Study of cosmic radio bursts in lab-scale plasmas

Coherent and incoherent cosmic radio bursts are abundant both in our solar system and in deep space. The solar radio bursts (SRB) from our Sun are relatively well understood. A commonly-favored explanation of the SRB is that the electromagnetic radio waves are emitted from the Langmuir waves, which are driven by energetic electron beams via bump-on-tail instability. Though this scenario has been widely verified, the conversion efficiency of the Langmuir-radio waves remains still controversial. Another interesting radio emission is the fast-radio-burst (FRB), which is believed to be originating with extremely high fluence from a point-like (i.e. in the astrophysical scale) source located outside the Milky way. However, the exact mechanism of FRB is obscure. In this talk, I present a theory and simulations of a recently-conceived, novel model for the coherent radio emission from plasmas. Our model is based on the concept of the plasma dipole oscillation (PDO), which is a stand-alone, localized plasma oscillation embedded in a plasma. It can be potentially a source of a strong cosmic radio bursts at fundamental and high harmonics of the plasma oscillation with high efficiency and diversely different polarization properties. We discovered a new solution of the fluid plasma equations, which theoretically proves that the PDO can really exist. The generation of the PDO and radio-bursts in laboratory-scale plasmas using colliding laser pulses has been demonstrated by 2D and 3D particle-in-cell simulations1, 2. Study of generating the similar PDO by colliding electron beams is under progress, to make the system reproduce the emission from space plasmas in the laboratory scale. Plans for experiments of the PDO emission is briefed.