Experimental performance of an E x B chopper system

Beam operation of a novel E x B chopper system has started in the low-energy beam transport (LEBT) section of the accelerator-driven neutron source FRANZ. The chopper is designed for low-energy high-perveance beams and high repetition rates, and will finally operate with 120 keV protons. It combines a static magnetic deflection field with a pulsed electric compensation field in a Wien filter-type E x B configuration. The chopper was designed, manufactured and successfully commissioned at the required repetition rate of 257 kHz using a 14 keV helium beam with up to 3.5 mA of beam current. Beam pulses with rise times of (120 +/- 10) ns, flat-top lengths of (85 +/- 10) ns to (120 +/- 10) ns and full width at half maximum (FWHM) between (295 +/- 10) ns and (370 +/- 10) ns were experimentally achieved.