Enhancing whistler wave‐Electron interaction by the use of specially modulated VLF wave injection

Abstract

It is shown that interactions between artificially injected whistler mode waves and electrons can be strongly enhanced if the frequency and amplitude of the injected signal are appropriately programmed. The frequency variation produces efficient and steady changes in the particles energy and pitch angle through an extension of the cyclotron‐resonance interval. The amplitude modulation might prove necessary in certain interactions to avoid instability of the phase trapping mechanism. Sixteen interactions evolving in a duct centered at a geomagnetic field line with L=4 are studied by following the (test particle) evolution of the equatorial pitch angle and energy, and obtaining the required (ground) transmitter spectrogram format. Transmission using the proposed modulation with sufficient accuracy to match the real magnetosphere appears feasible and could be attempted in the near future.

Controlled precipitation of radiation belt electrons

“…On the basis of Figures 2a and 2b, and for a wave propagating away from the equator, it would be desirable to have the wave frequency increase with time, so that it can stay in resonance with 500 keV electrons as it propagates to regions of lower resonance frequency. Chirped modulations have been previously discussed and were successfully employed in ground‐based VLF wave‐injection experiments [ Brinca , 1981; Helliwell et al , 1990], leading to enhanced rapid wave‐growth and emission triggering. On the other hand, such coherent modulation schemes may scatter some particles more at the expense of others which are scattered less.…”

“…In the largely collisionless magnetospheric medium, the primary means of attenuation of such highly oblique whistler mode waves is Landau damping due to suprathermal electrons. To quantitatively determine the extent to which the waves are Landau damped, we use the formulation of Brinca [1981], involving the determination of the imaginary part of the refractive index due to a specified distribution of suprathermal electrons. We use an electron distribution of f ( v ) = 2 × 10 5 v −4 cm −6 ‐s 3 as an approximate fit to recent measurements [ Bell et al , 2002] of 100 eV to 1 keV electrons with the HYDRA instrument on the Polar spacecraft [ Scudder et al , 1995].…”

Whistler mode illumination of the plasmaspheric resonant cavity via in situ injection of ELF/VLF waves

“…To this end, we introduce the concept of the magnetospheric cavity enhancement factor (see below) to quantify the combined effects of magnetospheric reflections and Landau damping along the ray path. Landau damping, the primary damping mechanism for obliquely propagating whistler waves in the collisionless magnetospheric medium, is calculated using the formulation of Brinca [1981] and an electron distribution of f ( v ) = 2 × 10 5 v −4 cm −6 −s 3 as an approximate fit to recent energetic electron measurements [ Bell et al , 2002]. Figures 1a and 1b show two sample ray paths, as calculated using the Stanford VLF ray tracing code [ Inan and Bell , 1977], and the associated Landau damping for each path.…”

Variable frequency VLF signals in the magnetosphere: Associated phenomena and plasma diagnostics

“…These results suggest that transmitted ramp slope can be varied with frequency to give particular relationships among frequency, phase equator location, and phase equator motion, for given resonant electrons. The use of variable sloped transmissions to control the interaction in a predetermined manner was proposed by Brinca [1981] for cases in which the electron becomes trapped by the wave field.…”