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Author: Abhay Ram Publisher: ISBN: Category : Languages : en Pages : 10
Book Description
This paper summarizes the theoretical and numerical results we have obtained for the excitation and propagation of electron Bernstein waves in spherical tokamak plasmas. Keywords: ECR heating; Electron Bernstein wave emission; Electron Bernstein wave heating; mode conversion; RF heating.
Author: Abhay Ram Publisher: ISBN: Category : Languages : en Pages : 10
Book Description
This paper summarizes the theoretical and numerical results we have obtained for the excitation and propagation of electron Bernstein waves in spherical tokamak plasmas. Keywords: ECR heating; Electron Bernstein wave emission; Electron Bernstein wave heating; mode conversion; RF heating.
Author: Abhay Ram Publisher: ISBN: Category : Languages : en Pages : 56
Book Description
The high-beta operating regime of spherical tori (ST), such as in the National Spherical Torus Experiment (NSTX) and the Mega Amp Spherical Tokamak (MAST), makes them attractive fusion devices. For access to such high beta regimes it is necessary to heat and to drive currents in ST plasmas. In the electron cyclotron range of frequencies such plasmas are overdense to conventional electron cyclotron waves. However, in this frequency range, electron Bernstein waves (EBW) offer an attractive alternative as they have no density cutoffs. Electron Bernstein waves can be excited in an ST plasma by mode conversion of the extraordinary or the ordinary mode at the upper hybrid resonance. The applications of EBWs in STs range from plasma start-up and heating of the plasma to modifying and controlling its current profile. The controlling of the current profile could provide better confinement as well as help suppress neoclassical tearing modes. The mode conversion to EBWs has been detailed in a variety of papers. This paper deals with two particular topics that further quantify the role of EBWs in spherical tori. interests. The first topic is on the relevance of relativistic effects in describing the propagation and damping of EBWs. The second topic is on plasma current generation by EBWs.
Author: Abhay Ram Publisher: ISBN: Category : Languages : en Pages : 28
Book Description
The high-beta operating regime of spherical tokamaks (ST), such as in NSTX and MAST, make them attractive fusion devices. For access to such high beta regimes, it is necessary to heat and to drive currents in ST plasmas. While such plasmas are overdense to conventional electron cyclotron waves, electron Bernstein waves (EBW) offer an attractive means toward this purpose. The applications of EBWs in STs range from plasma start-up and heating of the ST plasma to modifying and controlling its current profile. The controlling of the current profile could provide better confinement as well as help suppress neoclassical tearing modes. This paper deals with two particular topics. The first topic is on the relevance of relativistic effects in describing the propagation and damping of EBWs. The second topic is on plasma current generation by EBWs.
Author: Abhay Ram Publisher: ISBN: Category : Languages : en Pages : 48
Book Description
The conventional ordinary and extraordinary modes in the electron cyclotron range of frequencies are not suitable for heating of and/or driving currents in spherical tori (ST) plasmas. However, electron Bernstein waves offer an attractive possibility for heating and current drive in this range of frequencies. In this paper, we summarize our theoretical and numerical results which describe the excitation of electron Bernstein waves in ST plasmas when the extraordinary mode or the ordinary mode are coupled into the plasma from an external source. In our discussion on the conversion of the ordinary mode to electron Bernstein waves (via the slow extraordinary mode) we illustrate very important physics, relevant to this conversion process, that has been ignored in previous studies. The particular physics has to do with the conversion of the slow extraordinary mode to the fast extraordinary mode that can then propagate out of the plasma and thus reduce the mode conversion to electron Bernstein waves. This reduction in the mode conversion can occur even when the wave numbers are such that the ordinary mode cutoff and the slow extraordinary mode cutoff are coincident in space. Furthermore, we also consider the emission of electron Bernstein waves from a thermal plasma. This emission mode converts to extraordinary and ordinary modes in the vicinity of the upper hybrid resonance. We describe the general relationship between the conversion coefficients when exciting electron Bernstein waves using either the extraordinary mode or the ordinary mode, and the emission coefficients when thermally emitted electron Bernstein waves convert to the extraordinary and ordinary modes.
Author: Joan Decker Publisher: ISBN: Category : Languages : en Pages : 10
Book Description
Spherical tori (ST) are tight aspect ratio machines that are attractive as fusion energy devices due to their accessibility to high-beta regimes. Since STs are overdense, current drive (CD) using electron cyclotron (EC) waves is difficult and inefficient, particularly near the outboard edge where trapping of electrons in the magnetic field is significant. However, it has been shown that, in the EC range of frequencies, it is possible to externally excite electron Bernstein waves (EBW) by mode conversion (MC) at the outboard edge of a ST plasma [1]. In addition, EBWs can propagate in the plasma without density limits and are strongly damped at any harmonic of the EC resonance [2]. Current drive by EBW has been recently demonstrated in toroidally confined fusion plasmas [3]. Using our kinetic code DKE [4], we solve the kinetic equation with Fokker-Planck (FP) collisions and quasilinear (QL) diffusion due to EBW. In addition, we account for the effects of magnetic trapping of electrons, which are important in ST. We show that large current densities can be driven in high-\beta regimes of ST, and that off-axis current is primarily driven by the Ohkawa [5] mechanism while near-axis current is driven by the Fisch-Boozer [6] mechanism.
Author: Abhay Ram Publisher: ISBN: Category : Languages : en Pages : 16
Book Description
The conventional ordinary and extraordinary modes in the electron cyclotron range of frequencies are not suitable for heating of and/or driving currents in spherical tori (ST) plasmas. However, electron Bernstein waves offer an attractive possibility for heating and current drive in this range of frequencies. In this paper, we summarize our theoretical and numerical results which describe the excitation and propagation of electron Bernstein waves in ST plasmas. Keywords: ECR heating; Electron Bernstein wave emission; Electron Bernstein wave heating; mode conversion; RF heating.
Author: Abhay Ram Publisher: ISBN: Category : Languages : en Pages : 22
Book Description
HIn previous publications [A.K. Ram and S.D. Schultz, Phys. Plasmas 7, 4084 (2000); A. Bers, A.K. Ram, and S.D. Schultz, in Proceedings of the Second Europhysics Topical Conference on RF Heating and Current Drive of Fusion Devices, edited by J. Jacquinot, G. Van Oost, and R.R. Weynants (European Physical Society, Petit-Lancy, 1998), Vol. 22A, pp. 237--240], it has been shown that, in overdense plasmas of the type encountered in spherical tori, electron Bernstein waves can be excited in a plasma by mode conversion of either an externally launched X mode or an O mode. The electron Bernstein waves are strongly absorbed by electrons in the region where the wave frequency matches the Doppler broadened electron cyclotron resonance frequency or its harmonics. The strong absorption also implies that electron Bernstein waves are emitted by a thermal plasma. These waves can then mode convert to the X mode and to the O mode and be observed external to the plasma. In this paper an approximate kinetic model describing the coupling between the X mode, the O mode, and the electron Bernstein waves is derived. This model is used to study the mode conversion properties of electron Bernstein wave emission from the plasma interior. It is shown, analytically and numerically, that the energy flow conversion efficiencies of the electron Bernstein wave to the X mode and to the O mode are the same as the energy flow conversion efficiency of the X mode to electron Bernstein waves and of the O mode to the electron Bernstein waves, respectively. This has important experimental consequences when designing experiments to heat overdense plasmas by electron Bernstein waves.
Author: Abhay Ram Publisher: ISBN: Category : Languages : en Pages : 8
Book Description
In the electron cyclotron range of frequencies (ECRF), electron Bernstein waves (EBW) offer an attractive means for driving plasma currents in spherical tori (ST) such as NSTX. Previously it has been shown that, for ECRF waves, relativistic effects significantly modify the propagation and damping of the extraordinary and ordinary modes. A fully relativistic dispersion code R2D2 has been developed for studying the relativistic characteristics of all ECRF waves. In this paper we report on initial results obtained from this code which illustrate the relativistic modifications to the propagation and damping of EBWs. We find that even at temperatures relevant to present spherical tori, the relativistic dispersion properties of EBWs are significantly different from their non-relativistic counterpart.
Author: Gerardo Giruzzi Publisher: World Scientific ISBN: 9812381899 Category : Science Languages : en Pages : 613
Book Description
This workshop was concerned with the interaction of electromagnetic waves and hot plasmas, a subject of great importance in the framework of research on controlled thermonuclear fusion.
Author: Abhay Ram Publisher: ISBN: Category : Languages : en Pages : 10
Book Description
The high-beta magnetically confined plasmas in spherical tori (ST), like NSTX and MAST, provide a unique opportunity for a wide variety of applications of electron Bernstein waves (EBW). These applications range from heating of the ST plasma to modifying and controlling its current profile. Using the fully relativistic dielectric tensor for a Maxwellian distribution function, this paper presents initial results illustrating the effect of relativity on the dispersion characteristics of EBWs. It is found that, even at temperatures relevant to present STs, the relativistic dispersion properties of EBWs are significantly different from their non-relativistic counterpart.
Author: Abhay Ram
Author: Abhay Ram
Author: Abhay Ram
Author: Abhay Ram
Author: Abhay Ram
Author: Joan Decker
Author: Abhay Ram
Author: Abhay Ram
Author: Abhay Ram
Author: Gerardo Giruzzi
Author: Abhay Ram