Abstract
Beam operation of a novel $E\ifmmode\times\else\texttimes\fi{}B$ 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 $E\ifmmode\times\else\texttimes\fi{}B$ 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 $(120\ifmmode\pm\else\textpm\fi{}10)\text{ }\mathrm{ns}$, flat-top lengths of $(85\ifmmode\pm\else\textpm\fi{}10)\text{ }\mathrm{ns}$ to $(120\ifmmode\pm\else\textpm\fi{}10)\text{ }\mathrm{ns}$ and full width at half maximum (FWHM) between $(295\ifmmode\pm\else\textpm\fi{}10)\text{ }\mathrm{ns}$ and $(370\ifmmode\pm\else\textpm\fi{}10)\text{ }\mathrm{ns}$ were experimentally achieved.
Highlights
Chopper systems are essential tools to impose a certain time structure on a particle beam
Beam pulses with at least a 50 ns flattop at a repetition rate of 257 kHz have to be shaped in the low-energy beam transport (LEBT) section at a beam energy of Wb 1⁄4 120 keV
The E × B concept combines the advantages of magnetic deflection, i.e., stable deflection without risks of voltage breakdown, and of electric deflection, i.e., operation with low power consumption even at high repetition rates
Summary
Chopper systems are essential tools to impose a certain time structure on a particle beam Such time structures are key parameters for the operation of most accelerator facilities. For the low-energy beam transport (LEBT) section of the accelerator-driven “Frankfurt Neutron Source at the SternGerlach-Zentrum” (FRANZ) [1], a novel E × B chopper [2] has been designed and successfully commissioned. It combines a static magnetic deflection field with a pulsed electric compensation field in a Wien filter-type E × B configuration in order to form an ion beam chopper. In this paper, based on updated results of [3], the chopper requirements, the chopping concept, the optimization of the electric and magnetic fields, as well as numerical and experimental results are presented
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