CESR as Light Source

1
CESR as Light Source

• David L. Rubin
• for the CESR Operations Group
• Cornell University
• Laboratory for Elementary-Particle Physics

2
- Introduction to CESR - CESR Operating Status -
Multi-bunch optics - Low emittance tuning -
Single beam optics - Low emittance layout
3
CESR

• CESR operates with counterrotating
• beams of electrons and positrons
• - Beam energy ranges from 1.5-5.5 GeV
• Injector
• - Linac 300MeV electrons 150MeV
• positrons
• - Synchrotron booster accelerates to full
• storage ring energy
• - Linac/synchrotron cycle at 60Hz
• - Electron gun pulses at up to 72MHz
• to fill CESR with bunches spaced 14ns
• Bunch configuration
• - Traditionally 9 equally spaced trains
• - As many as 6 bunches/train with
• 14ns spacing
• - Itotal 250 mA/beam

4
CESR operating status
CHESS optics
Electrons 200 mA - 30 bunches Positrons 180
mA - 22 bunches Lifetime 12 hours Fill length
3hours ?h 140 nm ?v 1-2 nm X-ray beam
position stability lt 30 ?m.
5
CESR operations
Sunday operation
Ion trapping
23.5 hours beam
23.25 hours beam
6
CESR multi-bunch operation
Colliding beam configuration 4 electrostatic
deflectors generate differential closed orbit
distortion that separates electron and
positron bunch trains.
9X5 Beginning fall 2008 interaction
region low ? optics replaced with simple FODO
lattice structure. (L0) Vertical separators
removed (L3) and the 9X5 configuration is no
longer viable.
7
CESR multi-bunch operation
Beginning September 2009 10 trains 4
bunches/train electrons and positrons
CHESS operation today 4 positron trains and 6
electron trains with 6 bunches/train
8
Low Emittance Tuning
Having removed the low-? insertion and CLEO
1.5T solenoid and rotated IR quadrupoles
and vertical separators We have eliminated
sources of transverse coupling, vertical
dispersion and vertical beam size New optics
configuration permits significant reduction in
vertical emittance Operation with
counterrotating beams limits the number of
bunches. High bunch current /good lifetime/ low
vertical emittance are mutually
exclusive
9
Low Emittance Tuning

• -Principle component of the CesrTA project is to
  reduce vertical emittance
• and develop procedures to monitor and maintain
  low emittance
• -Survey and alignment - survey network
• -Digital beam position monitor electrons will
  permit single bunch/single pass
• real time nondestructive measurement of
• - Orbit
• - Optical functions
• - Transverse coupling
• - Dispersion
• On line analysis and modeling software will
  deploy corrector magnets
• (vertical steering, quadrupoles, skew quads)
  to
• preserve minimum emittance as well as beam
  position

10
Accelerator RD

• Single beam operation?
• Pretzel configuration (electrons and
  positrons)
• - Constrains optics (precludes low
  horizontal emittance)
• - Complicates injection
• (injected bunch collides with
  opposite species stored beam)
• - Limits number of bunches
• - Impedes low emittance tuning
• (beam is off axis in all magnets)
• Single beam (positrons)
• - Lower horizontal emittance optics
• - More bunches (lower bunch current,
  smaller vertical beam size, longer lifetime)
• - More efficient injection (top off ?)
• - Reduced vertical emittance
• - No ion trapping

11
Single beam optics
Based on existing Ring layout (Machine studies
experiments are underway)
5GeV Positrons gt180 bunches I 250mA ?h
50nm ?v 200pm
12
Low Emittance layout
Rearrange hard bends for single beam operation
- Lower horizontal emittance - Space for
undulator/wiggler
Existing layout
Low emittance (single beam) layout
13
Lattice development
Today September 2009 Machine studies New ring layout New ring layout
Emittancenm (h/v) 140/1 110/1 52/0.2 15/0.1 7/0.05
Bunches 30/22 40/40 gt180 gt180 gt180
Current/beam mA 175 225 250 250 250
Particle species e e- e e- e e e
Horizontal Tune 10.57 10.21 14.57 14.57 14.57
EnergyGeV 5.3 5.3 5.0 5.0 3.5
14
Summary

• Today - 2 beam operation 175mA/beam, 52 bunches
• Beginning Fall 2009
• - 2 beams, 225mA/beam (80 bunches)
• Single beam existing layout (?)
• Positrons, 250mA, gt180 bunches, 50nm
• Single beam - low emittance layout
• Positrons, 250mA, gt180 bunches, 15nm