RF
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Open Access
Abstract: Two 500 MHz HOM damped normal conducting cavities have been installed in the Diamond storage ring to ensure continuity of operation of Diamond in the event of a failure of one of the two existing superconducting cavities. Following receipt from the manufacturer, the cavities were incorporated into an assembly including vacuum pumping, cooling and interlocked diagnostics and then tested for vacuum integrity and RF performance. Both cavities were then conditioned up to high power in Diamond's RF test facility before being installed in the storage ring in August and November 2017. Conditioning and operation has been carried out using a new digital LLRF system. Results of acceptance tests and commissioning with power and beam are presented, together with the current status of the hybrid RF system and options for further improvement of the system in the near future.
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Jun 2018
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RF
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Open Access
Abstract: In BPM systems, the dependence of measured position on beam current is a well-known behaviour due to many factors. Measurements were carried out at Diamond Light Source with the pilot-tone compensated RF front end developed at Elettra and they evidenced a strong link between that issue and the integral non-linearity (INL) of the ADCs. A potential way to reduce this dependence is to change the gain of the preamplifiers following the beam current variation, trying to coerce the ADC into working as close as possible to a specific level. In this paper, along with the results of the tests performed at Diamond, which confirm once again the effectiveness of the front end and of the compensation strategy, an alternative technique is proposed to mitigate the current dependence by using the pilot tone itself. The idea is to maintain constant the total amplitude at the input of the ADCs, which is composed of the signal from the beam plus the pilot tone. Our data demonstrate how, by changing the latter in a convenient way during the current variations, we can achieve a reduction of the dependence by a factor of 10 considering an equivalent current ramp from 10 to 300 mA.
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Mar 2018
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RF
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Open Access
Abstract: The Diamond Light Source storage ring has been in operation using superconducting RF cavities since 2007. Diamond has four superconducting cavity modules with two usually installed at any one time. The four cavities perform differently in many aspects such as reliable operating parameters and time in service, with the longest in continuous service for 7 years without failure and the shortest failing after only 8 months. All Diamond superconducting RF cavities suffered many fast vacuum trips in their early years, but after many years of efforts, the performance of the cavities have now been effectively managed by weekly conditioning, partial warm-up during shut down and cavity voltage level control. We will discuss our experience with superconducting RF cavities and our future plan.
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Jan 2018
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RF
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Open Access
Abstract: The Diamond storage ring operates with two CESR-B type Superconducting RF cavities. The cavities suffer from trips with a sudden loss of accelerating field if operated above a certain voltage. Consequently the cavities are operated at voltages up to 1.4 MV for better reliability. These cavities are iris coupled and have fixed Qext. At these lower operating voltages, the optimum condition for beam loading is satisfied at powers around 100 kW. For operation at 300 mA with two cavities, the power needed per system exceeds 200 kW. Therefore 3 stub tuners are used to lower the Qext to move the optimum condition close to 200kW. Additionally, the step due to the difference in the height of the coupling waveguide on the cavity and that of the vacuum side waveguide on the window results in a standing wave between the cavity and the window even at matched operation. The 3 stub tuner further enhances this standing wave. Numerical simulation reveals that the standing wave field from the cavity penetrates into the coupling waveguide increasing the probability of multipactor and breakdown in the coupler region. The results of multipactor simulations in this region with CST Studio are discussed.
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Jan 2018
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B23-Circular Dichroism
RF
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Diamond Proposal Number(s):
[10415, 12668]
Abstract: The design and synthesis of water soluble, amino-acid-functionalised naphthalenediimides (NDIs) as potential ligands of native G-quadruplexes is reported. The NDIs were tested on a panel of oncogene promoters, on the human telomeric sequence h-telo, and on double-stranded DNA. Out of the ligands tested, NDI 3 (Nϵ-Boc-l-lysine NDI) exhibited a highly discriminating nature by only stabilising the oncogene promoter c-kit2, which is up-regulated up to 80 % in ovarian, gastrointestinal, and breast malignancies.
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Jun 2017
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Insertion Devices
RF
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Open Access
Abstract: The characterisation of the multi-bunch dynamics at the Diamond light source is performed with an advanced TMBF system that is capable of operating fast grow damp experiments thus allowing the exploration of many machine conditions. We report here the latest results of the measurement campaign, the implication on the machine impedance model and some of the intricacies of the analysis and interpretation of the experimental data.
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May 2017
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RF
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Open Access
Abstract: In order to avoid longitudinal multibunch instabilities potentially caused by the addition of normal conducting RF cavities into the Diamond storage ring, a longitudinal feedback was installed. The main components are newly developed feedback electronics, in-house built modulator and amplifier, and a low Q kicker cavity. This paper describes the performance of the cavity as well as the full longitudinal feedback system as it is installed on the machine and tested before the installation of the normal conducting RF cavities.
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May 2017
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RF
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Open Access
Abstract: Analogue low level RF (LLRF) systems have been used to date for both Diamond storage ring and booster RF cavities. They have been in operation for nearly ten years without a major problem. However, digital LLRF can offer new desirable functionalities such as fast data logging, 'probe blip' blockage and automation of routine tasks. Better performance is also envisaged with up to date hardware. A digital LLRF system has been developed with Alba Synchrotron as a common platform for the storage ring and booster, including superconducting and normal conducting RF cavities. The new digital LLRF is based on Virtex6 FPGA and fast ADCs and DACs. One system has been built and verified in the Diamond booster with beam. The design will be implemented for all other Diamond RF cavities.
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May 2017
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Accelerator Physics
Electrical Engineering
Insertion Devices
Magnets
RF
Theoretical Physics
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Abstract: A simple method, based on layer by layer direct summation, is used to determine the local dipolar fields in uniformly magnetized thin films. The results show that the dipolar constants converge ~1/m where the number of spins in a square film is given by (2m+1)^2. Dipolar field results for sc, bcc, fcc, and hexagonal lattices are presented and discussed. The results can be used to calculate local dipolar fields in films with either ferromagnetic, antiferromagnetic, spiral, exponential decay behavior, provided the magnetic order only changes normal to the film. Differences between the atomistic (local fields) and macroscopic fields (Maxwellian) are also examined. For the latter, the macro B-field inside the film is uniform and falls to zero sharply outside, in accord with Maxwell boundary conditions. In contrast, the local field for the atomistic point dipole model is highly non-linear inside and falls to zero at about three lattice spacing outside the film. Finally, it is argued that the continuum field B (used by the micromagnetic community) and the local field B_loc(r) (used by the FMR community) will lead to differing values for the overall demagnetization energy.
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Aug 2016
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NONE-No attached Diamond beamline
RF
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Open Access
Abstract: Diamond's CESR-B cavities are iris coupled and have fixed Qext. For reliability, the cavities are operated at lower voltages. This results in the optimum condition for beam loading being satisfied at a much lower power typically about 100 kW. For operation at 300 mA with two cavities, the RF power needed per system exceeds 200 kW. Consequently, the cavities need to be operated under-coupled. To lower the Qext and move the optimum operating point nearer to 200kW, 3 stub tuners are used in the waveguide feed line. The difference in the height of the coupling waveguide on cavity and that of the vacuum side waveguide on the window assembly results in a step transition which affects the Qext. The present window/step location results in Qext higher than that without the window. The Qext can be lowered by re-locating the RF window or by shifting the step change in the waveguide cross-section from its present location. This needs modification to the Pump Out box. The pros and cons of the proposed modification to the pump out box in terms of standing waves and multipacting characteristics studied with CST Studio are discussed in this paper.
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Jun 2016
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