Diamond Annual Review 2019/20
96 97 D I A M O N D L I G H T S O U R C E A N N U A L R E V I E W 2 0 1 9 / 2 0 D I A M O N D L I G H T S O U R C E A N N U A L R E V I E W 2 0 1 9 / 2 0 Machine Operation and Development RichardWalker,Technical Director I n 2019/20, our 13 th year of operations, a total of 208 days (4,992 hours) were scheduled for beamline operations, 203 days of User Mode, and 5 beamline start-up days. The majority of the beam delivery was in standard multibunch mode (900 bunch train) or “hybrid”mode (686 bunch train + a single bunch) with total current of 300mA. In addition, there was one day inMay 2019 and two days in August 2019 of “low-alpha”mode to produce short bunches (3.5 ps rms). All beamline operations were carried out in top-upmode. The annual operating statistics are shown in Fig.1.The MeanTime Between Failures (MTBF) for the year was 104.7 hours, an improvement over the previous year and our 5 th successive year exceeding the target minimum of 72 hours.The overall uptime (beam delivered as a percentage of scheduled hours) also remained high at 98.2%. Cryogenic Permanent Magnet Undulator The first of a new series of cryogenic permanent magnet undulators (CPMUs) has been installed in Diamond, to provide an increase in photon flux on a number of beamlines, especially in the hard X-ray region. These devices differ from an earlier type of CPMU that was installed several years ago, in that they use more advanced permanent magnet material PrFeB, which is cooled to liquid Nitrogen temperature (77K) rather than NdFeB cooled to 150K. The new device (see Fig. 2) was designed and built in-house. RF upgrades Diamond’s two new normal conducting radiofrequency (RF) cavities are now fully operational in the storage ring, providing a valuable back-up to the superconducting cavities. Use of these cavities in recent low-alpha special beam conditions for users, allowed the superconducting cavities to be operated at a reduced voltage, resulting in a clear increase in reliability. Diamond has recently taken delivery of a third normal-conducting cavity, that will be installed in the storage ring in 2021, to give further machine resilience. Accelerating fields in the normal conducting cavities are regulated by two new digital low-level RF (DLLRF) units, which offer an adaptability and flexibility that the previous analogue control loops did not have. Further DLLRF units are in development to give a common platform for all RF cavities. An RF pulse-compression, so-called SLED (SLAC Energy Doubler) cavity, is being tested in the linear accelerator (linac). The SLED cavity (see Fig. 3) will double the instantaneous power delivered by either one of the two high- power klystron amplifiers, ensuring continuity of linac operation even in the event of failure of one of the two klystrons. Diagnostics developments Emittance is a key performance parameter for all modern synchrotron light sources, since it determines the brightness of the radiation served to user beamlines. Diagnostics with high spatial resolution are needed both to measure the emittance accurately, particularly in the vertical plane, but also provide a suitable signal for a feedback system. Diamond uses X-ray pinhole cameras to image the electron beam via its emitted X-rays. To improve the spatial resolution of the cameras, we are investigating the use of LIGA (X-ray lithography) technology. LIGA enables the fabrication of high-aspect ratio structures using highZ materials, such that the pinhole aperture size can be precisely controlled at the micron level, much more precise and reproducible thanourstandardpinholesbuiltusingtungstenbladesandshims.Furthermore, each 10mm x 10mm LIGA screen can have 15 different pinhole sizes (in order to optimise the resolution) with nine apertures each, providing redundancy in case of any deterioration (see Fig. 4). The DiamondMulti-Bunch Feedback (MBF) system requires a critical timing reference derived from the machine master oscillator, that locks data converter sampling to the bunch arrival time at a Beam Position Monitor (BPM) output. Any operational adjustment to the Radio Frequency (RF) and injection systems can change this timing relationship and require manual adjustment, typically every 20 days. Recently, a Delayed Orbit Reference Improvement Scheme (Doris) has been developed, that directly phase locks the MBF timing to the BPM outputs, automatically compensating for any operational changes to the beam timing. Doris has been in operation in the storage ring now for three months, and no operator manual adjustments have been needed during that time. Fig. 5 shows the significant improvement in phase stability of the MBF since Doris was installed. Diamond-II Work on Diamond-II, the planned upgrade of Diamond, has also progressed significantly during the year. A draft Conceptual Design Report (CDR) was reviewed and endorsed by an international committee of experts in April 2019, and the final version of the CDR subsequently published in May 2019. We then entered theTechnical Design Report phase of the project which should complete at the end of 2021. An international Machine Advisory Committee has been established to provide advice to the project, which met for the first time in February 2020. Accelerator physics, engineering and vacuum studies are continuing. Fig. 6 shows an example of a full CAD model for one of the four girder types, which makes up one half of a cell of the storage ring. Figure 1. Mean Time Between Failures (MTBF) and Uptime by operating year. Figure 2. The recently installed Cryogenic Permanent Magnet Undulator. Figure 3. The SLED cavity during assembly on its support structure. Figure 4. X-ray pinhole camera images of the electron beam in the storage ring. The images are from nine identical 12.5 micron pinhole apertures, but only the central three are illuminated fully by the X-ray beam. Figure 5. Multi-bunch feedback (MBF) timing phase error showing the improvement after “Doris” was installed. Figure 6. 3D CAD model of one of the Diamond-II girders: green – dipole (bending) magnets, red – quadrupole (focusing) magnets, yellow – sextupole (1 st order non-linear correction) magnets, pink – octupole (2 nd order non-linear correction) magnets.
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