Submicrosecond Synchronization of Multiple Chopper Systems

Synchronous-chopper neutron velocity selectors are often preferable to crystal monochromators. We have investigated the degree of synchronization which may be achieved with choppers using commercially available hysteresis-synchronous motors. With many commercial variable frequency generators, period instability limits synchronization to ± 15 microseconds. Using signal generators of high period stability (e. g. crystal oscillators, digital frequency dividers, very stable power amplifiers) synchronization to within 1 microsecond is readily achieved. At this level, small fluctuations in friction are readily observable. Magnetic instability can produce drifts over long periods unless careful attention is paid to motor requirements. Extensive experimental results will be presented.