April 15-17

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Abstracts

Author: Abhay K. Ram
Requested Type: Poster
Submitted: 2019-02-22 12:08:37

Co-authors: K. Hizanidis, R.J. Temkin

Contact Info:
M.I.T.
NW16-260, 77 Massachusetts Ave
Cambridge, MA   02139
US

Abstract Text:
The nonlinear interaction of electrons with a high intensity, spatially localized Gaussian beam in the electron cyclotron (EC) range of frequencies is described by the relativistic Lorentz equation. The electromagnetic Gaussian beam is analytically formulated to be a superposition of plane waves at a fixed EC frequency. The wave vector and polarization of each plane wave satisfies the local dispersion characteristics for a cold magnetized plasma. The beam is spatially localized perpendicular to its direction of propagation. The interaction of electrons with a beam is significantly different from that with a large amplitude plane wave. There are two distinct set of electrons that result from wave-particle interactions. One set is reflected by the ponderomotive force due to the spatial variation of the beam, while the other set traverses the entire width of the beam. Both sets of electrons can be trapped in the plane waves that constitute the beam, and readily exchange energy and momentum with the beam. The wave-particle interactions cannot be described by the usual quasilinear theory which ignores nonlinear modifications to the orbits of electrons. We find that the interaction of the electrons with the Gaussian beam depends on the polarization of the beam – whether it is made up of ordinary waves or extraordinary waves – and by its direction of propagation relative to the ambient magnetic field. The energy and momentum gained by the electrons is influenced by the location of the interaction region with respect to the position of the electron cyclotron resonance. Our studies lend credence to claims made in the early 1990s that high powered, pulsed microwaves will lead to efficient heating and steady-state current drive in fusion plasmas through nonlinear wave-particle interactions [1].

[1] E.B. Hooper et al., “MTX Final Report,” [https://www.osti.gov/scitech/servlets/purl/10194124] (1994).

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