Exploration of Collisionless Shocks in Solar Research
This presentation by David Burgess from Queen Mary University of London discusses the current research areas related to collisionless shocks within the solar context. It highlights the physics of shock formation, particle acceleration mechanisms, and the importance of parameters like shock normal angle and Mach number. Features include electron acceleration, turbulence, nonstationarity, and the implications for solar phenomena such as coronal mass ejections (CMEs) and solar flares. The focus is on stimulating further exploration in understanding solar atmospheric dynamics.
Exploration of Collisionless Shocks in Solar Research
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Presentation Transcript
Shocks! David BurgessAstronomy UnitQueen Mary, University of London
This presentation was given at: Workshop on Solar Kinetics and MHD, 25-27 Feb 2008, RAL Cosener's House, Abingdon, UK. This is not a comprehensive tutorial about collisionless shocks in the solar context. The aim is only to give an indication of some current areas of interest in shock research, and in particular to draw attention to some areas and questions that could be interesting to pursue further in the context of the solar atmosphere and corona.
Shocks: • Converting flow to thermal energy Without collisions … • All the important physics is kinetic • Particle reflection • Instabilities • Particle acceleration
What parameters are important? • Shock normal angle : quasi-parallel versus quasi-perpendicular • Mach Number • Plasma beta • Simulation method (hybrid, PIC, etc) • Mass ratio • Dimensionality
Some Topics … • Electron acceleration • Nonstationarity • Turbulence
Electron Acceleration at Qperp • Fast Fermi by mirror reflection • Highest energies (but lowest efficiency) at close to perpendicular
Effect of including structure • Test particle electrons in fields from 2D hybrid simulation • Structure: power law energy spectra up and downstream
Nonstationarity at Qperp Shocks • Hybrid: nonstationary at low enough • PIC: overturning via over-reflection of ions • Effect controlled by and mass ratio used in simulations …
Nonstationarity at Qperp Shocks • With realistic mass ratio foot dynamics controlled by electromagnetic two stream instability • With implications for (eg) shock surfing acceleration
Nonstationarity at Oblique Shocks • PIC simulations • Away from perpendicular, standing whistler can dominate structure • Nonstationarity via competition of different mechanisms
Kinetic Effects in Turbulence • Kinetics and the “dissipation” scale • What is the “energy cascade” at kinetic scales? • What happens with multiple kinetic scales? • Control of temperature and temperature anisotropy with linear instabilities
Shocks in the Corona Flares …
