Research Frontiers 2020 Research Frontiers 2020 120 II. Machine Operation In FY2020, the SPring-8 operation of beam injection from the SACLA linac to the storage ring was started. The total operation time of the entire SPring-8 accelerator complex was 5284.6 h. The operation time of the storage ring was 5274.8 h, 81.7% of which (4309.0 h) was devoted to SR experiments. Most of the user time was taken up by beam accumulation and topping-up by beam injection from the SACLA linac. There was no serious machine trouble in the storage ring that might have led to interruptions of user time for more than two hours. The total downtime caused by failures amounted to 7.4 h, which accounted for 0.17% of the total user time. The considerably shorter downtime than in previous years has led to an excellent storage ring availability of 99.7%. The availability this year was calculated by excluding, from the planned user time, a certain period when normal user operation was not available owing to the COVID-19 state of emergency. For 99.4% of the user time in FY2020, the stored beam current was maintained at 100 mA by the top-up operation wherein the stored beam was filled up on demand at any time. Extreme stability of better than 0.1% in the light source intensity was achieved by the top-up operation. The operation statistics of SPring-8 for the last fi ve fiscal years are shown in Fig. 1. The large variety of operation modes for the SR experiments is one of the characteristics of SPring-8. The operation modes are classified into two types: the several-bunch and hybrid-filling modes. The several- bunch mode consists of equally spaced bunches or trains of bunches, for example, 203 bunches or 29 trains of 11 bunches. The hybrid-filling mode is composed of a long train of bunches and isolated single bunches. The operation modes of SPring-8 are listed in Table 1 with the share of each operation mode in FY2020. In the operation with beam injection from the SACLA linac, the spurious bunch sweeping system in the SACLA linac and the bunch cleaning system in the storage ring are activated to maintain a sufficient isolated bunch purity. Table 2 shows the beam parameters of the storage ring. Fig. 1. Operation statistics for last five fi scal years. Table 1. Operation modes in FY2020 Table 2. Beam parameters of SPring-8 storage ring 0 1000 2000 3000 4000 5000 6000 Tuning Refill Down Time User Time Hours 5281.6 5270.4 769.6 4.6 28.7 194.7 4478.7 4512.0 99.3 5284.6 5274.8 964.6 3.6 7.4 718.2 4309.0 4464.0 99.7 5285.7 5271.2 701.7 5.6 40.5 206.3 4537.9 4584.0 99.0 5329.8 5316.7 721.8 5.3 43.1 168.9 4559.6 4608.0 98.9 4951.7 4941.1 803.1 23.1 229.2 4125.5 4152.0 99.4 3.4 Refill Down Time Achieved User Time Planned User Time Availability (%) Accelerator Operation Time Storage Ring Operation Time Tuning & Study (Acc. & BL) Mean Time Between Failures FY2016 FY2017 FY2018 FY2020 FY2019 203 bunches 4 bunch-train × 84 11 bunch-train × 29 1/7-filling + 5 single bunches 2/29-filling + 26 single bunches 1/14-filling + 12 single bunches 4/58-filling + 53 single bunches Single bunch current (mA) Share of operation time (%) 32.6 14.0 14.6 20.8 5.1 0 0 3 1.4 1.6 1.0 11/29-filling + 1 single bunch 12.9 5 Energy [GeV] 8 Number of buckets 2436 Tunes ( / ) 41.14 / 19.34 ν ν x ν ν y Current [mA]: Bunch length ( ) [psec] σ σ 13 Horizontal emittance [nm • rad] 2.4 * single bunch 12 multi bunch 100 Vertical emittance [pm • rad] 4.8 * +2 / +2 * * * Coupling [%] 0.2 RF Voltage [MV] 14.4 * * ~ 16 Momentum acceptance [%] Beam size ( σ σ x / σ σ y )* [ μ μ m] Long ID section 333 / 7 ID section 316 / 5 BM1 section 94 / 12 3.2 ( ~ 256 MeV) BM2 section 100 / 12 Beam divergence ( σ σ x '' / σ σ y '' )* [ μ μ rad] Long ID section 8 / 0.7 ID section 9 / 1.0 BM1 section 58 / 0.5 BM2 section 68 / 0.5 Lifetime [hr]: Operational chromaticities ( ξ ξ x / ξ ξ y ) 100 mA (multi bunch) ~ 250 1 mA (single bunch) ~ 30 Horizontal dispersion [m]: Long ID section 0.153 ID section 0.146 BM1 section 0.039 BM2 section 0.059 Fast orbit stability (0.1 – 200 Hz) [ μ μ m] : horizontal (rms) ~ 4 ~ 1 vertical (rms) * Assuming 0.2% coupling * * Power saving mode * * * With bunch-by-bunch feedback
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