1. General Design of C-ADS Accelerator Physics
Zhihui Li
On behalf of IHEP-IMP Joint Accelerator Physics Group of C-ADS
Institute of High Energy Physics

2. Outline Introduction Design philosophy Design status of each part.
Roadmap of C-ADS.
Specifications for the C-ADS driver Linac.
Layout of C-ADS linac
Design philosophy
Measures to maintain high reliability.
Cavity types and lattice structure.
Frequency of the two injectors
Beam dynamics.
Design status of each part.
Summary

3. Road map of C-ADS project

4. Main specifications of the C-ADS driver linac
Particle
Proton
Energy
1.5
GeV
Current 10 mA
Beam power 15 MW
Frequency
162.5/325/650
MHz
Duty factor
100 %
Beam Loss
<1 (0.3)
W/m
Beam trips/year
<25000
<2500
<25
1s<t<10s
10s<t<5m
t>5m

5. Superconducting Linac if preferred for C-ADS accelerator
Characters of C-ADS accelerator.
Low beam loss.
High reliability.
CW operation
S.C. Linac is preferred.
High power efficiency.
Linear trajectory.
Large aperture.
Independent powered short cavity.

6. Progress on C-ADS Linac physical design
Started at at IHEP and IMP.
IHEP: Frequency 352MHz, spoke cavity, 40mA in dynamics design, 10mA in engineering design.
IMP: S.C. CH cavity.
: 325MHz, 10mA in dynamics design, checked with 20mA.
C-ADS project was really launched at the beginning of 2011.
, the IHEP-IMP Joint accelerator physics group.
, first Experts’ review meeting on C-ADS physics design.
3 schemes for injector I and main linac by IHEP.
325MHz (RFQ (3.0MeV)+spoke (0.12, 0.21, 0.4) )+650 MHz elliptical (0.63, 0.82)
325MHz (RFQ (3.0MeV)+R.T. CH (6MeV)+spoke (0.14, 0.33) ) +650MHz elliptical (0.63, 0.82) .
162.5MHz (RFQ (2.5MeV)+HWR(0.09) )+325MHz spoke (0.21, 0.4) +650MHz elliptical (0.63, 0.82)
2 schemes for injector II by IMP
325 MHz (RFQ(3.0MeV) +S.C. CH )
162.5 MHz (RFQ (2.5 MeV) + HWR (0.09) )

7. Layout of the C-ADS linac
Main linac

8. Design philosophy

9. Fault tolerance design to maintain high reliability and availability
The accelerator design needs to have some capabilities of functioning with a number of faulty components, meeting the nominal operational goals (energy, current and stability).
Automated procedures of the accelerator control system need to guarantee the prompt detection of faulty components and consequent machine retune in a short time, with no (or very short) beam interruptions.
Local compensation-for main linac (Energy>10MeV)
“Hot stand by” spare – injector (Energy<10 MeV).

10. Local compensation-for main linac (Energy>10MeV)
Details will be presented by Dr. Fang Yan!
Application conditions:
Short independently powered cavities.
Energy great than 10 MeV.
Why local compensation?
Fast retuning;
Several components failure happen!
Considered components
Cavity
Coupler, LLRF, power amplifier, cavity, …
Solenoid and quadrupole.
Parameters setting
30% of margin for RF cavity is reserved for compensation
Study strategy
Failure happen at beginning, middle and end of each section;
Study of beam behaviors after local rematching.
Results:
Works for main linac.

11. Cavities in the main Linac
Spoke or HWR?
HWR:
lower cost, more compact;
Higher Bpeak/Eacc
650MHz or 1.3GHz for elliptical cavity?
650MHZ
Larger aperture
More efficient
One less frequency jump
Should we re-optimize the cavities （2 types）to reduce the peak magnetic field in the compensation mode, to below 70 or 80 mT?

12. Cavities in the main accelerator
Cavity type b
Energy (MeV)
# of Cavity /CM
Lattice
Spoke021
10-34
30/5
RSR
Spoke040
34-178
72/9
RRSRR
Ellip063
28/7
RRRRT
Ellip082
80/16
RRRRRT
Total length: ~310 m
Total number of cavities: 210

13. Lattice design Good lattice design Focusing elements Economic.
Beam dynamics:
Combining good acceleration and efficiency.
Meeting reliability requirements.
Immune to important beam instabilities and small emittance growth.
Less sensitive to errors.
Less stringent to hardware.
Economic.
Technical feasibility.
Focusing elements
Defocusing effect of SC cavities at low energy.
Spoke sections: S.C. solenoid
Saving longitudinal space.
Efficient at low energy.
Elliptical sections:
Warm quadrupoles.
Design principles
Phase advance per cell: <900.
keep phase advance per meters adiabatically changing along linac.
Ratio of transverse and longitudinal phase advance satisfy the equipartition condition.

14. Lattice design Parameter settings:
I.Gonin et. all, proceedings of IPAC10
Parameter settings:
reference design of SSR0 of Project-X.
Cavity: cavity length (EM design)+117 mm one both sides.
Solenoid: effective length + 75 mm on both sides.
100 mm for BPM.
800 mm for transition between crymodules.
Another 100 mm is left if two cavities are adjacent. 75

15. Lattice design 500 mm is left between two cavities.
Coupler, HOM damper;
Prevent cross-talk between adjacent cavities;

16. Lattice design
For the injector, compact lattice because of low velocity!
For the main linac:
About 400 mm drift space is reserved in both sides of each focusing period!
Periodic property can be maintained within same sections even at the segmentation point.
Benefits the local compensation.

17. Frequency of the injectors
Beam dynamic.
From the viewpoint of beam dynamics in main linac: 325 MHz favored.
Acceleration structure:
RFQ:
162.5MHz :
larger section -> reduce heat density.
larger aperture
325MHz:
LEDA
973 ADS RFQ in IHEP
Superconducting structure
162.5MHz: HWR
325MHz: spoke
325MHz
RFQ+spoke
injector I
162.5MHz
RFQ+HWR
injector II

18. Beam dynamics Very strong space charge effects even at 10 mA!
High intensity beam dynamics design recipes should be applied in design!

19. Possible instabilities
Parametric resonance driven by Transverse - longitudinal coupling
Stable condition: sl0<1.7st0.
Transverse mismatch instability
Stable condition: st0<900.
Longitudinal mismatch instability
Stable condition: sl0<900.
Emittance exchange
Resonance free region in the Hoffman chart;
Equipartition design:
Beam collective instabilities
HOM induced instabilities

20. Principles in beam dynamics design
Design recipes
Phase advance in all planes below 90 degree;
Approximate equipartitionning design;
Large apertures to avoid losses;
Emittance ratios close to 1 (in our case: 0.8, decided by RFQ);
Goals:
Envelope smooth;
Phase advance per meter smooth;
Emittance growth minimized;

21. Phase advance settings
Acceleration gradient is limited by the longitudinal phase advance.
Longitudinal phase advance limitations.
Phase advance law in our design.

22. Development status of each part

23. Design status of Injector I
Two candidates of superconducting section scheme need to be decided:
Spoke 011T solution – high-beta cavity to accelerate low-beta particle.
Spoke 012 solution.
Details will be presented in the following talk

24. Design status of Injector II
ECR LEBT RFQ 4-5m MEBT SC-segment HWR C.M *Sole parts FDF-B-FDF-B keV MeV MeV = = g~0.09
option A1 A2 B
Length of cell
630 mm
Number of cell 16 7？
Number of cavities 7
Number of solenoids 18 6
Focusing period SR
SRR
SR？
Total length
11.2 m
Cryomodules 2 1
Emittance growth (0.99)
10(t)/6.1(l) %
Emittance growth (RMS)
3.2(t)/2.0(l)
Basic frequency is MHz
Ion source extraction voltage is 35 kV
Extraction energy of RFQ is 2.1 MeV
HWR is the main road to develop
CH cavity will be R&D

25. Design status of Injector II
The details of Injector II design will be presented By Prof. Yuan He.

26. Design status of the main linac
The base line is determined.
4 kinds of cavities.
Total number of cavities: 210.
Total length: 310 m.
Intensive beam dynamics study is performed.
Approximated equipartitioning.
Design with different emittance ratios.
Local compensation study.
Error analysis.
Focused on emittance growth control.
Details will be presented by Dr. Fang Yan.

27. Summary
A baseline design for the main linac has been chosen for the review.
Fault tolerance design.
Local compensation in main linac.
“hot-stand-by” spare for Injectors.
Two injectors.
With different frequency: 325MHz and 162.5MHz.
RFQ: dynamics and structure design progress well.
Superconducting section: both have more than one proposals and need to be decided.
Works to be done.
Integration of injector and main linac, front-to-end simulations should be done to prove the performance of the design.
Comparison study of different lattice design.
Commissioning and operation modes study for the linac in phases.
Beam instabilities study ……

28. Thank you for your attention!