1. MEBT1&2 design study for C-ADS
Huiping Geng
Institute of High Energy Physics, CAS
Beijing, China

2. Contents Introduction
Beam dynamics design and multi-particle tracking results of MEBT1
Beam dynamics design and multi-particle tracking results of MEBT2
Summary

3. What’s MEBT1 or MEBT2?
Injector-1 front end layout:

4. Design criteria for MEBT1
Transporting and matching beam from RFQ to the following spoke section
Short reduce space charge effect and cost
Strong and uniform focusing
Element parameter reasonable ( buncher voltage, quadrupole strength, etc.)
Reserve enough space for beam diagnostics

5. Magnetic field gradient (T/m) /Effective electric field (kV)
MEBT1 layout and main parameters
2060 mm
100 60 Q1
600 Q2 Q3 Q4 Q5 Q6
GAP1
GAP2
RFQ
Spoke section
Element
Length (mm)
Aperture (mm)
Magnetic field gradient (T/m)
/Effective electric field (kV) Q1 60 30
35.5 Q2 50
-25.6 Q3 70
15.1 Q4
-14.2 Q5
-14.4 Q6
-13.0
Buncher-1
600 36
81.8
Buncher-2
67.7

6. Beam envelope (rms) evolution in MEBT1
Smooth evolution in both transverse and longitudinal planes !

7. Multi-particle tracking result for MEBT1
Special attention has to be paid to the halo particles in the long. phase space.

8. Multi-particle tracking result for MEBT1 (cont.)
Emittance growth: 1% in transverse
0% in longitudinal

9. MEBT1+spoke011T
Smooth connection from MEBT1 to spoke section !

10. MEBT1+spoke011T (cont.) Emittance growth: 4% in transverse
2% in longitudinal

11. MEBT1+spoke011T (cont.) Phase space at the exit of spoke011T section:
Special attention has to be paid to the halo particles ( especially in the longitudinal plane) !

12. Design criteria for MEBT2
Bend beam from injector-1 to main linac
Matching from the first spoke section to spoke 021 cavity
Achromatic
Maximum dispersion function not too big
Short reduce space charge effect and cost
Uniform focusing----avoid sharp envelope change
Element parameter reasonable (buncher voltage, quadrupole strength, etc.)
Reserve enough space for installation and beam diagnostics

13. MEBT2 layout
10 Quad + 5 Buncher + 2 solenoid+2 Bend
Total length is 10 m.
Quad
Buncher
Bend
Solenoid
Backup buncher
1.2m
45cm
Doublet: focus and keep beam size smooth variation in dispersion section
Buncher-1:
Keep beam length as short as possible at buncher-2
650MHz , NC cavity
Shorter
Higher effective voltage
A maximum feasible voltage of 100 kV is assumed
Dispersion section:
2 Bend + 5 Quad
Achromatic
Bend angle is 20 degree
No buncher in this section
Spoke 021 cells:
High cavity voltage is needed to do longitudinal matching and keep beam line compact
One Spoke 021 module has four cavities, compensation is guaranteed
Two cavity mode or four cavity mode are both applicable
Standard spoke 021 cavity cell
Triplet:
focus the beam to a round beam

14. MEBT2 main parameters Beam energy : 10 MeV Current : 10 mA Element
Length (mm)
Aperture (mm)
Amplitude
B1&B2
327 40
0.5 T Qs
100 60
18.6 T/m (max.)
Solenoid-1
150 50
1.3 T/m
Solenoid-2
1.8 T/m
Buncher-1*
<400
100 kV
Buncher-2
445
233 kV
Buncher-3
256 kV
* Buncher-1 is a 650MHz normal conducting cavity.

15. Beam envelope (rms) in MEBT2
Transverse: uniform focusing, smooth evolution
Longitudinal: maximum rms buncher length is 20 degrees!

16. Multi-particle tracking result for MEBT2
Nonlinear effect is shown in the longitudinal phase space due to the lack of bunching in the long dispersive section.

17. Multi-particle tracking result for MEBT2 (cont.)
Emittance growth: 6% in transverse
13% in longitudinal

18. MEBT2+spoke 021

19. MEBT2+spoke 021 (cont.) Emittance growth happens mainly in MEBT2.
Beam size much less than aperture.

20. MEBT2+spoke 021 (cont.)
After the spoke021 section, the nonlinear effect in the longitudinal plane seems to be smoothed out.

21. Summary MEBT1 dynamics design completed ;
Tracking with realistic particle distribution from RFQ shows a 1% emittance growth in the transverse plane, no longitudinal emittance growth is observed ;
A reasonably good solution has been found for MEBT2 at the moment;
Tracking with Gaussian particle distribution shows a 6% and 13% beam emittance growth in transverse and longitudinal plane, respectively;
Better solutions of MEBT2 are to be studied.

22. Work to be done
Improving the achromatism matching with space-charge included
Reducing longitudinal emittance growth
Further optimizing MEBT2 beam dynamics.
Tracking with 3D Spoke021 field
Designing beam diagnostics and collimation.
Any comments and suggestions will be greatly appreciated !

23. Thanks !