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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, similar to 20 degrees-30 degrees 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 similar to 3 to 7 x 10(4) s(-1) are obtained for hectometric waves, leading to amplification by e(10) 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 10(4)km above the ionosphere may form the observed conics. A possible source of turbulence could be inertial Alfven waves, suggesting a connection between the auroral acceleration and generation of coherent radio emissions.

Plain Language Summary Jupiter, as many astrophysical magnetized objects, is a powerful emitter of nonthermal radio emissions. The coherent process required for their generation is likely the cyclotron maser instability (CMI). However, the exact conditions of wave amplification are not known precisely at Jupiter. With Juno mission, for the first time, it is possible to explore the auroral regions of Jupiter, where the particles are accelerated and the nonthermal emissions produced. With several crossing of the radio sources, the free energy used by the CMI can now be identified. It corresponds to conic-like distributions, characterized by an accumulation of particles just outside the loss cones. Applying the CMI theory, large growth rates are obtained, showing that the conics probably play a central role in the wave generation source. The formation of the conics could be due to an interaction with a low-frequency Alfvenic turbulence. This suggests a close relationship between the radio wave generation and the particle acceleration, as at Earth, the details of the scenario being, nevertheless, slightly different.