Saturation of electron cyclotron maser by lower-hybrid waves

We perform a numerical study on the quasilinear relaxation of an electron cyclotron maser on the initially dominant mode. We focus thereby on a situation where the initially dominant modes are quasi-electrostatic lower hybrid (lh) waves, which have not been treated in preceding studies. To this end, we chose 0.2 ≤ ω_p/ω_Be < 0.5 (ω_p: plasma-, ω_Be: electron cyclotron frequency) and an initial losscone distribution of energetic electrons of the form f(p, μ) ∼ p^{-ξe-μ2/μ20} (p: momentum, μ: pitch angle cosine). Superimposed on this is a damping Maxwellian background. From our calculations, we find that multiple peaks in the lower-hybrid wave intensity can occur if the initial loss cone distribution is sufficiently broad. We also find that quasilinear relaxation with respect to lower-hybrid waves does not destroy the capability of the electron distribution to amplify transverse (XOZ) waves, which therefore become dominant at a later stage. The comparison with observations shows that the calculated shape of a single peak in the lower-hybrid energy density displays a remarkable similarity to solar radio spikes.