1. Physics design on Injector-1 RFQ
OUYANG Huafu

2. Contents RFQ R&D background at IHEP C-ADS RFQ design philosophy
C-ADS RFQ dynamic design
C-ADS RFQ structure design
C-ADS RFQ water-cooling design and thermal analysis
Summary

3. RFQ R&D background at IHEP
A High-duty factor proton RFQ accelerator for ADS study has been constructed at IHEP (973 ADS RFQ)
Nice performance with a transmission rate about 93% and an output beam current of 44mA with a duty of 7%.
Progress in high-duty factor operation from about 7% to 15% is achieved
44.5mA pulsed current with a transmission about 93% and beam duty factor of 7.15%.
973 ADS RFQ in the installing process

4. RFQ R&D background at IHEP
Main parameters of 973 ADS RFQ
This 4.75 long RFQ consists of two segments, which are resonantly coupled by a coupling cell. Each segment is formed by two technical modules.
Input Energy
75keV
Output Energy
3.5MeV
Peak Current
50mA
Structure Type
4-Vane
RF Frequency
352.2MHz
Inter-vane voltage
65kV
Maximum Surface E
33MV/m (1.8Kilp)
Structure Power
458[1.4*PSuperfish (327kW)]
Beam Power
175kW
Total Power
638kW
Total Length
4.75m
One technical module (1.2m long)

5. C-ADS RFQ design philosophy
A proper beam current (15mA), injection (35keV) and output (3.2MeV) energy.（beam requirement for C-ADS　LINAC 10mA）
An appropriate length. < 4.8m (Similar to 973 ADS RFQ, the foreseen RFQ will consist of 2 physical resonantly coupled segments, and each segment includes 2 technical modules with a length less than 1.2m)
Higher beam transmission preferable. > 98% (beam loss worsens the deformation of RFQ, vice versa, deformation lows the beam transmission )
As low as possible for RF power dissipation per unit length and per area. (to this end, a low inter-vane voltage 55kV chosen)
As low as possible for the output beam emittance. (0.2.mm.mrad/0.2 .mm.mrad/0.0612MeV.Deg)

6. C-ADS RFQ design philosophy
6. Redundant water-cooling capability and water-cooling control protection ways.
7. Conservative RF coupler design to low the load of RF coupler and ensure the reliability of coupler. (4 RF power coupler,　80kW for each RF　coupler)
8. To take full use of the successful experiences of the former 973 ADS RFQ designing, machining and operation at IHEP. (similar structure is chosen as the former due to the near working frequency of the two RFQ)

7. C-ADS RFQ dynamic design
The standard LANL chain of RFQ Codes Curli, RFQuick, Pari and Parmteqm are used to design the RFQ. For these codes, the design RFQ are physically divided into four sections, ie., Radial Matching Section (RMS), Shaper, Gentle Buncher (GB) and Accelerator. In order to get a good beam transmission and a better bunching, both the shaping and the bunching energy are chosen to be comparatively lower values. At present, the dynamic design is finished.

8. Table 1: Main RFQ design parameters
Value
Frequency (MHz)
325
Injection energy (keV) 35
Output energy (MeV)
3.2128
Beam current (mA) 15
Beam duty factor
100%
Inter-vane voltage V (kV) 55
Beam transmission
98.7%
Average bore radius r0 (mm)
2.775
Vane tip curvature (mm)
r / r0
1.0
Maximum surface field (MV/m)
28.88 (1.62Kilp.)
Cavity power dissipation (kW)
[1.4* Psuperfish (194.96)]
Total power (kW)
320.94
Avg. Copper power/Length (kW/m)＊
41.68　　 （Psuperfish）
Avg. Copper power/Area (W/cm2)＊
3.25　　 （Psuperfish）
Max. copper power/Area (W/cm2)＊
3.77　　（ Psuperfish）
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
Gap1(entrance) (cm)
1.10
Gap2(exit) (cm)
Accelerator length (cm)
469.95

9. C-ADS RFQ dynamic design
Main parameter variation with cell number

10. C-ADS RFQ dynamic design
The beam transmission is about 98.7%

11. C-ADS RFQ dynamic design
Particle distributions in phase space at the entrance and exit of RFQ

12. C-ADS RFQ dynamic design
Transmission versus input beam parameters

13. C-ADS RFQ structure design
RFQ consists of 2 physical resonantly coupled segments, and each segment includes 2 technical modules connected together with flanges. 4 four dipole rods are installed on the entrance plate, both sides of the coupling plate and the end plate. There are 64 plug tuners with a diameter of 55mm and nominated penetration of 5.2mm into the cavity. 16 vacuum port bodies will be machined separately and then brazed together with RFQ cavity. There are 8 RF coupler ports and 4 ports will be used. At present, the structure design is basically finished.
The mechanical length for the for the 4 modules
(1) mm (2) mm (3) mm (4) mm.
One quadrant of the RFQ 3-dimension structure

14. C-ADS RFQ structure design
Similar structure as the former 973 ADS RFQ at IHEP is chosen due to the near working frequency of the two RFQ, highly time-saving in optimization of the structure and the mechanical drawing afterwards.
One quadrant of the RFQ transverse shape

15. C-ADS RFQ structure design
Nominated penetration of 0.7mm into the cavity compensates the frequency drop caused by the vacuum port.
Shape and size of the vacuum port

16. C-ADS RFQ structure design
Thickness: 18mm
Shape and size of the coupling plate

17. C-ADS RFQ structure design
Position: (31.719，31.719)
Diameter: 15mm
Length: mm
Position, shape and size of the dipole stabilization rod

18. C-ADS RFQ structure design
The shape and size of the beginning cell, the coupling cell and the end cell

19. C-ADS RFQ structure design
The frequency interval between the operation quadrupole mode and its neighboring quadrupole modes is about –3.6MHZ and 3.5MHZ. For 973 ADS RFQ, the value is +-3MHZ.

20. C-ADS RFQ structure design
The frequency interval between the operation quadrupole mode and its neighboring dipole modes is about –5.4MHZ and 5.55MHZ. For 973 ADS RFQ, the value is +-5MHZ.

21. C-ADS RFQ water-cooling design and thermal analysis
Water-cooling serves two functions in an RFQ. One is to take away the power dissipated on the inside surface of the RFQ by the RF field to maintain the thermal stability and to limit the deformation of RFQ. The other is to be used to tune the RFQ basically without effecting the field distribution profile when the RFQ is out of resonance, since the beam transmission of RFQ is very sensitive to the field profile, the ordinary frequency tuning method by the movable tuners is no more adopted in a RFQ operation.

22. C-ADS RFQ water-cooling design and thermal analysis
Water-cooling components:
4 cavity bodies (vanes and walls)
64 tuners
16 vacuum ports
4 RF power couplers
2 end plates and 8 rods on them
1 coupling plate and 8 rods on it

23. C-ADS RFQ water-cooling design and thermal analysis

24. C-ADS RFQ water-cooling design and thermal analysis
Tunnel temperature choice: 20oC
The thermal analysis model of ANSYS (1/8 cross section of RFQ)

26. C-ADS RFQ water-cooling design and thermal analysis
Temperature rise at the end of module versus velocity of
the cooling-water

27. C-ADS RFQ water-cooling design and thermal analysis
The maximum deformation versus velocity of the cooling water

28. C-ADS RFQ water-cooling design and thermal analysis
The frequency drift Δf at the end of module versus velocity of the cooling water

29. C-ADS RFQ water-cooling design and thermal analysis
Positions of the water channels vary with the velocity of
the cooling water

30. C-ADS RFQ water-cooling design and thermal analysis
The optimization results
Tunnel temperature choice:
20oC
Temperature of cooling water:
Velocity of cooling water:
3.5m/s
Positions of water channels:
Channel 1 (0.00,33.00)
Channel 2 (0.00,58.00)
Channel 3 (0.00,93.60)
Channel 4 (43.0,103.0)
The optimization of water-cooling channel positions for
the velocity 3.5m/s of the cooling water and
water temperature of 20 0C.

31. C-ADS RFQ water-cooling design and thermal analysis
To tune the RFQ basically without effecting the field distribution profile when the RFQ is out of resonance.
The frequency shift sensitivity to the temperature is about -5 kHz/ oC.
The frequency shift versus the water-cooling temperature

32. Water-cooling design and thermal analysis (tuning)
In a RFQ operation, to tune RFQ by adjusting the vane water temperature when RFQ is out of resonance.
The frequency shift sensitivity to the vane water temperature is
about -50 kHz/ oC when Twall=20 oC.
The frequency shift sensitivity to the wall water temperature is
about 42 kHz/ oC when Tvane= 20 oC.
The frequency shift versus the vane water temperature at Twall=20 oC
The frequency shift versus the wall water temperature at Tvane=20 oC

33. Summary
A good dynamic design with high beam transmission, low power dissipation and low longitudinal emittance is got.
RFQ structure design proceeds well and rapidly due to much experience from the former 973 ADS RFQ built at IHEP.
Two dimension thermal analysis is used for the water-cooling design. Three dimension thermal analysis will be just used for checking the water-cooling design.
Mechanical design is being taken based on the present physical design.

34. THANK YOU!