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FREQUENT RECOGGING: EFFECTS ON THE BEAM

FREQUENT RECOGGING: EFFECTS ON THE BEAM. Wolfram Fischer RHIC Spin Collaboration Meeting 19 September 2002. Contents. Introduction Run 2001 lifetimes Cogging effects Effects on integrated luminosity Ldt Time lost Longitudinal — debunching Transverse — luminosity lifetime reduction

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FREQUENT RECOGGING: EFFECTS ON THE BEAM

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  1. FREQUENT RECOGGING:EFFECTS ON THE BEAM Wolfram Fischer RHIC Spin Collaboration Meeting19 September 2002

  2. Contents • Introduction • Run 2001 lifetimes • Cogging effects • Effects on integrated luminosity Ldt • Time lost • Longitudinal — debunching • Transverse — luminosity lifetime reduction • Summary

  3. Introduction • Assumptions: • Proton beams at g = 260, 56(112) bunches • Nb = 1011, eN = 20mm  xbeam-beam = 0.0037 / IP • Store length of 7 hours • Recogging (worst case) • Every 2 min • By 6(3) buckets • Expect adverse effects on: • Integrated luminosity Ldt try to estimate DLdt = (Ldt)recogging / (Ldt) • Polarization (A. Luccio, V. Ptitsyn, V. Ranjbar)

  4. Run 2001 lifetimes – p J. v. Zeijts, W. Fischer  De/e = 4% (1st hour) rms = 5%

  5. Run 2001 lifetimes – Au J. v. Zeijts, W. Fischer  De/e = 21% (1st hour) rms = 13%

  6. Beam-beam OFF Beam-beam ON Beam-beam OFF Moving crossing points if Dfrf0 DX IP DX BPM(x,y) BPM(x,y) v=5m·Dfrf Cogging effects • Cogging moves the collision points longitudinally • Beyond DX magnets and with crossing angles (intentional or unintentional) transverse beam separation changes  Transverse tunes change (beam-beam interaction)

  7. PLL Blue horizontal, Au after 3h store Cogged 3 buckets (fully separated longitudinally) Cogged 2 buckets Cogged 1 bucket DQmeas=0.0007  eN=22mm Beams colliding Sign of crossing angles (no tune change if all zero) P. Cameron Cogging effects – tune change

  8. 5th 4th Cogging effects – working point 17th 17th 13th 13th 9th 14th Out of collisionIn collision Frequent recogging requires 2 stable working points

  9. Ldt reduction – time lost • Cogging time: • Frequency ramp Df/Dt = 10Hz/8s (Dfmax = 10Hz) 4.4 s / 6 buckets • Overhead  5s (ev-lumi-off, ev-lumi-on, etc.) •  (DLdt)1– 8% • Experiment’s dead times: • Are certain detector components switched off during cogging?  (DLdt)2reduction • Fatalities • Aborted stores, • Completely debunched beams, • Lost beam synch clock, … •  (DLdt)3 – 15% (educated guess)

  10. Longitudinal – debunching • Every cogging step is somewhat non-adiabatic  longitudinal emittance growth  ultimately debunching • Run 2001: • 28 MHz system, 300kV • Dss / ss  1% / hr (1st hour), almost no debunching • Run 2003: • 197 MHz system, 3MV • Dss / ss  ??, debunching ?? • Difficult to estimate debunching effect (DLdt)4  –5% (educated guess)

  11. Transverse – luminosity lifetime • Run 2001: • Small tune changes (of order ~x) could result in dramatic changes in beam lifetimewith b*=2(1)m lattice (Yellow) • Run 2003: • Expect beam lifetime improvements for Run 2002 with nonlinear IR correction • Assume 30% beam lifetime reduction in uncogged state I(t) = I0 exp(T1/t1)exp(T2/t2) …  (DLdt)5  –10% • Emittance growth from recogging,difficult to estimate  (DLdt)6  –5% (educated guess)

  12. Summary I (DLdt)tot = P [1 – (DLdt)i] Not considered: - Additional experiments dead time for cogging- Loss in polarization

  13. Summary II • Frequent recogging may reduce the integrated luminosity by  50% • Risk of total beam loss is increased, but should be acceptable • Book keeping for colliding spin patterns is not trivial but manageable • Effect on polarization may need to be studied • Practical detector operation may be affected

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