Shocks!David BurgessAstronomy Unit

Queen 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:

All the important physics is kinetic

Particle reflection Instabilities Particle acceleration

Without collisions …

• Converting flow to thermal energy

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 …

Solar shocks continued …

CME

More solar shocks?

Dynamic Fibrils - Simulations