A5089564596- Magnetic confinement fusion research
- Ionosphere and magnetosphere dynamics
- Laser-Plasma Interactions and Diagnostics
- Plasma Diagnostics and Applications
- Particle accelerators and beam dynamics
- Solar and Space Plasma Dynamics
- Superconducting Materials and Applications
- Fusion materials and technologies
- Laser-induced spectroscopy and plasma
- Atomic and Subatomic Physics Research
- Astronomical Observations and Instrumentation
- Magneto-Optical Properties and Applications
- Magnetic Field Sensors Techniques
- Astronomy and Astrophysical Research
- Geophysics and Gravity Measurements
- Physics of Superconductivity and Magnetism
- Atomic and Molecular Physics
- Particle Accelerators and Free-Electron Lasers
- Laser Design and Applications
- Spacecraft and Cryogenic Technologies
- Spectroscopy and Laser Applications
- Optical Polarization and Ellipsometry
- Calibration and Measurement Techniques
- Dust and Plasma Wave Phenomena
- Adaptive optics and wavefront sensing
University of California, Los Angeles
2015-2024
University of Wisconsin–Madison
2006-2021
The University of Texas at Austin
1984-2021
General Atomics (United States)
2018-2021
University of California, San Diego
2020-2021
National Institute for Fusion Science
2008-2018
California State University, San Marcos
2018
Palomar College
2018
Fusion (United States)
1988-2014
Plasma Technology (United States)
1988-2014
This article reviews digital spectral analysis techniques that yield experimental insight into plasma turbulence. Methods to quantify the statistical properties of fluctuations and measure particle heat flux caused by electrostatic are presented. Furthermore, study nonlinear coupling process turbulence redistribution energy among different modes discussed. The impact on fusion research is demonstrated with results collected Langmuir probes, heavy-ion beam laser scattering in tokamak TEXT....
A double-pass, radially viewing, far-infrared laser-based POlarimeter-INTerferometer (POINT) system utilizing the three-wave technique has been implemented for diagnosing plasma current and electron density profiles in Experimental Advanced Superconducting Tokamak (EAST). POINT operated routinely during most recent experimental campaign provides continuous 11 chord line-integrated Faraday effect measurement throughout entire discharge all heating schemes conditions (including ITER relevant...
The object of this review is to summarize the achievements research on Alcator C-Mod tokamak [Hutchinson et al., Phys. Plasmas 1, 1511 (1994) and Marmar, Fusion Sci. Technol. 51, 261 (2007)] place that in context quest for practical fusion energy. a compact, high-field tokamak, whose unique design operating parameters have produced wealth new important results since it began operation 1993, contributing data extends tests critical physical models into parameter ranges regimes. Using only...
Strong asymmetries in the spectrum and magnitude of low frequency (ω ≪ ωci) density fluctuations Texas Experimental Tokamak (TEXT) are described. Microturbulence is investigated under a variety plasma parameters comparison with mixing length theory made. Broadband (Δω/ω ≥ 1, Δk/k⊥ 1.5, propagating electron diamagnetic drift direction) observed throughout cross-section, but they peak at limiter possess strong up-down asymmetry which inverts reversal current direction. The spatial distribution...
Externally applied magnetic fields are used on the Texas Experimental Tokamak (TEXT) to study possibility of controlling particle, impurity and heat fluxes at plasma edge. Fields with toroidal mode number n = 2 or 3 multiple poloidal numbers m (dominantly 7) used, a poloidally toroidally averaged ratio radial field components 〈|br/Bø〉 ≅0. 1%. Calculations show that it is possible produce mixed islands stochastic regions edge (r/a ≥ 0.8) without affecting interior. The expected structure...
For high-density Ohmic discharges in the TEXT (Texas Experimental) tokamak, a distinct ion mode (i.e., density fluctuations propagating diamagnetic drift direction) is observed microturbulence spectra. The magnitude and spectral characteristics of this are identified. Onset feature occurs at plasma densities where clear saturation evident global energy-confinement time ${\ensuremath{\tau}}_{E}$. A possible connection between experimentally theoretically predicted properties instabilities...
The spectra, magnitude and spatial distribution of low-frequency (ω ≪ ωci) density fluctuation have been measured by two independent experimental methods in the edge plasma TEXT tokamak. Good agreement between far-infrared laser scattering Langmuir probe measurements has achieved strengths each technique are evaluated. probes used to directly determine particle flux induced fluctuations (Γ ∝ ⟨ñ×B⟩) collective Thomson permits an extension these observations interior. Results presented for...
A multichannel far-infrared laser-based POlarimeter-INTerferometer (POINT) system utilizing the three-wave technique is under development for current density and electron profile measurements in EAST tokamak. Novel molybdenum retro-reflectors are mounted inside wall double-pass optical arrangement. Digital Phase Detector with 250 kHz bandwidth, which will provide real-time Faraday rotation angle phase shift output, have been developed use on POINT system. Initial calibration indicates...
A high-performance Faraday-effect polarimeter-interferometer system has been developed for the J-TEXT tokamak. This time response up to 1 μs, phase resolution < 0.1° and minimum spatial ∼15 mm. High permits investigation of fast equilibrium dynamics as well magnetic density perturbations associated with intrinsic Magneto-Hydro-Dynamic (MHD) instabilities external coil-induced Resonant Magnetic Perturbations (RMP). The 3-wave technique, in which line-integrated Faraday angle electron...
The first equilibrium reconstruction of EAST current-density profile based on internal Faraday rotation measurements provided by the POlarimeter-INTerferometer (POINT) diagnostic is demonstrated using EFIT code. incorporates 11 simultaneous line-integrated density and effect from POINT to self-consistently reconstruct toroidal current a algorithm. It shown that can be applied improve accuracy core plasma q EAST. Comparisons magnetic surfaces reconstructed external data against those are...
Recent experiments on EAST have achieved the first long pulse H-mode (61 s) with zero loop voltage and an ITER-like tungsten divertor, demonstrated access to broad plasma current profiles by increasing density in fully-noninductive lower hybrid current-driven discharges. These discharges reach wall thermal particle balance, exhibit stationary good confinement (H98y2 ~ 1.1) low core electron transport, are only possible optimal active cooling of armors. In separate experiments, was...
A heavy ion beam probe has been used to measure the plasma space potential profiles in tokamak TEXT [Nucl. Fusion Technol. 1, 479 (1981)]. The Ohmic discharges studied were perturbed by externally produced resonant magnetic fields (an ergodic limiter or EML). Without these perturbations central is generally consistent with value calculated from radial momentum balance, using experimental values of density and temperature assuming a neoclassical poloidal rotation velocity. Exceptions...
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 double-pass, radially-viewing, multichannel far-infrared (FIR) polarimeter/interferometer system is under development for current density profile and electron measurements in the EAST tokamak. The utilizes three 432.5 μm CW formic acid FIR lasers pumped by CO2 lasers. Each of can generate high output power more than 30 mW per cavity. Two lasers, with slight frequency offset ( ∼ 1 MHz), will be made collinear counter-rotating circular polarization order to determine Faraday effect measuring...
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...
Recently, the far-infrared (FIR) laser (λ0=432 μm) Faraday rotation measurement system on MST has been upgraded. The dc flowing-gas discharge CO2 pump is replaced by a rf-excited, sealed at 9.27 μm (GEM select 100, Coherent Inc., Santa Clara, CA), which subdivided equally into three parts to simultaneously FIR cavities. total infrared power approximately 80 W 9R(20) line required formic acid molecule. Each cavity produces ∼12 mW, sufficient for 11 simultaneous chord...
The mission of the National Spherical Torus Experiment (NSTX) is demonstration physics basis required to extrapolate next steps for spherical torus (ST), such as a plasma facing component test facility (NHTX) or an ST based (ST-CTF), and support ITER. Key issues are transport, steady state high β operation. To better understand electron new high- k scattering diagnostic was used extensively investigate gyro-scale fluctuations with varying temperature gradient scale length. Results from n = 3...
One of the systems planned for measurement electron density in ITER is a multi-channel tangentially viewing combined interferometer-polarimeter (TIP). This work discusses current status design, including preliminary optical table layout, calibration options, error sources, and performance projections based on CO2/CO laser system. In two-color interferometry carried out at 10.59 μm 5.42 separate polarimetry plasma induced Faraday effect, utilizing rotating wave technique, made μm. The...
A laser-based far-infrared polarimeter-interferometer system utilizing the three-wave technique has been implemented on J-TEXT tokamak. The polarimeter determines Faraday effect by measuring phase difference between two collinear, counter-rotating, circularly polarized laser beams. first results of designed for have obtained in most recent experimental campaign. Simultaneous polarimetric and interferometric measurement is achieved, with resolution up to 0.1°, at bandwidth 50 kHz. temporal...
Experimental and modeling investigations on the DIII-D EAST tokamaks show attractive transport stability properties of fully noninductive, high poloidal-beta (βP) plasmas, their suitability for steady-state operating scenarios in ITER CFETR. A key feature high-βP regime is large-radius (ρ > 0.6) internal barrier (ITB), often observed all channels (ne, Te, Ti, rotation), responsible both excellent energy confinement quality properties. Experiments have shown that, with a ITB, very βN βP...
Motivated by the need to measure fast equilibrium temporal dynamics, non-axisymmetric structures, and core magnetic fluctuations (coherent broadband), a three-chord Faraday-effect polarimeter-interferometer system with time response high phase resolution has recently been installed on DIII-D tokamak. A novel detection scheme utilizing two probe beams detectors for each chord results in reduced noise increased [δb ∼ 1G up 3 MHz bandwidth]. First measurement were obtained during recent...
A full-scale 120 m path length ITER toroidal interferometer and polarimeter (TIP) prototype, including an active feedback alignment system, has been constructed undergone initial testing at General Atomics. In the TIP two-color interferometry is carried out 10.59 μm 5.22 using a CO2 quantum cascade laser (QCL) respectively while separate polarimetry measurement of plasma induced Faraday effect made μm. The system uses co-linear right left-hand circularly polarized beams upshifted by 40 44...