Haihong Che (NASA Goddard Space Flight Center)

Wednesday, May 21, 2014 - 1:00pm to 2:30pm
Plasma Seminars

Plasma Seminar
Wednesday, May 21 @ 1PM

Location: BAPSF Auditorium (15-17 Rehab Building)***
Refreshments at 12:30

Guest Seaker: Haihong Che (NASA / Goddard Space Flight Center)

Talk Title: " The Origin of Kinetic Turbulence in the Solar Wind"


Wind and outflow phenomena are common in astrophysical environments, such as in stars, supernovae, neutron stars as well as in normal galaxies and AGNs. The Sun provides the best laboratory to study important physical process in wind, such as turbulent transport and heating. Solar wind is the neutral charged plasma that escaped from solar corona and travels in space with velocity at hundreds of kilometers per second. Solar wind not only carries momentum but also advects fluctuations from the corona. The magnetic fluctuations in solar wind caused by solar activity such as solar flares can influence the environment of the Earth through interactions between magnetosphere and solar wind. Observations of magnetic fluctuations in the solar wind show that the power spectra of low frequency magnetic fluctuations on large scale approximately follow the Kolmogorov scaling law. However, a power-law spectra break at a high frequency appears to correspond to ion inertial length, a kinetic scale where ions demagnetize and decouple from electrons. These observations disfavor the long-held belief that the magnetic fluctuations on small kinetic scales come from the energy cascade of large scale Alfvenic turbulence, which predicts the frequency breakpoint should occur on scales that correspond to ion gyro-radius. On kinetic scales, wave-particle interactions dominate and lead to particle acceleration and heating, MHD theory becomes insufficient and a full kinetic treatment is required. What physical processes drive kinetic turbulence has been a puzzle for decades. In this talk, I will introduce a new idea for the origin of kinetic turbulence —that the kinetic turbulence and electron heating of solar wind originate from the inner corona. The idea is based on observations of nanoflares and accelerated electron beams from hundreds of eV to hundreds of keV in the corona. With particle-in-cell simulations, we found that the relative drift between nano-flare accelerated electron beams and the background core electron population drives a strong two-stream instability. The nonlinear evolution of the two-stream instability produces electromagnetic Weibel-like instability and give rise to kinetic Alfvenic wave and whistler wave turbulence through wave-wave interactions and forward and inverse energy cascades. At the same time, strong electron heating and Langmuir waves are produced. This model not only naturally produces the power spectra of kinetic turbulence and the relevant observations, but also simultaneously produces the electron heating in the solar wind. The generation of Langmuir waves can produce type III micro-radio bursts that resemble the well-studied type III bursts observed in solar flares.