide SEE yield curves for energies up to 5 keV---a range relevant for tokamaks. The effect of Li composition on SEE yield was determined by introducing O$_2$ or H$_2$O vapor during Li film growth in order to obtain uniform films of Li$_2$O or LiOH, respectively. Auger electron spectroscopy (AES) was used to probe the surface composition during measurements, and the results show that SEE yields are highest for Li with water contamination. [Preview Abstract] |
Wednesday, November 18, 2015 10:18AM - 10:30AM |
NO6.00005: Recent Advances in Applicability of TEMHD Driven Liquid Lithium as a Fusion Relevant PFC Matthew Szott, Peter Fiflis, Kishor Kalathiparambil, David N. Ruzic Liquid lithium displays increasing promise as a replacement to solid plasma facing components (PFC) in fusion device applications. Liquid PFCs reduce erosion and thermal stress damage, prolonging device lifetime, while lithium has been shown to decrease edge recycling, reduce impurities, and enhance plasma performance. The Liquid Metal Infused Trench (LiMIT) concept developed at UIUC successfully demonstrates horizontal and vertical thermoelectric magnetohydrodynamic (TEMHD) flow of liquid lithium through metal trenches for use as a PFC. Installed in the HT-7 tokamak and at the Magnum-PSI linear plasma device, the system performed effectively in fusion relevant conditions. In high heat flux tests, trench dry-out was observed, which exposes solid trench material due to higher TEMHD force on the area with the highest heat flux. A 3D free surface fluid model of dry-out and experimental tests conducted to mitigate the detrimental effect are described. The final designs for the upcoming test of LiMIT as a limiter for the EAST tokamak are discussed, along with velocity characteristics of steady-state TEMHD driven flow through the LiMIT system inclined up to 180 degrees from horizontal, which is necessary for broad applicability of a liquid lithium PFC system. [Preview Abstract] |
Wednesday, November 18, 2015 10:30AM - 10:42AM |
NO6.00006: An Overview of Recent PISCES Program PMI Results George Tynan, Russell Doerner, Shota Abe, Matthew Baldwin, Joseph Barton, Renkun Chen, Jordan Gosselin, Eric Hollmann, Daisuke Nishijima, Michael Simmonds, Yong Wang, Jonathan Yu The PISCES Program is focused on fundamental PMI studies of Be and W-based solid plasma facing components under steady-state and transient conditions.~ We will show results from studies in W, Be and mixed W-Be material systems.~ Topics of investigation include formation of near-surface nanobubbles from He plasma ion implantation, growth of W-fuzz from these bubbles in steady-state and transient conditions, D retention in Be and W and development of a D-retention model for both H/D isotope exchange and displacement damage experiments. ~ Initial studies of PMI in displacement damaged W are also presented, showing the effect of damage and exposure temperature on D retention, D diffusion, W thermal conductivity. ~ Be-based results include morphology evolution under high plasma flux exposure, Be erosion mechanisms, and retention in Be-based materials.~ Future plans and connections to fusion energy system requirements will be discussed. [Preview Abstract] |
Wednesday, November 18, 2015 10:42AM - 10:54AM |
NO6.00007: Materials research for PMI at Oak Ridge National Laboratory Chad Parish, Philip Edmondson, Fred Meyer, Mark Bannister, Lauren Garrison, Kinga Unocic, Xunxiang Hu, Yutai Katoh In order to improve the scientific understanding of how materials' structure influences plasma-materials interactions (PMI) and the material response to plasma effects, we have performed a series of ion- and neutron-irradiation experiments on tungsten (W). Single- and polycrystal tungsten developed second phase Re$+$Os precipitates due to transmutation from High-Flux Isotope Reactor (HFIR) neutron irradiation. The microstructure of these precipitates was investigated with electron and atom probe microscopy, while mechanical testing found a significant degradation in materials properties, such as toughness and strength, which will degrade PMI performance. We have also used a beam-deceleration module on an electron-cyclotron resonance ion source beamline at ORNL to study the effects of W crystallography (specifically surface normal) and the effect of beam incidence angle and beam energy on surface morphology after irradiation. Ongoing plasma-exposure experiments and neutron-irradiation campaigns will be described. [Preview Abstract] |
Wednesday, November 18, 2015 10:54AM - 11:06AM |
NO6.00008: Modeling of limiter heat loads and impurity transport in Wendelstein 7-X startup plasmas Florian Effenberg, Y. Feng, H. Frerichs, O. Schmitz, H. Hoelbe, R. Koenig, M. Krychowiak, T.S. Pedersen, S. Bozhenkov, D. Reiter The quasi-isodynamic stellarator Wendelstein 7-X starts plasma operation in a limiter configuration. The field consists of closed magnetic flux surfaces avoiding magnetic islands in the plasma boundary. Because of the small size of the limiters and the absence of wall-protecting elements in this phase, limiter heat loads and impurity generation due to plasma surface interaction become a concern. These issues are studied with the 3D fluid plasma edge and kinetic neutral transport code EMC3-Eirene. It is shown that the 3D SOL consists of three separate helical magnetic flux bundles of different field line connection lengths. A density scan at input power of 4MW reveals a strong modulation of the plasma paramters with the connection length. The limiter peak heat fluxes drop from 14 MWm$^{-2}$ down to 10 MWm$^{-2}$ with raising the density from 1$\times$10$^{18}$m$^{-3}$ to 1.9$\times$10$^{19}$m$^{-3}$, accompanied by an increase of the heat flux channel widths $\lambda_{q}$. Radiative power losses can help to avoid thermal overloads of the limiters at the upper margin of the heating power. The power removal feasibility of the intrinsic carbon and other extrinsic light impurities via active gas injection is discussed as a preparation of this method for island divertor operation. [Preview Abstract] |
Wednesday, November 18, 2015 11:06AM - 11:18AM |
NO6.00009: Enhancement of helium exhaust by resonant magnetic perturbations at TEXTOR-DED and LHD O. Schmitz, M. Kobayashi, A. Bader, S. Brezinsek, T.E. Evans, H. Funaba, M. Goto, K. Ida, O. Mitarai, T. Morisaki, G. Motojima, Y. Narushima, D. Nicolai, U. Samm, H. Tanaka, M. Yoshinuma, Y. Xu We demonstrate in this paper that resonant magnetic perturbation (RMP) fields can be used to enhance helium exhaust. Results from TEXTOR-DED as example for a tokamak with a pumped limiter and from the Large Helical Device LHD with the closed helical divertor as example for a heliotron device are presented. In both devices RMP fields are applied to generate a magnetic island located in the very plasma edge. The effective helium confinement time is decreased by up to 30{\%} at LHD and up to 45{\%} at TEXTOR-DED when RMP fields are applied. The measurements from both devices support that this reduction is caused by combination of enhanced outward transport of helium, improved coupling to the pumping systems yielding improved exhaust of helium from the SOL and reduced fueling efficiencies for both, injected and recycled helium. [Preview Abstract] |
Wednesday, November 18, 2015 11:18AM - 11:30AM |
NO6.00010: Impact of N$_{2}$ and Ne injection on partially detached divertor operation in JET H-mode plasmas Aaro J\"arvinen, Mathias Groth, Sebastijan Brezinsek, Sven Wiesen, Carine Giroud, Costanza Maggi, Guy Matthews, Bruce Lipschultz Partially detached divertor operation with N$_{2}$ and Ne injection in JET H-mode plasmas was experimentally investigated and simulated with EDGE2D-EIRENE in ITER-relevant, high-triangularity, vertical target configuration. The simulations reproduce the experimentally observed LFS heat and particle flux reduction with both N$_{2}$ and Ne radiation, when adjusting the impurity injection rate to reproduce the measurements of radiated power in the divertor. However, the simulations consistently underestimated the divertor D$_{\alpha}$ intensity by a factor of 3 - 5, indicating a shortfall in the radiation by fuel species. Whereas nitrogen radiation is concentrated in the divertor chamber in JET, neon radiation is predicted and measured to occur partially in the confined plasma. Therefore, neon injection is predicted to reduce the power crossing the separatrix in JET in partially detached divertor conditions. [Preview Abstract] |
Wednesday, November 18, 2015 11:30AM - 11:42AM |
NO6.00011: Studies of Neutral Penetration Depths Variation with Fueling Intensities of SMBI Zhanhui Wang, Yulin Zhou, Xueqiao Xu, Min Xu, Lin Nie, Hao Feng It is very important to find methods of increasing the fueling efficiency and penetration depth of supersonic molecular beam injection (SMBI) for tokamak plasma fueling and other edge plasma physics studies such as ELM control or mitigation. With the new trans-neut module of BOUT$++$ boundary plasma turbulence code, it has further studied neutral penetration depths variation with different fueling intensities of SMBI. The physical model used in the code includes the plasma density, heat and momentum transport equations along with neutral density and momentum transport equations. With the physical model, the molecular transport process during SMBI with various injection speeds and densities, are simulated and compared to study the fueling depth and efficiency. It finds that the radial convection of molecule, rather than the effect of thermal diffusion, dominates the molecular transport process during SMBI. To achieve a better fueling depth and efficiency, it finds increasing the radial injection velocity is more effective than just increasing the molecule injection density. [Preview Abstract] |
Wednesday, November 18, 2015 11:42AM - 11:54AM |
NO6.00012: Modeling of extinguishing ELMs in detached divertor plasmas A. Pigarov, S. Krasheninnikov, E. Hollmann, T. Rognlien Detached plasmas, the primary operational regime for divertors in next-step fusion devices, should be compatible with both good H-mode confinement and relatively small ELMs providing tolerable heat power loads on divertor targets. Here, dynamics of boundary plasma, impurities and material walls over a sequence of many type-I ELM events under detached divertor plasma conditions is studied with UEGDE-MB-W, the newest version of 2D edge plasma transport code, which incorporates Macro-Blob (MB) approach to simulate non-diffusive filamentary transport and various ``Wall'' (W) models for time-dependent hydrogen wall inventory and recycling. We present the results of multi-parametric analysis on the impact of the size and frequency of ELMs on the divertor plasma parameters where we vary the MB characteristics under different pedestals and divertor configurations. We discuss the conditions, under which small but frequent type-I ELMs (typical for high-power H-mode discharges on current tokamaks with hard deuterium gas puff) are not ``burning through'' the formed detached divertor plasma. In this case, the inner and outer divertors are filled by sub-eV, recombining, highly-impure plasma. Variations of impurity plasma content, radiation pattern, and deuterium wall inventory over the ELM cycle are analyzed. UEDGE-MB-W modeling results are compared to available experimental data. [Preview Abstract] |
Wednesday, November 18, 2015 11:54AM - 12:06PM |
NO6.00013: Investigation of the Effect of Collisionality on Scrape Off Layer Filaments using Three Dimensional Simulations Luke Easy, Fulvio Militello, John Omotani, Nick Walkden, Ben Dudson The propagation of filaments in the Scrape Off Layer (SOL) of tokamaks largely determines the plasma profiles in this region. Reactor relevant conditions will require interactions between neutrals and plasma in the divertor region to mitigate heat loads and sputtering. This is expected to increase the resistance to parallel currents in the SOL, and thus influence filament transport. 3D simulations have been used to study the influence of enhanced parallel resistivity on the dynamics of filaments. Filaments with the smallest perpendicular length scales, which were inertially limited at low resistivity (meaning that polarization rather than parallel currents determine their radial velocities), were unaffected by resistivity. For larger filaments, faster velocities were produced at higher resistivities, due to two mechanisms. Firstly parallel currents were reduced and polarization currents were enhanced, meaning that the inertial regime extended to larger filaments, and secondly a potential difference formed along the parallel direction so that higher potentials were produced in the region of the filament for the same amount of current to flow into the sheath. These results indicate that broader SOL profiles could be produced at higher resistivities. [Preview Abstract] |
Wednesday, November 18, 2015 12:06PM - 12:18PM |
NO6.00014: Impact of pedestal plasma density on linear and nonlinear edge-localized mode simulations using BOUT$++$ Defeng Kong, Jianguo Chen, Xueqiao Xu The BOUT$++$ simulations are used to study the linear and nonlinear characteristics of edge-localized mode at different collisionality via a density scan (pressure profiles are kept the same). For a force-balanced electric field Er with no net flow, linear results demonstrate that as the pedestal collisionality decreases, the growth rate of the peeling-ballooning modes decreases for high n but increases for low n (1 \textless n \textless 5), and the width of the growth rate spectrum becomes narrower and the peak growth shifts to lower n. The increase of low-n mode growth rate is due to the increase of both bootstrap current and Er. By increasing collisionality, nonlinear simulations show that (a) power spectrum becomes broad and flat; (b) the dominant mode changes from n$=$10 to n$=$35 . Bispectrum analysis shows that nonlinear mode coupling becomes stronger at high collisionality, especially for the high-n modes with n$\ge $20, resulting in the lack of dominant filamentary structures and reduced ELM energy loss. The impact of radial electric field Er on peeling and ballooning modes is different. The increase Er significantly enhances the linear growth rate of low-n peeling modes, but only weakly impacts on their nonlinear ELM energy loss; while the increase Er leads to large suppression of nonlinear ballooning fluctuation amplitudes, but only weakly impacts on their linear growth rates. [Preview Abstract] |
Wednesday, November 18, 2015 12:18PM - 12:30PM |
NO6.00015: Linear stability of drift-cyclotron loss cone waves in H-mode plasmas W.A. Farmer, G.J. Morales The drift-cyclotron loss cone mode was first studied in mirror machines. In such devices, particles with small pitch angles are not confined, creating a hole in the velocity distribution function that is a source of free energy and leads to micro-instabilities in the cyclotron-range of frequencies. It has been shown by deGrassie et al. [1] that particle loss also occurs for certain regions of velocity space in the H-mode, edge gradient region of a tokamak. In this case, gradient drift carries particles moving opposite to the plasma current (counter-Ip) preferentially into the divertor. The preferential loss of counter-Ip particles leads to an intrinsic toroidal velocity within the plasma. The present theoretical study explores the possibility that this depletion of portions of the distribution function may result in the destabilization of drift-cyclotron waves as in mirror machines. \\[4pt] [1] J. S. deGrassie, R. J. Groebner, K. H. Burrell, and W. M. Solomon. Nucl. Fusion 49, 085020 (2009)]. [Preview Abstract] |
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