The Utrecht 850 kV cascade generator I. Beam deflection and energy control

The beam deflection magnet and energy control system of the Utrecht cascade generator are described. The uniform-field magnet has entrance and exit slits located outside the magnetic held. Since the cascade generator produces a vertical beam, the most convenient choice for the angle of deflection was 90 degrees. The radius of curvature of the beam in the region of the uniform-field is 20 cm, which makes it possible to deflect a one MeV beam of He+ or DeT ions with a field of 14.5 kilograms. The value assembly of the magnet and slits can be repeated about the incoming beam in order to direct the beam to different experimental arrangements. Energy control is achieved in two steps: first the exciting current of the magnet is stabilized, the magnetic field being measured with a proton magnetic resonance fluxmeter, and second the high tension is controlled so as to maintain the deflected beam centered on the exit slit of the magnet. The expected energy resolution of the system has been verified down to an energy spread (full width at half maximum) of 0.15% in proton energy. At the resolution a useful beam (~ 2 μA is obtainable with a high-frequency ion delivering a total beam of about 40 μA protons