A5082962963- Magnetic confinement fusion research
- Ionosphere and magnetosphere dynamics
- Fusion materials and technologies
- Laser-induced spectroscopy and plasma
- Laser-Plasma Interactions and Diagnostics
- Plasma Diagnostics and Applications
- Particle accelerators and beam dynamics
- Atomic and Molecular Physics
- Superconducting Materials and Applications
- Solar and Space Plasma Dynamics
- Atomic and Subatomic Physics Research
- Advanced MRI Techniques and Applications
- Ion-surface interactions and analysis
- Nuclear reactor physics and engineering
- Nuclear Physics and Applications
- Advanced materials and composites
- High-Temperature Coating Behaviors
- X-ray Spectroscopy and Fluorescence Analysis
- Quantum, superfluid, helium dynamics
- Nuclear Materials and Properties
- Diamond and Carbon-based Materials Research
- Metal and Thin Film Mechanics
- Mass Spectrometry Techniques and Applications
- Photoacoustic and Ultrasonic Imaging
- Spacecraft and Cryogenic Technologies
Auburn University
2014-2024
Max Planck Institute for Plasma Physics
2019
Max Planck Society
2019
University of Washington
2010-2013
American Institute of Aeronautics and Astronautics
2010-2013
University of Wisconsin–Madison
2005-2010
Princeton Plasma Physics Laboratory
2008
North Carolina State University
2006
Abstract After a long device enhancement phase, scientific operation resumed in 2022. The main new components are the water cooling of all plasma facing and water-cooled high heat flux divertor units. Water allowed for first long-pulse campaign. A maximum discharge length 8 min was achieved with total heating energy 1.3 GJ. Safe demonstrated attached detached mode. Stable detachment is readily some magnetic configurations but requires impurity seeding small pitch angle within edge islands....
The properties of emitting ions in a plasma provides both potential for diagnostics and key information required modeling. Generalized collisional radiative theory powerful tool the modeling low moderately dense plasmas. A new Python program is presented that solves ionization balance equations application to fusion, laboratory, astrophysical It produces generalized coefficients can be easily imported into existing codes spectral diagnostics. An overview code presented, along with selected...
Innovative charge-exchange recombination spectroscopy (CHERS), motional Stark effect (MSE), and Rutherford scattering diagnostics are now in operation on the Madison Symmetric Torus (MST) reversed-field pinch (RFP). The CHERS diagnostic measures impurity ion flow temperature, localized to 2cm with high time resolution (∼100kHz). A spectral MSE has been use for five years, measuring ∣B∣ down 0.2T precision (∼2%) good (10kHz). demonstrated robustness of this technique reliable measurement...
Abstract A mechanism for steady inductive helicity injection (SIHI) current drive has been discovered where the driving fluctuations are not generated by plasma but rather imposed injectors. Sheared flow of electron fluid distorts to current. The model accurately predicts time dependent toroidal current, injector impedance scaling, and profile produced in HIT-SI experiment. These results show that a stable equilibrium can be efficiently sustained with can, principle, controlled. Both large...
The Compact Toroidal Hybrid (CTH) is a low-aspect-ratio (), low-beta (%) torsatron with major radius of . CTH operable as pure stellarator, but most research on this device conducted hybrid discharges in which toroidal plasma current driven order to study magnetohydrodynamic instabilities and disruptions current-carrying stellarator plasmas. vacuum helical field produced by continuously wound coil poloidal periodicities , respectively. maximum on-axis toroid al magnetic encloses circular...
Abstract The low vapor pressure solvent 1‐chloropentane was used to directly spincast polystyrene (PS) films onto poly(methyl methacrylate) (PMMA) with smooth surfaces and sharp interfaces. Interface roughness after removal of the PS layer cyclohexane determined scanning force microscopy be <1 nm. Dynamic secondary mass spectroscopy revealed an interfacial width below resolution limit ∼10 Large area bilayers could created. In addition, direct spincasting allows production thin (<15 nm)...
A new custom-built duo spectrometer has been commissioned for fast localized Doppler measurements of plasma ions in the Madison Symmetric Torus. The instrument combines very high optical throughput (transmission efficiency 6% and etendue 0.80mm2sr divided into two simultaneous measurements) with good resolution (λ∕Δλ=5600). design is a double grating variant Czerny-Turner layout carefully optimized (100kHz) CVI line at 343.4nm. currently being applied speed charge exchange recombination...
We have increased substantially the electron and ion temperatures, density, total beta in plasmas with improved energy confinement Madison Symmetric Torus (MST). The is achieved a well-established current profile control technique for reduction of magnetic tearing reconnection. A sustained temperature >1 keV intensified reconnection-based heating followed immediately by control. In same plasmas, reaches 2 keV, thermal diffusivity drops to about m s −1 . global time 12 ms. This reported...
Low edge safety factor operation at a value less than two (q(a)=1/ι̷tot(a)&lt;2) is routine on the Compact Toroidal Hybrid device with addition of sufficient external rotational transform. Presently, operational space this current carrying stellarator extends down to q(a)=1.2 without significant n = 1 kink mode activity after initial plasma rise phase discharge. The disruption dynamics these low plasmas depend upon fraction helical field transform from coils that generated by current. We...
Abstract We report on the first experimental verification of theoretically predicted multiple bundles counter-streaming plasma flows in island-divertor scrape-off layer (SOL) stellarator Wendelstein 7-X. In standard toroidal field direction (counter-clockwise when looking from top) experiments, overall structure SOL flows, such as flow directions, number and magnitude velocities, are consistent with numerical predictions obtained EMC3-EIRENE. However, modelling does not predict changes...
Abstract Fundamental mechanisms governing the erosion and prompt re-deposition of tungsten impurities in tokamak divertors are identified analyzed to inform lifetime plasma-facing components ITER other future devices. Various experiments conducted at DIII-D benchmark predictive models presented, leveraging DiMES removable sample exposure probe capability Metal Rings Campaign, which toroidally symmetric rows tungsten-coated tiles were installed divertor. In divertors, width electric sheath is...
The impurity ion temperature evolution has been measured during three types of impulsive reconnection events in the Madison Symmetric Torus reversed field pinch. During an edge event, drop stored magnetic energy is small and heating observed to be limited outer half plasma. Conversely, a global event large, significant at all radii. For both kinds events, sufficient explain increase thermal energy. However, not lead heating. core remain constant. results suggest that required for ions heated...
Pellet fuelling of improved confinement Madison Symmetric Torus (MST) plasmas has resulted in high density and plasma beta. The discharges been increased fourfold, a record beta (β tot = 26%) for the reversed-field pinch (RFP) achieved. At higher β, new regime instabilities is accessed which local interchange global tearing are calculated to be linearly unstable, but experimentally, no severe effect, e.g., disruption, observed. instability, normally driven by current gradient, pressure...
By manipulating magnetic reconnection in Madison Symmetric Torus (MST) discharges, we have generated and confined for the first time a reversed-field pinch (RFP) plasma with an ion temperature >1 keV electron of 2 keV. This is achieved at toroidal current about 0.5 MA, approaching MST's present maximum. The manipulation begins intensification discrete events, causing to increase several kiloelectronvolts. then quickly suppressed inductive profile control, leading capture portion added heat...
Neutral tungsten is the primary candidate as a wall material in divertor region of International Thermonuclear Experimental Reactor (ITER). The efficient operation ITER depends heavily on precise atomic physics calculations for determination reliable erosion diagnostics, helping to characterize influx impurities into core plasma. following paper presents detailed structure neutral using multiconfigurational Dirac-Fock method, drawing comparisons with experimental measurements where...
In the last decade, Coherence Imaging Spectroscopy (CIS) has shown distinctive results in measuring ion flow velocities edge of magnetically confined plasma devices. Its 2D spatially resolved measurement capabilities and its high optical throughput are ideal for investigating impurity behavior complex 3D magnetic island topology Wendelstein 7-X (W7-X). However, a highly precise stable calibration method is required reliable diagnostic operation. A new level precision stability been achieved...
Abstract Drifts affect particle, momentum, and energy transport in the scrape-off layer (SOL) of tokamaks stellarators, altering plasma flows creating asymmetries between divertors. To understand how drifts SOL W7-X island divertor, an experiment was performed to compare plasmas with matched core parameters but opposite magnetic field directions, therefore drift directions. Parallel flow measurements made coherence imaging spectroscopy are interpreted aid a diagnostic forward model 1D simple...
Measurements of localized ion heating during magnetic reconnection in the Madison Symmetric Torus reversed field pinch [R. N. Dexter, D. W. Kerst, T. Lovell, S. C. Prager, and J. Sprott, Fusion Technol. 19, 131 (1991)] are presented using two beam-based diagnostics: Charge exchange recombination spectroscopy Rutherford scattering. Data have been collected from three types impulsive event, which resistive tearing mode activity associated with is present either edge plasma, core or throughout...
The first sustainment of toroidal plasma current 50 kA at up to 3 times the injected currents, added in quadrature, using steady inductive helicity injection is described. Separatrix currents-currents not linking injectors-are sustained 40 kA. Decreases n=1 mode poloidal magnetic field higher amplifications indicate more quiescent, direct drive. Results are achieved HIT-SI (with a spheromak major radius 0.3 m) during deuterium operations immediately after helium operation. These results...
A time-dependent helicity balance model applied to a spheromak helicity-injection experiment enables the measurement of relaxation time during sustainment phase spheromak. The experiment, Helicity Injected Torus with Steady Inductive injection (HIT-SI), studies formation and through inductive injection. captures dominant plasma behavior seen in HIT-SI by using an empirical helicity-decay rate, composite Taylor state both content system calculate resulting current. During single-injector...
The passive stability of vertically elongated current-carrying toroidal plasmas has been investigated in the Compact Toroidal Hybrid, a stellarator/tokamak hybrid device. In this experiment, fractional transform f, defined as ratio imposed external rotational from stellarator coils to total transform, was varied 0.04 0.50, and elongation κ 1.4 2.2. Plasmas that were unstable evidenced by motion plasma vertical direction. Vertical drifts are measured with set poloidal field pickup coils. A...
Abstract Long-lived metastable states in neutral tungsten are shown to potentially impact measurements of erosion from plasma facing components. Time-dependent collisional radiative modeling is used analyze the role these emission and ionization. The large number non-quasistatic atomic can take on order milliseconds reach equilibrium, depending conditions, causing be affected by populations. Previous using 400.88 nm line could effects. Therefore, a scheme for measuring relative fractions...
Confinement in the reversed field pinch (RFP) has been shown to increase strongly with current profile control. The MST RFP can operate two regimes: standard regime a naturally occurring density profile, robust reconnection and dynamo activity; improved confinement strong reduction reconnection, transport. New results plasmas include observation of two-fluid Hall effect dynamo, determination that m = 0 edge resonant mode is nonlinearly driven, tearing modes lock wall via eddy currents shell....