OEDIPUS-C observations of electrons accelerated by radio frequency fields at whistler-mode frequencies

Simultaneous measurements of transmitted 500 kHz electric fields and of ele ctron fluxes nonlinearly energized by those fields were made during the ion ospheric flight of the rocket double payload OEDIPUS C. Given the local pla sma parameters, 500 kHz corresponded to the whistler mode of cold-plasma pr opagation. As the separation between each payload end increased from 153 to 537 m, enhanced electron fluxes were detected at energies up to 20 keV, at the receiver end of the tether. Rf (radio frequency) electric fields creat ed by the OEDIPUS-C transmitter have been computed for positions close to t he whistler-mode group resonance cone and also for locations very close to the active dipoles. Test-particle trajectory tracings show that linear acce leration can account for the energy increases of electrons with starting en ergies up to about 100 eV. Neither resonant field-particle interactions of background energetic electrons nor strong turbulence of the background ther mal particles explain the creation of sounder-accelerated electrons at 1-10 keV. The calculated magnitudes of the very near potentials, up to 550 V, p oint to acceleration by intense fields in the rf sheath region. (C) 1999 Am erican Institute of Physics. [S1070-664X(99)00410-3].