March 7, 2007 LET Issues (Cai/Kubo/Zisman) Global Design Effort 1 Low-Emittance Tuning Issues and Plans Yunhai Cai, Kiyoshi Kubo and Michael S. Zisman

March 7, 2007 LET Issues (Cai/Kubo/Zisman) Global Design Effort 1

Low-Emittance Tuning Issues and Plans

Yunhai Cai, Kiyoshi Kuboand

Michael S. ZismanLET Group Conveners


Introduction• LET is critical to achieving DR vertical

emittance specification– tools and techniques for doing this already are

operational at a number of facilities • challenge is to simulate realistic ring configurations

and make sure we have the hardware and software to carry out the task

• There do not appear to be any major single-particle dynamics obstacles in the way of successful LET– issues of collective effects are another matter,

but are beyond the scope of this plan


Tasks (1)• Need to evaluate tolerances for lattice

imperfections– strength errors (fixable easily with individual

power supplies)– alignment errors (e.g., 30 m or 100 m)– roll errors– field quality (multipole errors)

• Need to define set of methods for lattice diagnostics– response matrix? – other?


Tasks (2)• Need to evaluate required numbers and

locations of correctors (lattice dependent)– orbit correctors– skew quadrupoles

• separate magnets or trim windings

• Need to evaluate performance requirements of monitors (assume turn-by-turn)– fixed solidly to adjacent quadrupole (+ nearby

sextupole)• want offset in linear regime of bpm response

– noise level– roll error


Tasks (3)• Need to evaluate relative merits of

correctors vs. magnet movers– quadrupoles + sextupoles?– quadrupoles only?

• If movers are needed, what range of motion is required? (± 1 mm?)– what setting accuracy? (10 m?)

• What software is needed to measure and correct the ring?– how fast does it need to be?

• need real-time measurements and rapid correction if ring changes quickly


Comments

• To be safe, should validate 2 pm emittance with both e− and e+ at appropriate intensity– most work to date done with electrons only

• If (weak) solenoids are used for e-cloud suppression, are these enough to limit vertical emittance reduction?

• Not all lattices are “equal”– need to simulate algorithms on all candidate

designs– need realistic model for wiggler (maps)


Notes from Talks (1)

• ANL aims to demonstrate y/x ≤ 1/400

– should give y of 2 pm

• ALS achieved y/x = 1/1000

– resulting in y of 5 pm

• Combination of orbit, vertical dispersion, coupling correction is needed– reaching |Dy| ≤ 2 mm suffices at APS

– use harmonic SK knobs for coupling control

• Fast and reliable size measurement at 2 pm not easily done



• CESR-TA can test both e− and e+

• Measure coupling and phase by shaking beam at betatron tune– look at bpm response– get good correction of phases and coupling

• slow measurement (40 s) and prompt (not real time) correction– need to automate procedures (or put Sagan on call 24/7?)

• Proposed bpm upgrade will speed up measurement

• Challenge to measure the small beam size– laser wire; x-ray imager (very fast bunch-by-bunch)



• New ATF bpms will allow progress toward getting 2 pm vertical emittance– permit better response matrix optics correction

and BBA data– use improved laser wire for measurements

• DANE saw vertical beam size growth due to clearing electrode impedance– must test “cures” to make sure they are not worse

than the disease

• Jones showed that not all lattices are equal– need to consider ground motion (esp. for upper

ring)


The Plan (1)

• Continue measurements at ATF with upgraded bpms (finish during FY08) to demonstrate 2 pm emittance– upgraded bpms needed

• Carry out measurements at APS at 5 GeV to demonstrate 2 pm emittance (by mid-2009)– most resources available; need upgraded

diagnostics

• Carry out measurements at CESR-TA to give 2 pm emittance with positrons (by mid-2009)– need operations support and upgraded diagnostics


The Plan (2)

• Continue simulations to get tolerances, numbers and strengths of correctors (dipoles, skew quadrupoles)– present effort at ANL, Cockcroft, Cornell, INFN,

KEK, LBNL, SLAC– need to evaluate baseline + alternative lattices– complete by end of 2008 or early 2009

• “releases” engineering effort once lattice is frozen

• Continue work on realistic maps for wigglers and other elements


Concluding Comments

• Experiments planned or under way at existing facilities should demonstrate what is needed– ATF, APS, CESR-TA, DANE

• Improvements in beam size diagnostics and/or bpms are needed– bunch-by-bunch capability required for beam size

• Improvements in analysis software to get real-time correction will be needed

• Thanks to speakers for excellent, well-focused presentations

Documents

March 7, 2007 LET Issues (Cai/Kubo/Zisman) Global Design Effort 1 Low-Emittance Tuning Issues and Plans Yunhai Cai, Kiyoshi Kubo and Michael S. Zisman