R. Lunsford
A5008453412- Magnetic confinement fusion research
- Fusion materials and technologies
- Superconducting Materials and Applications
- Particle accelerators and beam dynamics
- Plasma Diagnostics and Applications
- Laser-Plasma Interactions and Diagnostics
- Ionosphere and magnetosphere dynamics
- Nuclear Materials and Properties
- Spectroscopy Techniques in Biomedical and Chemical Research
- Solar and Space Plasma Dynamics
- Spectroscopy and Chemometric Analyses
- Nuclear reactor physics and engineering
- Laser-induced spectroscopy and plasma
- Particle Accelerators and Free-Electron Lasers
- Astro and Planetary Science
- Diamond and Carbon-based Materials Research
- Gas Dynamics and Kinetic Theory
- Electronic Packaging and Soldering Technologies
- Metal and Thin Film Mechanics
- Geomagnetism and Paleomagnetism Studies
- Atomic and Molecular Physics
- Electromagnetic Launch and Propulsion Technology
- Nuclear Physics and Applications
- Spacecraft and Cryogenic Technologies
- Atmospheric Ozone and Climate
Princeton Plasma Physics Laboratory
2015-2024
Princeton University
2017-2024
HUN-REN Centre for Energy Research
2021
Oak Ridge National Laboratory
1983-2020
United States Naval Research Laboratory
2012-2016
Thomas Jefferson National Accelerator Facility
2014
Office of Naval Research
2014
Research Support Instruments (United States)
2010-2013
K Lab (United States)
2012
University of Maryland, College Park
2004-2008
Abstract The objectives of NSTX-U research are to reinforce the advantages STs while addressing challenges. To extend confinement physics low- A , high beta plasmas lower collisionality levels, understanding transport mechanisms that set performance and pedestal profiles is being advanced through gyrokinetic simulations, reduced model development, comparison NSTX experiment, as well improved simulation RF heating. develop stable non-inductive scenarios needed for steady-state operation,...
In ASDEX Upgrade with full-tungsten wall, boronization is an important tool to control tungsten sources and allow reliable operation at low collisionality. The duration of the beneficial effects limited by erosion boron layer, in particular on ion-cyclotron antenna limiters. We report results from experiments exploring injection boron-rich powders tokamak plasmas as a way replenish coating extend lifetime effects. Pure nitride were introduced gravitationally plasma discharges rates up 60...
The neoclassical transport optimization of the Wendelstein 7-X stellarator has not resulted in predicted high energy confinement gas fueled electron-cyclotron-resonance-heated (ECRH) plasmas as modelled (Turkin et al 2011 Phys. Plasmas 18 022505) due to levels turbulent heat observed experiments. electron-turbulent-heat appears non-stiff and is electron temperature gradient (ETG)/ion (ITG) type (Weir 2021 Nucl. Fusion 61 056001). As a result, Te can be varied freely from 1 keV–10 keV within...
Abstract In state-of-the-art stellarators, turbulence is a major cause of the degradation plasma confinement. To maximize confinement, which eventually determines amount nuclear fusion reactions, turbulent transport needs to be reduced. Here we report observation confinement regime in stellarator that characterized by increased and reduced fluctuations. The transition this driven injection submillimetric boron powder grains into plasma. With line-averaged electron density being kept...
The National Spherical Torus Experiment (NSTX) has undergone a major upgrade, and the NSTX Upgrade (NSTX-U) Project was completed in summer of 2015.NSTX-U first plasma subsequently achieved, diagnostic control systems have been commissioned, H-mode accessed, magnetic error fields identified mitigated, physics research campaign carried out.During ten run weeks operation, NSTX-U surpassed record pulse-durations toroidal (TF), high-performance ~1 MA plasmas comparable to best sustained near...
We present a device for controlled injection of variety materials in powder form. The system implements four independent feeder units, arranged to share single vertical drop tube. Each unit consists 80 ml reservoir, coupled horizontal linear trough, where layer is advanced by piezo-electric agitation at speed proportional the applied voltage, until it falls into dropper has been tested with number impurities low (B, BN, C), intermediate (Si, SiC), and high Z (Sn) microscopic structures...
We report the first successful use of lithium (Li) to eliminate edge-localized modes (ELMs) with tungsten divertor plasma-facing components in EAST device. Li powder injected into scrape-off layer upper successfully eliminated ELMs for 3–5 s EAST. The ELM elimination became progressively more effective consecutive discharges at constant delivery rates, and Dα baseline emission was reduced, both signatures improved wall conditioning. A modest decrease stored energy normalized confinement also...
Abstract A newly installed Lithium Granule Injector (LGI) was used to pace edge localized modes (ELM) in DIII-D. ELM pacing efficiency studied injecting lithium granules of nominal diameter 0.3–0.9 mm, speed 50–120 m s −1 and average injection rates up 100 Hz for 0.9 mm 700 0.3 granules. The triggering found depend strongly on size the injected granules, with close 100% obtained lower smaller sizes, weakly depending granule velocity. Robust demonstrated ITER-like plasmas entire shot length,...
Pulsed injections of boron carbide granules into Wendelstein 7-X stellarator (W7-X) plasmas transiently increase the plasma stored energy and core ion temperatures above reference W7-X experimental programs by up to 30%. In a series 4 MW electron cyclotron resonance heating experiments, PPPL Probe Mounted Powder Injector provided 50 ms bursts 100 μm every 350 at estimated quantities ranging from approximately 1 mg/pulse over 30 mg/pulse. For each injection, was observed initially drop...
Abstract Using a recently installed impurity powder dropper (IPD), boron (<150 μ m) was injected into lower single null (LSN) L-mode discharges in WEST. IPDs possibly enable real-time wall conditioning of the plasma-facing components and may help to facilitate H-mode access full-tungsten environment The this experiment featured I p = 0.5 MA, B T 3.7 T, q 95 4.3, t pulse 12–30 s, n e,0 ∼ 4 × 10 19 m −2 , P LHCD 4.5 MW. Estimates deuterium particle fluxes, derived from combination visible...
Abstract The choice of first wall material is paramount importance for the plasma start-up conditions in ITER and future fusion power plants. In this context, present work focuses on correlations between impurity sources total radiated during tungsten (W) Environment Steady-state Tokamak (WEST). objective to highlight experimental indications a preferable combination scenario materials. Until 2019, WEST featured full high Z with all limiters exposing only W surfaces plasma. To study impact...
Abstract The full W environment that is now foreseen for ITER puts strong emphasis on experimental results obtained in present devices similar conditions. In this context, the WEST tokamak well equipped to bring key contributions preparation of operation, thanks its capability perform long pulses dominant electron heating, torque-free scheme based RF systems, and ITERgrade actively cooled divertor. Recent interest cover understanding tungsten contamination evaluation conditioning methods,...
Significant engineering and physic progress was made by the upgrade of a flowing liquid lithium limiter (FLiLi) inserted into EAST H-mode discharges in 2016. The includes an improvement Li coverage uniformity, no macroscopic surface erosion plasma materials interaction, effective removal 55% discharge heat flux using high pressure He cooling during ohmic discharges, demonstrated ability to restart flow for second experiment performed week after first. With increasing rate, fuel particle...
The injection of boron (B) and nitride (BN) powders into ASDEX Upgrade H-mode discharges have demonstrated effective control tungsten influx in low density/collisionality operational regimes, similar to conventional boronization methods. Sub-mm powder particles are gravitationally accelerated the upper edge a lower single null plasma with boundary shape roughly conforming poloidal midplane limiters. Visible spectroscopy measurements at one outer limiter showed increases both B N signal...
The Maryland Centrifugal Experiment MCX [R. F. Ellis, A. B. Hassam, and S. Messer, Phys. Plasmas 8, 2057 (2000)] studies supersonic rotation enhanced confinement produced by the application of an electric field perpendicular to axial confining mirror magnetic field; radial shear in is predicted stabilize magnetohydrodynamic (MHD) interchange modes. 2.6 m length, maximum 1.9 T, midplane 0.33 T; inner coaxial core driven a 10 KV capacitor bank, producing which drives azimuthal rotation....
Real-time lithium powder injection has been applied to long-pulse (>30 s) H-mode plasmas in EAST. This replenishes the active surface that is routinely consumed by plasma-wall interactions. The real-time of Li into long discharges effectively suppresses impurity influx and controls recycling on EAST, with an ITER-like tungsten upper divertor. With injection, concentrations W, Mo, C were reduced 50% compared ELMy discharges. During two effects play a role suppression impurities influx:...
Abstract Controlled particulate injections from the PPPL impurity powder dropper (IPD) into Large Helical Device have demonstrated positive effects on wall conditions both an intra and inter-shot basis. Injections over a range of densities, input powers, pulse lengths, heating schemes, injection quantities main ion species show conclusive evidence improvement to plasma conditions. Successful are confirmed by spectroscopic measurements as well real-time visible camera signals. In 7 s long...
Injection of impurities in the form sub-millimeter powder grains is performed for first time Large Helical Device (LHD) plasma, employing Impurity Powder Dropper (IPD) (Nagy et al., 2018), developed and built by PPPL. Controlled amounts boron (B) nitride (BN) are injected into helical plasma. Visible camera imaging, UV charge exchange spectroscopy measurements show that effectively penetrate plasma two different magnetic configurations. The prompt effects on characterized as injection rate...
Abstract W7-X completed its plasma operation in hydrogen with island divertor and inertially cooled test unit (TDU) made of graphite. A substantial set plasma-facing components (PFCs), including particular marker target elements, were extracted from the vessel analysed post-mortem. The analysis provided key information about underlying plasma–surface interactions (PSI) processes, namely erosion, transport, deposition as well fuel retention graphite components. net carbon (C) erosion...
The ability of an injected lithium granule to promptly trigger edge localized mode (ELM) has been established in multiple experiments. By horizontally injecting granules ranging diameter from 200 microns 1 mm into the low field side EAST H-mode discharges we have determined that with >600 are successful triggering ELMs more than 95% time. It was also demonstrated below 600 efficiency decreased roughly size. Granules were radially outer midplane velocities ~80 m s−1 upper single null ITER...
Abstract Recently an improved confinement regime, characterized by reduced turbulent fluctuations has been observed in the Large Helical Device upon injection of boron powder into plasma (Nespoli et al 2022 Nat. Phys. 18 350–56). In this article, we report more detail experimental observations increased temperature and decrease across cross section, on extended database. particular, compare powders different materials (B, C, BN), finding similar improvement turbulence response for three...
Abstract WEST L-mode plasmas with dominant electron heating and no core torque source have observed improvements in confinement during boron (B) powder injection. These results are reminiscent of previous injection experiments on other devices gaseous impurity seeding WEST. During injection, the stored energy increased up to 25% due enhanced ion heat particle confinement. The were not indicative an L-H transition. To identify mechanisms causality chain behind these confinement, we employ...
Abstract The transport of impurities supplied by a multi‐species impurity powder dropper (IPD) in the large helical device (LHD) is investigated using three‐dimensional peripheral plasma fluid code (EMC3‐EIRENE) coupled with dust simulation (DUSTT). trajectories particles (Boron, Carbon, Iron, and Tungsten) dropped from IPD are studied full‐torus geometry. reveals an appropriate size optimum operational range drop rates for investigating without inducing radiation collapse. also predicts...