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A beam of super-thermal, hot electrons was injected into maxwellian plasmawith a density gradient along a magnetic field line. 1.5D particle-in-cellsimulations were carried out which established that the EM emission is producedby the perpendicular component of the beam injection momentum. The beam has apositive slope in the distribution function in perpendicular momentum phasespace, which is the characteristic feature of a cyclotron maser. The cyclotronmaser in the overdense plasma generates emission at the electron cyclotronfrequency. The frequencies of generated waves were too low to propagate awayfrom the injection region, hence the wavelet transform shows a pulsating wavegeneration and decay process. The intensity pulsation frequency is twice therelativistic cyclotron frequency. Eventually, a stable wave packet formed andcould mode couple on the density gradient to reach frequencies of the order ofthe plasma frequency, that allowed for propagation. The emitted wave is likelyto be a z-mode wave. The total electromagnetic energy generated is of the orderof 0.1% of the initial beam kinetic energy. The proposed mechanism is ofrelevance to solar type III radio bursts, as well as other situations, when theinjected electron beam has a non-zero perpendicular momentum, e.g. magnetron.

Electron cyclotron maser emission mode coupling to the z-mode on a longitudinal density gradient in the context of solar type III bursts