DYNAMICS OF PONDEROMOTIVE SELF-FOCUSING IN PLASMAS

The space‐time evolution of nonlinear self‐focusing of a coherent electromagnetic beam in a plasma is calculated. Parameters are considered for which the dominant nonlinearity is the ponderomotive force and the plasma response is hydrostatic. A simple nonlinear wave equation with a saturable, exponential nonlinearity is presented and solved in the paraxial limit. Nondimensional scaled variables are introduced, and both steady‐state and time‐dependent numerical solutions of the scaled equation are calculated in the limit of cylindrical symmetry. Self‐focusing can be important both for high‐power lasers in inertial‐confinement‐fusion applications and for heating of magnetically confined plasmas with intense, pulsed free‐electron lasers.

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