Lect15Plasmas

Lect15Plasmas - ECE 3030 Electromagnetic Fields and Waves...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
1 ECE 3030 Electromagnetic Fields and Waves Fall 2009 Lecture 15 2009/10/1 Waves in Dispersive Media Wave Propagation in Plasmas Phase and Group Velocities 1 Swartz and Rana 06/5/25 Electromagnetic Fields and Waves – Fall 2009 Lecture 15: Instructor: Dr. Wesley E. Swartz z E ( z,t ) Plasmas What is a plasma? A plasma is an assembly of positive and negative charged particles with a net zero time-average charge density. Examples of Plasmas: Gases in which the electrons have been stripped off the atoms – resulting in a mixture of positive ions and electrons. Examples: 3 Swartz and Rana 06/5/25 Electromagnetic Fields and Waves – Fall 2009 Lecture 15: Examples: Surface of the Sun Hydrogen ions and electrons in a fusion reactor Earth’s Ionosphere Atoms and electrons making up solids (semiconductors, metals, etc) can also be described as a plasma - although in this case the positive charges are fixed. Plasmas In plasmas, electrons are not attached to any one particular positive ion (or atom) but move about freely. On average (spatial and temporal average), plasmas are charge neutral (i.e. electrons tend to spend more time in the vicinity of the positive ions (or atoms) than away from them – hence the pictures shown. positive ions negative electron cloud 4 Swartz and Rana 06/5/25 Electromagnetic Fields and Waves – Fall 2009 Lecture 15: A solid state plasma A gaseous plasma Waves in Plasmas – Electron Dynamics What happens when a plasma is subjected to a time-dependent E-field (like that of a plane wave)? In most plasmas, the positive ions (or atoms) are much heavier than the negative electrons and one may ignore the motion of the ions in response to an E-field for simplicity () z k j o e E x r E = ˆ x E k 5 Swartz and Rana 06/5/25 Electromagnetic Fields and Waves – Fall 2009 Lecture 15: Let the displacement of the electrons at the location from their average position be given by the vector Newton’s second law gives: t r d , r t r E e t r F t t r d m , , , 2 2 = = z +ve ions -ve electron cloud H Waves in Plasmas – Material Polarization x z z k j o e E x r E = ˆ t r E e t t r d m , , 2 2 = E k H 6 Swartz and Rana 06/5/25 Electromagnetic Fields and Waves – Fall 2009 Lecture 15: Use phasors to solve the differential equation: To get: r E m e r d 2 ω = Dipole moment phasor r d e r p = = r E e r d m = 2 ( ) { } ( ) { } t j t j e r d t r d e r E t r E
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

Page1 / 3

Lect15Plasmas - ECE 3030 Electromagnetic Fields and Waves...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online