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We introduce a novel structured controller design for the electron beam stabilization problem of the UK’s national synchrotron light source. Because changes to the synchrotron will not allow the application of existing control approaches, we develop a novel method to diagonalize the multi-input multi-output (MIMO) system. A generalized singular value decomposition (GSVD) is used to simultaneously diagonalize the actuator response matrices, which is applicable to an arbitrary number of actuator dynamics in a cross-directional setting. The resulting decoupled systems are regulated using mid-ranged control and the controller gains derived as a function of the generalized singular values. In addition, we exploit the inherent block-circulant symmetry of the system. The performance of our controller is demonstrated using simulations that involve machine data.

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.

A single crystal CVD diamond detector with graphitic wire electrodes running beneath the diamond surface has been fabricated. This detector design is novel in that there is no surface metallisation present within the active region, and so the detector is a uniquely transmissive X-ray beam diagnostic instrument. This detector is designed to simultaneously measure the position, profile, and flux of an incident beam. It has applications in beam position and profile monitoring, and active beam feedback and stabilisation. To achieve this, a short-pulse laser, focused to micron-sizes using adaptive optics, can be used to graphitise arbitrary wire paths within bulk diamond. Presented in this paper is a transmissive X-ray pixel detector design with a 50-micrometre pixel pitch created using this technique. This pixel detector is produced by fabricating two separate arrays of parallel wires running under the surface of a diamond plate. The two arrays run perpendicular to each other, and parallel to the diamond surface. They are separated within the material by a depth of 100 microns. The parallel wires within each array are separated by 50-microns, and this is what determines the pixel pitch. Each of the crossing points between two wires from each array acts as a pixel. The signal from each pixel may be read out by measuring the signal current from each wire in one array whilst applying a bias voltage alternately to each wire in the other, perpendicular array. Alternatively, it is proposed to modulate the bias applied to each wire at a different frequency, from which the 2-dimensional beam profile may also be measured using a lock-in technique. This paper will provide an overview of the fabrication techniques for this first prototype detector, and provide a discussion of signal readout methods that will be used. An outline of the planned experimental tests is given.A single crystal CVD diamond detector with graphitic wire electrodes running beneath the diamond surface has been fabricated. This detector design is novel in that there is no surface metallisation present within the active region, and so the detector is a uniquely transmissive X-ray beam diagnostic instrument. This detector is designed to simultaneously measure the position, profile, and flux of an incident beam. It has applications in beam position and profile monitoring, and active beam feedback and stabilisation. To achieve this, a short-pulse laser, focused to micron-sizes using adaptive optics, can be used to graphitise arbitrary wire paths within bulk diamond. Presented in this paper is a transmissive X-ray pixel detector design with a 50-micrometre pixel pitch created using this technique. This pixel detector is produced by fabricating two separate arrays of parallel wires running under the surface of a diamond plate. The two arrays run perpendicular to each other, and parallel to the diamond surf...

We report on the use of single-crystal chemical vapour deposition (scCVD) diamond X-ray beam diagnostics at Diamond Light Source Ltd (DLS) for beamline commissioning and day-to-day beamline operation. It is demonstrated that such detectors can offer synchrotron beamlines a measurement of the X-ray beam position with resolutions of a few 10nm at kHz bandwidths. It is straightforward to extract extremely valuable spectral information of both beam motion and intensity, aiding beamlines in determining the source of vibrations or other beam instabilities. In this paper we discuss the motivation behind the use of single-crystal diamond detectors for monitoring monochromatic X-ray beams, and advantages over other diagnostic techniques are discussed. In order to absolutely quantify the performance of the diamond detectors in use at DLS an experiment has been conducted with three diamond X-ray beam position monitors installed on a beamline, longitudinally separated along the beam path by ∼10 millimeters and intercepting the same incident X-ray beam. Measurements from each of the three diamond detectors were synchronously acquired at kHz bandwidths. Other, independent measurements were employed to corroborate the measurements obtained from the three X-ray beam position monitors. The uncorrelated position measurement noise recorded by the synchronous measurements and is shown to be less than 1% of beam size at this bandwidth. Longer integration times resulted in correspondingly less measurement noise.

Maintaining the stability of the X-ray beam relative to the sample point is of paramount importance for beamlines and users wanting to perform cutting-edge experiments. The ability to detect, and subsequently compensate for, variations in X-ray beam position with effective diagnostics has multiple benefits: a reduction in commissioning and start-up time, less ‘down-time’, and an improvement in the quality of acquired data. At Diamond Light Source a methodical evaluation of a selection of monochromatic X-ray Beam Position Monitors (XBPMs), using a range of position detection techniques, and from a range of suppliers, was carried out. The results of these experiments are presented, showing the measured RMS noise on the position measurement of each device for a given flux, energy, beam size, and bandwidth. A discussion of the benefits and drawbacks of each of the various devices and techniques is also included.

This paper describes the design and implementation of an FPGA-based transverse multibuch feedback system for Diamond Light Source. The system is designed to damp instabilities of the electron beam up to 250~MHz in both horizontal and vertical planes. The feedback algorithm and diagnostics features are implemented and verified using SystemVerilog HDL language on a Xilinx XCV2P30 FPGA.

Electron beam stability at the source points of synchrotron radiation is an accepted requirement for the preservation of the low emittance provided in 3rd generation light sources. With emittances approaching 1nm rad this typically requires sub micrometer positional stability at the source point over time scales from milliseconds to at least hours and ideally much longer. These challenges are routinely met by the use of fast orbit feedback systems. This contribution sets out to first establish a relevant representation of stability over many orders of magnitude in time and looks at available stable references. To complement this, data on the electron and X-ray beam stability achieved at various operational light sources is compared.

In this paper we demonstrate significant improvements to the stability of the monochromatic X-ray beam intensity on several beamlines at Diamond, using a modulation of the pitch axis of the DCM with a piezoelectric actuator. The modulation is detected on an intensity diagnostic (e.g. an ion chamber) using a software lock-in technique. The detected amplitude and phase are used in a feedback to keep the DCM at the peak of the rocking curve, or any arbitrary position 'off-peak' which might be desired to detune the DCM and reject unwanted harmonics. A major advantage of this software based system is the great flexibility offered, using standard, readily available instrumentation. Measurements of the short and long-term performance of the feedback on several beamlines are presented, and the limitations of such a feedback are discussed.