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First look at beam background in 2012 CMS

First look at beam background in 2012 CMS. Replacing the RF Fingers. Replacement of the rf -fingers element at 18.3m right of IP5 has improved the vacuum behavior.

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First look at beam background in 2012 CMS

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  1. First look at beam background in 2012CMS CMS

  2. Replacing the RF Fingers • Replacement of the rf-fingers element at 18.3m right of IP5 has improved the vacuum behavior. • The typical vacuum increase at injection (above a few E13 total injected protons per beam) is not there anymore in 2012 (so far). Fill 2267 (2011) Vacuum on the right shooting up when the total current exceeds 4E13 Fill 2497 (2012) Vacuum not changing up to a current of 9E13. This value was never reached in 2011 without a sudden increase in the vacuum 18.3m right of IP5 CMS

  3. Vacuum through the ramp, squeeze • Typically the pressure at increases during the ramp by Δ5e-10 mbar (183.1R5) Δ1e-10 mbar (183.1L5) • Δ2e-10 (183.1R5) ; Δ1e-10 (183.1L5) due to luminosity Fill 2497 (2012) CMS

  4. Beam Gas Measurement • CMS, beam gas measurement based on “quiet” non-colliding bunches (>= 900 ns far away from previous colliding bunch) • Beam 1 and Beam 2 background rates published separately • Calculate normalized rate Hz/cm2/1011particles • Measure online the albedo contamination • Commissioned in 2011, and well correlated to beam gas vacuum CMS

  5. Beam Gas Measurement 2012 • Same as 2012, except online albedo subtraction still to be applied (next day or two) • Beam gas < 10 Hz/1011/cm2 • Pressure < few E-9 mbar BKDG 5 = B2 Typical Fill 2515 (2012) BKDG 4 = B1 CMS

  6. Summary • Vacuum around IP5 in 2012 much improved compared to 2011 • Normally in the E-10 mbar range or few E-9 mbar • No CMS operational problems associated to beam backgrounds so far • Outlook for next report: • Online Muon-Halo monitoring • Comparison of offline beam-gas measurement with online beam-gas measurement CMS

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