Significance of Wave-Particle Interaction Analyzer for direct measurement of nonlinear wave-particle interactions

We study the statistical significance of the Wave Particle Interaction Analyzer (WPIA) for measurement of the energy transfer process between energetic electrons and whistler-mode chorus emissions in the Earth's inner magnetosphere. The WPIA measures a relative phase angle between the wave vector and velocity vector of each particle and computes an inner product W(t), while W(t) is equivalent to the variation of the kinetic energy of energetic electrons interacting with plasma waves. The WPIA measurements will be realized by the Software-type WPIA in the SPRINT-B/ERG satellite mission. In the present study, we evaluate the feasibility of WPIA by applying the WPIA analysis to the simulation results on whistler-mode chorus generation. We compute W(t) of a wave electric field observed at a fixed point assumed in the simulation system and a velocity vector of each energetic electron passing through the assumed point. By integrating W(t) in time, we obtain significant values of W_{int} in the kinetic energy and pitch angle ranges as expected from the evolution of chorus emissions in the simulation result. The statistical significance of the obtained W_{int} is evaluated by calculating the standard deviation σ_W of W_{int}. We show that W_{int} greater than σ_W is obtained in the velocity phase space corresponding to the wave generation and acceleration of relativistic electrons. We conduct another analysis of a distribution of energetic electrons in the wave phase space using the same dataset of the simulation results. We clarify that the deviation of the distribution in the wave phase space is found in the velocity phase space corresponding to the large W_{int} values, which is consistent with formation of nonlinear resonant currents assumed in the generation mechanism of chorus emissions. The present study suggests that the statistical significance of the WPIA can be evaluated by calculating σ_W of W_{int}, and reveals the feasibility of the WPIA, which will be on board the upcoming SPRINT-B/ERG satellite, for direct measurement of wave-particle interactions.