Chopper layout for spectrometers at long pulse neutron sources

We discuss the implications of a long pulse neutron source for the chopper system of direct geometry time-of-flight spectrometers. While the same conditions apply for the layout of the resolution defining choppers as on reactor based instruments, we emphasize the multi-chromatic nature of the instruments. The chopper system must not only provide a unique assignment of the wavelength to each pulse, but also provide adopted time frames matching the respective energy of the pulse. We propose a chopper system consisting of disc choppers, heavy T0 choppers and a newly developed Fan chopper to account for the various challenges due to the long pulse nature.