CESR as Light Source

David L. Rubin

for the CESR Operations Group

Cornell University

Laboratory for Elementary-Particle Physics

April 28, 2009 CHESS Site Visit 2

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

April 28, 2009 CHESS Site Visit 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

April 28, 2009 CHESS Site Visit 4

CESR operating status

Electrons 200 mA - 30 bunchesPositrons 180 mA - 22 bunchesLifetime ~ 12 hoursFill length ~ 3hoursh ~ 140 nmv ~ 1-2 nmX-ray beam position stability < 30 m.

CHESS optics

April 28, 2009 CHESS Site Visit 5

Sunday operation

CESR operations

23.5 hours beam 23.25 hours beam

Ion trapping

April 28, 2009 CHESS Site Visit 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.

April 28, 2009 CHESS Site Visit 7

CESR multi-bunch operation

CHESS operation today4 positron trains and 6 electron trains with 6 bunches/train

Beginning September 200910 trains 4 bunches/trainelectrons and positrons

April 28, 2009 CHESS Site Visit 8

Low Emittance Tuning

Having removed the low- insertion and CLEO 1.5T solenoid and rotated IR quadrupoles and vertical separatorsWe 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

April 28, 2009 CHESS Site Visit 9

-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

Low Emittance Tuning

April 28, 2009 CHESS Site Visit 10

Accelerator R&D

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

April 28, 2009 CHESS Site Visit 11

Single beam optics

5GeVPositrons>180 bunches I = 250mAh = 50nmv ~ 200pm

Based on existing Ring layout (Machine studies experiments are underway)

April 28, 2009 CHESS Site Visit 12

Existing layout

Low emittance(single beam)layout

Low Emittance layout

Rearrange hard bends for single beam operation - Lower horizontal emittance - Space for undulator/wiggler

April 28, 2009 CHESS Site Visit 13

Today September 2009

Machine studies

New ring layout

Emittance[nm] (h/v) 140/1 110/1 52/0.2 15/0.1 7/0.05

Bunches 30/22 40/40 >180 >180 >180

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

Energy[GeV] 5.3 5.3 5.0 5.0 3.5

Lattice development

April 28, 2009 CHESS Site Visit 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, >180 bunches, 50nm• Single beam - low emittance layout

Positrons, 250mA, >180 bunches, 15nm