Harmonic Maser Emissions from Electrons with Loss-cone Distribution in Solar Active Regions

Abstract Electron cyclotron maser emission (ECME) is regarded as a plausible source for coherent radio radiations from solar active regions (e.g., spikes). In this Letter, we present 2D3V fully kinetic electromagnetic particle-in-cell simulation to investigate the wave excitations and subsequent nonlinear processes induced by energetic electrons in loss-cone distribution. The ratio of plasma frequency electron gyrofrequency ω pe /Ω ce set 0.25, adequate region conditions. As main result, obtain strong emissions at second-harmonic X mode (X2). While fundamental (X1) Z are amplified directly via instability, X2 can be produced coalescence between two modes X1 modes. This represents novel generation mechanism harmonic plasmas with low value , which may resolve escaping difficulty explaining ECME mechanism.