A5054576414- Magnetic confinement fusion research
- Ionosphere and magnetosphere dynamics
- Particle accelerators and beam dynamics
- Solar and Space Plasma Dynamics
- Plasma Diagnostics and Applications
- Laser-Plasma Interactions and Diagnostics
- Dust and Plasma Wave Phenomena
- Quantum chaos and dynamical systems
- Geomagnetism and Paleomagnetism Studies
- Quantum Information and Cryptography
- Superconducting Materials and Applications
- Optical Network Technologies
- Laser-induced spectroscopy and plasma
- Quantum Computing Algorithms and Architecture
- Gyrotron and Vacuum Electronics Research
- Cold Atom Physics and Bose-Einstein Condensates
- Astro and Planetary Science
- Quantum optics and atomic interactions
- Theoretical and Computational Physics
- Quantum Mechanics and Applications
- Advanced Fiber Laser Technologies
- Nonlinear Photonic Systems
- Nonlinear Dynamics and Pattern Formation
- Earthquake Detection and Analysis
- Nonlinear Waves and Solitons
Massachusetts Institute of Technology
2015-2024
Plasma Technology (United States)
2015-2024
Fusion Academy
2015-2024
Fusion (United States)
2014-2024
National Technical University of Athens
2006-2023
Karlsruhe Institute of Technology
2017
National and Kapodistrian University of Athens
2017
University of Alabama in Huntsville
2009-2010
Oak Ridge National Laboratory
2001-2007
Higashihiroshima Medical Center
2006
Optimal design and use of electron cyclotron heating requires that accurate relatively quick computer codes be available for prediction wave coupling, propagation, damping current drive at realistic levels EC power. To this end, a number have been developed in laboratories worldwide. A detailed comparison these is desirable since they variety methods modelling the behaviour effects waves. The approach used benchmarking study to apply small representative cases. Following minor remedial work...
The conventional ordinary O-mode and the extraordinary X-mode in electron cyclotron range of frequencies are not suitable for core heating high-β spherical tokamak plasmas, like National Spherical Torus Experiment [M. Ono, S. Kaye, M. Peng et al., Proceedings 17th International Atomic Energy Agency Fusion Conference (International Agency, Vienna, 1999), Vol. 3, p. 1135], as they weakly damped at high harmonics frequency. However, Bernstein waves (EBW) can be effective driving currents...
It is well known that absolute instabilities can be located by prescribed mappings from the complex-frequency plane to wavenumber through dispersion relation D(ω,k)=0. However, in many systems of physical interest polynomial ω while transcendental k, and implementation this mapping procedure particularly difficult. If one maps consecutive deformations Fourier integral path (originally along real k axis) into plane, points having (∂D/∂k)=0 are readily detected distinctive feature their local...
A detailed study of lower hybrid current drive (LHCD) in ITER is provided, focusing on the wave propagation and mechanisms. combination ray-tracing Fokker–Planck calculations are presented for various plasma scenarios, frequency polarization. The dependence driven location power deposition upon coupled spectrum systematically determined, order to set objectives antenna design. respective effects finite-power levels, magnetic trapping, spectra accounted quantitatively estimated. sensitivity...
In tokamak fusion plasmas, coherent fluctuations in the form of blobs or filaments are routinely observed scrape-off layer. Radio frequency (RF) electromagnetic waves, excited by antenna structures placed near wall a tokamak, have to propagate through layer before reaching core plasma. While effect on properties RF waves has not been quantified experimentally, it is interest carry out theoretical study determine if can affect propagation characteristics waves. Usually, difference between...
The propagation and scattering of electromagnetic waves in dielectric media is theoretical experimental interest a wide variety fields. An understanding observational results generally requires numerical solution Maxwell equations---usually implemented on conventional computers using sophisticated algorithms. In recent years, advances quantum information science the development have piqued curiosity about taking advantage these resources for an alternate approach to equations. This...
The density fluctuations and blobs present in the edge region of magnetic fusion devices can scatter radio frequency (RF) waves through refraction, reflection, diffraction, coupling to other plasma waves. This, turn, affects spectrum RF electromagnetic power that reaches core plasma. usual geometric optics analysis scattering by accounts for only refractive effects. It is valid when amplitude small, order 10%, compared background density. In experiments, with much larger amplitudes are...
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...
Spectral measurements have been made of charged fusion products produced in deuterium + helium-3 filled targets irradiated by the OMEGA laser system [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)]. Comparing energy shifts four particle types has allowed two distinct physical processes to be probed: Electrostatic acceleration low-density corona and loss high-density target. When burn occurred during pulse, were dominated effects. Using a simple model for accelerating field region, time...
A large-amplitude high-frequency modulated wave launched by an external source significantly changes the plasma equilibrium. The adiabatic Vlasov distribution function of electrons is found for one-dimensional initial-and boundary-value problems. nonlinear dispersion relation derived to all orders in electric-field amplitude. new mode below electron frequency exists. In this state described a double-humped function.
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)...
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...
In magnetic fusion devices, radio frequency (rf) waves in the electron cyclotron (EC) and lower hybrid (LH) range of frequencies are being commonly used to modify plasma current profile. ITER, EC expected stabilize neoclassical tearing mode (NTM) by providing island region [R. Aymar et al., Nucl. Fusion 41, 1301 (2001)]. The appearance NTMs severely limits pressure leads degradation confinement. LH could be ITER profile closer edge plasma. These rf propagate from excitation structures core...
The evolution of a charged particle distribution function under the influence coherent electromagnetic waves in plasma is determined from kinetic theory. For waves, dynamical phase space particles an inhomogeneous mix chaotic and regular orbits. persistence long time correlations between motion invalidates any simplifying Markovian or statistical assumptions--the basis for usual quasilinear theories. generalized formalism this Letter leads to hierarchy equations reduced function. operators,...
In modern magnetic fusion devices, such as tokamaks and stellarators, radio frequency (RF) waves are commonly used for plasma heating current profile control, well certain diagnostics. The frequencies of the RF range from ion cyclotron to electron frequency. launched structures, like waveguides straps, placed near wall in a very low density, tenuous region device. electromagnetic fields have propagate through this scrape-off layer before coupling power core plasma. is characterized by...
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...
The National Spherical Torus Experiment (NSTX) has explored the effects of shaping on plasma performance as determined by many diverse topics including stability global magnetohydrodynamic (MHD) modes (e.g., ideal external kinks and resistive wall modes), edge localized (ELMs), bootstrap current drive, divertor flux expansion, heat transport. Improved capability been crucial to achieving βt∼40%. Precise shape control achieved NSTX using real-time equilibrium reconstruction. simultaneously...
Electromagnetic waves are an inherent part of all plasmas—laboratory fusion plasmas or astrophysical plasmas. The conventional methods for studying properties electromagnetic rely on discretization Maxwell equations suitable implementing classical, present day, computers. traditional methodology is not efficient quantum computing implementation—a future computational source offering a tantalizing possibility enormous speed up and significant reduction in cost. This paper addresses two topics...
A new phenomenon of coherent acceleration ions by a discrete spectrum electrostatic waves propagating perpendicularly to uniform magnetic field is described. It allows the energization whose initial energies correspond region phase space that below chaotic domain. The ion orbits domain are described very accurately using perturbation analysis second order in wave amplitudes. This shows takes place only when contains at least two frequencies separated an amount close integer multiple...
Substantial radio-frequency power in the ion-cyclotron range of frequencies can be effectively coupled to a tokamak plasma from poloidal current strap antennas at edge. If there exists an ion–ion hybrid resonance inside plasma, then some antenna, delivered into by fast Alfvén waves, mode converted ion-Bernstein waves. In confinement fields mode-converted waves damp and locally on electrons [A. K. Ram A. Bers, Phys. Fluids B 3, 1059 (1991)]. The usual mode-conversion analysis that studies...
In previous publications [A. K. Ram and S. D. Schultz, Phys. Plasmas 7, 4084 (2000); A. Bers, Ram, in Proceedings of the Second Europhysics Topical Conference on RF Heating Current Drive Fusion Devices, edited by J. Jacquinot, G. Van Oost, R. Weynants (European Physical Society, Petit-Lancy, 1998), Vol. 22A, pp. 237–240] it has been shown that, overdense plasmas type encountered spherical tori, electron Bernstein waves can be excited a plasma mode conversion either an externally launched X...
In the CDX-U spherical torus, agreement between radiation temperature and Thomson scattering electron profiles indicates approximately 100% conversion of thermally emitted Bernstein waves to X mode. This has been achieved by controlling density scale length (L(n)) in region with a local limiter outside last closed flux surface, shortening L(n) theoretically required value for optimal conversion. From symmetry process, prospects efficient coupling heating current drive scenarios are strongly...