Spontaneous chirping whistler excitation in RT-1


Seminar by Haruhiko Saitoh, Tokyo University



Meeting-ID: 669 3495 4307
Kenncode: 306031
Schnelleinwahl mobil
+496938079884,,66934954307#,,,,*306031# Deutschland
+496950500951,,66934954307#,,,,*306031# Deutschland




Interaction between waves and charged particles plays essential roles in geospace and space weather activities. Whistler mode chorus emissions, characterized by non-linear growth and frequency chirping, are common in planetary magnetospheres. They are regarded as the origin of relativistic acceleration of particles in the radiation belts and pulsating aurora caused by the pitch angle diffusion and subsequent precipitation of electrons into the atmosphere. Intensive investigations so far by means of theory, numerical simulation, and spacecraft observations revealed several interesting features of chorus emissions. However, there has been a sustained desire to conduct experiments on this topic in laboratory in a more controlled environment with good reproducibility and high-resolution diagnostics. Here we present the first spontaneous excitation of chirping whistler waves in an ”artificial magnetosphere”, a levitated dipole experiment. Magnetic levitation of the superconducting dipole field magnet minimizes the particle loss along field lines and mimics the geospace environment in a laboratory. In hot-electron high-β (β is plasma pressure normalized by magnetic pressure) plasma with temperature anisotropy, generated by electron cyclotron resonance heating with microwaves, we measure abrupt emergence of falling- and rising- tone whistler waves. The observed fluctuations consist of electromagnetic and electro- static modes, both of which show strong correlation with plasma pressure. Series of experiments show that the generation and nonlinear growth of coherent chorus emissions are a ubiquitous phenomenon in dipole magnetic configuration, and are dominated by common physics in space and laboratories. Because geospace activities critically affect the advanced technologies of modern society as well as climate change, it is urgently needed to establish reliable space weather modeling based on accurate understanding of wave particle interactions in space. We anticipate that laboratory realization of chorus-like whistler waves in magnetospheric geometry will accelerate the synergistic investigation of space weather system.