Experimental performance of an E×B chopper system

Beam operation of a novel E×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×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

Experimental Performance of an E×B Chopper System

eam operation of an E×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. It combines a static magnetic deflection field with a pulsed electric compensation field in a Wien filter-type E×B configuration**. Helium ions with 14 keV energy were successfully chopped at the required repetition rate of 257 kHz. The maximum chopped beam intensity of 3.5 mA, limited by the given test ion source, corresponds to a generalized perveance of 2.7·10-3. For the design species and energy, 120 keV protons, this is equivalent to a beam current of 174 mA. Beam pulses with rise times of 120 ns, flat top lengths of 85 ns to 120 ns and Full Width at Half Maximum (FWHM) between 295 ns and 370 ns were experimentally achieved

Beam Dynamics in the LEBT for FRANZ

The two Low Energy Beam Transport (LEBT) sections of the accelerator-driven neutron source FRANZ* consist of four solenoids. The first section with two solenoids will match the 120 keV proton beam into a chopper system**. Downstream from the chopper system a second section with two more solenoids will match the beam into the acceptance of the following RFQ. The accelerator will be operated using either a 2 mA dc beam or a pulsed beam with intensities from 50 mA to 200 mA at 250 kHz repetition rate. The high intensity of these ion beams requires the consideration of space-charge effects. Particle simulations with varying parameter sets have been performed in order to determine the settings providing best transmission and beam quality. Loss profiles along the transport channel were computed to identify hotspots. Simulation results for best transmission at lowest emittance growth will be presented