The investigators will study the effects of Coulomb collisions on incoherent scatter radar spectra detected from the topside ionosphere where ionized hydrogen and helium are the dominant ion species. The study will focus on very high frequency radar observations conducted at the Jicamarca Radio Observatory using antenna beams pointed perpendicular to Earth's magnetic field. Measurements of plasma temperatures using the Jicamarca incoherent scatter radar with antenna beams pointed perpendicular to the magnetic field have been elusive to radar practitioners for many years. This study will make use of recent progress in modeling the effects of Coulomb collisions. If successful, the results will lead to the development of a multi-component collisional incoherent scatter spectrum model needed for enhanced observations of the upper ionosphere at Jicamarca. The development of the model will be based on the simulation of charged particle trajectories embedded in a collisional magnetized plasma. The model will be first tested and validated with the standard topside experiments at Jicamarca that utilize antenna beams pointed off perpendicular from the magnetic field. After the results are validated for these pointing directions, experiments will be performed with the antenna pointed perpendicular to the magnetic field. The goal is to measure plasma drifts, densities, and temperatures in the topside ionosphere at this viewing angle. This will greatly enhance the measurement capabilities at Jicamarca. The model and fitting procedure will be made available to other users of the Jicamarca radar. The study will be conducted by a post-doctoral researcher, who plans to return to the Jicamarca Radio Observatory and continue his career as a member of the observatory staff.
The research goal of this award was to carry out theoretical and experimental studies of the effects of Coulomb collisions on incoherent scatter spectrum measurements of the topside ionosphere where the dominant ion species are H+ and He+. The study was mainly focused to radar observations conducted at the Jicamarca Radio Observatory using antenna beams pointed perpendicular to the Earth’s magnetic field. This investigation led to the development of a multi-component collisional incoherent scatter spectrum model as needed for topside perpendicular-to-B applications at Jicamarca. The development of this spectrum model was based on the simulation of charged particle trajectories embedded in collisional magnetized plasmas. In addition, this study also led the development of a multi-beam incoherent scatter radar technique that allows the simultaneous measurement of plasma drifts, densities and temperatures of the equatorial ionosphere, an objective not previously achieved by the standard radar techniques applied at Jicamarca. Activities For the proposed research some theoretical and experimental activities were conducted during the two-year post-doc period. These activities are summarized next. CUDA-based simulation of charged particle trajectories in O+, H+ and He+ plasmas based on the Langevin equation and Fokker-Planck collision model. Statistical analysis of the simulated trajectories. Time evolution of velocity and displacement distributions was analyzed in order to characterize the collision process. Revision of the numerical library of the particle trajectory statistics (single-particle ACF’s and Gordeyev integrals) needed for the computation of the collisional incoherent scatter spectrum. Comparison of the resultant collisional spectrum model with standard incoherent scatter theories. Development and test of a multi-beam incoherent scatter radar technique that interleaves perpendicular and off-perpendicular radar observations in order to maximize the number of ionospheric parameters that can be estimated simultaneously. Test of the proton gyro-resonance experiment at Jicamarca using different antenna configurations in order to improve radar signal quality. Processing of radar data and inversion of ionospheric parameters. Results The simulation studies that were conducted led to the following important conclusions. Coulomb collision effects (as modeled by the Fokker-Planck equation with Spitzer coefficients) on the ion motion can be approximated as a Brownian motion (Gaussian) process for H+, He+, and O+ (ionospheric) plasmas. In the case of the electrons, Brownian motion does not capture all the details of the electron ACFs because the electron displacement distributions are not Gaussian. The approximation is not appropriate in this case. Electron displacement statistics are independent of the plasma configuration, therefore, electron ACFs are the same for H+, He+, and O+ plasmas. Based on these results, we extended the collisional incoherent scatter spectrum model that was developed by Milla and Kudeki [2011] to the case of multiple-ion component plasmas. However, the parameterization of this model is still a pending task.
