DISPERSION OF WAVES IN HOT PLASMAS (thesis)

Technical Report · Fri Jun 01 04:00:00 EDT 1962

OSTI ID:4799936

Liemohn, H B

Submitted to Univ. of Washington, STASeattle!. The propagation characteristics of small-amplitude waves in hot plasmas are discussed assuming specific functional forms for the equilibrium distributions. The spacetime behavior of initial density perturbations (acoustic mode) was analyzed, including second-order effects, using a one-dimensional Cauchy velocity distribution of the form (v/sup 2/ + a/sup 2/)/sup -2/. The thermal effects on right-hand circularly polarized electromagnetic waves propagating along a magnetic field in a plasma (longitudinal extraordinary mode) were evaluated for a three-dimensional Cauchy distribution of the form (v/sup 2/ + a/sup 2/)/sup -3/ and a step-function distribution. In the latter case the relativistic corrections for the propagation characteristics were studied qualitatively using a stepfunction momentum distribution. For the acoustic mode, the initial density perturbation of the plasma was assumed to be sinusoidal in space. The first-order solution had an exact analytic form which gave damped oscillations at a thermally shifted plasma frequency. The thermal damping was similar to that originally obtained by Landau. The nonlinear interference between the density wave and its field produced second harmonics in both space and time which appeared in the second- order solution. The harmonic structure sug gested a spectral decay'' of the initial perturbation energy. In general, the oscillation frequency and damping decrement increased with temperature so that at sufficiently high temperatures all forms of ordered motion were destroyed by the random thermal motion. The nonrelativistic dispersion equation for the longitudinal extraordinary mode was solved for all frequencies including cyclotron resonance. In general, thermal effects reduced the infinite discontinuity in phase at the cyclotron resonance to a finite value and caused thermal damping of the propagating wave below resonance. The absorption coefficient increased with temperature and could appreciably decrease the intensity of signals propagating through hot media. The results were applied to whistler propagation along geomagnetic field lines in the exosphere. If the observed frequency cutoff arose from thermal damping, a temperature of 10/sup 5/ deg K was required in the electron component near the geomagnetic equator at four earth radii geocentric. Solutions of the dispersion equation for a relativistic plasma were calculated at certain frequencies, and the qualitative behavior of the index of refraction was evident from these specific results. Relativistic effects were found to lower the cyclotron resonance and the frequency at which the index vanishes. (auth)

• Research Organization: Boeing Scientific Research Labs., Seattle
• NSA Number: NSA-16-029901
• OSTI ID: 4799936
• Report Number(s): D1-82-0174
• Country of Publication: Country unknown/Code not available
• Language: English

Related Subjects

ABSORPTION
BACKGROUND
CYCLOTRON RADIATION
DAMPING
DENSITY
DIFFERENTIAL EQUATIONS
DISPERSION RELATIONS
DISTRIBUTION
DISTURBANCES
EARTH
ELECTROMAGNETIC WAVES
ENERGY
FREQUENCY
HIGH TEMPERATURE
IONOSPHERE
MAGNETIC FIELDS
MOMENTUM
OSCILLATIONS
PHYSICS
PLASMA
POLARIZATION
RADIO WAVES
REFRACTION
RELATIVITY THEORY
RESONANCE
SIGNALS
SOUND
SPACE
SPECTRA
TEMPERATURE
VELOCITY
WHISTLERS