1. SRF Crabbing Cavity R&D
JEFFERSON LAB
ELECTRON-ION COLLIDER
JLEIC Collaboration Meeting – Fall 2016
SRF Crabbing Cavity R&D
Jefferson Lab – October 05-07, 2016

2. Outline Crabbing concept Crabbing cavities – History
KEK Crabbing Cavity
TM110 class cavities
New geometries
RF tests on proofs-of-principle cavities
Crabbing cavity R&D for LHC High Luminosity Upgrade
RF properties
HOM spectrum and HOM couplers
Design and engineering of prototypes
Crabbing cavity designs for JLEIC

3. Crabbing Concept Crabbing cavities:
Luminosity management in linear or circular colliders with head on collision  Crab crossing
Emittance exchange in beams
X-ray pulse compression
Beam diagnostics
Crab crossing – Proposed by R.B. Palmer
R.B. Palmer, Energy scaling, crab crossing and the pair problem, SLAC-PUB-4707

4. The 1st Superconducting Crabbing Cavity
Beam E B
KEK Crabbing Cavity*
Frequency
508.9
MHz
LOM
410.0
Nearest HOMs
630.0, 650.0, 680.0
Ep*
4.24
MV/m
Bp*
12.23 mT
Bp*/Ep*
2.88
mT/(MV/m)
[R/Q]T
48.9 Ω
Geometrical Factor (G)
227.0
RTRS
1.11×104 Ω2
At ET* = 1 MV/m
Operating mode: TM110 mode
Two crabbing cavities
High energy ring (HER)
Low energy ring (LER)
*K. Hosoyama et. al., “Crab Cavity for KEKB”, Proc. of the 7th Workshop on RF Superconductivity, p.547 (1998)
Complex HOM Damping Scheme

5. KEK Crabbing Cavity Performance
Global crabbing scheme
Peak luminosity achieved: 2.1×1034 /cm2/s
One crab cavity installed on each ring
High energy ring (HER): 8 GeV e–
Low energy ring (LER): 3.5 GeV e+
Crossing angle: 22 mrad
Crab cavities operated under high current beam from
Vt = 1.5 MV for LER
Vt = 1.6 MV for HER
K. Hosoyama et. al., “Development of the KEK-B Superconducting Crab Cavity”

6. Squashed elliptical design
TM110 Class Cavities
Deflection mostly through interaction with magnetic field
Presence of lower-order mode (TM010)
TM110 mode is degenerate in cylindrical geometry
Squashed cross-section
Large with respect to wavelength compared to new designs
Disadvantageous for low frequency
Advantageous for high frequency
Able to accommodate large apertures
Squashed elliptical design
Few degrees of freedom in the design
Higher order multipole components
Relatively low real estate gradient
Couplers on beam line

7. Compact Cavities with New Geometries
55 cm
89 cm
7 cm
Aperture
500 MHz
30 cm
46 cm
952.6 MHz
18 cm
RF-Dipole Cavity
18 cm
38 cm
Why we need compact cavities?
Compact designs at low frequencies
Dimensional constraints  Separation between two beam pipes
Solution  Designs operating in
TEM-like designs
TE-like designs

8. New Geometries and Concepts
Cavities operating in TEM-like modes
4-rod cavity
4 quarter-wave resonators (deflection from both E and H)
Parallel-bar cavity
2 half-wave resonators (deflection from E)
Evolved into rf-dipole
Cavities operating in TE-like mode (cannot be pure TE)
RF-dipole
Double quarter-wave
Ridged waveguide
4-rod cavity
Parallel-bar cavities
RF-Dipole cavity
Double quarter-wave cavity
Ridged waveguide cavity

9. RF-Dipole Deflecting/Crabbing Cavities
499 MHz Deflecting Cavity for
Jefferson Lab 12 GeV Upgrade
Proof-of-principle cavities
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
287.2
125.0 Ω
Geometrical Factor (G)
105.9
138.7
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

10. 499 MHz Deflecting Cavity
Proof-of-principle cavity designed as the rf separator for Jefferson Lab 12 GeV upgrade
Fabricated in-house at Jefferson Lab – HyeKyoung Park (JLab)

11. 750 MHz Crabbing Cavity
Proof-of-principle cavity designed initial frequency for Jefferson Lab MEIC
Dissertation – Alex Castilla (ODU)

12. Crabbing Cavities for LHC High Luminosity Upgrade
Proton beam energy: 7 TeV
Crossing angle: 0.59 mrad
Requires two crabbing systems at:
IP1 (ATLAS) – Vertical crabbing
IP5 (CMS) – Horizontal crabbing
Proof-of-principle cavity
Luminosity increase due to crab cavities
Specifications
RF frequency (fc) = MHz
Total transverse voltage per beam per side = 13.4 MV
Total 16 crabbing cavities per type
Transverse voltage per cavity = 3.4 MV
Beam aperture = 84 mm

13. 400 MHz Crabbing Cavity
Surface treatment and rf testing done at Jefferson Lab
Cavity reached a Vt of 7.0 MV
Retested with Nb coated flanges provided by CERN
Test I – April, 2012
Q0 increased by a factor of 3 from 4×109 to 1.2×1010
Test II – June, 2014
Test at CERN – October, 2014
Multipacting was processed easily and did not reoccur
Low Q0 due no magnetic field compensation

14. LHC Crabbing Cavities
Requires compact designs due to low operating frequency and beam pipe separation
TM110 squashed elliptical geometries are not favorable
Novel designs operating in TEM-like or TE-like modes
4-Rod Cavity
Operating in TEM mode
Double Quarter Wave Cavity
Operating in TE-like mode
E Field
B Field
RF-Dipole Cavity
Operating in TE-like mode

15. RF-Dipole Crabbing Cavity
Proof of Principle Cavity
P-o-P Cavity
Prototype Cavity
Frequency
400
MHz
1st HOM
590
633.5 Vt
3.4 MV Ep 37 33
MV/m Bp 64 57 mT
[R/Q]t
287
430 Ω G
141
107
RtRs
4.0×104
4.6×104 Ω2
53 cm
34 cm
Prototype Cavity
281 mm
194 mm
Prototype cavity
Well separated HOMs
Reduced surface electric and magnetic fields
High shunt impedance
Improved multipacting levels compared to P-o-P cavity
Reduced multipole components
*S.U. De Silva and J.R. Delayen, PRAB 16, (2013)
#S.U. De Siva and J.R. Delayen, PRAB 16, (2013)

16. HOM Coupler Designs of RFD Cavity
FPC
H-HOM
(Hi-pass filter)
V-HOM
(selective coupling)
Collaboration – Zenghai Li (SLAC)
Two HOM couplers
Horizontal HOM (HHOM) coupler
Vertical HOM (VHOM) coupler
Modes up to 2 GHz are well damped below requirement impedance
Couplers at locations of low field region on cavity body
Minimizes RF heating on the coupler components
Location preserves field symmetry
Electrical center moved by only 50 microns
H-HOM coupler with 30 degree hook orientation with no change to filter elements
Selective coupling (V-HOM) to reduce the number of filters
7 mm offset incorporated into the probe tip to enhance coupling to the dipole modes at around 2 GHz
Small RF power leakage through the coupler, ~1.5W, due to asymmetry

17. HHOM High Pass Filter High pass filter
50 Ω probe (Cu)
T (Nb)
Hook (Nb)
High pass filter
Simple filter design  Cuts off fundamental mode
Damps horizontal deflecting and accelerating modes
Demountable coupler
Low fields in the filter
Rejection of operating mode
Multipacting trajectories in the gap removed dB

18. Thermal Analysis – HHOM Coupler
Courtesy – HyeKyoung Park (JLab)
Thermal analysis of the filter for power dissipation at 3.4 MV from
FPC and
HOM of 752 MHz with 1 kW power
50 Ω probe (Cu)
T (Nb)
Hook (Nb)
Gasket
(A)
(B)
Filter Part
Power Dissipation
@ 3.4 MV
Operating Mode
HOM
Hook (Nb)
60 mW
7 µW
T (Nb)
2 µW
6 µW
Probe (Cu)
49 mW
0.5 W
Gasket
0.1 W
1 mW
2K on the surface where contacting the HV
2K on the coupler surface assuming heat stationing

19. HOM Damping for RFD Cavity
Qext calculated using Omega3P (SLAC ACE3P suite) for modes up to 2 GHz
Solid lines are the impedance budget for dipole HOMs (blue) and accelerating HOMs (red) respectively
Damping scheme meets the LHC High-Luminosity Upgrade impedance requirements

20. RFD Cavity & HOM Coupler Fabrication
Courtesy: Niowave Inc.
Two cavities
Completed fabrication of sub-assemblies
Fabricated Cu prototypes of
Demountable HHOM coupler
VHOM coupler probe
Cu HOM
Couplers
Nb H-HOM
Coupler

21. RFD Cavity Manufacturing and Processing
Cavity Processing Plan
End cap sub-assembly for Bulk BCP
Tuner tab welding in Electron Beam Welder
Frequency Measurement

22. Design and Engineering of Prototypes
Magnetic Shielding
Courtesy – Nic Templeton (STFC, UK)
Design for SPS Beam Test
He Vessel
Courtesy – Raphael Leuxe (CERN)

23. Fundamental Power Coupler Tuner Design Courtesy – Kurt Artoos (CERN)
Tuner Engineering
Fundamental Power Coupler
Tuner sensitivity – kHz/mm with 0.5 mm deflection each side
Tuner Design Courtesy – Kurt Artoos (CERN)

24. SPS-CERN Cryomodule Design
Cryo Jumper
Tuning System
VHOM Coupler
HHOM Coupler
Warm Magnetic Shielding
Helium Vessel
Vacuum Vessel

25. Crabbing Cavity for JLEIC
Horizontal local crabbing system
Two interaction points
Four crabbing cavity locations – per interaction point (per beam - per side)
Crabbing cavity frequency – MHz
Luminosity > 1033 cm-2s-1
Parameter
Electron
Proton
Units
Beam energy 10
100
GeV
Beam current
0.72
5.0 A
Bunch frequency
952.6
MHz
Crab crossing angle 50
mrad
Betatron function at IP cm
Betatron function at crab cavity
200
750 m
Integrated transverse voltage
per beam per side
2.8
14.5 MV e– p

26. 952.6 MHz Cavity – Single Cell Cavity
Single cell cavity designs with varying beam aperture radii
RF properties
Peak surface fields increase
Shunt impedance decrease
17.4 cm
16.7 cm
15.9 cm
5 cm
6 cm
7 cm
(A)
(B)
(C)
Frequency
952.6
MHz
Aperture 50 60 70 mm
1st HOM
1431.0
1420.4
1411.5
Vt*
0.157 MV
Ep*
4.2
4.8
5.4
MV/m
Bp*
9.3
11.3
13.6 mT
[R/Q]t
136 81 Ω G
145
155
166
RtRs
2.0×104
1.3×104
8.3×103 Ω2
* Et = 1 MV/m

27. 952.6 MHz Cavity – Multi-Cell Cavity
A 3-cell design study with varying beam aperture
Low surface fields
High shunt impedance
Presence of lower order modes
Requires a notch filter in damping LOMs
(A)
(B)
(C)
Frequency
952.6
MHz
Aperture 50 60 70 mm
LOM
790, 879
773, 870
757, 862
1st HOM
1409
1383
1335
Vt*
0.157 MV
Ep*
4.7
5.1
5.6
MV/m
Bp*
8.7
10.0
11.4 mT
[R/Q]t
494
323
219 Ω G
161
170
179
RtRs
8.0×104
5.5×104
3.9×104 Ω2
* Et = 1 MV/m

28. HOM and Wakefield Spectra
50 mm Aperture
60 mm Aperture
70 mm Aperture
Single bunch wakefield excitation with a bunch length of 30 mm

29. Summary
KEK crabbing cavity – First demonstration of successful implementation and operation of a superconducting crabbing cavity
No crabbing cavity has been demonstrated on a machine with proton beam
Promising compact crabbing cavity designs
Concept has been successfully tested with Proof-of-Principle cavities
Prototype cavity designing for LHC High Luminosity Upgrade including HOM couplers are completed
Prototype cavities for SPS beam test at CERN are ongoing
Next steps for crabbing cavities for JLEIC
Dimensional constraints  Transverse and longitudinal
Beam aperture size
Specifications on HOM impedance budget
Finalize on cavity beam aperture diameter
Design of FPC and HOM coupler designing
Prototype cavity fabrication and rf test

30. Acknowledgements
ODU – Jean Delayen, HyeKyoung Park, Rocio Olave, Alex Castilla, Salvadore Sosa
JLAB – HyeKyoung Park, Ed Daly, Tom Powers, Kirk Davis
SLAC – Zenghai Li, Oleksiy Kononenko
CERN
Rama Calaga, Ofelia Capatina, Raphael Leuxe, Carlo Zanoni, Teddy Capelli and the team
Benoit Salvant, Nic Biancacci
Cockroft Institute / STFC, UK – Graeme Burt, Tom Jones, Nic Templeton, Jamie Mitchell
Fermilab – Giorgio Apollinari, Tom Nicol, Leonardo Ristori
LBNL – Alex Ratti