Spontaneous emission of magnetic field fluctuations in Solar wind-like suprathermal plasmas

Heavy ions in solar wind have been observed to flow faster than protons, with temperatures exceeding the mass proportionality respect to protons. The identification and explanation of the physical processes responsible for ion heating may provide the key to explain why the temperature of the outer solar atmosphere and expanding corona forming the solar wind is several orders of magnitude higher than that of the photosphere. Possible explanations of the preferential acceleration and heating of ions often involve linear kinetic theory, which allows for a wide number of heavily damped waves (or higher-order modes), which could play a secondary role in the energization of solar wind plasmas. Also, linear theory predicts instability thresholds in the temperature distribution of protons which are consistent with data from the Solar Wind Experiment (SWE). However, it has also been observed that proton velocity distributions appear to be strongly anisotropic, displaying a pronounced non-Maxwellian profile of particles exceeding thermal energies. These velocity distributions are often modeled with a family of specific functional describing both the low-energy Maxwellian core and the high-energy power-law tails, popularly known in the literature as kappa-distributions. Furthermore, short wavelength magnetic fluctuations with small amplitude are present even in the absence of plasma instabilities. These spontaneous fluctuations are intimately linked to the linear response of perturbations via the fluctuation-dissipation theorem. The various collective modes of fluctuations are constrained by the structure of the higher-order modes determined by the electromagnetic kinetic dispersion relation. In this work, we examine the propagation and excitation of parallel Alfvén-cyclotron waves in a suprathermal proton solar wind-like plasma, as described by a kappa-like distribution function, by taking care of the often ignored higher-order modes which modify the structure of the spontaneous emitted electromagnetic fluctuations. Also, we study the emitted magnetic energy for several values of the proton temperature near the instability threshold predicted from linear theory.