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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

FREQUENT RECOGGING:EFFECTS ON THE BEAM

Wolfram Fischer

RHIC Spin Collaboration Meeting19 September 2002

contents
Contents
  • Introduction
  • Run 2001 lifetimes
  • Cogging effects
  • Effects on integrated luminosity Ldt
    • Time lost
    • Longitudinal — debunching
    • Transverse — luminosity lifetime reduction
  • Summary
introduction
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)
run 2001 lifetimes p
Run 2001 lifetimes – p

J. v. Zeijts, W. Fischer

 De/e = 4% (1st hour) rms = 5%

run 2001 lifetimes au
Run 2001 lifetimes – Au

J. v. Zeijts, W. Fischer

 De/e = 21% (1st hour) rms = 13%

cogging effects

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)
cogging effects tune change

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
cogging effects working point

5th

4th

Cogging effects – working point

17th

17th

13th

13th

9th

14th

Out of collisionIn collision

Frequent recogging requires 2 stable working points

ldt reduction time lost
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)
longitudinal debunching
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)
transverse luminosity lifetime
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)
summary i
Summary I

(DLdt)tot = P [1 – (DLdt)i]

Not considered:

- Additional experiments dead time for cogging- Loss in polarization

summary ii
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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