A5038900835- Magnetic confinement fusion research
- Ionosphere and magnetosphere dynamics
- Laser-Plasma Interactions and Diagnostics
- Fusion materials and technologies
- Solar and Space Plasma Dynamics
- Plasma Diagnostics and Applications
- Atomic and Subatomic Physics Research
- Particle accelerators and beam dynamics
- Superconducting Materials and Applications
- Magnetic Bearings and Levitation Dynamics
- Electric Motor Design and Analysis
- Spectroscopy and Laser Applications
- Electromagnetic Launch and Propulsion Technology
- Particle Accelerators and Free-Electron Lasers
- Advanced MEMS and NEMS Technologies
- Geomagnetism and Paleomagnetism Studies
- Astronomical Observations and Instrumentation
- Laser-induced spectroscopy and plasma
- Microgrid Control and Optimization
- Gyrotron and Vacuum Electronics Research
- Physics of Superconductivity and Magnetism
- Atmospheric Ozone and Climate
- Climate Change and Health Impacts
- Advanced Sensor Technologies Research
- Vacuum and Plasma Arcs
Korea Institute of Fusion Energy
2013-2023
Fusion (United States)
2013
Fusion Academy
2013
University of California, Davis
2001-2011
University of California System
2002
Seoul National University
1994-1999
A wide variety of fast ion driven instabilities are excited during neutral beam injection (NBI) in the National Spherical Torus Experiment (NSTX) [Nucl. Fusion 40, 557 (2000)] due to large ratio velocity Alfvén velocity, Vfast∕VAlfvén, and high beta. The Vfast∕VAlfvén ITER 39, 2137 (1999)] NSTX is comparable. modes can be divided into three categories: chirping energetic particle (EPM) frequency range 0 120kHz, toroidal eigenmodes (TAE) with a 50kHz 200kHz, compressional global (CAE GAE,...
In this Letter we report the first clear experimental observation of density gradient stabilization electron temperature driven turbulence in a fusion plasma. It is observed that longer wavelength modes, ${k}_{\ensuremath{\perp}}{\ensuremath{\rho}}_{s}\ensuremath{\lesssim}10$, are most stabilized by gradient, and accompanied about factor 2 decrease plasma effective thermal diffusivity.
We report observation of a new high performance regime in discharges the National Spherical Torus Experiment, where H mode edge "pedestal" temperature doubles and energy confinement increases by 50%. The spontaneous transition is triggered large edge-localized mode, either natural or externally 3D fields. transport barrier grows inward from edge, with doubling both pedestal pressure width spatial extent steep radial electric field shear. dynamics suggest that fields could be applied to...
The National Spherical Torus Experiment (NSTX) has made considerable progress in advancing the scientific understanding of high performance long-pulse plasmas needed for future spherical torus (ST) devices and ITER.Plasma durations up to 1.6 s (five current redistribution times) have been achieved at plasma currents 0.7 MA with non-inductive fractions above 65% while simultaneously achieving β T N values 17% 5.7 (%m -1 ), respectively.A newly available motional Stark effect diagnostic...
The mission of the National Spherical Torus Experiment (NSTX) is to extend understanding toroidal physics low aspect ratio (R/a≃1.25) in collisionality regimes. NSTX designed operate with up 6 MW high harmonic fast wave (HHFW) heating and current drive, 5 neutral beam injection (NBI) co-axial helicity (CHI) for noninductive startup. Initial experiments focused on establishing conditions that will allow achieve its aims simultaneous βt high-bootstrap fraction, develop methods operation, which...
Major parts of an IR–visible two-color interferometer (TCI) on KSTAR have been upgraded for the multi-chord operation: (1) a diode-pumped-solid-state (DPSS) laser (660 nm) replacing former HeNe (633 nm), (2) vacuum-compatible vibration isolator with titanium retro-reflectors, and (3) full digital phase comparator real-time density signals. The commercial compact DPSS suits multiple chord configuration its strong beam power (500 mW) long coherent length (>100 m). Ti retro-reflectors...
Theory and experiments have shown that electron temperature gradient (ETG) turbulence on the gyro-scale, k⊥ρe ≲ 1, can be responsible for anomalous thermal transport in NSTX. Electron scale (high-k) is diagnosed NSTX with a high-k microwave scattering system [D. R. Smith et al., Rev. Sci. Instrum. 79, 123501 (2008)]. Here we report stabilization effects of density electron-scale fluctuations set neutral beam injection heated H-mode plasmas. We found absence from measurements correlated large...
In this letter, we report the first observation of fast response electron-scale turbulence to auxiliary heating cessation in National Spherical Torus eXperiment [Ono et al., Nucl. Fusion 40, 557 (2000)]. The was made a set RF-heated L-mode plasmas with toroidal magnetic field 0.55 T and plasma current 300 kA. It is observed that spectral power (measured high-k collective microwave scattering system) decreases significantly following RF occurs less than 200 μs. large drop has short time delay...
The gyrocenter shift phenomenon explained the mechanism of radial electric field formation at high confinement mode transition in fusion devices. This Letter reports that theory is also applicable to low temperature collisional plasmas such as arc discharges by generalization resulting from a short mean free path compared with gyroradius. retrograde motion cathode spots discharge investigated through model expanded formula shift. It found reversed formed front when they are under magnetic...
The far infrared tangential interferometer/polarimeter (FIReTIP) of the National Spherical Torus Experiment (NSTX) has been set up to provide reliable electron density signals for a real-time feedback control system. This work consists two main parts: suppression fringe jumps that have prohibiting plasma from use in direct actuators and conceptual design system including FIReTIP, hardware, software takes advantage NSTX (PCS). By investigating numerous shot data after July 2009 when new...
Dispersion interferometers have been used to measure line integrated electron densities from many fusion devices. To optically suppress noise due mechanical vibrations, a conventional dispersion interferometer typically uses two nonlinear crystals located before and after the plasma along laser beam path. Due long path, it can be difficult overlap fundamental second harmonic beams for heterodyne focus on crystal plasma, especially when aperture of is small, i.e., order mm. overcome such...
As an important future energy source nuclear fusion researchers have been trying to solve the problem of radial electric field formation: key factor H-mode (high confinement mode) phenomena. Although a profound analysis has developed on turbulence suppression by E×B flow (E is and B magnetic field) as basic mechanism transition, origin its relation with neutrals are not fully explained. In this paper novel model formation achieved gyrocenter shifts during charge exchange reactions ion...
A multi-energy soft x-ray (ME-SXR) array is used for the characterization of resistive wall modes (RWMs) in National Spherical Torus Experiment (NSTX). Modulations time history ME-SXR emissivity profiles indicate existence edge density and core temperature fluctuations good agreement with slow evolution n = 1 magnetic perturbation measured by poloidal radial RWM coils. The characteristic 20–25 Hz frequency SXR diagnostics approximately that stable RWM, which also near peak resonant field...
Completion of a multichannel far-infrared (FIR) tangential interferometer/polarimeter is under way for the National Spherical Torus Experiment, measurement plasma electron density and toroidal magnetic-field distributions. The system based on three-wavelength configuration, which was first developed by Rommers Howard in RTP tokamak [Plasma Phys. Controlled Fusion 38, 1805 (1996)]. probe beams enter through windows midplane Bay-K, are reflected back to detectors retro-reflectors. three FIR...
Abstract Dispersion interferometers (DI) are widely used to measure line integrated electron densities in many fusion devices. A recent development of a heterodyne single crystal DI (SCDI) with laser wavelength 1064 nm (Lee et al 2021 Rev. Sci. Instrum. 92 033536) allows an easier and simpler optical setup by using only one, instead two, nonlinear crystal. It is found that the reported SCDI acoustic-optical modulator (AOM) has different beam paths between frequency-shifted, via AOM,...
Interferometer/polarimeter systems based on far infrared lasers have suffered from lack of frequency modulation techniques that can allow higher intermediate (IF) for a fast time resolution together with stable operation including low drift. This is mainly due to the intrinsic narrow gain profile lasers. It known Stark effect broaden laser as has been demonstrated in laboratory. A Stark-tuned optically pumped (FIR) CH3OH two additional FIR at 119 μm successfully implemented tangential...
A new concept of turbulence transport and diffusion coefficient are derived from the microscopic ( is localized electric field B magnetic field) drifts at boundary fusion devices by characterization gyrocentre shift induced collisions among electrons, ions neutrals. It found that when viscosity force ion–neutral collision counted, Reynolds numbers poloidal ion flow in vicinity tokamak separatrix vary over critical value between turbulent laminar flows depending on plasma parameters such as...
Three experimental cases of cross-field diffusions in the magnetized plasmas reported to be related with Bohm diffusion are investigated based on ion current induced by ion-neutral collisions. High coefficient for original Bohm/Simon experiments and recent strongly pulsed can explained gyro-center shift combined short circuit effect, which is different from turbulence-induced transport nuclear fusion devices. It deduced that Bohm's interpretation 1/B dependence came fact effect his...
A tangential far infrared interferometer/polarimeter system has been upgraded for the measurement of two-dimensional electron density and toroidal magnetic field profiles on National Spherical Torus Experiment (NSTX). The employs a three-wavelength configuration that simultaneously produces interferometric phase shift Faraday rotation polarimetric data from single detector each channel. Three CH/sub 3/OH lasers (/spl lambda/=119 /spl mu/m) including Stark-tuned laser cavities are optically...
The edge interferometry channel of the far infrared tangential interferometer polarimeter (FIReTIP) is used to characterize localized density fluctuations during L/H transition in conjunction with other diagnostic systems on National Spherical Tokamak Experiment (NSTX). With high IF frequency employing a “Stark-tuned” laser as local oscillator, it possible measure absolute level at time resolution. Density fluctuation measurements using FIReTIP are feasible both field side and low boundary...
THz techniques have been widely employed In magnetic fusion plasma diagnostics, including far infrared Interferometry, polarimetry, and scattering to measure electron density profiles, field strength fluctuations, respectively. The high densities anticipated for next generation devices will further extend the applicability of diagnostics temperature profiles fluctuations by cyclotron emission imaging, imaging reflectometry.
Three examples of electric field formation in the plasma are analyzed based on a new mechanism driven by ion-neutral collisions. The Gyro-Center Shift analysis uses iteration three equations including perpendicular current induced momentum exchange between ions and neutrals when there is asymmetry over gyro-motion. This method includes non-zero divergence that leads solution time dependent state. first example radial at boundary nuclear fusion device, which key factor high-confinement mode...