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

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

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

Synchronization Parameters 100 GeV/c protons: L = 2153.78 m, f = 952.6 MHz, h = 6844 (bunch spacing = 31.47 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 0.999956 6844 0.0000 90 0.999946 -0.0222 -0.0098 80 0.999931 -0.0533 -0.0236 70 0.99991 -0.0987 -0.0436 60 0.999878 -0.1685 -0.0745 6845 0.1462 0.0646 50 0.999824 -0.2843 -0.1258 0.0303 0.0134 40 0.999725 -0.4975 -0.2200 6846 0.1317 0.0583 30 0.999511 -0.9579 -0.4237 6847 -0.0142 -0.0063 20 0.998901 -2.2715 -1.0047 6851 -0.0710 -0.0314

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

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

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

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

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

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

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