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DEFLECTING CAVITY OPTIONS FOR RF BEAM SPREADER IN LCLS II. December 4 th , 2013. RF Spreader System Requirements. CDR CHAPTER 7: ELECTRON COMPRESSION AND TRANSPORT. Three rf cavity design options Superconducting rf -dipole cavity Normal conducting rf -dipole cavity - PowerPoint PPT Presentation
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Page 1
Suba De SilvaJean Delayen, Rocio Olave, Todd Satogata, Geoff Krafft
Center for Accelerator ScienceDepartment of Physics, Old Dominion University
DEFLECTING CAVITY OPTIONS FOR RF BEAM SPREADER IN LCLS II
December 4th, 2013
Page 2
RF Spreader System Requirements
• Three rf cavity design options– Superconducting rf-dipole cavity– Normal conducting rf-dipole cavity– Normal conducting 4-rod cavity
Parameter Value Unit
Electron energy 4.0 GeVAngle of deflection (θdef) 0.75 / 1.0 mradTransverse voltage (VT) 3.0 / 4.0 MV
RF frequency (f) 325 MHz
CDR CHAPTER 7: ELECTRON COMPRESSION AND TRANSPORT
3-Way Beam Spreader
Septum
Vertical RF Transverse Deflector
To Dump
x
zV
t
y
xB
Septum
y
xB
Vertical Beam Separation
Page 3
Superconducting RF-Dipole Cavity
SC RFD Cavity Units
Frequency 325 MHz
Nearest HOM 508 MHz
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 Ω
RTRS 1.95×105 Ω2
At ET* = 1 MV/m
• RF-Dipole Design
• RF Fields and Surface Fields
• Beam aperture of 40 mm– Considering cavity processing– Low wakefield impedance budget
• Any dimensional constraints ?
Electric field
Magnetic field
CavityLength =
70 cm
Bar length = 41 cm
Bar height = 4.4 cm
θAngle = 50 deg
Cavity diameter =
34 cm
Page 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
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
• No lower order modes• Widely separated HOMs
• Reduced field non-uniformity with increased bar height
-0.01
-0.005
0
0.005
0.01
-10 -5 0 5 10
δVT
/ VT
Offset across the beam aperture (mm)
Vertical Horizontal
1.0E-01
1.0E+00
1.0E+01
1.0E+02
1.0E+03
1.0E+04
0 500 1000 1500
R/Q
[Ω]
Frequency [MHz]
Deflecting VerticalAcceleratingDeflecting Horizontal
183 MHz
Page 5
Field Non-Uniformity• Voltage deviation at 20 mm
– Horizontal: 5.0% 0.2%– Vertical: 5.5% 2.4%
-0.3
-0.25
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
0 2 4 6 8 10 12 14 16 18 20
δVT
/ VT
Offset (mm)
Design (A) in xDesign (B) in xDesign (A) in yDesign (B) in y
(A)
(B)
• Shaped loading elements– To reduce filed non-uniformity across
the beam aperture– Suppress higher order multipole
components
Page 6
Current RF-Dipole Cavities499 MHz Deflecting Cavity for Jefferson Lab 12 GeV Upgrade
750 MHz Crabbing Cavity for MEIC*
*A. Castilla et.al., in Proceedings of the 3rd IPAC, New Orleans, Louisiana (2012), p. 2447.
• Total crabbing voltage – 13.4 MV per beam per side
• Per cavity – 3.4 MV
400 MHz Crabbing Cavity for LHC High Luminosity Upgrade
• Deflecting voltage – 3.8 MV
• Crabbing voltage– Electron beam – 1.5 MV– Proton beam – 8.0 MV
Page 7
Properties of RF-Dipole Cavity Designs
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 MHz
Nearest HOM 777.0 589.5 1062.5 MHz
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 Ω
RTRS 1.0×105 4.0×104 1.7×104 Ω2
At ET* = 1 MV/m
750 MHz Crabbing Cavity for MEIC at Jefferson
Lab*
499 MHz Deflecting Cavity forJefferson Lab 12 GeV Upgrade
400 MHz Crabbing Cavity for LHC High Luminosity Upgrade
24 cm
44 cm
34 cm
53 cm
19 cm
35 cm
*A. Castilla et.al., in Proceedings of the 3rd IPAC, New Orleans, Louisiana (2012), p. 2447.
Page 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
1.0î 108
1.0î 109
1.0î 1010
1.0î 1011
0.0 5.0 10.0 15.0
Q0
ET (MV/m)
1.0î 109
1.0î 1010
1.0î 1011
0.0 1.5 3.0 4.5
Q0
ET (MV/m)
1.0î 109
1.0î 1010
1.0î 1011
0.0 14.3 28.6 42.9
Q0
ET (MV/m)
1.0î 109
1.0î 1010
1.0î 1011
0.0 21.9 43.8 65.7
Q0
ET (MV/m)
1.0E+09
1.0E+10
0.0 1.5 3.0 4.5 6.0 7.5
Q0
VT (MV)1.0E+09
1.0E+10
0.0 1.5 3.0 4.5 6.0 7.5
Q0
EP (MV/m)1.0E+09
1.0E+10
0.0 1.5 3.0 4.5 6.0 7.5
Q0
BP (mT)
1.0E+09
1.0E+10
0 5 10 15 20
Q0
ET (MV/m)
Quench
3.78
Page 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
1.0E+09
1.0E+10
0 5 10 15 20
Q0
ET (MV/m)1.0E+09
1.0E+10
0.0 1.5 3.0 4.5 6.0 7.5
Q0
VT (MV)1.0E+09
1.0E+10
0.0 1.5 3.0 4.5 6.0 7.5
Q0
EP (MV/m)1.0E+09
1.0E+10
0.0 1.5 3.0 4.5 6.0 7.5
Q0
BP (mT)
Multipacting levels observed below 2.5 MV
1.0E+08
1.0E+09
1.0E+10
0 5 10 15 20
Q0
ET (MV/m)1.0E+09
1.0E+10
0.0 1.5 3.0 4.5 6.0 7.5
Q0
VT (MV)1.0E+09
1.0E+10
0 20 40 60 80
Q0
ET (MV/m)1.0E+09
1.0E+10
0 28 56 84 112 140
Q0
ET (MV/m)
3.4 5.0
QuenchLimited
by rf power
Multipacting levels observed below 2.5 MV
Design goal – 10 MV1.0E+09
1.0E+10
0 5 10 15 20
Q0
ET (MV/m)
Page 10
Normal Conducting RF-Dipole Cavity
NC RFD Cavity Units
Frequency 325 MHz
Nearest HOM 518 MHz
VT* 0.46 MV
Ep* 3.2 MV/m
Bp* 3.8 mT
[R/Q]T 8367 Ω
Geometrical Factor 48.3 Ω
RTRS 4.0×105 Ω2
At ET* = 1 MV/m
• 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
Electric field
Magnetic field
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
* 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
Page 11
Normal Conducting RF-Dipole Cavity
• 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
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
Page 12
Normal Conducting 4-Rod Cavity
NC RFD Cavity Units
Frequency 325 MHz
Nearest HOM 518 MHz
LOM 226 MHz
VT* 0.46 MV
Ep* 3.4 MV/m
Bp* 7.2 mT
[R/Q]T 1.9×104 Ω
Geometrical Factor 37.3 Ω
RTRS 7.2×105 Ω2
At ET* = 1 MV/m
• 4-Rod Design *
• RF Fields and Surface Fields
• Beam aperture of 25 mm– Due to strong relation with shunt
impedance (RT)
* C.W. Leemann, C. G. Yao, “A Highly Effective Deflecting Structure” in Proceedings of the 1990 Linear Accelerator Conference, Albuquerque, New Mexico, p. 232
Cavity diameter = 45 cm
Cavity length = 45 cm
Rod diameter = 3.1 cm
Rod length = 21 cm
Rod gap = 2 cm
Magnetic field
Electric field
Page 13
Normal Conducting 4-Rod Cavity
• 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
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
Page 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
* 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.
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
Page 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 MHz
Nearest HOM 508 518 349 MHz
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 MV
Pdiss per caivty 4.8(At 4.2 K) 5.2×103 6.5×103 W
At ET* = 1 MV/m