Calculation of the beam loss in the 270 degree bending magnet system of the medical accelerator

The transportation process of the electron beam in the 270 degree bending magnet system of the medical accelerator is studied under the one-order approximation, and the influence of the initial condition to the beam transportation and loss is analyzed for the calculation of the radiation dose. The theory of the beam transportation, combined with the Monte Carlo sampling method is applied. The simulation result shows that the energy spread is the main factor resulted in the beam loss. The data on the position, energy and direction of the lost electrons obtained through the simulation can be supplied as input to deal with the radiation problem. The result gives that the loss rate of the electron beam is 13.5%, and the direction of the main loss is toward the upside of the irradiating head of the accelerator with the radius 1mm, angle spread 5mrad, and energy spread 10% of the initial beam. (authors)