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SPring-8 Upgrade: Lattice Design of a Very Low-Emittance Storage Ring

LER2011. K. Soutome (JASRI / SPring-8) on behalf of SPring-8 Upgrade Working Group. SPring-8 Upgrade: Lattice Design of a Very Low-Emittance Storage Ring. Lattice Team K. Soutome , Y. Shimosaki, T. Nakamura, M. Takao, T. Tanaka. Talk based on the work by

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SPring-8 Upgrade: Lattice Design of a Very Low-Emittance Storage Ring

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  1. LER2011 K. Soutome (JASRI / SPring-8) on behalf of SPring-8 Upgrade Working Group SPring-8 Upgrade: Lattice Design of a Very Low-Emittance Storage Ring Lattice Team K. Soutome, Y. Shimosaki, T. Nakamura, M. Takao, T. Tanaka Talk based on the work by Y. Shimosaki, IPAC2011,"Lattice Design of a Very Low-emittance Storage Ring for SPring-8-II"

  2. "Diffraction Limited" Light Source in Both H. and V. Directions for ~10keV Photons e ~ 10pmrad Ultimate Target of Machine Upgrading SPECTRA E = 6 GeV I = 100 mA k = 0.02 sd = 0.12% bx = 1 m by = 1 m 10 keV Photon by Hybrid Undulator by T.Watanabe

  3. 4 ´ [ 9´(Normal Cell, DB) + (Matching Cell) + (Long Straight) + (Matching Cell) ] Present Lattice Structure of the SPring-8 SR Normal MatchingLSMatching C = 1436 m E = 8 GeV e = 3.4 nmrad （eeff = 3.7 nmrad）

  4. Way of Upgrading Convert present DB cell to Multi-Bend cell. Reuse the present machine tunnel. Keep the number and position of present ID-BLs. Lower the energy: 8GeV 6GeV (or lower) Hard X-ray is covered by undulator upgrading (short period). Reduce the emittance with damping wigglers. Control the coupling (if necessary). Strong Q Large Nat. Chrom. Small Dispersion Strong SX Small DA 2B: 1.9nmrad(Non-Achomat, 6GeV) 3B: 0.43nmrad 4B: 0.16 nmrad 6B: 0.07 nmrad (Achomat) : : "Chromaticity Wall" (J.Bengtsson, EPAC08) We set 6B lattice as a candidate of a new ring.

  5. Multi-Bend Lattice ×M Half-Length B at Both Ends of Unit Cell (Achromat) D.Einfeld and M.Plesko, NIMA335 (1993) 402 〜 3 × Theoretical Minimum Emittance (TME)

  6. 2B (eeff = 2.09nmrad) 3B (eeff = 0.54nmrad) Multi-Bend Lattice 4B (eeff = 0.19nmrad) 6B (e = 0.07nmrad) 2009

  7. 6B Lattice unit unit unit unit matching matching Multi-Bend Lattice bx〜1m by〜1m hx = 0 LB/2 LB/2 LB LB LB LB

  8. DA @ Inj. Point Multi-Bend Lattice Normalized by b1/2

  9. 8B 12B 10B Multi-Bend Lattice e ∝ (NB-1)-3 NB: LB/2 at both ends → (NB-1)

  10. Number of B ↓ Quad. Tune Chrom.(abs) Dispersion ↓ Chromaticity Cor. Sextupoles ↓ Dynamic Apt. Multi-Bend Lattice too small DA for M > 6

  11. 6B Lattice Design (typical)

  12. v. 110921

  13. Use 6B lattice with 0.7 T / 0.9 T / 1.4 T bending field, vary QF and QD and find optics having the emittance of less than 90pmrad. Bending Field Dependence of Chromaticity Nat. Chrom. & Rad. Power & Emit. Reduction by DW 0.7 T

  14. - I transformation Basic Idea: Cancellation of SX Kicks within a Cell (Hor.) small but non-zero DA Interleaved SX Configuration within a Cell SD SD SD SD SD SD SF/2 SF SF SF SF SF SF/2

  15. - I transformation Actual Consraints we put in SX Optimization To increase SX degree of freedom, we relaxed the constraints and added harmonic SXs outside the arc. 12-family (mirror sym.) Interleaved SX Configuration within a Cell SD SD SD SD SD SD SF/2 SF SF SF SF SF SF/2 close but not the same strength

  16. Interleaved SX Configuration between Cells - I transformation Horizontal Cell 1 Cell 5 Cell 3 Dyx ~p Betatron phase advance Dyx ~ 25p Vertical Cell 5 Cell 1 Cell 3 We found the vertical constraint is effective. DA becomes double in vertical direction. Dyy ~ 3p cf.) "sextupole symmetrization" in SLS

  17. Strategy of Lattice Design • Linear Optics • “as low natural-chromaticity as possible” • (so that SX becomes weak) • Tune Selection • (1) avoidance of strong resonances • (2) phase adjustment for interleaved sextupole configuration • Design of Nonlinear Optics • harmonic method with interleaved SX for correcting • (1) linear chromaticity • (2) nonlinear resonances independent of Dp/p (on- and off-mom.) • (3) nonlinear resonances by Q and SX for off-mom. • (4) higher order resonances for on-mom. • (5) amplitude-depence of tune Iteration (tune survey, etc)

  18. Design of Nonlinear Optics Isolated Resonance Hamiltonian (Qx, Qy): Tune Resonant Potential Induced by SX without Dp/p Set to ~ 0 (Off-momentum) Resonant Potential by Q Cancel (Off-momentum) Resonant Potential by Sx Suppress + “(On-momentum) Higher Order Resonant Potentials by Sx”

  19. Sextupole Optimization (latest) Amplitude- and Energy-Dependence of Tune

  20. Sextupole Optimization (latest)

  21. Sextupole Optimization(latest) Dynamic Aperture w/o Error @ Inj. Point (LSS) bx = 24.2 m, by = 7.8 m sx = 40 mm DA Boundary x: integer resonance y: sextupole resonance Frequency Map (d = 0%)

  22. Sextupole Optimization(latest) DA w/ SX Alignment Error (s = 10mm, cutoff 2s)

  23. Sextupole Optimization (latest) Momentum Acceptance

  24. Planar ID (lU = 14.4mm, L = 3m) ×28 （the same number as present @ normal straights） Damping by Insertion Devices Residual dispersion must be suppressed: Dhx < 1mm At user-time: 67pmrad → around 30 pmrad

  25. At user-time：67pmrad　→ around 30pmrad Add DWs (lDW = 50mm, LDW = 4m) at LSSs. Damping Wigglers DWs are used to realize an extremely small emittance less than 20pmrad. They can also be used to keep the emittance at some value during user-time (compensation of ID gap change).

  26. Emittance and Energy Spread Touschek Lifetime Intrabeam Scattering & Touschek Lifetime w/o ID Bunch Length (rms): 7.7 – 10 ps cf.) 1nC/bunch  0.2mA/bunch Control of bunch length is under consideration. Ref.) K.Bane, PRST-AB 5 (2002) 084403. K.Kubo, PRST-AB 8 (2005) 081001.

  27. Brilliance About 103 times higher brilliance than that of the present storage ring (0.5 ~ 100 keV). 1023 New (6GeV, 300mA) Present (8GeV, 100mA) by T.Tanaka

  28. ID Parameters (tentative)

  29. 30m-LSS for Beam Injection 2p Dyx, Dyy One example of LSS Optics (to be optimized) No Sextupoles (Linear) Low Natural Chromaticity Betatron-Phase Matched High b for Beam Injection also for Damping Wigglers / RF p

  30. A high-quality injection beam is needed. At SPring-8 we have XFEL Linac, which will be used as a full-energy injector to the storage ring. Injector XFEL(SACLA) Booster SR Energy: 8 GeV (max.) Emittance: 40 pm.rad Energy Spread: 0.01 % Bunch Length: 30 fs (rms) Electron Charge: 300 pC – 1 nC Design Parameters (typical)

  31. SPring-8 upgrade plan is under discussion. 6B lattice is a current tagret : e 〜 70 pmrad (natural, at 6GeV) →　< 20 pmrad (w/ damping) Brilliance > 1023 Studies are ongoing including further optimization of lattice. DAY-3 K.Fukami, "Strong Magnets for Ultimate Storage Rings" T.Nakamura, "A Fast Kicker System for Beam Injection" Summary

  32. IPAC2011 Papers T. Watanabe, et al. Current Status of SPring-8 Upgrade Plan Y. Shimosaki, et al.Lattice Design of a Very Low-emittance Storage Ring for SPring-8-II T. Nakamura Bucket-by-bucket On/Off-axis Injection with Variable Field Fast Kicker M. Masaki, et al. A Proposal of Short X-ray Pulse Generation from Compressed Bunches by mm-wave iFEL in the SPring-8 Upgrade Plan K. Fukami, et al. Beam-based Alignment for Injection Bump Magnets of the Storage Ring using Remote Tilt-control System

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