TRAPPING OF THE PHERMEX BEAM IN A MIRROR FIELD

An experiment is underway at Los Alamos Nat ional Laboratory to trap the 1-kA. 30-MeV PHERMEX beam in a magnetic mirror. The eventual aim is to accelerate the beam to 50 MeV by ramping up the magnetic field. Tan- gential injection of the beam through a soft iron noz- zle is employed. Because the nozzle is placed within the magnetic mirror, energy must be extracted from the beam in one bounce time to prevent particles returning to the nozzle. A design to make the bounce time as long as possible is described, and two schemes to damp the axial motion are considered. Numerical simulations Of the device show considerable axial spreading of the beam in one bounce time. Estimates are made of nega- tive mass instability growth rates and the damping to be expected from the experimentally measured beam energy spread. Experimental results obtained to date are described.