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Instruments / Technical Area	Publication Details	Published
VMXm-Versatile Macromolecular Crystallography microfocus	VMXm - A sub-micron focus macromolecular crystallography beamline at Diamond Light Source Anna J. Warren , Jose Trincao , Adam D. Crawshaw , Emma V. Beale , Graham Duller , Andrew Stallwood , Mark Lunnon , Richard Littlewood , Adam Prescott , Andrew Foster , Neil Smith , Guenther Rehm , Sandira Gayadeen , Christopher Bloomer , Lucia Alianelli , David Laundy , John Sutter , Leo Cahill , Gwyndaf Evans Journal Of Synchrotron Radiation 31, 1593 - 1608 DOI: 10.1107/S1600577524009160 Open Access Show Abstract ▼ Abstract: VMXm joins the suite of operational macromolecular crystallography beamlines at Diamond Light Source. It has been designed to optimize rotation data collections from protein crystals less than 10 µm and down to below 1 µm in size. The beamline has a fully focused beam of 0.3 × 2.3 µm (vertical × horizontal) with a tuneable energy range (6–28 keV) and high flux (1.6 × 1012 photons s−1 at 12.5 keV). The crystals are housed within a vacuum chamber to minimize background scatter from air. Crystals are plunge-cooled on cryo-electron microscopy grids, allowing much of the liquid surrounding the crystals to be removed. These factors improve the signal-to-noise during data collection and the lifetime of the microcrystals can be prolonged by exploiting photoelectron escape. A novel in vacuo sample environment has been designed which also houses a scanning electron microscope to aid with sample visualization. This combination of features at VMXm allows measurements at the physical limits of X-ray crystallography on biomacromolecules to be explored and exploited.	Nov 2024
Magnets	Correction of 10 Hz orbit distortion from Diamond's I10 fast switching chicane M. J. Furseman , C. P. Bailey , S. Gayadeen , G. Rehm , W. A. H. Rogers ICALEPCS2017 DOI: 10.18429/JACoW-ICALEPCS2017-TUPHA118 Open Access Show Abstract ▼ Abstract: The I10 beamline at Diamond Light Source is configured to study circular dichroism. To increase signal to noise ratio between the two beam polarisations and increase temporal resolution the beamline is fed by two separate IDs that are typically configured with opposite handed polarisations. A chicane of steering magnets with programmable power supplies is used to provide 10 Hz switching between the two photon beams by producing a dynamic closed bump that alternates the on-axis trajectory of the electron beam between the two IDs. In order to maintain the closed bump and make the switching transparent to the rest of the photon beamlines the phase and amplitude of the sine functions applied to the chicane magnets must be exactly correct. In this paper the linear scheme that was used to correct the residual 10 Hz orbit distortion is presented. Future work that uses the fully programmable nature of the magnet power supply controllers to correct high order distortions is also discussed.	Jan 2018
Controls	Optimal control of perturbed static systems for synchrotron electron beam stabilisation Sandira Gayadeen , Stephen R. Duncan , Guenther Rehm Ifac-Papersonline 50, 9967 - 9972 20th IFAC World Congress DOI: 10.1016/j.ifacol.2017.08.1576 Show Abstract ▼ Abstract: This paper considers the problem of designing an optimal controller for the linear static system associated with electron beam stabilisation systems in synchrotrons. The relationship between the actuators and sensors used for electron beam control in synchrotrons is modelled as a static response matrix which is typically ill-conditioned. Singular Value Decomposition (SVD) is commonly used to invert the response matrix and modes associated with small singular values are either discarded or filtered. In this paper, a robust control approach is used to determine the optimal static controller to the perturbed system. It is demonstrated how this approach compares to the use of Tikhonov regularisation for an inverse-based controller. A detailed example from the Diamond Light Source synchrotron is presented, applying both the inverse-based method and the robust control approach to stabilise electron beam motion.	Jul 2017
Magnets	Performance of the fast orbit feedback system with the double-double bend achromat Installed in Diamond Light Source S. Gayadeen , G. Rehm IPAC2017 DOI: 10.18429/JACoW-IPAC2017-TUPIK113 Open Access Show Abstract ▼ Abstract: At Diamond Light Source, the Double-Double Bend Achromat (DDBA) lattice upgrade involved the conversion of one cell of the storage ring from a double bend achromat (DBA) structure to a double-DBA (DDBA). The new cell includes corrector magnets that are different in design to the DBA corrector magnets. The DDBA vacuum chamber cross section is also different from the DBA cells and includes both stainless steel and copper sections over which corrector magnets are fitted. The performance of the Fast Orbit Feedback (FOFB) used for electron beam stabilisation with the DDBA cell installed is presented in this paper. Firstly the different corrector magnet dynamic responses are characterised and secondly the closed loop performance of the FOFB is measured and analysed for the upgraded lattice.	May 2017
Magnets	A procedure for the characterization of corrector magnets S. Gayadeen , M. Furseman , G. Rehm IBIC2016 DOI: 10.18429/JACoW-IBIC2016-WEPG43 Show Abstract ▼ Abstract: At Diamond Light source, the main assumption for the Fast Orbit Feedback (FOFB) controller design is that the corrector magnets all have the same dynamic response. In this paper, a procedure to measure the frequency responses of the corrector magnets on the Diamond Storage Ring is presented and the magnet responses are measured and compared in order to assess whether this assumption is valid. The measurements are made by exciting a single corrector magnet with a sinusoidal input and measuring the resulting sinusoidal movement on the electron beam using electron Beam Position Monitors (eBPMs). The input excitation is varied from 10 Hz to 5 kHz using a 10 mA sine wave. The amplitude ratio and the phase difference between the input excitation and the beam position excitation are determined for each input frequency and the procedure is repeated for several magnets. Variations in both gain and phase across magnets are discussed in this paper and the effect of such variations on the performance of the FOFB controller performance is determined.	Sep 2016

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