A5034411191- Magnetic confinement fusion research
- Ionosphere and magnetosphere dynamics
- Laser-Plasma Interactions and Diagnostics
- Particle accelerators and beam dynamics
- Plasma Diagnostics and Applications
- Laser-induced spectroscopy and plasma
- Solar and Space Plasma Dynamics
- Nuclear Physics and Applications
- Fusion materials and technologies
- Superconducting Materials and Applications
- Nuclear reactor physics and engineering
- Gyrotron and Vacuum Electronics Research
- Atomic and Molecular Physics
- Particle Accelerators and Free-Electron Lasers
- Nuclear Materials and Properties
- Ion-surface interactions and analysis
- Nuclear and radioactivity studies
- Laser Design and Applications
- Magnetic Field Sensors Techniques
- Nuclear Engineering Thermal-Hydraulics
- Mass Spectrometry Techniques and Applications
- Non-Destructive Testing Techniques
- Graphite, nuclear technology, radiation studies
- Electron and X-Ray Spectroscopy Techniques
- Integrated Circuits and Semiconductor Failure Analysis
University of Wisconsin–Madison
2015-2024
Wheaton College - Illinois
2019
Oak Ridge National Laboratory
2011
KTH Royal Institute of Technology
2007
University of Michigan–Ann Arbor
1998-2003
University of California, Los Angeles
2002
Wren Laboratories (United States)
1964
The Wisconsin high-temperature superconductor axisymmetric mirror experiment (WHAM) will be a high-field platform for prototyping technologies, validating interchange stabilization techniques and benchmarking numerical code performance, enabling the next step up to reactor parameters. A detailed overview of experimental apparatus its various subsystems is presented. WHAM use electron cyclotron heating ionize build dense target plasma neutral beam injection fast ions, stabilized by...
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...
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....
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.
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...
This paper explores the feasibility of a break-even-class mirror referred to as BEAM (break-even axisymmetric mirror): neutral-beam-heated simple capable thermonuclear-grade parameters and $Q\sim 1$ conditions. Compared with earlier experiments in 1980s, would have: higher-energy neutral beams, larger denser plasma at higher magnetic field, both an edge core capabilities address magnetohydrodynamic kinetic stability higher-temperature plasmas. Axisymmetry high-field magnets make this...
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...
Packet-drop function for a time-division multiplexing network using 100-Gb/s, 8-b words is experimentally demonstrated by integrating all-optical header processing and payload demultiplexing with electrooptic packet routing. The processor consists of two levels logic gates based on low birefringent nonlinear optical loop mirrors (NOLMs), the demultiplexer two-wavelength NOLM. Both devices are driven synchronized lasers timing jitter under 1 ps. contrast ratios both 10:1 that router 17 dB....
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...
First measurements of the current-density profile in core a high-temperature reversed-field pinch are presented. The is observed to peak during sawtooth cycle and broaden promptly at crash. This change can be linked magnetic relaxation dynamo which predicted drive antiparallel current plasma core. For high-confinement discharges, suppressed strongly peak.
Abstract Recent experiments in the lithium tokamak experiment- β (LTX- ) have extended duration, performance, operating conditions, and diagnosis of flat-temperature profile, low-recycling regime first observed LTX. As expected, Li retains hydrogen suppresses edge neutral cooling, allowing increased electron temperature, roughly equal to core T e . Flat temperature profiles had been obtained transiently LTX, as plasma density decayed following cessation gas puffing. Careful control over...
The multichannel far-infrared (FIR) heterodyne polarimeter-interferometer system on the Madison Symmetric Torus (MST) is now operational. combined consists of 11 channels with variable radial and toroidal spacing. Poloidal magnetic field determined by measuring Faraday rotation FIR laser beam after propagation through plasma use a phase technique. polarimeter has 3 mrad rms noise level 1 ms temporal resolution while interferometer nedl=1×1012 cm−2 time response μs. Absolute calibration...
We report an increase in particle confinement with plasma biasing a reversed field pinch. Miniature sources are used as electrodes to negatively bias the at edge $(r/a\ensuremath{\sim}0.9)$. Particle content increases and ${\mathrm{H}}_{\ensuremath{\alpha}}$ radiation decreases upon application of global roughly doubles result. Energy is not significantly affected by edge. Measurements potential, impurity flow, floating potential fluctuations indicate that strong flows produced electrostatic reduced.
Zonal flow appears in toroidal, magnetically confined plasmas as part of the self-regulated interaction turbulence and transport processes. For toroidal having a strong magnetic field, zonal is predominately poloidally directed. This Letter reports first observation that toroidally The measurements are made just inside last closed flux surface reversed field pinch have dominant poloidal field. A limit cycle oscillation between strength amplitude plasma potential fluctuations observed, which...
The multi-region relaxed magnetohydrodynamics (MRxMHD) has been successful in the construction of equilibria three-dimensional (3D) configurations. In MRxMHD, plasma is sliced into sub-volumes separated by ideal interfaces, each undergoing relaxation, allowing formation islands and chaos. resulting equilibrium a stepped pressure profile across sub-volumes. code (SPEC) (S R Hudson et al, Phys. Plasmas 19, 112502 (2012)) was developed to calculate MRxMHD numerically. this work, we have...
Confinement of runaway electrons has been observed for the first time in a reversed field pinch during improved-confinement plasmas Madison Symmetric Torus. Energy-resolved hard-x-ray flux measurements have used to determine velocity dependence electron diffusion coefficient, utilizing computational solutions Fokker-Planck transport equation. With improved-confinement, fast diffusivity drops by 2 orders magnitude and is independent velocity. This suggests change mechanism away from...
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...
The first experimental evidence of anisotropic electron energization during magnetic reconnection that favors a direction perpendicular to the guide field in toroidal, magnetically confined plasma is reported this Letter. Magnetic plays an important role particle heating, energization, and transport space laboratory plasmas. In toroidal devices like Madison Symmetric Torus, discrete events release large amounts energy from equilibrium field. Fast x-ray measurements imply non-Maxwellian,...
Experimental discharges with pulsed poloidal current drive (PPCD) in the Madison Symmetric Torus reversed field pinch are investigated using a semi-analytic equilibrium model gyrokinetic turbulence code Gene. PPCD cases, plasma currents of 500 kA and 200 kA, exhibit density-gradient-driven trapped electron mode (TEM) an ion temperature gradient mode, respectively. Relative to expectations tokamak core plasmas, critical gradients for onset these instabilities found be greater by roughly...
Blackbody levels of emission in the electron cyclotron range frequencies have been observed from an overdense (ωpe∼3ωce) Madison Symmetric Torus [Dexter et al., Fusion Technol. 19, 131 (1991)] reversed field pinch plasma, a result electrostatic Bernstein waves emitted core and mode converted into electromagnetic at extreme plasma edge. Comparison measured radiation temperature with profiles by Thomson scattering indicates that conversion efficiency can be as high ∼75%. Emission is...
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...
The behavior of energetic ions is fundamentally important in the study fusion plasmas. While well-studied tokamak, spherical torus, and stellarator plasmas, relatively little known reversed field pinch plasmas about dynamics fast effects they cause as a large population. These studies are now underway Madison Symmetric Torus with an intense 25 keV, 1 MW hydrogen neutral beam injector (NBI). Measurements time-resolved ion distribution via high energy particle analyzer, well beam-target...
Internal fluctuations arising from energetic-particle-driven instabilities, including both density and radial magnetic field, are measured in a reversed-field-pinch plasma. The peak near the core where fast ions reside shift outward along major radius as instability transits n = 5 to 4 mode. During this transition, strong nonlinear three-wave interaction among multiple modes accompanied by enhanced fast-ion transport is observed.