ELECTRON TRAJECTORIES IN A HELICAL WIGGLER WITH A UNIFORM AXIAL-GUIDEFIELD - A COMPARISON OF NUMERICAL RESULTS WITH RESULTS OBTAINED USINGAN APPROXIMATE BUT ANALYTICAL METHOD

A comparison is made between two methods of calculating electron traje ctories in a magnetic field consisting of a helical wiggler and a unif orm axial guide field. The code SOLITUDE, developed by Gouard, was use d to calculate with high precision the trajectories of electrons whose initial positions and velocities were chosen at random from a Gaussia n distribution. After propagation through an adiabatic entry, the posi tions and velocities at the point where the wiggler field becomes stea dy were used as input to an analytical calculation developed by Donohu e and Rullier. Although the calculation is analytic, the method involv es truncating the true Hamiltonian, and is therefore not exact. Despit e this, generally good agreement is found between the trajectories gen erated by the two methods, in both the normal and reversed-field confi gurations. The analytical approach provides physical insight into cert ain unusual aspects of some of the numerically generated trajectories. Several illustrative examples are compared in detail.