Research Frontiers 2021 Research Frontiers 2021 116 II. Machine Operation The operation statistics for the last five fiscal years are shown in Fig. 1. The linear accelerator of the X-ray Free- Electron Laser (XFEL) facility, SACLA, has been used as a full-time injector for the SPring-8 storage ring since 2020. In FY2021, all the user time was taken up by beam accumulation and topping-up by beam injecting from the SACLA linac. The operation time of the storage ring was 5300.2 h, 83.5% of which (4426.9 h) was devoted to the SR experiments. This excellent figure for the user time represents a storage ring availability of 99.7%. The total downtime caused by failures amounted to 10.0 h, accounting for 0.22% of the total user time. For 99.6% of the user time in FY2021, the stored beam current stayed at 100 mA by the top-up operation wherein the stored beam was filled up on demand at any time. Extreme stability of the light source intensity of better than 0.1% was achieved by the top-up operation. The 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 such as 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 FY2021. 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 suffi cient isolated bunch purity. Table 2 summarizes the beam parameters of the storage ring. Fig. 1. Operation statistics for five most recent fiscal years. Table 1. Operation modes in FY2021 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 5300.2 5300.2 860.2 3.1 10.0 553.4 4426.9 4440.0 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 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 FY2017 FY2018 FY2020 FY2021 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 (%) 41.1 3.2 30.8 8.1 0 3.2 0 3 1.4 1.6 1.0 406 × 11/29-filling + 1 single bunch 13.5 5 Energy [GeV] 8 Number of buckets 2436 Tunes ( / ) 41.14 / 19.325 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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