Simultaneous Multiple Frequency Interferometry: An Application of Homodyne Phase Measurement.

摘要

Microwave interferometry of plasmas involving only multiple homodyne phase measurement is considered in the limits of very low and very high collisionality. Starting with an assumed Langevin model of a weakly ionized gaseous plasma the expressions for the complex propagation constant(s) of probe(s) are simplified for these limiting cases. Emphasis is on the imaginary component of the propagation constant which accounts for the phase shifting phenomena. Simultaneous use of two probing frequencies enables phase determination of both the time-dependent electron density and 'effective' collision rate which are line-integrated along the probe propagation length. Extension to a triple frequency interferrometric system allows additional determination of the line-integrated square of the electron density due to the incorporation of higher order terms in a Taylor series expansion. If a reasonable functional form for the longitudinal variation in plasma density is assumed, the plasma spatial profile can then be estimated. Throughout, plasmas are assumed to be transversely uniform. In addition, physical interpretation of a real 'effective' collision rate can be simplified in these collisional limits to be directly proportional to an energy distribution averaged momentum transfer rate. 8 refs., 1 fig.