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105 items found (0 items not approved), displaying 1 to 10.[First/Prev] 1, 2, 3, 4, 5, 6, 7, 8 [Next/Last]

Instruments / Technical Area	Publication Details	Published
Diagnostics	X-ray pinhole camera spatial resolution using high aspect ratio LIGA pinhole apertures N. Vitoratou , L. Bobb , G. Rehm , A. Last IBIC2022 DOI: 10.18429/JACoW-IBIC2022-MOP18 Open Access Show Abstract ▼ Abstract: X-ray pinhole cameras are employed to provide the transverse profile of the electron beam from which the emittance, coupling and energy spread are calculated in the storage ring of Diamond Light Source. Tungsten blades separated by shims are commonly used to form the pinhole aperture. However, this approach introduces uncertainties regarding the aperture size. X-ray lithography, electroplating and moulding, known as LIGA, has been used to provide thin screens with well-defined and high aspect ratio pinhole apertures. Thus, the optimal aperture size given the beam spectrum can be used to improve the spatial resolution of the pinhole camera. Experimental results using a LIGA screen of different aperture sizes have been compared to SRW-Python simulations over the 15-35 keV photon energy range. Good agreement has been demonstrated between the experimental and the simulation data. Challenges and considerations for this method are also presented.	Nov 2022
Accelerator Physics	Symmetry exploitation in orbit feedback systems of synchrotrons for computational efficiency Idris Kempf , Paul J. Goulart , Stephen R. Duncan , Guenther Rehm Ieee Transactions On Nuclear Science DOI: 10.1109/TNS.2021.3052553 Show Abstract ▼ Abstract: Structural symmetries in the storage ring of synchrotrons are intentionally created during the design phase of the magnetic lattices, but they are rarely considered in the design of control algorithms that stabilize the beam of accelerated particles. The choice of control algorithm, however, is limited by the high actuation frequency and the large number of inputs and outputs. Standard control algorithms for synchrotrons are based on a singular value decomposition (SVD) of the orbit response matrix. SVD controllers exploit neither the structural symmetries nor exhibit any speed advantages. By considering the periodicity and the reflection properties of the betatron function, we show that these structural symmetries are inherited by the orbit response matrix. We then show that the resulting block-circulant and centrosymmetric properties of the matrix can be used for different computationally efficient decompositions of the controller. We also address the case of broken symmetry caused by odd placements of individual magnets and monitors. Our efficient decomposition enables the use of more advanced control techniques for synchrotrons, such as control algorithms that require real-time optimization. These advanced control techniques can in turn increase the stability of photon beams in synchrotron light sources.	Jan 2021
Controls	Multi-array electron beam stabilization using block-circulant transformation and generalized singular value decomposition Idris Kempf , Stephen R. Duncan , Paul J. Goulart , Guenther Rehm 59th IEEE Conference on Decision and Control (CDC) DOI: 10.1109/CDC42340.2020.9303752 Show Abstract ▼ Abstract: 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.	Dec 2020
I18-Microfocus Spectroscopy	A single-crystal diamond X-ray pixel detector with embedded graphitic electrodes C. Bloomer , M. E. Newton , G. Rehm , P. S. Salter Journal Of Synchrotron Radiation 27 DOI: 10.1107/S160057752000140X Open Access Show Abstract ▼ Abstract: The first experimental results from a new transmissive diagnostic instrument for synchrotron X-ray beamlines are presented. The instrument utilizes a single-crystal chemical-vapour-deposition diamond plate as the detector material, with graphitic wires embedded within the bulk diamond acting as electrodes. The resulting instrument is an all-carbon transmissive X-ray imaging detector. Within the instrument's transmissive aperture there is no surface metallization that could absorb X-rays, and no surface structures that could be damaged by exposure to synchrotron X-ray beams. The graphitic electrodes are fabricated in situ within the bulk diamond using a laser-writing technique. Two separate arrays of parallel graphitic wires are fabricated, running parallel to the diamond surface and perpendicular to each other, at two different depths within the diamond. One array of wires has a modulated bias voltage applied; the perpendicular array is a series of readout electrodes. X-rays passing through the detector generate charge carriers within the bulk diamond through photoionization, and these charge carriers travel to the nearest readout electrode under the influence of the modulated electrical bias. Each of the crossing points between perpendicular wires acts as an individual pixel. The simultaneous read-out of all pixels is achieved using a lock-in technique. The parallel wires within each array are separated by 50 µm, determining the pixel pitch. Readout is obtained at 100 Hz, and the resolution of the X-ray beam position measurement is 600 nm for a 180 µm size beam.	May 2020
Accelerator Physics	Continuous energy measurement of the electron beam in the storage ring of Diamond Light Source with resonant spin depolarization Niki Vitoratou , Pavel Karataev , Guenther Rehm Physical Review Accelerators And Beams 22 DOI: 10.1103/PhysRevAccelBeams.22.122801 Open Access Show Abstract ▼ Abstract: Electron spin polarization occurs naturally in an electron storage ring due to spin-flip synchrotron radiation. The equilibrium polarization level that is achieved in Diamond Light Source was studied theoretically and experimentally. A novel approach that enables measurements during user operation is presented, compatible with beams of small vertical emittance in the range of pm rad. An array of four custom-made scintillation detectors has been installed around the beam pipe downstream from the collimators to capture a significant fraction of the lost particles and witness the depolarization process in the presence of a background loss rate. A new concept for detecting the depolarization resonance even when it coincides with higher-order betatron resonances was introduced. The momentum compaction factor was measured to be in very good agreement with the storage ring numerical model. In the end, we measured a good long-term stability of the beam energy during user operation time.	Dec 2019
	Spatial resolution of an X-ray pinhole camera using a multi-layer monochromator L. Bobb , G. Rehm IBIC2019 DOI: 10.18429/JACoW-IBIC2019-TUPP038 Show Abstract ▼ Abstract: X-ray pinhole cameras are widely used for beam emittance monitoring at synchrotron light sources. Due to the reduction in beam emittance expected for the many fourth generation machine upgrades, the spatial resolution of the pinhole camera must be improved accordingly. It is well known that there are many contributions to the point spread function. However, a significant contribution arises from diffraction by the pinhole aperture. Given that diffraction is dependent on the spectral distribution of the incident synchrotron radiation, the spatial resolution can be improved by using a monochromatic beam. For optimal performance, the photon energy should be matched to the pinhole aperture size. Here we investigate the spatial resolution of the pinhole camera as a function of photon energy using a multi-layer monochromator.	Nov 2019
Detectors Diagnostics	Fast feedback using electron beam steering to maintain the X-ray beam position at a monochromatic X-ray diagnostic at Diamond Light Source C. Bloomer , G. Rehm , A. Tipper IBIC2019 DOI: 10.18429/JACoW-IBIC2019-MOPP032 Open Access Show Abstract ▼ Abstract: A new feedback system is being developed at Diamond Light Source, applying a modulation to the position of the electron beam to keep the synchrotron X-ray beam fixed at the sample-point. Beamline detectors operating in the 100-1000Hz regime are becoming common, and the X-ray beam stability demanded by beamlines is thus of comparable bandwidths. In this paper we present a feedback system operating at these bandwidths, using a diagnostic instrument permanently installed in the X-ray beam path to measure the error in beam position at the sample point, and fast air-cored magnets to apply a small modulation to the electron beam to compensate. Four magnets are used to generate electron beam bumps through an ID straight. This modulation of the beam away from the nominal orbit is small, less than 10 microns, but should be sufficient to compensate for the bulk of the X-ray motion observed at the sample. It is small enough that the impact on the machine will be negligible. This system aims to maintain X-ray beam stability to within 3% of a beam size, at bandwidths of up to 500Hz.	Nov 2019
Accelerator Physics	Characterisation of closed orbit feedback systems G. Rehm IBIC2019 DOI: 10.18429/JACoW-IBIC2019-WECO01 Open Access Show Abstract ▼ Abstract: Closed orbit feedback is applied at nearly all synchrotrons. Detailed investigations continue to be performed on the mathematical modelling of the spatial part (i.e. related to Orbit Response Matrix) and the dynamic part (i.e. the controller). This talk will serve as a summary of the ARIES workshop on closed orbit feedback organized by ALBA in November 2018. Benefits of recent advances compared to the traditional implementations will be highlighted.	Nov 2019
Diagnostics	Continuous beam energy measurements at Diamond Light Source N. Vitoratou , P. Karataev , G. Rehm International Beam Instrumentation Conference (7th) DOI: 10.18429/JACoW-IBIC2018-MOPB16 Open Access Show Abstract ▼ Abstract: Resonant Spin Depolarization (RSD) is a well-known technique that has been employed by Diamond Light Source (DLS) for beam energy measurements. In this project, we study a new approach to make RSD compatible with user beam operation and provide a continuously updated online measurement. An array of four custom-made scintillation detectors has been installed around the beam pipe, downstream of collimators to capture the highest fraction of lost particles and maximize the count rate. The excitation is gated to half of the stored bunches and the acquisition system counts losses in both halves independently. Using the count in the un-excited part for normalisation suppresses external factors that modify the loss rate. Different parameters of the measurement, like excitation kick strength and duration have been explored to optimise depolarisation and to increase the reliability of the measurement.	Jan 2019
Detectors	A single crystal CVD diamond x-ray beam diagnostic with embedded graphitic wire electrodes Chris Bloomer , Guenther Rehm , Patrick Salter , Mark Newton 13th International Conference on Synchrotron Radiation Instrumentation – SRI2018 DOI: 10.1063/1.5084689 Show Abstract ▼ Abstract: 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.	Jan 2019

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