1. Conventional Synchronization Schemes
V.S. Morozov on behalf of MEIC study group
Special MEIC Accelerator R&D Meeting on the Topic of Beam Synchronization
July 23, 2015
F. Lin

2. Overview
Issue: energy-dependence of ion velocity desynchronizes them w electrons
Conventional schemes involving magnet movement
Moving magnets in the ion collider ring
Moving whole arcs or a small number of magnets in chicane(s)
With or without harmonic jump
Moving magnets in the electron collider ring & adjusting RF in both rings
Moving (almost) whole arcs or a small number of magnets in chicane(s)
Some combination of the above two schemes

3. Pros & Cons Moving ion magnets Moving electron magnets
Pros: does not require changes in RF and CEBAF injection
Con: moving superconducting magnets not trivial
Moving electron magnets
Pro: warm magnets simpler to move
Cons: requires adjustment of RF and possibly CEBAF injection
Combination of ion and electron magnet movement
Pro: simplifies the difficulties of each of the above schemes
Con: have to deal with a combination of all difficulties of the two schemes
Moving (almost) whole arcs (arguments reversed for chicane)
Pros: relatively small change in magnet spacings, less or no special engineering, doable without harmonic jump
Con: have to deal with a large number of magnets
Harmonic jump
Pros: simplifies synchronization in any scheme (smaller magnet movement, smaller RF adjustment), highly beneficial to detection and polarimetry (great reduction of systematic errors, no need for bunch by bunch polarization measurement)
Cons: potential for a dynamic instability (needs study, Derbenev and Terzic talks), have to consider synchronization of the second IP

4. Synchronization Parameters
100 GeV/c protons: L = m, f = MHz, h = 6844 (bunch spacing = cm)
Observations
A path-length chicane probably not practical without harmonic jump for the whole momentum range
When moving whole arcs without harmonic jump
Maximum transverse shift R = L /  = 24.9 cm where  = 523.4
With ~256 gaps between arc dipoles and quadrupoles, max gap change = 8.9 mm
When moving whole arcs with harmonic jump
R = (bunch spacing) /  = 34 mm
Max gap change = 1.2 mm
p (GeV/c) 
Without harmonic jump
With harmonic jump h
l (m)
f (MHz)
100
6844
0.0000 90 80 70 60
6845
0.1462
0.0646 50
0.0303
0.0134 40
6846
0.1317
0.0583 30
6847 20
6851

5. Path-Length Chicane Options
Chicane in a straight
Chicane in an arc

6. Straight Chicane: Naïve Look
Triangular chicane with 20 m base and 1 m height  ~10 cm additional path length, solves some of the problem
Chicane with double the height  ~40 cm additional path length, solves the whole problem, looks attractive
1 m
20 m
2 m
20 m 6

7. Straight Chicane: Realistic Estimate
Assume 3 m long dipoles each bending by 50 mrad (6 100 GeV/c, max sagitta of 2 cm) and require 40 cm path length increase
4 dipoles
8 dipoles
12 dipoles
16 dipoles 7

8. Straight Chicane: Realistic Estimate
Consider solving half the problem, 20 cm path length increase
4 dipoles
8 dipoles
12 dipoles 8

9. Arc Chicane Concept (A. Hutton)
Reserve space for two extra dipoles in each arc, otherwise regular arc lattice
Arc bending angle is fixed (i.e. incoming and outgoing angles are fixed) and cord length is fixed (i.e. the coordinates of the arc ends are fixed)
Two extremes of a 10 dipole arc
Longest orbit: two dipoles at arc ends are off
Shortest orbit: two dipoles in the middle of the arc are off
Intermediate cases: the end and middle dipoles are partly powered 9

10. Maximum change in magnet spacing
Arc Chicane
Using current 22.8 m FODO cell design (8 m 3 T dipoles with 3.4 m separation)
One chicane per arc (also helps with synchronization of the 2nd IP), one extra FODO cell per arc
Takes up cells, which could otherwise be used for chromaticity compensation
x = 52 cm
x = -69 cm
Total bending angle and z length are fixed
# of FODO cells
# of magnet moved
Path length change
Radial movement range
Maximum change in magnet spacing 3
4 dipoles, 5 quads
10 cm
+52 / -69 cm
20 mm 4
6 dipoles, 7 quads
+36 / -39 cm
14 mm 5
8 dipoles, 9 quads
+28 / -29 cm
11 mm 10

11. Conclusions
Conventional synchronization schemes involving magnet movement
Moving ion magnets
Moving electron magnets and adjusting RF in both rings
Combination of electron and ion magnet movement and RF adjustiment
Synchronization much harder without harmonic jump
Substantial magnet movement and optionally RF adjustment
Path-length chicane
Probably not practical without harmonic jump
Arc chicane much more efficient than a straight one
Would like to run with different numbers of bunches for other important reasons anyway  need to study the “gear change” effect