Experiments on Forming Intense Rings of Electrons Suitable for the Acceleration of Ions

Electrons were injected from a 3.3-MeV 300-A accelerator into a circular orbit in a pulsed magnetic field. Trapped ring currents of 150 A were magnetically compressed from 19- to 3.5-cm radius and simultaneously accelerated from 3.3 to 18 MeV. The rms dimensions of the cross section of the ring after compression were $a=2.3\mathrm{}\pm 0.2$ mm radially and $b=1.6\mathrm{}\pm 0.2$ mm axially. The lifetime of the ring, typically 5.5 msec, was determined by the decay of the magnetic field after compression and could be decreased by the addition of hydrogen gas, indicating the focusing effect of the trapped positive ions.