Chuyu Liu 01142020 MachineDetector meeting Basis features of space charge The tune spread with space charge at 575 GeVnucleon is 01 The beam core suffers the strongest tune depression ID: 803351
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Slide1
Exploration of a better working point for space charge dominated RHIC beam
Chuyu Liu
01/14/2020
Machine/Detector meeting
Slide2Basis features of space charge
The tune spread with space charge at 5.75 GeV/nucleon is ~0.1.
The beam core suffers the strongest tune depression.
The tune spread shape looks like a upside down tie with beam core at the bottom.The measured tunes are the bare tunes moved (very little) by indirect space charge.
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Slide3Moving tunes up to alleviate emittance blow-up
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Old tunes
Current tunes
Slide44
Slide5Results
As a result, measurements by STAR and IPMs both confirmed smaller beam size (1.5 mm versus 1.7 mm).
Higher blue beam intensity with improved blue beam injection efficiency.
The integrated lumi with higher tunes is 40% higher than that with lower tunes.
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Slide6Notes on beam development
Close communication between STAR and CAD was very helpful to reveal inconsistency of beam size/emittance between measurements and expectations.
CAD operation
took the heavy lift of the beam development and continued optimization for further gain of luminosity.
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Slide7Further exploration of the working point
Higher loss is expected due to the fact that beam core will be sitting on 9
th
, 10th resonance which will be excited even more with beam-beam.
Less emittance blow-up is expected due to the fact that the beam core is further away from integer resonance.
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Option 1: moving tunes further up
Option 2: moving tunes below integer