A5083512229- Magnetic confinement fusion research
- Ionosphere and magnetosphere dynamics
- Solar and Space Plasma Dynamics
- Plasma Diagnostics and Applications
- Geomagnetism and Paleomagnetism Studies
- Particle accelerators and beam dynamics
- Laser-Plasma Interactions and Diagnostics
- Superconducting Materials and Applications
- Astro and Planetary Science
- Laser-induced spectroscopy and plasma
- Atomic and Subatomic Physics Research
- Fusion materials and technologies
- Characterization and Applications of Magnetic Nanoparticles
- Fluid Dynamics and Turbulent Flows
- Nuclear Physics and Applications
- Gyrotron and Vacuum Electronics Research
- Magnetic Field Sensors Techniques
- Particle Accelerators and Free-Electron Lasers
- Geophysics and Gravity Measurements
- Electrohydrodynamics and Fluid Dynamics
- Electron and X-Ray Spectroscopy Techniques
- Semiconductor materials and devices
- Magnetic and Electromagnetic Effects
- Adaptive optics and wavefront sensing
- Astrophysics and Star Formation Studies
University of Wisconsin–Madison
2016-2025
Fusion (United States)
2014-2024
Massachusetts Institute of Technology
2014
University of California, Los Angeles
2002-2014
Fusion Academy
2014
Max Planck Institute for Plasma Physics - Greifswald
2014
Helmholtz-Zentrum Dresden-Rossendorf
2014
Magnetic Development (United States)
2013
Oak Ridge National Laboratory
2011
Max Planck Society
2007
Abstract Magnetic fields are ubiquitous in the Universe. The energy density of these is typically comparable to fluid motions plasma which they embedded, making magnetic essential players dynamics luminous matter. standard theoretical model for origin strong through amplification tiny seed via turbulent dynamo level consistent with current observations. However, experimental demonstration mechanism has remained elusive, since it requires conditions that extremely hard re-create terrestrial...
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...
Fusion power has been increased by a factor of 3 in DIII-D tailoring the pressure profile to avoid kink instability $H$-mode plasmas. The resulting plasmas are found have neoclassical ion confinement. This reduction transport losses beam-heated with negative central shear is correlated dramatic density fluctuations. Improved magnetohydrodynamic stability achieved controlling plasma width. In deuterium highest gain $Q$ (the ratio fusion input power), was 0.0015, corresponding an equivalent...
The noninductive part of the measured current profile has been determined for DIII-D plasmas. A technique determining flux surface average quantity $\mathbf{E}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbf{B}$ and a model resistivity separates into inductive portions. Analysis shows directly that neoclassical is adequate to explain experimental observations, while Spitzer not, large exists in plasmas which neutral beam drive pressure driven bootstrap currents are expected.
The confinement and the stability properties of DIII-D tokamak [Plasma Physics Controlled Nuclear Fusion Research 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. 1, p. 159] high-performance discharges are evaluated in terms rotational magnetic shear, with an emphasis on recent experimental results obtained from negative central shear (NCS) experiments. In NCS discharges, a core transport barrier is often observed to form inside region accompanied by reduction fluctuation...
The scaling of cross-field heat transport with relative gyroradius ρ* was measured in low (L) and high (H) mode tokamak plasmas using the technique dimensionally similar discharges. scalings electron ion thermal diffusivities were determined separately a two-fluid analysis. For L-mode plasmas, diffusivity scaled as χe∝χBρ1.1±0.3* (gyro-Bohm-like) while χi∝χBρ−0.5±0.3* (worse than Bohm-like). results independent method auxiliary heating (radio frequency or neutral beam). Since fluids had...
Beyond a certain heating power, measured and predicted distributions of neutral beam injection (NBI) driven currents deviate from each other even in the absence MHD instabilities. The most reasonable explanation is redistribution fast NBI ions on time scale smaller than current time. hypothesis by background turbulence discussed. Direct numerical simulation test particles given field electrostatic indicates that for parameters thermal particle diffusion can indeed be similar. High quality...
A tokamak discharge has been formed and maintained through helicity injection, by use of only an external dc low-energy electron beam. The discharge, in a 5-kG toroidal field, evolved to steady-state circular cross section with q(a)=10, q(0)=4, which was for more than 400 L/R periods, the time (60 msec) limited cathode bias supply. density profile reached line-averaged n${\ifmmode\bar\else\textasciimacron\fi{}}_{e}$=2\ifmmode\times\else\texttimes\fi{}${10}^{13}$...
Investigations of the effects rf on plasma potential measurements with electron emitting probes and methods for interpreting data are presented. Techniques correspond to floating inflection point single-emitting differential probes, respectively. A simple method measurement fluctuations is given which makes use time-averaged probe I–V characteristics.
The Wisconsin Plasma Astrophysics Laboratory (WiPAL) is a flexible user facility designed to study range of astrophysically relevant plasma processes as well novel geometries that mimic astrophysical systems. A multi-cusp magnetic bucket constructed from strong samarium cobalt permanent magnets now confines 10 m$^3$, fully ionized, magnetic-field free in spherical geometry. parameters $ T_{e}\approx5$ $20$ eV and $n_{e}\approx10^{11}$ $5\times10^{12}$ cm$^{-3}$ provide an ideal testbed for...
The spontaneous formation of magnetic islands is observed in driven, antiparallel reconnection on the Terrestrial Reconnection Experiment. We here provide direct experimental evidence that plasmoid instability active at electron scale inside ion diffusion region a low collisional regime. experiments show island occurs smaller system size than predicted by extended magnetohydrodynamics or fully collisionless simulations. This more effective seeding emphasizes their importance to naturally...
The kinetic stability of collisionless, sloshing beam-ion (\(45^{\circ}\) pitch angle) plasma is studied in a 3D simple magnetic mirror, mimicking the Wisconsin High-temperature superconductor Axisymmetric Mirror (WHAM) experiment. collisional Fokker-Planck code CQL3D-m provides slowing-down distribution to initialize kinetic-ion/fluid-electron Hybrid-VPIC, which then simulates free decay without external heating or fueling. Over \(1\)–\(10\;\mathrm{\mu s}\), drift-cyclotron loss-cone (DCLC)...
Reliable operation of discharges with negative central magnetic shear has led to significant increases in plasma performance and reactivity both low confinement, L-mode, high H-mode, regimes the DIII-D tokamak [Plasma Physics Controlled Nuclear Fusion Research 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. 1, p. 159]. Using neutral beam injection early initial current ramp, a large range have been produced durations lasting up 3.2 s. The total noninductive (beam plus...
Discharges exhibiting the highest plasma energy and fusion reactivity yet realized in DIII-D tokamak [Plasma Physics Controlled Nuclear Fusion Research, 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. I, p. 159] have been produced by combining benefits of a hollow or weakly sheared central current profile [Phys. Plasmas 3, 1983 (1996)] with high confinement (H mode) edge. In these discharges, low-power neutral beam injection heats electrons during initial ramp, “freezes in”...
A noninductive current drive concept, based on internal pressure-driven currents in a low-aspect-ratio toroidal geometry, has been demonstrated the Current Drive Experiment Upgrade (CDX-U) [Forest et al., Phys. Rev. Lett. 68, 3559 (1992)] and further tested DIII-D [in Plasma Physics Controlled Nuclear Fusion Research, 1986, Proceedings of 11th International Conference, Kyoto (International Atomic Energy Agency, Vienna, 1987), Vol. 1, p. 159]. For both experiments, electron cyclotron power...
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...
Pressure driven currents are observed in an electron cyclotron resonance (ECR) heated, small-aspect-ratio toroidal plasma the CDX-U device. A current of 1.05 kA was generated with \ensuremath{\sim}8 kW ECR power. At this level, poloidal field created by these is significantly larger than vacuum and produces closed flux surfaces a tokamak geometry. After surface formation we hypothesize that bootstrap to maintain discharge. This internally may offer attractive method start up
Significance The problem of solar wind heating is one the long-standing fundamental problems space plasma physics. We propose that electron component heated by electrons streaming from hot corona and slowly losing their energy due to weak Coulomb collisions. Our first-principle kinetic derivation predicts scaling temperature with heliocentric distance, which in good agreement observations. theory reveals role non-Maxwellian distribution function mechanism, it may be valuable for interpreting...
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...
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.
An axisymmetric magnetic field is applied to a spherical, turbulent flow of liquid sodium. induced dipole moment measured which cannot be generated by the interaction mean with field, indicating presence electromotive force. It shown that should vanish for any laminar flow. Also observed production toroidal from poloidal (the $\ensuremath{\omega}$ effect). Its potential role in discussed.
The role of turbulence in current generation and self-excitation magnetic fields has been studied the geometry a mechanically driven, spherical dynamo experiment, using three-dimensional numerical computation. A simple impeller model drives flow that can generate growing field, depending on Reynolds number Rm=micro0sigmaVa fluid Re=Vanu flow. For Re<420, is laminar transition governed by threshold Rmcrit=100, above which eigenmode observed primarily dipole field transverse to axis symmetry...