1. DEFLECTING CAVITY OPTIONS FOR RF BEAM SPREADER IN LCLS II
December 4th, 2013

2. RF Spreader System Requirements
CDR CHAPTER 7: ELECTRON COMPRESSION AND TRANSPORT
3-Way Beam Spreader
Vertical Beam Separation
Parameter
Value
Unit
Electron energy
4.0
GeV
Angle of deflection (θdef)
0.75 / 1.0
mrad
Transverse voltage (VT)
3.0 / 4.0 MV
RF frequency (f)
325
MHz
Three rf cavity design options
Superconducting rf-dipole cavity
Normal conducting rf-dipole cavity
Normal conducting 4-rod cavity

3. Superconducting RF-Dipole Cavity
RF-Dipole Design
RF Fields and Surface Fields
Beam aperture of 40 mm
Considering cavity processing
Low wakefield impedance budget
Any dimensional constraints ?
Cavity
Length = 70 cm
Bar length =
41 cm
Bar height = 4.4 cm θ
Angle = 50 deg
Cavity diameter =
34 cm
SC RFD Cavity
Units
Frequency
325
MHz
Nearest HOM
508
VT*
0.46 MV
Ep*
2.6
MV/m
Bp*
3.6 mT
Bp*/Ep*
1.4
mT/
(MV/m) U*
0.049 J
[R/Q]T
2133 Ω
Geometrical Factor
91.5
RTRS
1.95×105 Ω2
At ET* = 1 MV/m
Electric field
Magnetic field

4. Superconducting RF-Dipole Cavity
Required deflection can be achieved by one cavity
Compensation for beam loading
Only fundamental deflecting mode is considered
At a beam offset of 5 mm with a transverse voltage variation of δVT = 0.002VT
Average beam current of 0.02 mA
Multipacting is expected to be processed easily
No lower order modes
Widely separated HOMs
Reduced field non-uniformity with increased bar height VT
4.0 MV Ep 23
MV/m Bp 32 mT
Operating Temperature
2.0 / 4.2 K
Surface Resistance (RS) [Rres = 10 nΩ]
10.9 / 58.7 nΩ Q0
8.4 / 1.6
×109
Power Dissipation (Pdiss)
0.9 / 4.8 W QL
5.5×106
Loaded Bandwidth 59 Hz
Compensation for beam loading
1.4 kW
183 MHz

5. Field Non-Uniformity Shaped loading elements
To reduce filed non-uniformity across the beam aperture
Suppress higher order multipole components
Voltage deviation at 20 mm
Horizontal: 5.0%  0.2%
Vertical: 5.5%  2.4%
(A)
(B)

6. Current RF-Dipole Cavities
499 MHz Deflecting Cavity for
Jefferson Lab 12 GeV Upgrade
400 MHz Crabbing Cavity for
LHC High Luminosity Upgrade
Deflecting voltage – 3.8 MV
Total crabbing voltage – 13.4 MV per beam per side
Per cavity – 3.4 MV
750 MHz Crabbing Cavity for MEIC*
Crabbing voltage
Electron beam – 1.5 MV
Proton beam – 8.0 MV
*A. Castilla et.al., in Proceedings of the 3rd IPAC, New Orleans, Louisiana (2012), p

7. Properties of RF-Dipole Cavity Designs
499 MHz Deflecting Cavity for
Jefferson Lab 12 GeV Upgrade
Frequency
499.0
400.0
750.0
MHz
Aperture Diameter (d)
40.0
84.0
60.0 mm
d/(λ/2)
0.133
0.224
0.3
LOM
None
Nearest HOM
777.0
589.5
1062.5
Ep*
2.86
3.9
4.29
MV/m
Bp*
4.38
7.13
9.3 mT
Bp*/Ep*
1.53
1.83
2.16
mT/
(MV/m)
[R/Q]T
982.5
287.0
125.0 Ω
Geometrical Factor (G)
105.9
140.9
136.0
RTRS
1.0×105
4.0×104
1.7×104 Ω2
At ET* = 1 MV/m
24 cm
44 cm
400 MHz Crabbing Cavity for
LHC High Luminosity Upgrade
34 cm
53 cm
750 MHz Crabbing Cavity for MEIC at Jefferson Lab*
19 cm
35 cm
*A. Castilla et.al., in Proceedings of the 3rd IPAC, New Orleans, Louisiana (2012), p

8. 499 MHz RF-Dipole Cavity
Multipacting was easily processed during the 4.2 K rf test
Design requirement of 3.78 MV can be achieved with 1 cavities
Achieved fields at 2.0 K
ET = 14 MV/m
VT = 4.2 MV
EP = 40 MV/m
BP = 61.3 mT
Quench
3.78

9. 400 MHz RF-Dipole Cavity Multipacting levels were easily processed
Achieved fields at 4.2 K
ET = 11.6 MV/m
VT = 4.35 MV
EP = 47 MV/m
BP = 82 mT
Limited by rf power at 4.2 K
Achieved fields at 2.0 K
ET = 18.6 MV/m
VT = 7.0 MV
EP = 75 MV/m
BP = 131 mT
3.4
5.0
Quench
Limited by rf power
Multipacting levels observed below 2.5 MV
Design goal – 10 MV
Multipacting levels observed below 2.5 MV

10. Normal Conducting RF-Dipole Cavity
RF-Dipole Design *
RF Fields and Surface Fields
Beam aperture of 25 mm
Due to the dependence on transverse shunt impedance (RT)
Considering cavity processing
Bar length = 31 cm
Cavity length = 37 cm
Cavity height = 26 cm
Bar height = 1.5 cm
Bar width = 6 cm
Cavity width = 15 cm
NC RFD Cavity
Units
Frequency
325
MHz
Nearest HOM
518
VT*
0.46 MV
Ep*
3.2
MV/m
Bp*
3.8 mT
[R/Q]T
8367 Ω
Geometrical Factor
48.3
RTRS
4.0×105 Ω2
At ET* = 1 MV/m
Electric field
Magnetic field
* T. Luo, D. Summers, D. Li, “Design of a Normal Conducting RF-dipole Deflecting Cavity”, in Proceedings of the 2013 International Particle Accelerator Conference, Shanghai, China, WEPFI091

11. Normal Conducting RF-Dipole Cavity
Total Power Requirement VT
4.0 MV Ep 28
MV/m Bp 33 mT
Surface Resistance (RS)
4.7 mΩ
Shunt Impedance (RT) 86 MΩ Q0
1.03×104
Power Dissipation (Pdiss)
186 kW
Peak dPdiss/dA
158
W/cm2
Per Cavity Power Requirement
VT per cavity
0.67 MV Ep
4.7
MV/m Bp
5.5 mT Q0
1.03×104
No. of Cavities 6
Power Dissipation (Pdiss) per cavity
5.2 kW
Peak dPdiss/dA per cavity
4.4
W/cm2
Total deflection can be achieved by 6 cavities
Surface heating at the loading elements are reduced by curving and requires cooling
RF properties can be further improved with reduced beam aperture

12. Normal Conducting 4-Rod Cavity
4-Rod Design *
RF Fields and Surface Fields
Beam aperture of 25 mm
Due to strong relation with shunt impedance (RT)
Cavity diameter = 45 cm
Cavity length = 45 cm
Rod diameter = 3.1 cm
Rod length = 21 cm
Rod gap = 2 cm
NC RFD Cavity
Units
Frequency
325
MHz
Nearest HOM
518
LOM
226
VT*
0.46 MV
Ep*
3.4
MV/m
Bp*
7.2 mT
[R/Q]T
1.9×104 Ω
Geometrical Factor
37.3
RTRS
7.2×105 Ω2
At ET* = 1 MV/m
Magnetic field
Electric field
* C.W. Leemann, C. G. Yao, “A Highly Effective Deflecting Structure” in Proceedings of the 1990 Linear Accelerator Conference, Albuquerque, New Mexico, p. 232

13. Normal Conducting 4-Rod Cavity
Total Power Requirement VT
4.0 MV Ep 29
MV/m Bp 63 mT
Surface Resistance (RS)
4.7 mΩ
Shunt Impedance (RT)
153 MΩ Q0
8.0×103
Power Dissipation (Pdiss)
104.4 kW
Peak dPdiss/dA
583
W/cm2
Per Cavity Power Requirement
VT per cavity
1.0 MV Ep
7.3
MV/m Bp
15.8 mT Q0
8.0×103
No. of Cavities 4
Power Dissipation (Pdiss) per cavity
6.5 kW
Peak dPdiss/dA per cavity 36
W/cm2
Total deflection can be achieved by 4 cavities
Localized surface magnetic field has higher cooling requirements per cavity
Surface heating at the end of the rods requires cooling
RF properties can be substantially improved with reduced beam aperture, compared to NC RFD cavity

14. 499 MHz Normal Conducting 4-Rod Cavity
499 MHz 2-cell 4-rod cavity*
Cu coated stainless steel can
Uses parallel cooling mechanism
RF power coupled using magnetic coupling at the end of the cavity
Maximum reached rf power = 5.2 kW
Limited by the cooling of rf power coupler
2-cell 4-rod cavity
Frequency
499
MHz
Shunt Impedance (RT)
210 MΩ QL
2.5×103 Q0
5.0×103 VT
~ 0.75 MV
Max Power Dissipation (Pdiss) per cavity
5.2 kW
* C. Hovater, G. Arnold, J. Fugitt, L. Harwood, R. Kazimi, G. Lahti, J. Mammosser, R. Nelson, C. Piller, L. Turlington, “The CEBAF RF Separator System”, in Proceedings of the 1996 Linear Accelerator Conference, Geneva, Switzerland, p. 77.

15. Summary
Total deflection of 4.0 MV can be achieved by one cavity using the SC RF-Dipole Cavity
Considering the distance between rf spreader system and end of linac needs to look into liquid He supply by
A transfer line
A separate refrigerator
NC RFD requires 6 cavities and has low rf power requirements
NC 4-Rod cavity requires 4 cavities
Similar rf cavity is currently being used successfully at Jefferson Lab rf separator system
SC RFD
NC RFD
NC 4-Rod
Units
Frequency
325
MHz
LOM -
None
Nearest HOM
508
518
349
VT*
0.46 MV
Ep*
2.6
3.2
3.4
MV/m
Bp*
3.6
3.8
7.2 mT
RTRS
1.95×105
4.0×105
7.2×105 Ω2
No. of cavities 1 6 4
VT per cavity
4.0
0.67
1.0
Pdiss per caivty
4.8
(At 4.2 K)
5.2×103
6.5×103 W
At ET* = 1 MV/m