A novel coil system is described that enables the magnetic angle-changing t
echnique to be used at higher energies. The system consists of coils of wir
e that are combined with specially shaped iron cores in such a way as to pr
eserve localization of the magnetic field. The system extends the operation
al energy range of previous systems consisting of solenoids alone by a fact
or of 25. Measurements of the electron impact excitation of the n=2 states
of helium are presented as an example of the use of the device. (C) 2000 Am
erican Institute of Physics. [S0034-6748(00)00509-8].