A5045936385- Magnetic confinement fusion research
- Ionosphere and magnetosphere dynamics
- Plasma Diagnostics and Applications
- Solar and Space Plasma Dynamics
- Laser-Plasma Interactions and Diagnostics
- Particle accelerators and beam dynamics
- Fusion materials and technologies
- Superconducting Materials and Applications
- Laser-induced spectroscopy and plasma
- Magnetic Field Sensors Techniques
- Particle Accelerators and Free-Electron Lasers
- Geomagnetism and Paleomagnetism Studies
- Quantum, superfluid, helium dynamics
- Spacecraft and Cryogenic Technologies
- Characterization and Applications of Magnetic Nanoparticles
- Atomic and Subatomic Physics Research
- Magnetic properties of thin films
- Advanced X-ray Imaging Techniques
- Fluid Dynamics and Turbulent Flows
- Gyrotron and Vacuum Electronics Research
- Nuclear Physics and Applications
- Medical Imaging Techniques and Applications
- Geophysical and Geoelectrical Methods
- Non-Destructive Testing Techniques
- Electromagnetic Compatibility and Measurements
University of Wisconsin–Madison
2012-2024
Washington College
2017
University of California, Los Angeles
2002
United States Department of Commerce
1992
HSX is a quasi-helically symmetric (QHS) stellarator currently under construction at the Torsatron-Stellarator Laboratory of University Wisconsin - Madison. This device unique in its magnetic design that field spectrum possesses only single dominant (helical) component. avoids large direct orbit losses and low-collisionality neoclassical associated with conventional stellarators. The restoration symmetry to confining makes confinement this analogous an axisymmetric q = 1/3 tokamak.The magnet...
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...
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...
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...
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...
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...
The bulk fluid velocity is measured spectroscopically with 10 μs time resolution in the Madison Symmetric Torus (MST) reversed-field pinch (RFP) [Fusion Technol. 19, 131 (1991)], a diagnostic capability used to study fast flow dynamics associated locked modes and RFP dynamo. phase of tearing accelerate between sawtooth events, reaching maximum speed about 20 km/s few ms. Both slow down at crash ≊100 μs. This deceleration scale as calculated for from action electromagnetic torque on magnetic...
A series of detailed experiments has been conducted in three laboratory plasma devices to measure the dynamo electric field along equilibrium line (the α effect) arising from correlation between fluctuating flow velocity and magnetic field. The is obtained probe measurement E×B drift electron diamagnetic drift. major findings are following: (1) effect accounts for current generation, even time dependence through a ‘‘sawtooth’’ cycle; (2) at low collisionality explained primarily by widely...
Energetic electrons generated by electron cyclotron resonance heating are observed to drive instabilities in the quasihelically symmetric stellarator device. The coherent, global fluctuations peak plasma core and measured frequency range of 20-120 kHz. Mode propagation is diamagnetic drift direction driving species. When quasihelical symmetry broken, mode no longer observed. Experimental observations indicate that unstable acoustic rather than Alfvénic.
In this paper measurements of momentum and current transport caused by driven tearing instability are reported. The done in the Madison Symmetric Torus reversed-field pinch [R. N. Dexter, D. W. Kerst, T. Lovell, S. C. Prager, J. Sprott, Fusion Technol. 19, 131 (1991)] a regime with repetitive bursts causing magnetic field reconnection. It is established that plasma parallel profile flattens during these reconnection events: flow decreases core increases at edge. relaxation phenomenon similar...
Current-carrying, toroidal laboratory plasmas typically cannot be sustained with an electron density above the empirical Greenwald limit. Presented here are tokamak experiments in Madison Symmetric Torus a up to unprecedented level about 10 times this This is thought made possible part by thick, stabilizing, conductive wall, and high-voltage, feedback-controlled power supply driving plasma current. The radial profile of current flattens around twice limit, without edge collapse routinely...
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.
A cause of observed anomalous plasma momentum transport in a reversed-field pinch is determined experimentally. Magnetohydrodynamic theory predicts that nonlinear interactions involving triplets tearing modes produce internal torques redistribute momentum. Evidence for the torque acquired by detecting correlation redistribution with mode triplets, elimination one triplet, and external driving modes.
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,...
Measurements and simulations show that plasma relaxation processes in the reversed field pinch drive redistribute both magnetic flux momentum. To examine this process, a new 3D Mach B-dot probe has been constructed. This collects ion saturation currents through six molybdenum electrodes arranged on flattened vertices of an octahedron made boron nitride (BN). The current flows configurable voltage dividers for measurement returns one selectable return equally spaced along 12 cm BN arm. In...
The leading terms of the magnetic field spectrum for Helically Symmetric Experiment [Fusion Technol. 27, 273 (1995)] at low are determined by analyzing orbits passing particles. images produced intersection electron with a fluorescent mesh recorded charge coupled device and transformed into coordinates using neural network. To obtain spectral components, then fit to an analytic expression that models drift electrons. results confirm first time quasihelical stellarators have large effective...
The first period of physics operation the Madison Symmetric Torus (MST) reversed field pinch [Plasma Physics and Controlled Nuclear Fusion Research 1988 (IAEA, Vienna, 1989), Vol 2, p. 757] has produced information on sawtooth oscillations, edge magnetic electrostatic fluctuations, equilibrium parameters at large plasma size. Sawtooth oscillations are prevalent all values parameter might constitute discrete dynamo events. Both fluctuations sufficient magnitude to be relevant transport in...
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...
In this Letter we report an experimental study of fully developed anisotropic magnetic turbulence in a laboratory plasma. The has broad (narrow) spectral power the perpendicular (parallel) direction to local mean field extending beyond ion cyclotron frequency. Its ${k}_{\ensuremath{\perp}}$ spectrum is asymmetric and electron diamagnetic directions. wave number scaling for short wavelength fluctuations shows exponential falloff indicative dissipation. A standing structure found minor radial toroidal
Dissipation range cascades in plasma turbulence are described and spectra formulated from the scaled attenuation wavenumber space of spectral energy transfer rate. This yields characterized by product a power law exponential fall-off, applicable to all scales. Spectral indices fall-off depend on scaling dissipation, strength nonlinearity, nonlocal effects when dissipation rates multiple fluctuation fields different. The theory is used derive for MHD with magnetic Prandtl number greater than...
This paper explores the behavior of runaway electrons in tokamak plasmas at low electron density, plasma current, and magnetic field using experimental data from Madison Symmetric Torus (MST) computational NIMROD nonlinear resistive 3D MHD code. Density thresholds for onset suppression are determined experimentally steady plasmas, with a population electrons, resonant perturbations different poloidal mode numbers applied. Poloidal number m = 3 suppress while 1 have little effect. difference...