Experiments on forming, compressing and extracting electron rings for the collective acceleration of ions

In experiments related to the development of the electron-ring accelerator, electrons were injected into a pulsed magnetic field to form rings that were then compressed radially to a small size. The injected beam had a current of about 150 A at an energy of 3.3 MeV with an energy spread of ±0.1% and a pulse length duration of 20 nsec. At low intensity, an increase in the minor radius of the ring and a large loss of electrons was observed to occur during the compression cycle. At high intensity, cooperative phenomena that caused a large increase in the energy spread accompanied by particle loss were observed. Theoretical interpretation of these observations suggests that the primary source of electron loss and enlargement of the axial dimension was the crossing of single-particle resonances during compression in the presence of large magnetic field nonlinearities and perturbations. The cooperative phenomena are interpreted as resulting from a negative mass instability. Despite the large minor radius and small number of electrons, experiments on extracting the ring were performed; under acceleration the ring failed to retain its integrity because of inadequate self-focusing.