Coupling to Electron Bernstein Waves in Tokamaks PDF Download
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Author: Abraham Bers
Publisher:
ISBN:
Category :
Languages : en
Pages : 7
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Author: Abraham Bers
Publisher:
ISBN:
Category :
Languages : en
Pages : 7
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Book Description
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
High-? spherical tokamak (ST) plasma conditions cut off propagation of electron cyclotron (EC) waves used for heating and current drive in conventional aspect ratio tokamaks. The electron Bernstein wave (EBW) has no density cutoff and is strongly absorbed and emitted at the EC harmonics, allowing EBWs to be used for heating and current drive in STs. However, this application requires efficient EBW coupling in the high-?, H-mode ST plasma regime. EBW emission (EBE) diagnostics and modelling have been employed on the National Spherical Torus Experiment (NSTX) to study oblique EBW to O-mode (B-X-O) coupling and propagation in H-mode plasmas. Efficient EBW coupling was measured before the L-H transition, but rapidly decayed thereafter. EBE simulations show that EBW collisional damping prior to mode conversion (MC) in the plasma scrape off reduces the coupling efficiency during the H-mode phase when the electron temperature is less than 30 eV inside the MC layer. Lithium evaporation during H-mode plasmas was successfully used to reduce this EBW collisional damping by reducing the electron density and increase the electron temperature in the plasma scrape off. Lithium conditioning increased the measured B-X-O coupling efficiency from less than 10% to 60%, consistent with EBE simulations.
Author: Abhay Ram
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Category :
Languages : en
Pages : 8
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The high beta operating regime of spherical tokamaks (ST), such as in NSTX and MAST, make them attractive fusion devices. To attain the high beta's there is a need to heat and to drive currents in ST plasmas. While ST plasmas are overdense to conventional electron cyclotron (EC) waves, electron Bernstein waves (EBW) offer an attractive possibility both for heating and for driving plasma currents. EBWs, which have no density limits, can propagate into the plasma core for frequencies above the electron cyclotron frequency fce [A.K. Ram and S.D. Schultz, Phys. Plasmas, 7, 4084 (2000)]. Since EBWs are not vacuum modes, they are excited inside the plasma by mode conversion of the traditional X and O modes. From ray tracing analysis we find that EBWs are strongly absorbed by electrons in the region where the wave frequency matches the Doppler broadened electron cyclotron resonance frequency or its harmonics [A.K. Ram and S.D. Schultz, Phys. Plasmas, 7, 4084 (2000)]. The strong and localized absorption implies that thermal emission of EBWs can occur for frequencies corresponding to the local Doppler-shifted electron cyclotron frequency. This emission then converts, at the UHR, to the X and O modes which are then observed in the vacuum region.
Author: Abhay Ram
Publisher:
ISBN:
Category :
Languages : en
Pages : 12
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Category : Ion acoustic waves
Languages : en
Pages : 34
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Author: Paul Bonoli
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Category :
Languages : en
Pages : 42
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Author: Mirela Cengher
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Category :
Languages : en
Pages : 192
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Author: Abhay Ram
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Category :
Languages : en
Pages : 4
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Author: N. J. Fisch
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Category : Alpha rays
Languages : en
Pages : 12
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Author: Yuichi Takase
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ISBN:
Category :
Languages : en
Pages : 16
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