Bulletin of the American Physical Society
56th Annual Meeting of the APS Division of Plasma Physics
Volume 59, Number 15
Monday–Friday, October 27–31, 2014; New Orleans, Louisiana
Session YI2: Technology of Plasma Facing Surfaces, Landau-Spitzer Award and Post Deadline Talk |
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Chair: Charles Skinner, Princeton Plasma Physics Laboratory Room: Bissonet |
Friday, October 31, 2014 9:30AM - 10:00AM |
YI2.00001: Landau-Spitzer Award: Fast-Ion Transport in the ASDEX Upgrade and DIII-D Tokamaks Invited Speaker: Manuel Garcia-Munoz Unprecedented insight into the fast-ion transport caused by a broad range of fluctuations has been made possible in the ASDEX Upgrade (AUG) and DIII-D tokamaks thanks to a new set of fast-ion diagnostics developed in the framework of a transatlantic collaboration. The temporal evolution of the fast-ion radial profile with velocity-space resolution has been measured in the AUG tokamak with the implementation of the Fast-Ion D-Alpha (FIDA) technique and associated analysis tools developed originally by the DIII-D group. Time resolved phase-space measurements of fast-ion losses made in DIII-D with a scintillator-based Fast-Ion Loss Detector (FILD) developed at AUG have revealed crucial details of the fast-ion dynamics in the presence of a broad range of MHD perturbations. The joint application of these techniques to AUG and DIII-D plasmas has advanced our understanding of the wave-particle interaction responsible for the fast-ion transport induced by Alfven Eigenmodes (AEs), Sawteeth and Edge Localized Modes (ELMs). Accurate measurements of the fast-ion radial profile have demonstrated the weak or negligible effect that microturbulence has on fast-ion transport. Additionally, multiple FILD and FIDA systems in both devices show a significant increase in EP loss due to externally applied 3D fields (such as those used for ELM control). A survey of the most relevant experimental and modelling results obtained through this collaboration will be presented. This work was carried out together with B. Geiger (IPP-Garching), W.W. Heidbrink (UC-Irvine), D. C. Pace, M. A. Van Zeeland (General Atomics) and the ASDEX Upgrade and DIII-D Teams. [Preview Abstract] |
Friday, October 31, 2014 10:00AM - 10:30AM |
YI2.00002: Plasma Sputtering Robotic Device for \textit{In-Situ} Thick Coatings of Long, Small Diameter Vacuum Tubes Invited Speaker: Ady Hershcovitch A novel robotic plasma magnetron mole with a 50 cm long cathode was designed fabricated {\&} operated. Reason for this endeavor is to alleviate the problems of unacceptable ohmic heating of stainless steel vacuum tubes and of electron clouds, due to high secondary electron yield (SEY), in the BNL Relativistic Heavy Ion Collider (RHIC). The magnetron mole was successfully operated to copper coat an assembly containing a full-size, stainless steel, cold bore, RHIC magnet tubing connected to two types of RHIC bellows, to which two additional pipes made of RHIC tubing were connected. To increase cathode lifetime, movable magnet package was developed, and thickest possible cathode was made, with a rather challenging target to substrate (de facto anode) distance of less than 1.5 cm. Achieving reliable steady state magnetron discharges at such a short cathode to anode gap was rather challenging, when compared to commercial coating equipment, where the target to substrate distance is 10's cm; 6.3 cm is the lowest experimental target to substrate distance found in the literature. Additionally, the magnetron developed during this project provides unique omni-directional uniform coating. The magnetron is mounted on a carriage with spring loaded wheels that successfully crossed bellows and adjusted for variations in vacuum tube diameter, while keeping the magnetron centered. Electrical power and cooling water were fed through a cable bundle. The umbilical cabling system is driven by a motorized spool. Excellent coating adhesion was achieved. Measurements indicated that well-scrubbed copper coating reduced SEY to 1, i.e., the problem of electron clouds can be eliminated. Room temperature RF resistivity measurement indicated that 10 $\mu $m Cu coated stainless steel RHIC tube has conductivity close to that of pure copper tubing. Excellent coating adhesion was achieved. Device detail and experimental results will be presented. [Preview Abstract] |
Friday, October 31, 2014 10:30AM - 11:00AM |
YI2.00003: High Performance Discharges in the Lithium Tokamak eXperiment (LTX) with Liquid Lithium Walls Invited Speaker: John Schmitt The possibility of a liquid metal first wall for a fusion reactor has been extensively discussed. Small-area liquid lithium limiters and divertor targets have been installed in tokamaks, but no confinement device has ever operated with a large-area liquid lithium wall. Here we report the first-ever successful operation of a tokamak with a large area (2 m$^{2}$, or 40{\%} of the total plasma surface area) liquid lithium wall in the Lithium Tokamak eXperiment (LTX). These results were obtained with a new, electron beam-based lithium evaporation system, which can deposit a lithium coating on the hot (300 C) wall of LTX in a five-minute period. Preliminary analyses of diamagnetic and other data for discharges operated with a liquid lithium wall indicate that confinement times increased by 10$\times$ compared to discharges with helium-dispersed solid lithium coatings. Ohmic confinement times exceeded ITER98P(y,2) scaling by up to a factor of four. LTX lacks auxiliary heating, so these confinement improvements represent changes in electron confinement. Spectroscopic analysis of the discharges using the John Hopkins University transmission grating extreme ultraviolet spectrometer indicates that oxygen levels in the discharges run against liquid walls were significantly reduced compared to discharges operated against solid lithium walls. This differs strongly from earlier trials of molten lithium walls in LTX, which showed evidence for strong oxygen influx from walls operated at similar temperatures. At present, the Thomson scattering system is undergoing upgrades and realignment, after which confinement times obtained with magnetic diagnostics will be compared with kinetic measurements. A second electron beam will be installed to extend liquid lithium wall operation to 4 m$^{2}$ coverage, or \textgreater 80{\%} of the total plasma surface area. Results with expanded liquid lithium wall area will be presented. [Preview Abstract] |
Friday, October 31, 2014 11:00AM - 11:30AM |
YI2.00004: In-situ erosion and deposition measurements of plasma-facing surfaces in Alcator C-Mod Invited Speaker: Harold S. Barnard The Accelerator Based In-situ Materials Surveillance (AIMS) diagnostic was recently developed to demonstrate the novel application of ion beam analysis (IBA) to in-vessel studies of plasma materials interactions in Alcator C-Mod. The AIMS diagnostic injects a 900 keV deuterium ion beam into the tokamak's vacuum vessel between plasma discharges while magnetic fields are used to steer the ion beam to plasma facing component (PFC) surfaces. Spectroscopic analysis of neutrons and gamma rays from the induced nuclear reactions provides a quantitative, spatially resolved map of the PFC surface composition that includes boron (B) and deuterium (D) content. Since AIMS is sensitive to low-Z elements and C-Mod regularly boronizes PFCs, the evolution of B and D on PFCs can be used to directly study erosion, deposition, and fuel retention in response to plasma operations and wall conditioning processes. AIMS analysis of 18 lower single null I-mode discharges show a net boron deposition rate of 6$\pm$2 nm/s on the inner wall while subsequent inner wall limited discharges and a disruption did not show significant changes in B. Measurements of D content showed relative changes of $>$2.5 following a similar trend. This suggests high D retention rates and net B deposition rates of $\sim$18 cm/year of plasma exposure are possible and depend strongly on the plasma conditions. Ex-situ IBA was also performed on the same PFCs after removal from C-Mod, successfully validating the AIMS technique. These IBA measurements also show that the B content on the inner wall varied toroidally and poloidally from 0 to 3000 nm, demonstrating the importance of the spatial resolution provided by AIMS and the sensitivity of PFCs to B-field alignment. AIMS upgrades are underway for operation in 2014 and we anticipate new measurements correlating the evolution of PFC surfaces to plasma configuration, RF heating, and current drive scenarios. [Preview Abstract] |
Friday, October 31, 2014 11:30AM - 12:00PM |
YI2.00005: The Effects of Temperature and Oxidation on Deuterium Retention in Solid and Liquid Lithium Films on Molybdenum Plasma-Facing Components Invited Speaker: Angela Capece Liquid metal plasma-facing components (PFCs) enable in-situ renewal of the surface, thereby offering a solution to neutron damage, erosion, and thermal fatigue experienced by solid PFCs. Lithium in particular has a high chemical affinity for hydrogen, which has resulted in reduced recycling and enhanced plasma performance on many fusion devices including TFTR, T11-M, FTU, CDX-U, LTX, TJ-II, and NSTX. A key component to the improvement in plasma performance is deuterium retention in Li; however, this process is not well understood in the complex tokamak environment. Recent surface science experiments conducted at the Princeton Plasma Physics Laboratory have used electron spectroscopy and temperature programmed desorption to understand the mechanisms for D retention in Li coatings on Mo substrates. The experiments were designed to give monolayer-control of Li films and were conducted in ultrahigh vacuum under controlled environments. An electron cyclotron resonance plasma source was used to deliver a beam of deuterium ions to the surface over a range of ion energies. Our work shows that D is retained as LiD in metallic Li films. However, when oxygen is present in the film, either by diffusion from the subsurface at high temperature or as a contaminant during the deposition process, Li oxides are formed that retain D as LiOD. Experiments indicate that LiD is more thermally stable than LiOD, which decomposes to liberate D$_2$ gas and D$_2$O at temperatures 100 K lower than the LiD decomposition temperature. Other experiments show how D retention varies with substrate temperature to provide insight into the differences between solid and liquid lithium films. [Preview Abstract] |
Friday, October 31, 2014 12:00PM - 12:30PM |
YI2.00006: GDT Experiments with Electron Heating Invited Speaker: Thomas C. Simonen Recent results\footnote{P.A. Bagryansky et. al., Nuc. Fusion 54 (2014)082001 and A.V. Anikeev et.al., at the OS2014 Conference, Taejon Korea, August 26-29, 2014 to be published.} from the Gas Dynamic Trap (GDT) experiment in Novosbirsk, Russia have achieved Thomson scattering measured electron temperatures of 600 to 750 eV, well above previous highest values of 250 eV in any mirror system. These new experiments thus demonstrate there is no fundamental low electron temperature restriction. In fact, the attained electron temperatures are sufficient for a 14 MeV D-T fusion neutron source for fusion materials evaluation and qualification. The linear GDT device, with extensive diagnostics, employs circular axisymmetric magnets with a high mirror ratio of 33. MHD stability, up to 60\% beta, is achieved by vortex radial flow shear aided by plasma outflow in the good curvature end regions. Heating is with 5 MW of neutral beams injected at 45 degrees augmented at lower densities by a MW of electron cyclotron heating. Importantly, the end wall magnetic field (relative to the mirror field) was reduced by a factor exceeding the square root of the ion-to-electron mass ratio, as suggested by theory. This talk will concentrate on the basic plasma physics understanding, puzzling aspects and future challenges associated with this interesting plasma experiment. [Preview Abstract] |
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