Longitudinal Top-Up Injection for Small Aperture Storage Rings

In 3rd generation light sources, achieving lower emittances requires smaller physical apertures. Top-up injection is essential for stable photon beam flux, but introduces beam disturbances in transversely on-axis injection chicanes. Various injection schemes like conventional, multipole kicker, swap, and longitudinal methods are discussed with considerations for beam transparency and injection chicane necessity. Challenges and solutions for maintaining beam stability and acceptance are explored.

• Injection Schemes
• Storage Rings
• Photon Beam
• Beam Stability
• Emittance

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1. Longitudinal Top-up Injection for Small Aperture Storage Rings M. Aiba, M. B ge, . Sa Hern ndez, F. Marcellini and A. Streun Paul Scherrer Institut LER 14, Frascati, 18.09.2014

2. Introduction Lower and lower horizontal emittances (to be) achieved in 3rd generation light sources Smaller physical/dynamic aperture available in corresponding low emittance storage rings (multi-bend achromat lattice) Top-up injection for stable photon beam flux Frequent injections to keep the e-beam current essentially constant Top-up compatible (Transparent to circulating bunches) Transversely on-axis Injection chicane introduces adverse beam disturbances although it is transparent to circulating bunches in principle Without injection chicane LER 14, Frascati, 18.09.2014

3. Conventional Scheme Septum + Injection chicane (pulsed) Off-axis injection* Transparent to circulating bunches (in principle) With injection chicane x' x' x x *Can be on-axis injection when the injection section is dispersive (P. Collier, Synchrotron phase space injection, see backup slide) LER 14, Frascati, 18.09.2014

4. Multipole kicker injection* Septum + Multipole-kicker Off-axis injection Quasi-transparent to circulating bunches Without injection chicane x' (Sextupole) x * H. Takaki et al., Phys. Rev. ST Accel. Beams, 13, 020705 (2010) LER 14, Frascati, 18.09.2014

5. Swap Injection* Bunch-by-bunch / The entire train at one time Septum + Short/Long-pulse dipole-kicker On-axis injection Pseudo-transparent to circulating bunches Without injection chicane x' x It fulfills our goals but may include some disadvantages * L. Emery and M. Borland, Proc. PAC 2003, pp.256-258 (2003) LER 14, Frascati, 18.09.2014

6. Longitudinal Injection Septum + Short-pulse dipole-kicker On-axis injection Transparent to circulating bunches Without injection chicane x' x z will the injected bunch be accepted? LER 14, Frascati, 18.09.2014

7. Longitudinal Acceptance (1) Equations of motion & RF bucket: dz = c dt + + + 2 3 ( ) 1 ( 3 T 3 ) eV t U d = 0 dt E t 0 0 Longitudin : c position al z Speed : of light Momentum : compaction dP dE Relative : momentum deviation, ~ P E RF bucket is modified by the energy dependent terms Electron : charge e voltage RF : V Radiation : per turn loss for the nominal energy U 0 : Nominal beam energy E 0 Revolution : period T 0 LER 14, Frascati, 18.09.2014

8. Longitudinal Acceptance (2) Golf-club acceptance Well known for the cases with acceleration* Because of energy dependent radiation loss in electron storage rings Long. acceptance plot with synchrotron radiation loss 5 - Synch. phase = 155 deg. - Bucket height ~5 % - Phase=0 corresponds to s the synch. phase ( ) 0 -5 -1.0 -0.5 0.0 0.5 1.0 Phase ( ) It allows an injection between two circulating bunches at the expense of slightly higher injection energy! (Need to match the injection orbit to the off-momentum closed-orbit) * e.g., P. M. Lapostolle, Los Alamos National Laboratory, LA-11601-MS (1989) LER 14, Frascati, 18.09.2014

9. Simulation (1) Application to MAX-IV 3 GeV lattice*/** Relevant parameters with 2 damping wigglers 7BA lattice functions 20 Parameter Value Unit H/V Beta (m) 15 Circumference Beam energy Momentum compaction Radiation loss per turn Damping time Hor./Ver./Long. RF frequency RF voltage (Fundamental/3HC) Hor. equilibrium emittance Betatron tune, Hor./Ver. 528 3.0 m 10 GeV - MeV ms MHz MV nm - 5 3.07 10-4 0.58 12 / 18 / 12 100 1.42/0.423 0.25 40.20 / 16.28 0 Hor. dispersion (cm) 10 5 0 0 5 10 15 20 25 Parameters corresponding to 5% bucket height s (m) * Lattice file, courtesy of S. C. Leemann ** Multipole injection is planned LER 14, Frascati, 18.09.2014

10. Simulation (2) Tracking (Elegant code*) Beta-beat, rms, 3~6% (H/V) Sextupole ver. misalignment 50 mm rms Quad roll error, 0.2 mrad rms Sextupole and Octupole roll error, 0.2 mrad rms Skew resonances + Injection error, 0.5 mm at the middle of straight section ( x~9 m, y~2 m) Injection beam**: Normalised emittance 10 m, Energy spread 0.1%, Bunch length 5 ps Errors: Normal resonances Linear coupling 40 machines generated: 100% efficiency for 39 (95% for 1) Robust against machine imperfections *M. Borland, Advanced Photon Source LS-287 (2000) **S. C. Leemann, Phys. Rev. ST Accel. Beams, 15, 050705 (2012) LER 14, Frascati, 18.09.2014

11. Simulation (3) On-axis injection (Fast injection) Septum + 2 short pulse kickers, ~1.8 mrad each Septum Kicker 10 Injection orbit matched to the off-momentum closed-orbit 5 x (mm) 0 -5 Closed orbit for dP=4.3% Injection orbit from inside Injection orbit from outside -10 -15 0 5 10 15 20 25 s (m) Separation of ~10 mm with reasonable kick angle. Straight section may be available for one more beamline if the septum is situated at the end. LER 14, Frascati, 18.09.2014

12. Short pulse kicker (1) Short pulse kicker R&Ds T. Naito et al., NIM-A, 571,p.599 (2007) D. Alesini et al., PRSTAB, 111002 (2010) 10 ns 10 ns 1/4 geometry Preliminary FEM field simulation Pulser voltage 28 kV Strip-line aperture ~27 mm diameter Integrated kick angle ~1.8 mrad@3 GeV Length ~1 m Matched to 50 Kicker with pulse length of <10 ns (100 MHz) has been developed Enough kick angle for MAX-IV example can be achieved LER 14, Frascati, 18.09.2014

13. Short pulse kicker (2) Very short pulser (spec. from a company) Output voltage 2 kV 5 kV 10 kV 20 kV 50 kV 100 kV 200 kV Rise time 0.1-1 ns 0.1-1 ns 0.1-1 ns 0.1-1 ns 0.1-1 ns 0.1-1 ns 0.2-1 ns Pulse width 0.2 - 3 ns 0.2 - 3 ns 0.2 - 3 ns 1 - 2 ns 1 - 2 ns 1 - 2 ns 1 - 2 ns Max repetition rate 300 kHz 200 kHz 100 kHz 10 kHz 2 kHz 1 kHz 1 kHz Very short pulser is commercially available Nano-second kicker is feasible Applicable to the rings with a common 500 MHz RF system LER 14, Frascati, 18.09.2014

14. Short pulse kicker (3) photons Closed orbit undulator Strip-line design to enable photon beam travel through kicker LER 14, Frascati, 18.09.2014

15. Comparison Longitudinal injection and Swap injection fulfill our goals Pros and Cons Bunch-by-bunch swap injection Bunch train swap injection Longitudinal injection On-axis injection Yes (+dP) Yes Transparent to circulating bunches Yes Pseudo Injection chicane No No Injector Small long. emittance Full bunch charge injector Another ring required Top-up dead-band As in normal top-up Wider dead-band As in normal top-up Kicker pulse length ~ bunch spacing ~ twice bunch spacing Long flat-top (?) Beam loss (radiation) A few orders of magnitude higher As in normal top-up ~twice LER 14, Frascati, 18.09.2014

16. New idea: Multipole kicker injection of off-momentum particles Septum + Multipole-kicker (in dispersive section) On-axis injection Quasi-transparent to circulating bunches Without injection chicane x' (Sextupole) Off-momentum Closed-orbit x LER 14, Frascati, 18.09.2014

17. Summary We investigated longitudinal injection scheme: On-axis transversely and top-up compatible Golf-club acceptance allows one to inject a bunch between two circulating bunches Robust against machine imperfections Required short pulse kicker is feasible Thank you for your attention! LER 14, Frascati, 18.09.2014

18. Backup slide LER 14, Frascati, 18.09.2014

19. Synchrotron phase space injection* Septum + Injection chicane (pulsed) On-axis injection Transparent to circulating bunches (in principle) With injection chicane x' x' Off-momentum Closed-orbit x x *P. Collier, Proc. of PAC 1995, pp.551-553 (1995) LER 14, Frascati, 18.09.2014