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Instruments / Technical Area	Publication Details	Published
RF	RF plans for the Diamond-II upgrade C. Christou , P. Gu , Pe. Marten , S. A. Pande , A. Rankin IPAC2021 DOI: 10.18429/JACoW-IPAC2021-MOPAB107 Open Access Show Abstract ▼ Abstract: The RF system for the proposed Diamond-II upgrade will be based on normal-conducting EU HOM-damped cavities powered by high powered solid state amplifiers and controlled by digital low level RF systems built on the microTCA platform. Reasons for these design choices are discussed, and experience of the selected technologies in the Diamond-I ring are reviewed. The storage ring will also include a third harmonic cavity, and the different design options for this device are discussed. RF design of the booster ring is presented, and details are given of an upgraded linac and gun design intended to improve the charge delivered for top-up.	Aug 2021
RF	Overview of superconducting RF cavity reliability at Diamond Light Source C. Christou , P. Gu , P. Marten , S. A. Pande , A. Rankin , D. Spink , L. T. Stant , A. Tropp International Conference on RF Superconductivity (19th) DOI: 10.18429/JACoW-SRF2019-THP025 Open Access Show Abstract ▼ Abstract: Diamond Light Source has been providing beam for users since January 2007. The electron beam in the storage ring is normally driven by two superconducting CESR-B cavities, with two similar cavities available as spares. Day-to-day reliability of the cavities, measured by storage ring MTBF, has improved enormously over the years. A full analysis of how this improvement has been achieved is given, with particular attention paid to cavity voltage and vacuum pressure management, and the scheduling and procedure of cavity conditioning. The benefits and risks of full and partial warm-ups of the cavities are discussed, and details and impacts of cavity failure and repair are presented.	Aug 2019
RF	Commissioning of the hybrid superconducting/normal conducting RF system in the Diamond storage ring C. Christou , A. G. Day , P. Gu , P. J. Marten , S. A. Pande , D. Spink , A. Tropp 9th International Particle Accelerator Conference DOI: 10.18429/JACoW-IPAC2018-THPMF007 Open Access Show Abstract ▼ 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.	Jun 2018
Electrical Engineering	Simulation of cavity conditioning for the diamond SCRF cavity S. A. Pande , C. Christou , Pengda Gu 9th International Particle Accelerator Conference IPAC2018 DOI: 10.18429/JACoW-IPAC2018-WEPMF062 Open Access Show Abstract ▼ Abstract: Diamond SCRF cavities are pulse conditioned every week in order to keep them operating reliably. During conditioning, the cavities are detuned in order to sweep the standing wave through the waveguide. To match these cavities at lower voltage (typically < 1.4 MV) and at higher power, 3 stub tuners are used in the waveguide feed. Simulations with CST studio show that a strong SW field exists between the RF window and the matching posts. As the cavity is detuned the electric field maximum passes through the window causing heating of the ceramic. Temperature measurements with thermal camera reveal that the temperature of the window increases to maximum when the cavity is detuned towards higher frequency. Based on the simulation results and the measurements, it was decided to reduce the conditioning voltage. These results are summarised.	Jun 2018
RF	Operation of Diamond superconducting RF cavities P. Gu , C. Christou , P. J. Marten , S. A. Pande , A. F. Rankin , D. Spink 8th International Conference on RF Superconductivity SRF2017 DOI: 10.18429/JACoW-SRF2017-MOPB016 Open Access Show Abstract ▼ 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.	Jan 2018
RF	Multipactor study in the coupler region of the Diamond SCRF cavities S. A. Pande , C. Christou , Pengda Gu , G. Burt 18th International Conference on RF Superconductivity SRF2017 DOI: 10.18429/JACoW-SRF2017-TUPB010 Open Access Show Abstract ▼ 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.	Jan 2018
Mechanical Engineering	Progress with the Diamond Light Source RF upgrade C. Christou , A. G. Day , M. J. Duignan , P. Gu , N. Hammond , P. Marten , S. A. Pande , D. Spink IPAC2017 DOI: 10.18429/JACoW-IPAC2017-THPIK112 Open Access Show Abstract ▼ Abstract: Failure of a superconducting cavity in the Diamond storage ring can lead to extended down-time because of the time required to remove the module from the ring, the inability to access the cavity without removal from the cryostat and the long time to repair of the module. To reduce the risk to storage ring operation, normal conducting cavities are being installed to support operation of the superconducting cavities. Two cavities will be introduced in 2017 and work is progressing with RF amplifiers, transmission lines and low-level RF as well as storage ring engineering and controls. A summary of progress so far is presented and the plan for installation and further RF upgrades is outlined.	May 2017
NONE-No attached Diamond beamline RF	Modifications to the pump out box to lower the QEXT of Diamond SCRF cavities S. A. Pande , C. Christou , P. Gu , G. Burt 7th International Particle Accelerator Conference, May 8 – 13, 2016. Busan, Korea. DOI: 10.18429/JACoW-IPAC2016-WEPMB060 Open Access Show Abstract ▼ 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.	Jun 2016
RF	A hybrid superconducting/normal conducting RF system for the Diamond Light Source storage ring C. Christou , A. G. Day , P. Gu , N. Hammond , J. Kay , M. Maddock , P. Marten , S. Pande , A. Rankin , D. Spink IPAC 2016 DOI: 10.18429/JACoW-IPAC2016-WEPOW047 Open Access Show Abstract ▼ Abstract: 300 mA beam in the Diamond Light Source storage ring is presently maintained by two 500 MHz superconducting (SC) CESR-B cavities. Cavity reliability is acceptable at voltages up to 1.4 MV per cavity but falls off rapidly above. Installation of extra cavities would reduce the voltage demand on the current cavities and also the operating power level of the amplifiers, with commensurate improvement in reliability. Furthermore, two recent SC cavity failures have resulted in machine down-time and reduced-current operation, and repair has proven to be prolonged and expensive. It is therefore planned to install two normal conducting (NC) cavities into the ring to support operation of the SC cavities and to act as a safeguard against any future SC cavity failures. Details are presented in this paper of plans and p	May 2016
NONE-No attached Diamond beamline	Optimization of window position on Diamond SCRF cavities S. A. Pande , C. Christou IPAC14 DOI: 10.18429/JACoW-IPAC2014-WEPRI049 Open Access Show Abstract ▼ Abstract: The Diamond storage ring uses CESR type superconducting cavities. These cavities have a fixed coupling resulting in fixed Qext which is considerably higher than the optimum. We use 3 stub tuners to match the cavities under these non-optimum conditions. Diamond Cavity-1 will soon be refurbished. This opportunity could be used to lower the Qext on the cavity. One of the options is to modify the coupling tongue geometry along with a matching section. This may require cutting off the beam tube with the coupler for rework or it may need to be newly fabricated. We investigated another option to lower the Qext of the cavity by optimising the location of the window with respect to the cavity, maintaining the same coupling tongue geometry. The height of the waveguide on the vacuum side of the window differs from that of the coupling waveguide on the cavity resulting in a step. The location of window with respect to the cavity makes a significant difference to the ultimate Qext obtained after putting the window in place. In this paper we present the results of our numerical simulations comparing the present and the proposed window position under different operating conditions.	May 2014

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