A fast mechanical shutter for submicrosecond time-resolved synchrotron experiments

A new high-speed high-repetition-rate X-ray beam shutter for time-resolved photocrystallography at synchrotron sources has been developed and tested. The new design is based on a commercially existing DC servomotor and a frequency-lock control capable linear amplifier. Accurate speed control combined with an air bearing results in extremely low jitter in the motor rotation. Measured jitter at rotation speeds of 12000 to 30000 r min⁻¹ is less than 2 ns at a 6σ confidence level. The chopper disc is interchangeable, allowing maximum flexibility. The chopper disc currently installed has 45 radial slots which allows synchronization from the 12th to the 20th subfrequencies of the orbit frequency of the Advanced Photon Source storage ring, corresponding to X-ray pulse frequencies of 13.6 to 22.6 kHz. At 30000 r min⁻¹ the opening time window with a 350 µm slot size is 2.11 µs, and correspondingly less with smaller openings, which may be compared with the 3.68 µs orbit time of the Advanced Photon Source. The shutter provides high accuracy and efficient use of X-rays at a modest cost.