ESS 200C – Space Plasma PhysicsSpace Plasma PhysicsAurora over Los Angeles (courtesy V. Peroomian)The Plasma StateThe Motion of Charged ParticlesESS 200C - Space Plasma PhysicsWinter Quarter 2006-2007Raymond J. WalkerDate Topic1/8 Organization and Introduction to Space Physics I1/10 Introduction to Space Physics II1/17 Introduction to Space Physics III1/19 The Sun I1/22 The Sun II1/24 The Solar Wind I1/29 The Solar Wind II1/31 First Exam 2/5 Bow Shock and Magnetosheath2/7 The Magnetosphere IDate Topic2/14 The Magnetosphere II2/16 The Magnetosphere III2/21 Planetary Magnetospheres2/23 The Earth’s Ionosphere2/26 Substorms3/5 Aurorae3/7 Planetary Ionospheres3/12 Pulsations3./14 Storms and ReviewSecond ExamSchedule of ClassesESS 200C – Space Plasma Physics• There will be two examinations and homework assignments.• The grade will be based on– 35% Exam 1– 35% Exam 2– 30% Homework• References– Kivelson M. G. and C. T. Russell, Introduction to Space Physics, Cambridge University Press, 1995.– Gombosi, T. I., Physics of the Space Environment, Cambridge University Press, 1998– Kellenrode, M-B, Space Physics, An Introduction to Plasmas and Particles in the Heliosphere and Magnetospheres, Springer, 2000.– Walker, A. D. M., Magnetohydrodynamic Waves in Space, Institute of Physics Publishing, 2005.Space Plasma Physics• Space physics is concerned with the interaction of charged particles with electric and magnetic fields in space.• Space physics involves the interaction between the Sun, the solar wind, the magnetosphere and the ionosphere.• Space physics started with observations of the aurorae.– Old Testament references to auroras.– Greek literature speaks of “moving accumulations of burning clouds”– Chinese literature has references to auroras prior to 2000BC• Aurora over Los Angeles (courtesy V. Peroomian)– Galileo theorized that aurora is caused by air rising out of the Earth’s shadow to where it could be illuminated by sunlight. (Note he also coined the name aurora borealis meaning “northern dawn”.)– Descartes thought they are reflections from ice crystals.– Halley suggested that auroral phenomena are ordered by the Earth’s magnetic field. – In 1731 the French philosopher de Mairan suggested they are connected to the solar atmosphere.• By the 11th century the Chinese had learned that a magnetic needle points north-south.• By the 12th century the European records mention the compass.• That there was a difference between magnetic north and the direction of the compass needle (declination) was known by the 16th century.• William Gilbert (1600) realized that the field was dipolar.• In 1698 Edmund Halley organized the first scientific expedition to map the field in the Atlantic Ocean.The Plasma State• A plasma is an electrically neutral ionized gas.– The Sun is a plasma– The space between the Sun and the Earth is “filled” with a plasma.– The Earth is surrounded by a plasma.– A stroke of lightning forms a plasma– Over 99% of the Universe is a plasma.• Although neutral a plasma is composed of charged particles- electric and magnetic forces are critical for understanding plasmas.The Motion of Charged Particles• Equation of motion• SI Units– mass (m) - kg– length (l) - m– time (t) - s– electric field (E) - V/m– magnetic field (B) - T– velocity (v) - m/s–Fgstands for non-electromagnetic forces (e.g. gravity) -usually ignorable.gFBvqEqdtvdmrrrrr+×+=• B acts to change the motion of a charged particle only in directions perpendicular to the motion.– Set E = 0, assume B along z-direction.– Equations of circular motion with angular frequency (cyclotron frequency or gyro frequency– If q is positive particle gyrates in left handed sense– If q is negative particle gyrates in a right handed sense222222mBvqvmBvqmBvqvBqvvmBqvvmyyxyxxyyx−=−==−==&&&&&&&mqBc=Ω• Radius of circle ( rc) - cyclotron radius or Larmorradius or gyro radius.– The gyro radius is a function of energy.– Energy of charged particles is usually given in electron volts (eV)– Energy that a particle with the charge of an electron gets in falling through a potential drop of 1 Volt- 1 eV = 1.6X10-19Joules (J).• Energies in space plasmas go from electron Volts to kiloelectron Volts (1 keV = 103 eV) to millions of electron Volts (1 meV = 106eV)• Cosmic ray energies go to gigaelectron Volts ( 1 geV = 109 eV).• The circular motion does no work on a particleqBmvvccc⊥⊥=Ω=ρρ0)()(221=×⋅==⋅=⋅ BvvqdtmvdvdtvdmvFrrrrrrrOnly the electric field can energize particles!• The electric field can modify the particles motion.– Assume but still uniform and Fg=0.– Frequently in space physics it is ok to set• Only can accelerate particles along• Positive particles go along and negative particles go along • Eventually charge separation wipes out– has a major effect on motion. • As a particle gyrates it moves along and gains energy • Later in the circle it losses energy.• This causes different parts of the “circle” to have different radii -it doesn’t close on itself.• Drift velocity is perpendicular to and• No charge dependence, therefore no currents 0≠Er0=⋅ BErrErBrEE−E⊥EEr2BBEuErrr×=ErBrBr• Any force capable of accelerating and decelerating charged particles can cause them to drift.– If the force is charge independent the drift motion will depend on the sign of the charge and can form perpendicular currents.• Changing magnetic fields cause a drift velocity.– If changes over a gyro-orbit the radius of curvature will change.– gets smaller when the particle goes into a region of stronger B. Thus the drift is opposite to that of motion.–ugdepends on the charge so it can yield perpendicular currents.2qBBFuFrrr×=BrqBmvc⊥=ρBErr×32213221qBBBmvqBBBmvug∇×=×∇=⊥⊥−rrr• The change in the direction of the magnetic field along a field line can cause motion.– The curvature of the magnetic field line introduces a drift motion.• As particles move along the field they undergo centrifugal acceleration. •Rcis the radius of curvature of a field line ( ) where , is