Propagation of Coherent Radiation in a Cylindrical Plasma Column

Abstract

Refraction plays a very significant role in the absorption of laser energy in high temperature plasmas. The geometry considered here is a long cylindrical magnetically confined plasma. The laser pulse is assumed to enter the plasma from the ends. It is then necessary that the radiation propagate the full length of the plasma so that it will be absorbed. The refraction of the laser radiation in the plasma column depends on the radial distribution of the density. Several representative density profiles are considered and solutions for the propagation are presented. It is shown that a profile with the maximum density on the axis is very difficult to heat over long distances; but, if the density has a minimum on the axis, then the plasma column acts like a “light pipe” and traps the laser beam. In this case the effective absorption length of the laser beam is also reduced.