Beam-beam experiments at BNL

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Beam-beam experiments at BNL

• Tanaji Sen

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Long-range at store
b 100m only smaller separations 8s (needs
to be explored) effect on Q, DQ large
b 1m large separations possible (gt40s)
effect on Q, DQ small
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Experiments to date

• April 5th 1 bunch per beam, interaction at
  nominal location
• April 12th 1 bunch per beam, interaction at IP6
• May 3rd - 10 bunches per beam, interaction at
  nominal location
• May 24th - 10 bunches per beam, interaction at
  nominal location, tune scan. Octupoles used to
  increase nonlinearities.
• May 30th - 10 bunches per beam, interaction at
  nominal location, operate near 0.75. Octupoles
  on.

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May 24th losses, tunes
Losses are small at separations gt 4 s at these
tunes
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Losses vs separation May 24th

• Yellow beam was moved
• Losses are larger in the blue beam
• Drop as separation increased from 8 to 11 s
• Flat between 8 to 6.5 s
• Drop as separation increased from 6 to 9 s

(2)
(1)
(3)
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May 30th initial tunes
Blue Qx0.735, Qy 0.742 Yellow Qx0.736,
Qy0.739
Beam was lost shortly after moving to these
tunes. This was the 2nd attempt to operate at
these tunes, beam was lost both times.
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Beam-beam simulations - BBSIM
11th
7th
Simulations imply impact of 11th order resonances
is weak
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Summary

• Effect of single parasitic explored at
  separations between 1 11s
• Nonlinearities were enhanced with the addition of
  octupoles
• At nominal tunes, effect of the parasitic is felt
  for separations 4 s
• Attempts to explore tunes near 0.75 resulted in
  beam loss
• Simulations show that effects are stronger near
  tune of 0.7 than near 0.72.
• Further simulations planned to study parameter
  space used in the experiments. Need to find ways
  to enhance beam-beam effect.