Velocity ratio measurement diagnostics and simulations of a relativistic electron beam in an axis encircling gyrotron

This paper reports on diagnostic experiments and simulations of a large-orbit, axis-encircling gyrotron. The electron's perpendicular to parallel velocity ratio /spl alpha/ is measured. The experimental diagnostic consists of an apertured portion of the beam which is passed through a cusped magnetic field then collected on a glass plate. The cross section of the beam is recorded on the glass plate in a radiation darkened pattern. From the gyro-radius, B-field, and beam energy, /spl alpha/ can be calculated. Particle distributions of the radiation darkened plate are in excellent agreement with numerical simulations of single particle orbits derived from the relativistic equations of motion. The experimental measurement of /spl alpha/ yields values from 0.9 to 1.4. The simulations predict an /spl alpha/ of 1.0 to 1.5.