Transmission Characteristics Of Radio Pulse In Different Physical Systems

We studied transmission of radio pulses in three different physical systems,including dispersive transmission of trans-ionospheric pulse pairs from lightning in the ionosphere,discharge of high-power radio pulses in the atmosphere,and transmission of extremely relativistic-intensity radio pulses of fast radio burst astronomical events in the environments of neutron stars.In the first part,we develop a new analytical method to calculate the linear propagation of ultrashort radio pulses in the ionosphere.Dispersive transmission of transionospheric pulse pairs(TIPPs)in the ionosphere is calculated by this method.TIPP is a satellites-recorded radio signal in thunderstorms,consists of two pulses,and exhibits obvious ionospheric-dispersion characteristics.Its generation mechanism is still unclear.According to the radiation waveform near the ground surface predicted in the latest TIPP theoretical model,we calculated its dispersion transmission in the ionosphere,obtained the signal profile at the satellite altitude,and reproduced the satellites-recorded dispersed spectra by wavelet analyses.The obtained time-frequency chromatograms and pulse broadening are consistent with satellite observation.The method is applicable for long-distance transmission of ultrashort radio pulses at other bands in the ionosphere.In the second part,we added the Monte-Carlo Collision(MCC)module for the collision between electrons and air molecules to the one-dimensional particle in cell code JPIC1d,and developed the JPIC1d-MCC code that can be applied to simulate atmospheric discharges.The MCC module contains 46 collision processes between electrons and air molecules such as nitrogen,oxygen and argon,covering four types of collisions including elasticity,excitation,ionization and attachment.In tens of GHz microwave discharge simulation,the time step in the MCC module is much smaller than that of PIC.We have improved the MCC algorithm to allow a 5 times larger time step than the maximum one in the original algorithm,which greatly increases the computational efficiency.Using the JPICld-MCC program,we verified the dispersion relationship of microwaves in air collisional plasmas and simulated the pulse truncation phenomenon of high-power microwave pulses on gas boundaries.In the third part,we added Quantum Electrodynamics(QED)effects such as nonlinear inverse Compton scattering and Breit-Wheeler process to the JPICld program,and developed JPIC1d-QED program to simulate electron-positron pair generation and strong QED effects.Using the JPICld-QED program,we simulated the quantum cascade process during the collision of extremely relativistic GHz microwave pulses and gamma photons.This basic interaction can be used to determine the upper field strength limit of fast radio bursts(FRB)nearby their sources.FRB is a high-energy radio transient signal with an extragalactic origin,and its generation mechanism is still unclear.Simulations show that FRBs with a field strength higher than 3 × 1012 V/cm will not be able to escape from the high-energy ray environment in neutron stars.This critical value is consistent with the maximum source field strength estimated from FRB observation data.This research provides the physical explanation of the ceiling energy of FRB observation.