ON THE AMPLIFICATION MECHANISM OF THE ION-CHANNEL LASER

The amplification mechanism of the Ion-Channel Laser (ICL) [1] in the low gain regime is studied. In this concept, a relativistic electron beam is injected into a plasma whose density is comparable to or lower than the beam's density. The head of the electron beam pushes out the plasma electrons, leaving an ion channel. The ion focusing force causes the electrons to oscillate (betatron oscillations) about the axis and plays a similar role to the magnetic field in a cyclotron autoreso-nance maser (CARM). Radiation can be produced with wave frequencies from microwaves to X rays depending on the beam energy and plasma density: ω ∼ 2γ3/2ωpe, where 7 is the Lorentz factor of the beam and wpe is the plasma frequency. Transverse (relativistic) bunching and axial (conventional) bunching are the amplification mechanisms in ICL's; only the latter effect operates in free electron lasers. The competition of these two bunching mechanisms depends on beam velocity v0z; their dependences on v0l cancel for the cyclotron autore-sonance masers. A linear theory is developed to study the physical mechanism and a PIC simulation code is used to verify the theory. The mechanism is examined as a possible explanation for experimentally observed millimeter radiation from relativistic electron beams interacting with plasmas. © 1990 IEEE