Injection, trapping, and acceleration of an electron beam in a stellatron accelerator

Abstract

The UCI modified betatron [Phys. Rev. Lett. 53, 266 (1984)] was converted into a stellatron accelerator by the addition of helical quadrupole coils to the betatron configuration. An experimental study of the injection, trapping, acceleration, and disruption of a beam in this apparatus has been conducted. The stellarator field applied was of up to 10 kG and with a rotational transform of ι/≃0.1– 0.15. Electrons were injected from a thermionic emitter typically operated by applying 20 kV, 2– 4 μsec pulses to the hot cathode, which emitted ∼3 A. A beam of ∼200 A was trapped in the torus and accelerated by the betatron field applied immediately after the injection. The beam life was extended by increasing the toroidal field. The beam current suffered a partial disruption after it reached its peak value. After that the beam lost electrons gradually, accompanied by generation of x rays, until the entire beam was lost close to the peak of the accelerating betatron field. Electron energies of up to ∼4 MeV were reached. The dependence of the beam current and its lifetime, upon the applied fields and injection conditions, was explored.

Physical Startup of the LEPTA Accumulator

“…Such a field geometry is characteristic for a modified betatron and its modifications -the stomatron [5]. But, in contrast to the stomatrons, developed and studied in the USA [6,7], the structure of the LEPTA accumulator does not possess azimuthal symmetry, and the spiral quadrapole field is present only on a short part of the orbit in the rectilinear section. In addition, in [2] an innovative injection scheme was proposed, making it possible to solve the main problem of stomatrons -introducing the beam into a longitudinal magnetic field without substantial perturbation of the beam parameters.…”