A5089549043- Magnetic confinement fusion research
- Superconducting Materials and Applications
- Ionosphere and magnetosphere dynamics
- Particle accelerators and beam dynamics
- Fusion materials and technologies
- Plasma Diagnostics and Applications
- Solar and Space Plasma Dynamics
- Plasma and Flow Control in Aerodynamics
- Nuclear reactor physics and engineering
- Geophysics and Sensor Technology
- Quantum chaos and dynamical systems
- Atomic and Subatomic Physics Research
- Physics of Superconductivity and Magnetism
- Laser-Plasma Interactions and Diagnostics
- Magnetic Field Sensors Techniques
- Engineering Applied Research
- Hydraulic and Pneumatic Systems
- Theoretical and Computational Physics
- Protein Structure and Dynamics
- Nuclear Engineering Thermal-Hydraulics
- Power System Optimization and Stability
- Anomaly Detection Techniques and Applications
- Soil, Finite Element Methods
- Vibration and Dynamic Analysis
- Epoxy Resin Curing Processes
Columbia University
2010-2021
Princeton Plasma Physics Laboratory
1991-2018
National Center on Addiction and Substance Abuse at Columbia University
1999-2006
Princeton University
1982-2002
General Atomics (United States)
2001-2002
Stevens Institute of Technology
1985
Progress in the area of MHD stability and disruptions, since publication 1999 ITER Physics Basis document (1999 Nucl. Fusion 39 2137–2664), is reviewed. Recent theoretical experimental research has made important advances both understanding control tokamak plasmas. Sawteeth are anticipated baseline ELMy H-mode scenario, but tools exist to avoid or them through localized current drive fast ion generation. Active other instabilities will most likely be also required ITER. Extrapolation from...
Nonlinear continuum mechanics of solids is a fascinating subject. All the assumptions inherited from an overexposure to linear behaviour and analysis must be re-examined. The standard definitions strain designed for small deformation problems may totally misleading when finite motion or large deformations are considered. includes phenomena like `snap-through', where bifurcation theory applied engineering design. Capabilities in this field growing at fantastic speed; example, modern...
Dissipation of plasma toroidal angular momentum is observed in the National Spherical Torus Experiment due to applied nonaxisymmetric magnetic fields and their plasma-induced increase by resonant field amplification resistive wall mode destabilization. The measured decrease profile compared calculations nonresonant drag torque based on theory neoclassical viscosity. Quantitative agreement between experiment found when effect toroidally trapped particles included.
A general circuit formulation of resistive wall mode (RWM) feedback stabilization developed by Boozer [Phys. Plasmas 5, 3350 (1998)] has been used as the basis for VALEN computer code that calculates performance an active control system in arbitrary geometry. The uses a finite element representation thin shell structure integral to model conducting walls. This is combined with stable and unstable plasma modes. Benchmark comparisons results large aspect ratio analytic current driven kink are...
Research in NSTX has been conducted to establish spherical torus plasmas be used for high β, auxiliary heated experiments. This device a major radius R0 = 0.86 m and midplane halfwidth of 0.7 m. It operated with toroidal magnetic field B0 ⩽ 0.3 T Ip 1.0 MA. The evolution the plasma equilibrium is analysed between discharges an automated version EFIT code. Limiter, double null lower single diverted configurations have sustained several energy confinement times. stored reached 92 kJ (βt 17.8%)...
Using newly developed techniques and improved diagnostics, rotating wall-stabilized discharges have been maintained in the DIII-D tokamak for 30 characteristic resistive wall decay times---significantly longer than was previously achieved. The terminating mode has directly identified using internal fluctuation its correlation with slowdown plasma rotation is established.
The National Spherical Torus Experiment (NSTX) has demonstrated the advantages of low aspect ratio geometry in accessing high toroidal and normalized plasma beta, βN ≡ 108⟨βt⟩ aB0/Ip. Experiments have reached βt = 39% 7.2 through boundary profile optimization. High plasmas can exceed ideal no-wall stability limit, βNno−wall, for periods much greater than wall eddy current decay time. Resistive mode (RWM) physics is studied to understand stabilization these plasmas. spectrum unstable RWMs...
Large Type-I edge-localized mode (ELM) heat pulses may limit the life of divertor targets in a burning plasma. Recent experiments show that pitch-resonant nonaxisymmetric magnetic perturbations plasma edge 0.0005 or less main field offer useful solution, but there is little room presently designed ITER for even small perturbation coils. We present proposed coil requirements ELM suppression, derived primarily from DIII-D suppression experiments. by calculated examples large arrays coils (e.g....
Sustained stabilization of the n=1 kink mode by plasma rotation at beta approaching twice stability limit calculated without a wall has been achieved in DIII-D combination error field reduction and sufficient drive. Previous experiments have transiently exceeded no-wall limit. However, demonstration sustained rotational remained elusive because found to decay whenever is stabilized. Recent theory [Boozer, Phys. Rev. Lett. 86, 5059 (2001)] predicts resonant response fields marginal low-n...
A proof of principle magnetic feedback stabilization experiment has been carried out to suppress the resistive wall mode (RWM), a branch ideal magnetohydrodynamic (MHD) kink under influence stabilizing wall, on DIII-D tokamak device [Plasma Phys. Controlled Fusion Research (International Atomic Energy Agency, Vienna, 1986), p. 159; Plasmas 1, 1415 (1994)]. The RWM was successfully suppressed and high beta duration above no-wall limit extended more than 50 times flux diffusion time. It...
Dedicated experiments in the DIII-D tokamak [J. L. Luxon, Nucl. Fusion, 42, 614 (2002)], Joint European Torus (JET) [P. H. Rebut, R. J. Bickerton, and B. E. Keen, Fusion 25, 1011 (1985)], National Spherical Experiment (NSTX) [M. Ono, S. M. Kaye, Y.-K. Peng et al., 40, 557 (2000)] reveal commonalities of resistive wall mode (RWM) stabilization by sufficiently fast toroidal plasma rotation devices different size aspect ratio. In each device weakly damped n=1 RWM manifests itself resonant field...
Internal coils, 'I-Coils', were installed inside the vacuum vessel of DIII–D device to generate non-axisymmetric magnetic fields act directly on plasma. These are predicted stabilize resistive wall mode (RWM) branch long-wavelength external kink with plasma beta close ideal limit. Feedback using these I-Coils was found be more effective as compared coils located outside vessel. Locating allows for a faster response and coil geometry also better coupling helical structure. Initial results...
Research on the National Spherical Torus Experiment, NSTX, targets physics understanding needed for extrapolation to a steady-state ST Fusion Nuclear Science Facility, pilot plant, or DEMO. The unique operational space is leveraged test theories next-step tokamak operation, including ITER. Present research also examines implications coming device upgrade, NSTX-U. An energy confinement time, τE, scaling unified varied wall conditions exhibits strong improvement of BTτE with decreased electron...
Research on the stability of spherical torus plasmas at and above no-wall beta limit is being addressed National Spherical Torus Experiment [M. Ono et al., Nucl. Fusion 40, 557 (2000)], that has produced low aspect ratio plasmas, R/a∼1.27 plasma current exceeding 1.4 MA with high energy confinement (TauE/TauE_ITER89P>2). Toroidal normalized have exceeded 25% 4.3, respectively, in q∼7 plasmas. The observed to increase then saturate increasing li. factor βN/li reached 6, limited by...
The major objective of the National Spherical Torus Experiment (NSTX) is to understand basic toroidal confinement physics at low aspect ratio and high βT in order advance spherical torus (ST) concept. In do this, NSTX utilizes up 7.5 MW neutral beam injection, 6 harmonic fast waves (HHFWs), it operates with plasma currents 1.5 MA elongations 2.6 a field 0.45 T. New facility, diagnostic modelling capabilities developed over past two years have enabled research team make significant progress...
Toroidal plasma rotation of the order a few per cent Alfvén velocity can stabilize resistive wall mode (RWM) and extend operating regime tokamaks from conventional, ideal magnetohydrodynamic (MHD) no-wall limit up to MHD ideal-wall limit. The stabilizing effect has been measured in DIII-D passively by measuring critical required for stability actively probing with externally applied resonant magnetic fields. comparison these measurements predictions rotational stabilization sound wave...
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 promising approach to maintaining stability of high beta tokamak plasmas is the use a conducting wall near plasma stabilize low-n ideal magnetohydrodynamic instabilities. However, with resistive wall, either rotation or active feedback control required more slowly growing modes (RWMs). Previous experiments have demonstrated that nearby can remain stable n=1 external kink above limit predicted at infinity. Recently, extension stabilized lifetime τL than 30 times time constant τw and...
External kink instabilities are suppressed in a tokamak experiment by either (1) energizing distributed array of independently controlled active feedback coils mounted outside segmented resistive wall or (2) inserting second having much higher electrical conductivity. When the off and highly conducting is withdrawn, excited plasma current gradients grow at rate comparable to magnetic diffusion wall.
One of the goals National Spherical Torus Experiment (NSTX) is to investigate physics global mode stabilization in a low aspect ratio device. NSTX has major radius R0 = 0.86 m, midplane half-width 0.7 and an on-axis vacuum toroidal field B0 ⩽ 0.6 T reached plasma current Ip 1.5 MA. Experiments have established wall-stabilized MHD operating space machine. The maximum βt βN 35% 6.5%, respectively, with reaching 9.5li. Collapses rotation been correlated violation n 1 ideal beta limit, no−wall,...
The National Spherical Torus Experiment (NSTX) offers an operational space characterized by high-beta (β t = 39%, β N > 7, ) and low aspect ratio ( A 1.27) to leverage the plasma parameter dependences of RWM stabilization rotation damping physics giving greater confidence for extrapolation ITER. Significant new capability research has been added device with commissioning a set six non-axisymmetric magnetic field coils, allowing generation fields dominant toroidal mode number, n , 1–3....
The main aim of the National Spherical Torus Experiment (NSTX) is to establish fusion physics principles spherical torus (ST) concept. NSTX device began plasma operations in February 1999 and current Ip was successfully brought up design value 1 MA on 14 December 1999. planned shaping parameters, elongation κ = 1.6-2.2 triangularity δ 0.2-0.4, were achieved inner wall limited, single null double diverted configurations. coaxial helicity injection (CHI) high harmonic fast wave (HHFW)...
Resistive wall mode (RWM) instabilities are found to be a limiting factor in advanced tokamak regimes with low internal inductance. Even small amplitude modes can affect the rotation profile and performance of these ELMing H discharges. Although complete stabilization RWM by plasma has not yet been observed, several discharges increased beam momentum power injection sustained good steady state for record durations. The first investigation active feedback control shown promising results:...
The resistive wall mode (RWM) poses a limit to the maximum β that can be sustained in magnetic fusion experiments. RWM stabilization physics at low aspect ratio is studied high-β National Spherical Torus Experiment (NSTX) [M. Ono, S. M. Kaye, Y.-K. Peng et al., Nucl. Fusion 40, 557 (2000)] plasmas (βt up 39%; βN 6.8) understand and alleviate this constraint. Plasmas with increased q NSTX have been maintained above computed ideal no-wall for more than 20 times no signs of growth cases where...