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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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