September 8, 2017, 1:00 pm - 2:00 pm

September 8, 1:00 pm - 2:00 pm

How Electron Beams Drive Cyclic Langmuir Collapse and Coherent Radio Emission

Haihong Che, University of Maryland, College Park

Electron beams accelerated by solar flares and nanoflares are believed to be responsible for several types of solar radio bursts observed in the corona and interplanetary medium, including flare-associated coronal Type U and J and interplanetary Type III radio bursts, and nanoflare-associated weak coronal type III bursts. The coherent radio emission is a powerful probe of the plasma environment of solar corona and the mechanism of acceleration and energetic particle propagation. The characteristic of the radio bursts is their drifting frequency being consistent with the local electron plasma frequency. However, how electron two-stream instability driven by electron beams produces coherent emission with a duration of several orders of magnitude longer than the linear saturation time is a long-standing puzzle. Recently Che, Goldstein,Diamond and Sagdeev [2017, doi: 10.1073/pnas.1614055114] show that continuous plasma coherent emission can be maintained by cyclic Langmuir collapse. I will present this new mechanism and discuss the new features that can be observed by space probes such as Wind, ACE and the near-future Parker Solar Probe. Also, electron beams are commonly discovered in the magnetosphere associated with magnetic reconnection and shock waves. The high spatial and time resolution field and particle data from the newly launched MMS provide possible in-situ observations to test the emission process near the acceleration source region.