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The formation condition of the virtual cathode (VC) formed by a self-focusing relativistic electron beam in plasma is studied theoretically and numerically. Together with the threshold function of the VC formation and the self-focusing condition, the parametric regions of forming the VC are found. Then the theoretical result is verified by the particle-in-cell (PIC) simulation, which further shows the phase-space characteristics of the VC formation. This study not only provides a theoretical basis for creating VC with a self-focusing relativistic electron beam in plasma but also helps in parameter selections for the related beam-plasma experiments and simulations. [ABSTRACT FROM AUTHOR]

An experimental study on electromagnetic (EM) radiation in an electron beam‐ion channel system is reported, which indicates the same result predicted by our previous theory. The system is formed in an arc plasma jet with a plasma density of 1017m−3, and the electron beam is driven by a voltage pulse of 20 kV. The result shows that the system can excite EM radiation in the range of the plasma frequency. The scheme is also hopeful to be used for generating high‐frequency and wide‐band EM radiation up to terahertz by enhancing the plasma density. [ABSTRACT FROM AUTHOR]