In one minute

Christof Baumgärtel, Ray Smith and Simon Maher address a design problem for charged-particle instruments: predicting trajectories in solenoids needs accurate fields, especially in the fringing regions at the ends. They describe a model that accurately predicts electron beam deflection both in the fringing field and at the centre of a solenoid. The model uses a direct action-at-a-distance force between charges, based on the Weber force, instead of fields. It is compared with a Maxwell-Lorentz field model and a commercial boundary element package, against experiments on three solenoids of different sizes. The direct-action model matches the experiments more accurately than the field-based models, especially for the shortest, 25 mm solenoid where the field is least uniform.

Accurately predicting electron beam deflections in fringing fields of a solenoid