A5076206641- Magnetic confinement fusion research
- Ionosphere and magnetosphere dynamics
- Plasma Diagnostics and Applications
- Laser-Plasma Interactions and Diagnostics
- Solar and Space Plasma Dynamics
- Particle accelerators and beam dynamics
- Superconducting Materials and Applications
- Magnetic Field Sensors Techniques
- Fusion materials and technologies
- Laser-induced spectroscopy and plasma
- Atomic and Molecular Physics
- Atomic and Subatomic Physics Research
- Geomagnetism and Paleomagnetism Studies
- Particle Accelerators and Free-Electron Lasers
- Nuclear Physics and Applications
- Characterization and Applications of Magnetic Nanoparticles
- Non-Destructive Testing Techniques
- Spacecraft and Cryogenic Technologies
- Electric Motor Design and Analysis
- Magnetic Properties and Applications
- Physics of Superconductivity and Magnetism
- Electrostatic Discharge in Electronics
- Fluid Dynamics and Turbulent Flows
- Metal and Thin Film Mechanics
- Quantum and electron transport phenomena
University of Wisconsin–Madison
2014-2024
University of Southern California
2016-2023
Los Angeles Medical Center
2022-2023
California State University, Long Beach
2023
California State University, Fullerton
2023
Princeton Plasma Physics Laboratory
2021-2022
E Ink (South Korea)
2020-2022
Oak Ridge National Laboratory
1998-2022
LAC+USC Medical Center
2016-2021
National Institutes for Quantum Science and Technology
2021
An auxiliary poloidal inductive electric field applied to a reserved pinch plasma reduces the current density gradient, slows growth of m=1 tearing fluctuations, suppresses their associated sawteeth, and doubles energy confinement time. Small sawteeth occur in improved state but with m=0 precursors. By requiring change toroidal flux embedding plasma, profile drive is transient, improvement encourges program reversed transport suppression using control.
Abstract This paper reviews the research on reversed field pinch (RFP) in last three decades. Substantial experimental and theoretical progress transformational changes have been achieved since review (Bodin 1990 Nucl. Fusion 30 1717–37). The experiments performed devices with different sizes capabilities. largest are RFX-mod Padova (Italy) MST Madison (USA). community includes also EXTRAP-T2R Sweden, RELAX Japan KTX China. Impressive improvements performance result of exploration two lines:...
With the addition of inductive poloidal current drive for profile control in Madison Symmetric Torus (MST) reversed field pinch, magnetic fluctuation amplitude halves, leading to reduced energy and particle transport. A four- five-fold increase confinement time ${\ensuremath{\tau}}_{E}\ensuremath{\sim}5\mathrm{ms}$ with both decreased Ohmic input power increased stored thermal coincides record low high electron temperature $\ensuremath{\sim}600\mathrm{eV}$ (for MST)....
We report the results of an experimental and theoretical international project dedicated to study quasi-single helicity (QSH) reversed field pinch (RFP) plasmas. The has involved several RFP devices numerical codes. It appears that QSH spectra are a robust feature common all experiments. Our expand reinforce evidence formation self-organized states with one dominant helical mode (Ohmic SH state) is approach complementary active control magnetic turbulence improve confinement in steady state RFP.
In the Madison Symmetric Torus (MST) reversed-field pinch [Fusion Technol. 19, 131 (1991)] magnetic oscillations become stationary (locked) in lab frame as a result of process involving interactions between modes, sawteeth, and field errors. Several helical modes phase locked to each other form rotating localized disturbance, disturbance locks an impulsive error generated at sawtooth crash, fields grow monotonically after locking (perhaps due unstable interaction error), over tens...
Reduction of core-resonant m=1 magnetic fluctuations and improved confinement in the Madison Symmetric Torus [Dexter et al., Fusion Technol. 19, 131 (1991)] reversed-field pinch have been routinely achieved through control surface poloidal electric field, but it is now known that has limited part by edge-resonant m=0 fluctuations. Now, refined field control, plus toroidal possible to reduce simultaneously This allowed high-energy runaway electrons, possibly indicative flux-surface...
We report the first experimental verification of magnetohydrodynamic (MHD) dynamo in reversed-field pinch (RFP). A burst MHD electric field is observed during sawtooth crash, followed by an increase local parallel current Madison Symmetric Torus RFP edge. By measuring each term, mean-field Ohm's law to hold within error bars both between and crashes.
Results obtained on the Madison Symmetric Torus (MST) reversed-field pinch [Fusion Technol. 19, 131 (1991)] after installation of design poloidal field winding are presented. Values βθe0≡2μ0ne0Te0/B2θ(a)∼12% achieved in low-current (I=220 kA) operation; here, ne0 and Te0 central electron density temperature, Bθ(a) is magnetic at plasma edge. An observed decrease βθe0 with increasing current may be due to inadequate fueling, enhanced wall interaction, growth a radial error vertical cut shell...
New developments in Faraday rotation polarimetry have provided the first measurements of current density profile and core magnetic fluctuations a high-temperature reversed field pinch. This has been achieved by fast-polarimeter system with time response up to 1 μs phase resolution <1 mrad. Recent experiments on Madison Symmetric Torus directly measured radial plasma interior amplitude 33 G, ∼1%. A broad spectrum is observed 100 kHz. Relaxation at sawtooth crash occurs timescale μs....
The change in magnetic energy and helicity has been measured during the sawtooth relaxation Madison Symmetric Torus reversed-field pinch. larger decay of (4.0%--10.5%), relative to (1.3%--5.1%), modestly supports conservation hypothesis Taylor's theory. However, observed is than simple magnetohydrodynamics prediction. Enhanced fluctuation-induced transport observed.
New profile measurements have allowed the electron thermal diffusivity to be estimated from power balance in Madison Symmetric Torus where magnetic islands overlap and field lines are stochastic. The show that (1) energy transport is conductive not convective, (2) measured diffusivities good agreement with numerical simulations of stochastic transport, (3) greatly reduced near reversal surface diffusion small.
Improved confinement has been achieved in the MST through control of poloidal electric field, but it is now known that improvement limited by bursts an edge-resonant instability. Through refined field control, plus toroidal we have suppressed these bursts. This led to a total beta 15% and reversed-field-pinch-record estimated energy time 10 ms, tenfold increase over standard value which for first substantially exceeds scaling characterized most reversed-field-pinch plasmas.
A high current plasma electron emitter based on a miniature source has been developed. The emitting is created by pulsed gas discharge. emission 1 kA at 300 V with pulse duration of 10 ms. prototype injector described in this paper will be used for 20 electrostatic injection experiment the Madison symmetric torus reversed-field pinch. replicated order to attain total requirement. simple design and proven very reliable operation. current, small size (3.7 cm diameter) low impurity generation...
Energy confinement comparable with tokamak quality is achieved in the Madison Symmetric Torus (MST) reversed field pinch (RFP) at a high beta and low toroidal magnetic field. Magnetic fluctuations normally present RFP are reduced via parallel current drive outer region of plasma. In response, electron temperature nearly triples doubles. The time increases ten-fold (to ∼10 ms), which L- H-mode scaling values for same plasma current, density, heating power, size shape. Runaway evidenced by...
An internal kink instability is observed to grow and saturate in a line-tied screw pinch plasma. Detailed measurements show that an ideal, mode begins growing when the safety factor q = (4pi2r2B(z))/(mu0I(p)(r)L) drops below 1 inside plasma; saturated state corresponds rotating helical equilibrium. In addition ideal mode, reconnection events are periodically flatten current profile change magnetic topology.
Noncollisional ion heating in laboratory and astrophysical plasmas the mechanism of conversion magnetic energy to thermal are not well understood. In Madison Symmetric Torus reversed-field pinch experiment, ions heated rapidly during impulsive reconnection, attaining temperatures exceeding hundreds eV, often excess electron temperature. The budget its mass scaling hydrogen, deuterium, helium were determined by measuring fraction released converted energy. ranges from about 10%-30% increases...
With the exploration of MA plasma current regime in up to 0.5 s long discharges, RFX-mod has opened new and very promising perspectives for reversed field pinch (RFP) magnetic configuration, made significant progress understanding improving confinement controlling stability. A big leap with respect previous knowledge expectations on RFP physics performance been by since last 2006 IAEA Fusion Energy Conference. self-organized helical equilibrium experimentally achieved (the Single Helical...
Recent results on electromagnetic turbulence from gyrokinetic studies in different magnetic configurations are overviewed, detailing the physics of and transport, effect equilibrium field scale lengths. Ion temperature gradient (ITG) is shown to produce stochasticity through nonlinear excitation linearly stable tearing-parity modes. The excitation, which catalyzed by zonal flow, produces an electron heat flux proportional β2 that deviates markedly quasilinear theory. Above a critical beta...
A non-linear Grad–Shafranov toroidal equilibrium reconstruction code (MSTFit) has been developed for the Madison Symmetric Torus. This is first such applied to unique magnetohydrodynamic (MHD) of reversed field pinch. new set Green's tables have computed impose boundary condition close-fitting conducting shell. The fitting routine sufficiently versatile incorporating data from a variety internal and external diagnostics, including novel constraint based on orbits heavy ion beam probe...
The fluctuation-induced Hall electromotive force, [deltaJ x deltaB]/nee, is experimentally measured in the high-temperature interior of a reversed-field pinch plasma by fast Faraday rotation diagnostic. It found that dynamo effect significant, redistributing (flattening) equilibrium core current near resonant surface during reconnection event. These results imply effects beyond single-fluid MHD are important for and magnetic reconnection.
Optimization of machine operation, including plasma position control, density control and especially feedback on multiple magnetohydrodynamic modes, has led RFX-mod to operate reliably at 1.5 MA, the highest current ever achieved a reversed field pinch (RFP). At high low magnetic topology spontaneously self-organizes in an Ohmical helical symmetry, with new axis helically twisting around geometrical torus. The separatrix island disappears leaving wide symmetric thermal structure large...
We report the first direct measurement of internal magnetic field structure associated with a 3D helical equilibrium generated spontaneously in core an axisymmetric toroidal plasma containment device. Magnetohydrodynamic bifurcation occurs reversed-field pinch when innermost resonant perturbation grows to large amplitude, reaching up 8% mean strength. Magnetic topology evolution is determined by measuring Faraday effect, revealing that, as grows, symmetry broken and established.
An overview of recent results from the MST programme on physics important for advancement reversed field pinch (RFP) as well improved understanding toroidal magnetic confinement more generally is reported. Evidence classical ions in RFP provided by analysis impurity and energetic created 1 MW neutral beam injection (NBI). The first appearance energetic-particle-driven modes NBI a plasma described. plasmas robustly access quasi-single-helicity state that has commonalities to stellarator...
<h3>Importance</h3> Preoperative testing for cataract surgery epitomizes low-value care and still occurs frequently, even at one of the nation's largest safety-net health systems. <h3>Objective</h3> To evaluate a multipronged intervention to reduce preoperative patients undergoing analyze costs from various fiscal perspectives. <h3>Design, Setting, Participants</h3> This study took place 2 academic medical centers, Los Angeles County University Southern California (LAC-USC) (intervention, n...
Plasma flow velocity fluctuations have been directly measured in the high-temperature magnetically confined plasma Madison Symmetric Torus (MST) Reversed-Field Pinch (RFP) [R. N. Dexter et al., Fusion Technol. 19, 131 (1991)]. These measurements show that are correlated with magnetic field such electromotive force 〈ṽ×B̃〉 approximately balances parallel Ohm’s law, E∥+〈ṽ×B̃〉∥=ηJ∥. This initial measurement is subject to limitations of spatial localization and other uncertainties, but evidence...