RESUMO
Following demand from the user community regarding the possibility of improving the experimental resolution, the dedicated high-intensity/extended Q-range SANS diffractometer KWS-2 of the Jülich Centre for Neutron Science at the Heinz Maier-Leibnitz Center in Garching was equipped with a double-disc chopper with a variable opening slit window and time-of-flight (TOF) data acquisition option. The chopper used in concert with a dedicated high-intensity velocity selector enables the tuning at will of the wavelength resolution Δλ/λ within a broad range, from 20% (standard) down to 2%, in a convenient and safe manner following pre-planned or spontaneous decisions during the experiment. The new working mode is described in detail, and its efficiency is demonstrated on several standard samples with known properties and on a completely new crystallizable copolymer system, which were investigated using both the conventional (static) and TOF modes.
RESUMO
A chopper system for time resolved pump-probe experiments with x-ray beams from a synchrotron is described. The system has three parts: a water-cooled heatload chopper, a high-speed chopper, and a millisecond shutter. The chopper system, which is installed in beamline ID09B at the European Synchrotron Radiation Facility, provides short x-ray pulses for pump-probe experiments with ultrafast lasers. The chopper system can produce x-ray pulses as short as 200 ns in a continuous beam and repeat at frequencies from 0 to 3 kHz. For bunch filling patterns of the synchrotron with pulse separations greater than 100 ns, the high-speed chopper can isolate single 100 ps x-ray pulses that are used for the highest time resolution. A new rotor in the high-speed chopper is presented with a single pulse (100 ps) and long pulse (10 micros) option. In white beam experiments, the heatload of the (noncooled) high-speed chopper is lowered by a heatload chopper, which absorbs 95% of the incoming power without affecting the pulses selected by the high speed chopper.