TM MODE RADIATION GUIDING IN AN REB-INDUCED PLASMA DUCT

An intense relativistic electron beam propagating through a plasma cre ates a low-density plasma duct capable of guiding a free-electron lase r mode, Tile beam dynamics plays an important role in the propagation of TM modes. For n(0b)(0)/n(0p)(0) approximate to b/a approximate to 0 .1 (where n(0b)(0) and n(0p)(0) are the beam and plasma densities resp ectively, and a and b are the x and y dimensions of tile duct) and bea m energy of about 2 MeV, the threshold current turns out to be about 2 0 kA. For marginal radiation guiding, the size of the plasma duct decr eases with beam voltage. Application of a strong DC magnetic field sho ws that an even narrower duct can guide high-frequency radiation.