Quasi-monoenergetic spectra from reactions in a beam-target plasma

We investigate the kinematics of two-body (m1+m2→m3+m4) fusion reactions occurring when a beam interacts with a plasma target. An exact expression for the energy spectrum of the product particles is derived. The derivation shows that there is an anisotropic lower limit on the energy of one of the product species. There is a range of beam energies for which this limit acts to suppress thermal broadening of the energy spectra of the particles emitted in the beam direction. The beam energy at which maximum suppression occurs is identified. At this beam energy, the width of the spectrum can be up to a couple of orders of magnitude narrower than the spectrum produced by a thermal plasma. The results indicate that the highly monoenergetic beams of fusion product particles may be produced from hot plasma targets.