<p>We analyzed properties of waves excited by mildly relativistic electron beams propagating along magnetic field with a ring-shape perpendicular momentum distribution in neutral and current-free solar coronal plasmas. These plasmas are subject to both the beam and the electron cyclotron maser (ECM) instabilities driven by the positive momentum gradient of the ring-beam electron distribution in the directions parallel and perpendicular to the ambient magnetic field, respectively. To explore the related kinetic processes self-consistently, 2.5-dimensional fully kinetic particle-in-cell (PIC) simulations were carried out.</p><p>To quantify excited wave properties in different coronal conditions, we investigated the dependence of their energy and polarization on the ring-beam electron density and magnetic field. In general, electrostatic waves dominate the energetics of waves and nonlinear waves are ubiquitous. In weakly magnetized plasmas, where the electron cyclotron frequency <em>&#969;<sub>ce</sub></em> is lower than the electron plasma frequency <em>&#969;<sub>pe</sub></em>, it is difficult to produce escaping electromagnetic waves with frequency <em>&#969;&#160;> &#969;<sub>pe </sub></em>and small refractive index <em>ck</em>/<em>&#969;</em>&#160;<em>< 1</em> (<em>k</em> and <em>c</em> are the wavenumber and the light speed, respectively). Highly polarized and anisotropic escaping electromagnetic waves can, however, be effectively excited in strongly magnetized plasmas with <em>&#969;<sub>ce</sub>/&#969;<sub>pe </sub>&#8805;&#160;1</em>. The anisotropy of the energy, circular polarization degree (CPD), and spectrogram of these escaping electromagnetic waves strongly depend on the number density ratio of the ring-beam electrons to the background electrons. In particular, their CPDs can vary from left-handed to right-handed with the decrease of the ring-beam density, which may explain some observed properties of solar radio bursts (e.g., radio spikes) from the solar corona.</p>
Oblique propagation of solitary electrostatic waves in magnetized plasmas with cold ions and nonthermal electrons