1. Investigation of Injection Schemes for SLS 2.0
Angela Saa Hernandez and Masamitsu Aiba
Investigation of Injection Schemes for SLS 2.0
1st Workshop on Low Emittance Lattice Design, Barcelona, April 23rd 2015

2. Motivation (1) SLS to be upgraded into a low emittance ring: SLS 2.0
Lattice ah04n (last “stable” version released)
E [GeV]
2.4
Circ [m]
288
ex [pm]
183
Qx / Qy
39.39 / 10.76
xx / xy /
Dp/p
1.04 e-3
jx / jy / jz
1.13 / 1 / 1.87
U0 [MV]
0.466
a1 / a2
1.3e-4 / 9.4e-4 2

3. Motivation (2)
Low emittance rings have smaller physical and dynamic aperture
Looking for injection scheme:
Top-up compatible
Minimum disturbance to circulating beam
Compatible with booster output parameters:
ex= 7 nm·rad, ey= 1 nm·rad, sz= 19 mm, Dp/p =8e-4
Compact layout (ideally compatible with installation of other device in the same straight section)
Transverse on-axis, or quasi on-axis, to relax requirements on dynamic aperture. (Also needed for round beam scheme) 3
1st Workshop on Low Emittance Lattice Design, Barcelona, April 23rd 2015

4. Options considered for SLS 2.0
Motivation (3)
Options considered for SLS 2.0
Type of injection
On-axis
Off-energy
Off-phase
Orbit bump
Conventional No
Yes
Synchrotron phase space
Longitudinal
Multipole kicker
Off-momentum
multipole kicker
Swap-out
Method:
Construct injection insertion in the lattice
Optimize parameters set of dipole kickers / pulsed sextupole / RF cavities
3D tracking simulations 4
1st Workshop on Low Emittance Lattice Design, Barcelona, April 23rd 2015

5. Conventional injection
Frequently adopted in electron storage rings, employs a static septum and a dynamic magnetic chicane (or kicker bump).
On-axis
Off-energy
Off-phase
Orbit bump No
Yes x x' x x' 5
1st Workshop on Low Emittance Lattice Design, Barcelona, April 23rd 2015

6. Conventional injection into SLS 2.0x'
Assuming bump half-sine time = 4 μs (as in SLS)
Kickers along long straight section, same positions as for SLS
Kicker deflection = 2.2 mrad to create maximum bump amplitude of 7 mm
injected septum bumped ideal closed
beam orbit orbit x
mm mm
mm mm
Use matching section to create a βx bump at IP? Would anyhow break lattice symmetry… 6
1st Workshop on Low Emittance Lattice Design, Barcelona, April 23rd 2015

7. Synchrotron phase-space injection
On-axis version of the conventional injection, already implemented in LEP*. The static septum and kicker bump have to be located in a dispersive section, such that the beam is injected off-momentum onto the dispersive closed orbit.
* P. Collier, Proc. of PAC 1995, pp (1995)
On-axis
Off-energy
Off-phase
Orbit bump
Yes No x x' x x'
Off-momentum
Closed-orbit
Application to SLS 2.0:
Dispersive straight section not compatible with our horizontal low emittance 7
1st Workshop on Low Emittance Lattice Design, Barcelona, April 23rd 2015

8. Longitudinal Injection
New on-axis injection scheme*, which uses the interplay of radiation damping and synchrotron oscillation in longitudinal phase-space to capture a bunch injected off-momentum and off-phase. Needs a static septum and a short-pulse dipole kicker.
*M. Aiba et al.,
PRSTAB, 18, (2015)
Phase=0 corresponds to synch. phase
On-axis
Off-energy
Off-phase
Orbit bump
Yes No x' x z 8
1st Workshop on Low Emittance Lattice Design, Barcelona, April 23rd 2015

9. Longitudinal Injection into SLS 2.0
500 MHz
100 MHz
d ≈ 4.5 %
Kicker profile
Kicker profile
Very tight kicker requirement: pulse length 2 ns
injecting in shaft at center point needs d > 8 %
injecting at d ≈ 4% is OK but  tighter kicker requirement (pulse length ~6 ns)
fRF [MHz] h
VRF [MV] js
sz [ps]/[mm]
500
480
1.15
166.1
9.9/3.0
100 96
0.6
129.1
36.8/11.0 9
1st Workshop on Low Emittance Lattice Design, Barcelona, April 23rd 2015

10. Longitudinal Injection into SLS 2.0
Tracking a bunch in Elegant for the 100 MHz option during turns: no losses observed
Injection at the corresponding c.o. 10
1st Workshop on Low Emittance Lattice Design, Barcelona, April 23rd 2015

11. Multipole kicker injection
Proposed and tested at KEK PF*. The injected bunch passes through the pulsed multipole magnet (typically 4pole or 6pole) with an offset from its center, being kicked by it, while the circulating bunches pass through the center and are not disturbed.
On-axis
Off-energy
Off-phase
Orbit bump No
*H. Takaki et al.,
PRSTAB, 13, (2010) x x'
(Sextupole) 11
1st Workshop on Low Emittance Lattice Design, Barcelona, April 23rd 2015

12. Multipole kicker injection into SLS 2.0x'
injected septum ideal closed
beam orbit x
mm mm mm
Injection point and multipole kicker on same straight section:
robust injection, not affected by magnet field errors or misalignments 12
1st Workshop on Low Emittance Lattice Design, Barcelona, April 23rd 2015

13. Multipole kicker injection into SLS 2.0 (2)
Tracking a bunch in Elegant for turns: ≈6% losses observed
b3∙L = m-2 13
1st Workshop on Low Emittance Lattice Design, Barcelona, April 23rd 2015

14. Off-momentum multipole kicker injection
On-axis version of the multipole kicker injection. It also employs a static septum and a multipole kicker, but the beam is injected with a momentum offset onto the closed orbit.
On-axis
Off-energy
Off-phase
Orbit bump
Yes No x x'
(Sextupole)
Off-momentum
Closed-orbit 14
1st Workshop on Low Emittance Lattice Design, Barcelona, April 23rd 2015

15. Off-momentum multipole kicker injection into SLS 2.0x'
injected septum ideal closed
beam orbit
Goal: flexible injection scheme, at D≠0, valid for standard and off-momentum multipole kicker injection x
mm mm mm 15
1st Workshop on Low Emittance Lattice Design, Barcelona, April 23rd 2015

16. Off-momentum multipole kicker injection into SLS 2.0 (2)
Injection Point
Multipole kicker 1
Multipole kicker 2
Off-momentum closed orbit
b3∙L = 25 m-2
b3∙L = 45 m-2 16
1st Workshop on Low Emittance Lattice Design, Barcelona, April 23rd 2015

17. Off-momentum multipole kicker injection into SLS 2.0 (3)
Tracking a bunch in Elegant for turns: ≈2% losses observed
true on-axis injection, not a betatron oscillation but actually the off-momentum orbit! 17
1st Workshop on Low Emittance Lattice Design, Barcelona, April 23rd 2015

18. Swap-out Injection
Proposed injection scheme for the APS upgrade*. Full current bunches are injected onto the closed orbit and the circulating bunches are kicked out. The swapping can be bunch-by-bunch (needs a short-pulse dipole kicker) or the entire bunch train at once (needs a long-pulse dipole kicker).
*L. Emery and M. Borland,
Proc. PAC 2003, pp (2003)
On-axis
Off-energy
Off-phase
Orbit bump
Yes No x' x
Application to SLS 2.0:
Bunch-by bunch: difficult/impossible to provide injection bunch with full charge for 500 MHz (1 mA) / 100MHz (5mA)
Entire bunch train: additional storage ring too expensive and no space in tunnel 18
1st Workshop on Low Emittance Lattice Design, Barcelona, April 23rd 2015

19. Conclusions Type of injection Results Status Conventional
Oscillations too close to beam pipe, needs increased βx at injection position
Not attractive…
Synchrotron phase space
Needs dispersion in the injection straight section. Dispersion bump not desired
Discarded
Longitudinal
RF gymnastics to match booster bunch into shaft for 500 MHz?
Feasibility of short pulse kicker for 500MHz?
compatible with round beam
Promising results for 100 MHz
Multipole kicker
Optimum matching to transfer line to be explored
incompatible with round beam
On going work…
Off-momentum Multipole kicker
Working on a flexible scheme to combine on- and off-momentum
Promising results
Swap-out
Needs an additional storage ring, or an injection chain capable of providing full-charge bunches 19
1st Workshop on Low Emittance Lattice Design, Barcelona, April 23rd 2015

20. Thanks for your attention!!!20
1st Workshop on Low Emittance Lattice Design, Barcelona, April 23rd 2015