1. Physics Design on Injector I
Zhihui LI
Institute of High Energy Physics, CAS

2. outline Introduction Cavity optimization.
The superconducting section based on spoke011T cavity.
The superconducting section based on spoke012.
Summary

3. Introduction Why 325MHz? Disadvantages.
Same as main linac, without frequency jump.
Same type cavity as the first two sections of the main linac.
Experience on the development of same kind of RFQ.
RF system.
Disadvantages.
Low beta cavity development.
No experience all over the world to learn.
Poor frequency instability because of thin gap width.
High beta cavity working at three-half-wavelength mode
Proved performance of same kind of cavity.

4. ECR ion source and LEBT Details will be presented by Dr. Yao Yang.
Beam energy (keV) 35
Proton intensity (mA)
20~30
Microwave frequency (GHz)
2.45
Microwave power (kW)
1.5-2
Emittance (rms, πmm mrad)
0.15~0.2
Proton fraction
>85%
Reliable operation
>120 h
 Total length (extraction electrode to RFQ entrance) ~ 1207mm
 The length from the extraction electrode to the edge of G1 ~ 130mm
 The pipe diameter ~ 98mm (front)/148mm (end)
The adjustable distance from G1 to G2 ~ 250mm to 400mm (bellows connected)
Details will be presented by Dr. Yao Yang.

5. RFQ Details will be presented by Prof. Ouyang in the other talks.
Parameters
Value
Frequency (MHz)
325
Injection energy (keV) 35
Output energy (MeV)
3.2128
Pulsed beam current (mA) 15
Beam duty factor
100%
Inter-vane voltage V (kV) 55
Beam transmission
98.7%
Input norm. rms emittance(x,y,z)(πmm.mrad)
0.2/0.2/0
Output norm. rms emittance(x/y/z) (πmm.mrad/MeV-deg)
0.2/0.2/0.0612
Vane length (cm)
467.75
Accelerator length (cm)
469.95

6. MEBT1 Details will be presented by Dr. Huiping Geng. Spoke section
Design criteria for MEBT1
1. Transporting and matching beam from RFQ to the following spoke section.
2. Short: reduce space charge effect and cost.
3. Strong and uniform focusing.
4. Element parameter.
5. Reasonable ( buncher voltage, quadrupole strength, etc.).
6. Reserve enough space for beam diagnostics.
2060 mm
100 60 Q1
600 Q2 Q3 Q4 Q5 Q6
GAP1
GAP2
RFQ
Spoke section

7. Cavity optimization

8. Spoke012 cavity

9. Spoke012 cavity bg Freq. MHz Uacc. Max MV Epeak MV/m Bpeak mT R/Q 0.12
325
0.82
32.5 54
125

10. Challenges on developing of low beta cavity.
Frequency stability
Mechanical stability
Is it possible to apply a proved relatively large-beta cavity to replace the low-beta cavity?

11. Acceleration efficiency of 2-gap structures
High beta cavity can be used to accelerate low beta particles!
If we define:
Then we call the cavity as SpokebgT

12. Cavity optimization Optimization goals Optimization parameters
Less cavity types;
Higher energy gain;
Optimization parameters
Cavity geometry beta;
Gap width;
With one kind of three half wave length cavity and spoke021 cavity, the energy range of the injector can be covered.

13. Cavity optimization Geometry of spoke011T spoke011T spoke012
Radius (mm)
249.0
216.0
Aperture (mm)
35.0
40.0
Spoke width (mm)
92.5
30.0
Iris to iris (mm)
182.5
79.0
Gap width (mm)
45.0
25.0
Spoke base radius (mm)
80.0
55.0
Top length (mm)
250.0
190.0
Geometry of spoke011T

14. Comparison of EM properties of spoke011T and spoke012
R/Q0 (W)
125
185
Vmax (MV)
0.81
1.94/0.91
Hmax (mT)
54.6 75
Emax (MV/m)
32.5
Loss (W)
1.0
4.0

15. Cavity optimization

16. Comparison of spoke011T and spoke012
Mechanical properties
Spoke009T
Spoke012
f/p (pipe free)
50.6Hz/Pa
135Hz/Pa
Tuning sensitivity
620kHz/mm
1319 kHz/mm

17. Injector I based on spoke011T cavity

18. Lattice structure Spoke 011T Spoke 021
Cavity working conditions: Epeak=32.5MV/m,
Bpeak=70 mT for spoke 021
75 mT for spoke 011T
Solenoid field strength: <3.2T

19. Zero current phase advance

20. Dynamics results

21. Beam size

22. Emittance evolution RMS emittance growth: T: <5 % L: <5 %
T: no significant growth
L: about 20% increase

23. Phase space distribution

24. Simulation results from RFQ to exit of superconducting section

25. Simulation results from RFQ to exit of superconducting section

26. Conclusions on the “spoke011T+spoke021” one CM scheme
8+4 cavities, without additional cavity types compared with the spoke 012 scheme;
Lowest beta of cavity is increased to 0.21, which performance is well proved at FNAL for Project-X in Lab;
CM length: ~11m;
Disadvantage: increased thermal load per cavity (4 times);

27. Injector I based on spoke012 cavity

28. Lattice
Epeak = MV/m,
Bpeak = 56 mT

29. Dynamics results-envelop

30. Beam size

31. RMS emittance evolution

32. 99% emittance evolution

33. Phase space distribution

34. Possible problems with one CM design
Higher field level;
Relatively long CM with too many components;
Small synchronous phase at exit;

35. Lattice design with two CM
18 cavities;
16 solenoids;
2 crymodules;
CM length=8.2 m;
Maximum surface electric field is reduced to 25 MV/m,
the corresponding maximum surface magnetic field is 48 mT

36. Dynamics results

37. Dynamics results

38. Dynamics results

39. Dynamics results

40. Dynamics results

41. Acceptance of schemes based on spoke 012 cavities
2 CM longitudinal acceptance and emittance
1 CM longitudinal acceptance and emittance

42. Comparison of the two different schemes based on spoke012 cavity
Dynamics behaving:
Single CM scheme is much better than 2 CM scheme;
Cavity:
Numbers: 18~13;
Gradient: 25 -> 33.25;
CM:
Alignment; ….

43. Summary
High-beta cavity working at three-half-wavelength mode can replace the function of low-beta cavity to accelerate low beta particles.
Both cavity and beam dynamics study shows the three-half-wavelength method is a good candidate way for the low-beta proton acceleration. Spoke011T is much better than spoke012 both in frequency and mechanical stabilities, but spok011T has a larger thermal load than spoke012.
A scheme based on spoke011T and spoke021 cavities to cover the injector I energy range is proposed. The beam dynamics results of schemes based on spoke011T and spoke012 cavities are both very good.
Two-cryomodule solution based on derated Spoke012 cavities and symmetrically varying lattice  has also been studied, but the dynamic performance is significantly worse than one-cryomodule solution ;

44. Thank you for your attention!