DEFLECTING CAVITY OPTIONS FOR
RF BEAM SPREADER IN LCLS II
Suba De Silva
Jean Delayen, Rocio Olave, Todd Satogata, Geoff Krafft
Center for Accelerator Science
Department of Physics, Old Dominion University
December 4th, 2013
Page 1
RF Spreader System Requirements
CDR CHAPTER 7: ELECTRON COMPRESSION AND TRANSPORT
3-Way Beam Spreader
Vertical Beam Separation
y
y
B
x
x
B
x
V
t
Parameter
Value
Unit
4.0
GeV
Angle of deflection (θdef)
0.75 / 1.0
mrad
Transverse voltage (VT)
3.0 / 4.0
MV
325
MHz
Electron energy
RF frequency (f)
To Dump
Septum
Septum
Vertical RF
Transverse
Deflector
•
Three rf cavity design options
–
–
–
Page 2
Superconducting rf-dipole cavity
Normal conducting rf-dipole cavity
Normal conducting 4-rod cavity
z
Superconducting RF-Dipole Cavity
•
•
RF-Dipole Design
Bar height
= 4.4 cm
Cavity
Length =
70 cm
•
–
–
Angle = 50 deg
θ
Bar length =
41 cm
•
Considering cavity processing
Low wakefield impedance budget
Any dimensional constraints ?
Cavity
diameter =
34 cm
RF Fields and Surface Fields
Electric
field
Beam aperture of 40 mm
Magnetic
field
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
1.95×105
Ω2
RTRS
At ET* = 1 MV/m
Page 3
Superconducting RF-Dipole Cavity
Required deflection can be achieved by
one cavity
VT
4.0
MV
Ep
23
MV/m
Bp
32
mT
2.0 / 4.2
K
10.9 / 58.7
nΩ
Q0
8.4 / 1.6
×109
Power Dissipation (Pdiss)
0.9 / 4.8
W
QL
5.5×106
Operating Temperature
Surface Resistance (RS) [Rres = 10 nΩ]
•
•
No lower order modes
Widely separated HOMs
1.0E+04
Deflecting Vertical
Accelerating
Deflecting Horizontal
1.0E+03
R/Q [Ω]
•
183 MHz
1.0E+02
1.0E+01
1.0E+00
1.0E-01
Loaded Bandwidth
59
Hz
Compensation for beam loading
1.4
kW
•
1000
1500
Reduced field non-uniformity with
increased bar height
Compensation for beam loading
0.01
Vertical
– 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
•
500
Frequency [MHz]
Multipacting is expected to be processed
easily
Horizontal
0.005
δVT / VT
•
0
0
-0.005
-0.01
-10
-5
0
5
Offset across the beam aperture (mm)
Page 4
10
Field Non-Uniformity
• Shaped loading elements
•
– To reduce filed non-uniformity across
the beam aperture
– Suppress higher order multipole
components
0.1
Voltage deviation at 20 mm
–
–
Horizontal: 5.0%  0.2%
Vertical: 5.5%  2.4%
0.05
(A)
0
δVT / VT
-0.05
(B)
-0.1
-0.15
Design (A) in x
Design (B) in x
Design (A) in y
Design (B) in y
-0.2
-0.25
-0.3
0
2
4
6
8
10
12
Offset (mm)
Page 5
14
16
18
20
Current RF-Dipole Cavities
499 MHz Deflecting Cavity for
Jefferson Lab 12 GeV Upgrade
• Deflecting voltage – 3.8 MV
400 MHz Crabbing Cavity for
LHC High Luminosity Upgrade
• 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.
Page 6
Castilla et.al., in Proceedings of the 3rd IPAC, New
Orleans, Louisiana (2012), p. 2447.
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
44 cm
24 cm
MHz
400 MHz Crabbing Cavity for
LHC High Luminosity Upgrade
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
750 MHz Crabbing Cavity
for MEIC at Jefferson Lab*
1.0×105
4.0×104
1.7×104
Ω2
35 cm
RTRS
53 cm
34 cm
At ET* = 1 MV/m
19 cm
*A. Castilla et.al., in Proceedings of the 3rd IPAC,
New Orleans, Louisiana (2012), p. 2447.
Page 7
499 MHz RF-Dipole Cavity
1.0×1011
•
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
1.0×1011
Q0 Q0 Q0 Q0
11
1.0×1010
1.0×10
1.0×1011
1.0×1010
Quench
1.0×1010
1.0×10109
1.0×10
1.0×109
1.0×109
8
10
1.0×10
1.0×1090.0
ET (MV/m)
3.0
4.5
VT (MV)
3.0
4.5
EP (MV/m)
3.0
4.5
BP (mT)
0.0
0.0
0.0
15
20
6.0
6.0
1.5
15.0
10.0
5.0
6.0
7.5
ET
(MV/m)
7.5
ET
(MV/m)
14.3
7.5
21.9
3.78
3.0
28.6
ET (MV/m)
43.8
ET (MV/m)
Page 8
4.5
42.9
65.7
–
–
–
–
ET = 14 MV/m
VT = 4.2 MV
EP = 40 MV/m
BP = 61.3 mT
400 MHz RF-Dipole Cavity
•
Multipacting levels were
easily processed
Quench •
Achieved fields at 4.2 K
1.0E+10
1.0E+10
Multipacting levels observed below 2.5 MV
1.0E+10
Q0 Q0 Q0 Q0
1.0E+10
1.0E+09
10
1.0E+08
E (MV/m) 0
3.0 T 1.0E+09 4.5
VT (MV) 0.0
3.0 1.0E+09
4.5
E (MV/m)
3.0 P1.0E+09 04.5
BP (mT) 0
Design goal – 10 MV
15
–
–
–
–
Limited
by rf
power
•
20 •
20
6.0 5
1.5
6.0
6.020
28
10
7.5
ET (MV/m)
3.0 3.4
4.5 5.0
7.5
VT (MV)
7.5 40
E (MV/m)
56 T
84
ET (MV/m)
15
6.0
60
80
112
Page 9
7.5
140
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
Normal Conducting RF-Dipole Cavity
•
•
RF-Dipole Design *
Cavity
length =
37 cm
Cavity
height =
26 cm
–
Bar
height =
1.5 cm
Bar
length =
31 cm
•
Beam aperture of 25 mm
Bar width =
6 cm
Cavity width
= 15 cm
–
Due to the dependence on transverse
shunt impedance (RT)
Considering cavity processing
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
4.0×105
Ω2
RF Fields and Surface Fields
Electric
field
Magnetic
field
RTRS
At ET* = 1 MV/m
* T. Luo, D. Summers, D. Li, “Design of a Normal Conducting RFdipole Deflecting Cavity”, in Proceedings of the 2013 International
Particle Accelerator Conference, Shanghai, China, WEPFI091
Page 10
Normal Conducting RF-Dipole Cavity
Per Cavity Power Requirement
Total Power Requirement
VT per cavity
0.67
MV
MV/m
Ep
4.7
MV/m
33
mT
Bp
5.5
mT
Surface Resistance (RS)
4.7
mΩ
Q0
1.03×104
Shunt Impedance (RT)
86
MΩ
No. of Cavities
VT
4.0
MV
Ep
28
Bp
1.03×104
Q0
Power Dissipation (Pdiss)
186
kW
Peak dPdiss/dA
158
W/cm2
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
Page 11
6
Normal Conducting 4-Rod Cavity
•
•
4-Rod Design *
Cavity length =
45 cm
Rod length
= 21 cm
Beam aperture of 25 mm
–
Cavity
diameter
= 45 cm
Due to strong relation with shunt
impedance (RT)
Rod diameter =
3.1 cm
Rod gap
= 2 cm
•
RF Fields and Surface Fields
Electric
field
Magnetic
field
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
1.9×104
Ω
37.3
Ω
7.2×105
Ω2
[R/Q]T
Geometrical Factor
RTRS
At ET* = 1 MV/m
* C.W. Leemann, C. G. Yao, “A Highly Effective Deflecting
Structure” in Proceedings of the 1990 Linear Accelerator
Conference, Albuquerque, New Mexico, p. 232
Page 12
Normal Conducting 4-Rod Cavity
Per Cavity Power Requirement
Total Power Requirement
VT per cavity
1.0
MV
MV/m
Ep
7.3
MV/m
63
mT
Bp
15.8
mT
Surface Resistance (RS)
4.7
mΩ
Q0
8.0×103
Shunt Impedance (RT)
153
MΩ
No. of Cavities
VT
4.0
MV
Ep
29
Bp
8.0×103
Q0
Power Dissipation (Pdiss)
Peak dPdiss/dA
•
•
•
•
104.4
kW
583
W/cm2
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
Page 13
4
499 MHz Normal Conducting 4-Rod Cavity
•
499 MHz 2-cell 4-rod cavity*
–
–
Cu coated stainless steel can
Uses parallel cooling mechanism
2-cell 4-rod cavity
•
•
RF power coupled using magnetic
coupling at the end of the cavity
Maximum reached rf power = 5.2 kW
–
Frequency
499
MHz
Shunt Impedance (RT)
210
MΩ
QL
2.5×103
Q0
5.0×103
VT
~ 0.75
MV
5.2
kW
Max Power Dissipation
(Pdiss) per cavity
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.
Page 14
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
SC RFD
Frequency
LOM
Nearest HOM
–
Similar rf cavity is currently being used
successfully at Jefferson Lab rf separator
system
Page 15
MHz
-
-
None
MHz
508
518
349
MHz
0.46
MV
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
1
6
4
4.0
0.67
1.0
MV
4.8
(At 4.2 K)
5.2×103
6.5×103
W
VT per cavity
NC 4-Rod cavity requires 4 cavities
Units
Ep*
No. of cavities
•
NC 4Rod
325
VT*
NC RFD requires 6 cavities and has
low rf power requirements
NC RFD
Pdiss per caivty
At ET* = 1 MV/m