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Instruments / Technical Area	Publication Details	Published
Accelerator Physics Optics	Emittance feedback for the Diamond-II storage ring using resonant excitation Shaun Preston , Teresia Olsson , Beni Singh 13th International Particle Accelerator Conference (IPAC ’22) DOI: 10.1088/1742-6596/2420/1/012025 Open Access Show Abstract ▼ Abstract: In the Diamond Light Source storage ring, the vertical emittance is kept at 8 pm rad during operation to maintain the source brightness for the users. This is achieved by a feedback which modifies the skew quadrupole strengths, but has disadvantages such as the introduction of betatron coupling and vertical dispersion. For the proposed Diamond-II upgrade, the storage ring will have a much smaller horizontal emittance, meaning a significantly larger coupling would be required to reach the target vertical emittance, negatively affecting the off-axis injection process. To solve this problem, a feedback using the transverse multibunch feedback striplines to drive the beam at a synchrotron sideband is planned. By driving the beam resonantly in this way, the emittance can be increased without modification of the optics. This paper describes simulations of the effects of linear and non-linear optics on the excitation as well as the impact of the machine impedance for the Diamond-II storage ring.	Jan 2023
Accelerator Physics	Measurements for emittance feedback based on resonant excitation at Diamond Light Source S. Preston , L. Bobb , A. F. D. Morgan , T. Olsson IBIC2022 DOI: 10.18429/JACoW-IBIC2022-WEP37 Open Access Show Abstract ▼ Abstract: In the Diamond storage ring, the vertical emittance is kept at 8 pm rad by an emittance feedback which modifies the strengths of skew quadrupoles. A new feedback using a stripline kicker to control the vertical emittance by exciting the beam resonantly at a synchrotron sideband is planned to avoid modification of the optics. This is crucial for the anticipated Diamond-II upgrade of the storage ring, which will have a much smaller equilibrium emittance than the existing machine. A larger coupling is therefore needed to keep the vertical emittance at the same level, potentially reducing the off-axis injection efficiency and lifetime. Measurements of the beam oscillation and emittance have been performed at the existing storage ring to characterise the effects of chromaticity and impedance on the optimal excitation frequency, where the emittance is increased significantly while the beam oscillation is kept low. The implications for simulating the emittance feedback for the Diamond-II storage ring are also discussed.	Nov 2022
Accelerator Physics	Orbit stability studies for the Diamond-II storage ring I. P. S. Martin , C. A. Abraham , D. Crivelli , H. Ghasem , B. Nicholson , T. Olsson , P. Sanchez-Navarro IPAC2022 DOI: 10.18429/JACoW-IPAC2022-THPOPT017 Open Access Show Abstract ▼ Abstract: The photon-beam positional stability relative to the beam size is a key performance parameter for storage ring light sources. The natural emittance of the Diamond-II ring will be lowered by a factor 16.7 compared to the existing ring, so the absolute stability requirement for the electron beam must reduce accordingly. In addition, advances in detector speed and resolution mean the tolerances are tighter compared to previous generations of storage rings, with a target of 3 % of beam size up to 1 kHz having been adopted for Diamond-II. In this paper we present studies of how the anticipated ground vibrations, girder motion and power supply ripple will affect the electron beam stability as a function of frequency.	Jul 2022
Accelerator Physics	Studies of transverse coupled-bunch instabilities from resistive-wall and cavity higher order modes for Diamond-II S. Wang , H.-C. Chao , R. Fielder , I. P. S. Martin , T. Olsson IPAC2022 DOI: 10.18429/JACoW-IPAC2022-WEPOMS010 Open Access Show Abstract ▼ Abstract: The transverse coupled-bunch instabilities from resistive-wall impedance and main cavity higher order modes (HOMs) are studied for the Diamond-II storage ring. The growth rates of all the coupled-bunch modes are calculated using both the results from tracking simulations and analytic formula, which show a good consistency. The instability threshold from the resistive-wall impedance is estimated and verified by simulation. The impact of the main cavity HOMs is studied in a similar way, and the results show instabilities from HOMs are much smaller than that from resistive-wall impedance.	Jul 2022
Insertion Devices	Impact of insertion devices on Diamond-II lattice B. Singh , H. Ghasem , J. Kallestrup , T. Olsson , R. Fielder , I. Martin IPAC2022 DOI: 10.18429/JACoW-IPAC2022-MOPOTK037 Open Access Show Abstract ▼ Abstract: The DIAMOND-II lattice is based on the ESRF-EBS cell, with the centre dipole replaced by a (chromatic) mid-straight, and a -I transformer, higher order achromat (HOA) & dispersion bumps to control the nonlinear dynamics. The majority of insertion devices currently on operation in Diamond will be either retained or upgraded as part of the Diamond-II program, and the new mid straights allow the total number of ID beamlines to be increased from 28 to 36.Therefore, it is important to investigate how IDs will affect the emittance, energy spread and linear and nonlinear beam dynamics. The kickmap approach has been used to model all IDs, including APPLE-II and APPLE-II Knot with active shim wires. In this paper, the outcome of these investigations will be presented and discussed.	Jul 2022
Optics	Emittance feedback for the Diamond-II storage ring using resonant excitation S. Preston , T. Olsson , B. Singh IPAC2022 DOI: 10.18429/JACoW-IPAC2022-TUPOMS035 Open Access Show Abstract ▼ Abstract: In the Diamond Light Source storage ring, the vertical emittance is kept at 8 pm rad during operation to maintain the source brightness for the users. This is achieved by a feedback which modifies the skew quadrupole strengths, but has disadvantages such as the introduction of betatron coupling and vertical dispersion. For the proposed Diamond-II upgrade, the storage ring will have a much smaller horizontal emittance, meaning a significantly larger coupling would be required to reach the target vertical emittance, negatively affecting the off-axis injection process. To solve this problem, a feedback using the transverse multibunch feedback striplines to drive the beam at a synchrotron sideband is planned. By driving the beam resonantly in this way, the emittance can be increased without modification of the optics. This paper describes simulations of the effects of linear and non-linear optics on the excitation as well as the impact of the machine impedance for the Diamond-II storage ring.	Jun 2022
Mechanical Engineering	Construction of an impedance model for Diamond-II R. T. Fielder , T. Olsson IPAC2021 DOI: 10.18429/JACoW-IPAC2021-MOPAB127 Open Access Show Abstract ▼ Abstract: Impedance models for accelerators have traditionally been presented in a static form, usually as tables or spreadsheets which must be read manually. As part of the Diamond-II upgrade work, we have developed an impedance model using a lattice structure. This allows more direct integration with simulation codes while keeping important information easily human readable. We present here a description of this implementation method, along with an overview of the Diamond-II impedance model derived from the latest engineering design.	Aug 2021
Electrical Engineering	Harmonic cavity design choice for lifetime increase in Diamond-II Teresia Olsson , R. Bartolini , I. P. S. Martin IPAC2019 DOI: 10.18429/JACoW-IPAC2019-TUPGW078 Open Access Show Abstract ▼ Abstract: The ongoing trend towards synchrotron light storage rings with ultralow emittance leads to a requirement for strong magnet gradients, which reduce the dynamic aperture and thus the Touschek lifetime of the machine. This is also the case for the planned upgrade of the Diamond Light Source. One option to increase the Touschek lifetime is to lengthen the electron bunches with a harmonic cavity operated close to a harmonic of the fundamental RF frequency. This paper presents studies of a harmonic cavity for Diamond-II with the focus on maximising the lifetime increase. It is foreseen that the ring will have to operate with a gap in the fill pattern to avoid instabilities and therefore multiparticle tracking was used to determine the effect on stability and lifetime for various cavity parameters taking into account transient beam loading.	Jun 2019

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