# hwk4 - energy in acoustic waves W a and plasma waves W...

This preview shows page 1. Sign up to view the full content.

Physics 762 Homework #4 Spring ‘11 Dr. Drake 1. Calculate the momentum carried by an electrostatic plasma wave from the general relation P = k ω k W, (1) where W is the wave energy. Take the cold plasma limit. Now calculate the momentum directly from the quasilinear equation for non-resonant electrons derived in class for plasma waves. For the nonresonant electrons show that there is an invariant that allows you to solve for the ﬁnal state of the distribution function for nonresonant particles. From this distribution function calculate the momentum gained by electrons as the wave energy increases from zero to its ﬁnal value. Show that the resulting momentum is the same as calculated from the general expression above. Therefore, explain how an electrostatic wave can carry momentum since it has no Poynting ﬂux. 2. Use the ﬂuctuation dissipation theorem derived in class to calculate the wave
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: energy in acoustic waves W a and plasma waves W plasma in the limit k/k De ± 1 with T e ² T i , e.g. , W = < L 3 X ω | E kw | 2 8 π > (2) where the sum over ω is around the acoustic resonance and similarly for the plasma waves. Which of the two waves produces the dominant contribution to the total energy W tot = T e / 2? Hint: expand the dielectric function ± kw around the resonance frequency for each of the waves. Don’t forget that the resonant frequencies have positive and negative values for a given value of k . 3. Consider a cylindrical system with a uniform magnetic ﬁeld B = B ˆ z and a radial electric ﬁeld E = E ˆ r . Transform to a rotating frame to eliminate the electric ﬁeld (assume E/B ± 1) and calculate the resultant “centrifugal” drift. Is this drift largest for ions or electrons?...
View Full Document

## This note was uploaded on 12/29/2011 for the course PHYSICS 762 taught by Professor Drake during the Fall '08 term at Maryland.

Ask a homework question - tutors are online