INTERACTION OF LANGMUIR WAVE-PACKETS WITH STREAMING ELECTRONS - PHASE-CORRELATION ASPECTS

An analytical model of the interaction between a localized wave packet and energetic electrons is presented. Electrostatic packets of tens t o a hundred wavelengths are considered in order to emulate the Langmui r waves observed in the auroral zone and in the solar wind. The phase information is retained, so the results can be applied to wave-particl e correlator measurements. The perturbed distribution function is expl icitly calculated and is shown-to be bounded over all phase space due to a broadening of resonance ascribable to the finite extent of the pa cket. Its resistive part (in phase or 180-degrees out of phase with th e electric field) maximizes for upsilon=omega/k, so that the associate d bunching of electrons enables assessment of the characteristic wavel ength. The changes in the wave profile due to the interaction with the energetic electrons are calculated. Broad wave packets grow or decay ''self-similarly'' with a rate given by the standard expression for a plane wave. Narrow, growing packets, on the other hand, quickly widen to sizes determined by the local distribution function. This sets a lo wer bound to the sizes of observed packets. Present results are suppor ted by test-particle simulations and are in accord with recent correla tor data of intense, localized Langmuir waves in the auroral zone.