Experimental Study of an ion cyclon resonance accelerator: presentation of his thesis

The Ion Cyclotron Resonance Accelerator (ICRA) uses the operating principles of cyclotrons and gyrotrons. The novel geometry of the ICRA allows an ion beam to drift axially while being accelerated in the azimuthal direction. Previous work on electron cyclotron resonance acceleration used waveguide modes to accelerate an electron beam [5]. This research extends cyclotron resonance acceleration to ions by using a high field superconducting magnet and an rf driven magnetron operating at a harmonic of the cyclotron frequency. The superconducting solenoid provides an axial magnetic field for radial confinement and an rf driven magnetron provides azimuthal electric fields for acceleration. The intent of the ICRA concept is to create an ion accelerator which is simple, compact, lightweight, and inexpensive. Furthermore, injection and extraction are inherently simple since the beam drifts through the acceleration region. However, use of this convenient geometry leads to an accelerated beam with a large energy spread. Therefore, the ICRA will be most useful for applications which do not require a monoenergetic beam. An ICRA designed to accelerate protons to 10 MeV would be useful for the production of radioisotopes, or neutron beams, as well as for materials science applications. As a first step toward producing an ICRA at useful energies, a low energy ICRA has been designed, built, and tested as a demonstration of the concept. Analytical theory and a full computer model have been developed for the ICRA. Beam measurements taken on the ICRA experiment have been compared with theory. The ICRA computer model uses realistic fields of the solenoid, magnetron, and electrostatic bend. This code tracks single particle trajectories from the ion source through the entire system to a target face. A full emittance injected beam can be modeled by tracking many single particle trajectories. The ICRA experiment is designed to accelerate a proton beam from 5 keV to 50 keV in 5 turns. A superconducting solenoid provides a 2.5 Tesla axial magnetic field. The accelerating structure built for the experiment operates at 152 MHz (4th harmonic) and provides 3 kV across 8 gaps. Measurements of the accelerated beam current vs. beam orbit radius indicate an energy distribution ranging from near zero to near the full design energy, with 7% of the beam current above 24 keV and 1% above 42 keV. Energy distributions generated using the ICRA computer model show reasonable agreement with the experimental data. After a small correction of the bend voltage, the computer model shows good agreement with the magnitude and shape of the experimental data for a wide range of turn number. Finally, a scheme for optimization of the basic ICRA design is given. Design parameters are identified which minimize cost and which maximize the accelerated beam current. Three 10 MeV proton designs are given which offer a compromise between low cost and a high quality beam.