Observation of Electron Conics by Juno: Implications for Radio Generation and Acceleration Processes

Using Juno plasma, electric and magnetic field observations (from JADE, Waves, and MAG instruments), we show that electron conic distributions are commonly observed in Jovian radio sources. The conics are characterized by maximum fluxes at oblique pitch angles, ~20°–30° from the B field, both in the upward and downward directions. They constitute an efficient source of free energy for the cyclotron maser instability. Growth rates of ~3 to 7 × 10⁴ s⁻¹ are obtained for hectometric waves, leading to amplification by e¹⁰ with propagation paths of 50–100 km. We show that stochastic acceleration due to interactions with a low-frequency electric field turbulence located a few 10⁴ km above the ionosphere may form the observed conics. A possible source of turbulence could be inertial Alfvén waves, suggesting a connection between the auroral acceleration and generation of coherent radio emissions.