Compton spectrograph for Bremsstrahlung spectra measurements

We describe the design, fabrication and calibration of magnetic spectrographs to infer Bremsstrahlung spectra by measuring the energy of Compton scattered electrons over the range 10-24 MeV. In addition to a momentum resolution of about 2 per cent, we require a good angular acceptance (±20 mrad) to give the maximum pulsed detector signal. Furthermore, the spectrograph must be compact and easy to fabricate. We decided on a simple uniform-field permanent-magnet dipole with 45 degree entrance and exit angles. The magnet gives a horizontal focal plane that is almost a straight line and sufficient vertical focusing to contain all electrons within the angular acceptance over the full energy range. The design is tolerant to variations in the field level - a global field shift moves the electrons laterally within the set focal plane.