1. Status and plans for crab crossing studies at JLEIC
Salvador Sosa, ODU
Vasiliy Morozov, JLab

2. Outline
Impact of beam crossing angle on luminosity and necessity of crab crossing
Outline of crab crossing schemes
Preliminary self-consistent set of crab crossing parameters
Start crab crossing simulations
Future Plans

3. Luminosity and need for Crabbing

4. Luminosity Reduction Factor
Crossing beam parameters θc
50 mrad σz
9.08 mm σx
18.04 µm φ
12.5 rad

5. Ion Collider Ring Figure-8 ring with a circumference of 2153.9 m
Two 261.7 arcs connected by two straights crossing at 81.7
Vertical doglegs to be added
R = m
Arc, 261.7 IP
disp. supp./
geom. match #3
geom. match #1
geom. match #2
det. elem.
disp. supp.
norm.+
SRF
tune
tromb.+
match
beam exp./
elec. cool.
ions
81.7
future 2nd IP
Polarimeter
IP crossing angle of 50 mrad
Luminosity requirement: 7.5x1033 cm-2s-1

6. Detector Region Layout
e- crab cavities
ion crab cavities IP e-
Compton polarimetry
forward ion detection
ions
forward e- detection
dispersion suppressor/
geometric match
spectrometers
Forward hadron spectrometer
low-Q2 electron detection
and Compton polarimeter p
(top view in GEANT4) e
ZDC

7. Baseline Ion IR Optics IR design features Modular design
Based on triplet Final Focusing Blocks (FFB)
Asymmetric design to satisfy detector requirements and reduce chromaticity
Spectrometer dipoles before and after downstream FFB, second focus downstream of IP
No dispersion at IP, achromatic optics downstream of IP
detector
elements
match/
beam compression IP
match/
beam expansion
geom. match/
disp. suppression
FFB
FFB
ions
Secondary focus
with large Dx for improved momentum resolution

8. Location of crab cavities
Crab Crossing
Effective head-on bunch collisions restored with 50 mrad crossing angle
Local crab scheme
Two cavities are placed at (2n+1)/2 phase advance relative to IP
Optimal x at locations of crab cavities for minimizing the required kicking voltage
Deflective crabbing using transverse electric field of SRF cavities (as at KEK-B)
Design and analysis completed
Prototype fabricated and characterized
Final testing with promising results
Location of crab cavities
π/2
3π/2
Multipole Tailoring
Beam Dynamics Studies

10. Crab crossing Design Parameters
S. Abeyratne et al, MEIC Design Summary, arXiv:
Parameter
Unit
Electron
Proton
Energy
GeV 10
100
Bunch frequency
MHz
952.6
Crossing angle
mrad 50
Betatron IP cm
Betatron crab cavity m
200
750 | 400
Integrated kicking
voltage MV
2.8
14.47 | 19.81
Deflecting (kicking)
voltage amplitude:

11. Bunch at IP with and w/o crabbing
Bunched Beam parameters
N particles
10,000
εnx σs
1 cm
Gaussian distribution
3 - sigma

12. Crab crossing plan
Optimize the crabbing system for best beam stability and minimum emittance impact
Study effects of and specify tolerances on crab cavity errors such as misalignment, amplitude and phase instability
Study and specify tolerances on cavity multipole components by estimating impact on the ring’s dynamic aperture
Specify high-order mode requirements
Specify requirement on the beam parameters such as maximum bunch length
Evaluate and optimize impedance of the crab cavities
Complete beam dynamics simulation using an optimized field map satisfying the determined requirements