Electron trajectories in a helical wiggler with a uniform axial guide field: a comparison of numerical results with results obtained using an approximate but analytical method

A comparison is made between two methods of calculating electron trajectories in a magnetic field consisting of a helical wiggler and a uniform axial guide field. The code SOLITUDE, developed by Gouard, was used to calculate with high precision the trajectories of electrons whose initial positions and velocities were chosen at random from a Gaussian distribution. After propagation through an adiabatic entry, the positions and velocities at the point where the wiggler field becomes steady were used as input to an analytical calculation developed by Donohue and Rullier. Although the calculation is analytic, the method involves truncating the true Hamiltonian, and is therefore not exact. Despite this, generally good agreement is found between the trajectories generated by the two methods, in both the normal and reversed-field configurations. The analytical approach provides physical insight into certain unusual aspects of some of the numerically generated trajectories. Several illustrative examples are compared in detail.