Physics 777 Plasma Physics and Magnetohydrodynamics MHD Instructor

Physics 777 Plasma Physics and Magnetohydrodynamics (MHD) Instructor: Gregory Fleishman Lecture 12. Particle Acceleration 18 November 2008

Plan of the Lecture • Elementary Concepts: DC Electric Fields and Adiabatic Motion • Fermi Acceleration • Stochastic Acceleration by Weak Turbulence • Acceleration by a Shock Wave • Acceleration by Strong Turbulence and Shock Ensemble • Other Examples of Particle Acceleration

Section 1. Elementary concepts of particle acceleration • How charged particles are being energized (accelerated)? • Role of magnetic and electric fields. • Adiabatic motion in a trap with moving walls. Regular acceleration/deceleration. • Stochastic acceleration due to random wall motion.

Section 2. Fermi Acceleration. Challenge: acceleration mechanism must ensure a power-law spectrum; frequently – over many orders of magnitude. Credit: Cronin et al (1997); Livio Scarsi (2008)

BUT: how magnetic clouds can accelerate particles?

Section 3. Stochastic Acceleration by Weak Turbulence.

Section 4. Acceleration by a Shock Wave.

RECALL

Shock front in SNR 1006

Section 5. Acceleration by Strong Turbulence and Shock Ensemble Superbubbles in SMC

Turbulent acceleration in solar flares Sample trajectory magnetic field lines • B 0 = 20 G, d. Bx ~ d. By ~ 20 G, d. Bz ~ 100 G • Outer scales lx=ly=1 km, lz=20 km Credit: L. Vlahos

Section 6. Other Examples of Particle Acceleration

Section 7. Homework • Complete written project report is due; no excuse.