Abhay K. Ram

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The high-β 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 β regimes it is necessary to heat and to drive currents in ST plasmas. In the electron cyclotron range of frequencies such plasmas are overdense(More)
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(More)
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(More)
This paper studies the coherent acceleration of ions interacting with two electrostatic waves in a uniform magnetic field B 0. It generalizes an earlier analysis of waves propagating perpendicularly to B 0 to include the effect of wavenumbers along B 0. The Lie transformation technique is used to develop a perturbation theory describing the ion motion, and(More)
Coupled theoretical and computational work is presented aimed at understanding and modeling stimulated Raman backscattering (SRBS) relevant to laser-plasma interactions (LPIs) in large-scale, nearly homogeneous plasmas. We address the following five observed, nonlinear phenomena associated with SRBS: coupling of SRBS to Langmuir decay interactions (LDIs);(More)
The conventional ordinary O-mode and the extraordinary X-mode in the electron cyclotron range of frequencies are not suitable for core heating in high-β spherical tokamak plasmas, like the National as they are weakly damped at high harmonics of the electron cyclotron frequency. However, electron Bernstein waves (EBW) can be effective for heating and driving(More)