1. CEPC Booster Zhang Chuang, Cui Xiaohao September 11,2015

2. Outline  1.General Description  2.Lattice  3.Dynamic Aperture Issues  4.Low Energy Injection  5.Injection and Ejection  6.Summary

3. 1. General Description Booster is in the same tunnel of the CEPC collider It is installed right at the up-side of the collider Its has almost the same layout with the main collider Bypass lines are added to keep away from detectors

4. 1. General Description It has 8 Arcs

5. 1. General Description It has 8 straight sections

6. 1. General Description  Provides beams for the collider with top-up frequency of 0.1 Hz.  Using 1.3 GHz RF system;  The injection energy of the booster is 6 GeV;  Magnetic Field is as low as 31 Gauss at injection. It has 2 Bypass Lines

7. Main Parameters ParameterSymbolUnitValue Injection EnergyE inj GeV6 Ejection EnergyE ej GeV120 Bending Radius  m6089 Bending FieldB ej /B inj T0.0657/0.00329 Bunch NumberNb48 Bunch PopulationNbNb10 2.1 Beam CurrentI beam mA0.83 SR power@120 GeVP SR MW2.5 Emittance@120 GeV  ej nm.rad6.3 Emittance@6 GeV  inj nm.rad0.0157 Transverse DampingTime@ 6GeV T damp s115.5967s

8. 2.Lattice  Simple Structure FODO cell 47.2m 120 FODODIS ARC Straight ARC Bypa ss Strai ght ¼ Ring

9. Lattice functions FODOARC SF SD

10. Lattice functions SUPRING

11. Bypass Lattice s ()Lc4(3)Lc()Lc4(3)Lc 6(3)Lc6(3)Lc 20(14)L c 4Lc+2L4Lc+2L 6(3)Lc6(3)Lc ()Lc4(3)Lc()Lc4(3)Lc ()Lc6(5)Lc()Lc6(5)Lc ()Lc6(5)Lc()Lc6(5)Lc

12. Different Lattice

13. 3. Dynamic Aperture Issues Two Questions: 1. How Many turns do we need for the DA tracking? 2. Is the DA large enough for our need? DA for 240 Turns DA for 5000 Turns -- No Energy Deviation

14.  Due to the weak damping at Low Energy, electrons in the booster should be stable at least during the time ramping to 120 GeV, 5s(30000Turns).  The beam size at low energy is determined by the injection. In the booster, on center injection is adopted, and the Linac emittance is 0.3mm.mrad. At the DA tracking point,  x =5mm,  y =2.9mm 。  Energy Spread of the Linac beam is 0.1%, so maybe a 0.5% energy acceptance is enough? Dynamic Aperture for 80000 Turns tracking, about 6  in the horizontal and 3  in the vertical.

15. FMA for the booster --- with Elegant

16. FMA for the booster --- Not crossing half integer

17. 4. Low Energy injection issues The bending field of CEPC booster is 614Gs at 120 GeV; To reduce the cost of linac injector, the injection beam energy for booster is chosen as low as 6 GeV with the magnetic field of 31 Gs. It needs to be tested if the magnetic field could be stable enough at such a low field against the earth field of 0.5-0.6 Gs and its variation? Try to find a way to increase the bending field at injection.

18. Low field stability test A BEPC bending magnet: B 0 =9028Gs @ I B =1060A; B 0 =30Gs @ I B =3A 。 Power supplies for ADS: 3A/5V, 15A/8V ;  I/I < 1  10 -4 。

19. Low field stability test

20. The earth field outside the magnet: B x =0.55  0.026Gs, B y =0.45  0.027Gs, B z =0.25  0.03 Gs  B= 0.8  0.04Gs Inside the magnet, B y =7.0  0.05Gs is dominated by residual field, B x =0.4  0.04Gs reduced due to the shielding while B z =0.25  0.03 Gs. The reason of the measured field variation (field itself or measurement error) is being investigated; The 24h field stability (  B ) for 30 Gs-150 Gs is about (1-2)  10 -3 ; The magnet ramps smoothly around the low fields with accuracy better than 1  10 -3 ; The field error  B y /B y  10 -4 for x  (-60, 60) mm and B y  (30-150) Gs The injected beam energy for booster of 6 GeV could be feasible in view of magnetic field stability.

21. 5. Injection and Ejection e  beams are injected from outside of the booster ring; Horizontal septum is used to bend beams into the booster; A single kicker downstream of injected beams kick the beams into the booster orbit.

22. Single kicker + 4 orbit bumps are used for beam extraction vertically from the booster; Septum magnets are applied to bend beams vertically into BTC;

23. Summary  A preliminary CEPC booster design is given.  The dynamic aperture and nonlinear dynamics optimization have to be done for the booster.  Low magnetic field is a central concern in the design of the booster.  Machine Error will be added in the future.

24. Thank You!