New light dawns for CELEROTON’s X-ray choppers at the ESRF

Why a Celeroton chopper?

Among its extensive array of beamlines, the ESRF’s highly specialized ID29 is dedicated to advanced X-ray crystallography, such as time-resolved studies in macromolecular crystallography (MX). The studies are designed to capture, in real-time, the dynamics of macromolecular structures as they undergo various exposures. By modulating the X-ray beam, the chopper allows for precise control over the timing and duration of the X-ray pulses, facilitating the observation of transient states and reaction intermediates with microsecond time resolution.

 The precise control mechanism of the chopping frequency and timing are completely synchronized with the experimental triggers at the end station. In addition, by chopping the X-ray beam, the device reduces the heat load on the sample carrier, allowing for fast sample replacement and minimizing radiation damage. This is a valuable attribute for preserving the integrity of sensitive biological crystals during exposure to high-intensity X-rays. As a result, the choppers enhance the quality of the diffraction data collected.

Lastly, a Celeroton chopper, compared to other methods of chopping light (piezo electric-based insertion devices) allows for greater experimental flexibility on ID29. Researchers can customize the timing and frequency of the X-ray pulses to suit specific experimental needs, whether they are studying fast biochemical reactions or slower conformational changes in macromolecules.

Technical features

The active magnetic bearing chopper of Celeroton consists of a dual hetero-/homopolar slotless/ironless, self-bearing electric machine (core CM-AMB-400) with an integrated chopper disc. The chopper disc (or rotor) has two slots in the axial direction for chopping the beam.

• High-Speed Operation: Celeroton choppers are renowned for their high rotational speeds, reaching up to several hundred thousand revolutions per minute (RPM). This high-speed capability is crucial for generating the short X-ray pulses needed for time-resolved studies.
• Compactness: The exceptional rotational speed means that high circumferential speeds can be achieved with smaller chopper disc diameters. The result is a compact chopper system measuring only 58 mm x 62 mm x 97 mm.
• Precision: The jitter of the chopped beam is typically lower than 10 ns. The low jitter (inferior to 1%) of the chopped beam is achieved thanks to the precision manufacturing of the rotor (specifically the slots), the fine balancing of the rotor, and accurate rotational speed control.
• Magnetic levitation: The active magnetic bearings let the chopper disc levitate without mechanical contact. This enables the choppers to operate in air and other gases, as well as in a vacuum (tested down to 10-6 mbar).
• Low vibrations: The advanced control technologies together with the active magnetic bearings result in vibrations generated by the chopper of less than 10 mN per axis. This low level minimizes any impact on the experiment, especially when compared to ball bearings systems. The low vibration values are made possible by advanced control algorithms using a notch filter to rotate the rotor around the center of inertia, thus preventing the dominant rotational speed synchronous vibrations, a further benefit of the active magnetic bearings.
• Reliability: Celeroton’s advanced engineering and active magnetic bearing technology provide robust and reliable performance, which is critical for the demanding operational environment of X-ray beamline at a synchrotron radiation source.

The chopper synchronization system with the end station triggers has been developed by Celeroton, as a dedicated project upgrade for the ID29 beamline. Combined with the customized magnetic bearing motor CM-AMB-400, Celeroton provides an ultra-fast chopper, with low jitter and vibrations, offering researchers a deeper insight into the kinetics of macromolecular crystallography. It enhances the ability to capture dynamic processes in biological macromolecules with high precision and minimal radiation damage, advancing our understanding of biological mechanisms and aiding in drug discovery, for example.

Celeroton is a leading Swiss company specializing in the development and production of ultra-high-speed electrical drive systems, including motors, generators, compressors and magnetically levitated choppers.