Early in 1968 a research group was set up at the Lawrence Radiation Laboratory to investigate the exciting new concept of accelerating ions by means of relativistic electron rings, which had been introduced and developed by Veksler, Sarantsev, and other workers at Dubna. The initial work of our group was reported at the first USSR National Conference on Particle Accelerators in 1968. In this report the author review the subsequent progress and the present program.

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.

The possibility of using the collective field of a large number of electrons to effect the acceleration of protons to high energies in a compact accelerator--or to permit acceleration of heavier ions in a manner not critically dependent on the charge-to-mass ratio of these ions--has been noted in an earlier Comment. A most attractive conceptual form for such an accelerator is the electron ring accelerator (ERA) and in the present Comment they direct attention to the basic phenomena--insofar as they know them--that govern the design and operation of an ERA. Briefly, the ERA concept visualizes the use of a compact ring of relativistic electrons that circulate in a plane perpendicular to an external magnetic field. The ring is partially neutralized by ions held in the potential well of the electrons. The electric field of these ions and the magnetic attractive forces between the circulating electrons then together act to overcome the electrostatic repulsion of the electrons and make possible the achievement of a configuration that is self-stable in the absence of external focusing fields. Acceleration of the ring with its accompanying ions, in a direction perpendicular to the plane of the ring, can be achieved (at the expense of the …