# Presentation: 295849

## FREQUENT RECOGGING:EFFECTS ON THE BEAM

**Wolfram Fischer**
- RHIC Spin Collaboration Meeting19 September 2002

## Contents

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

## Introduction

- Assumptions:
- Proton beams at  = 260, 56(112) bunches
- Nb = 1011, N = 20m  beam-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 Ldt = (Ldt)recogging / (Ldt)
- Polarization ( A. Luccio, V. Ptitsyn, V. Ranjbar)

## Run 2001 lifetimes – p

-  = 4% (1st hour)     rms = 5%

- J. v. Zeijts, W. Fischer

## Run 2001 lifetimes – Au

-  = 21% (1st hour)     rms = 13%

- J. v. Zeijts, W. Fischer

## Cogging effects

- <date/time>Wolfram Fischer

**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

## Cogging effects – working point

**13****th**

**17****th**

- Out of collisionIn collision

**9****th**

**14****th**

**13****th**

**17****th**

**Frequent recogging requires 2 stable working points **

## Ldt reduction – time lost

- Cogging time:
- Frequency ramp f/t = 10Hz/8s  (fmax = 10Hz) 4.4 s / 6 buckets
- Overhead  5s (ev-lumi-off, ev-lumi-on, etc.)
-  (Ldt)1   – 8%
- Experiment’s dead times:
- Are certain detector components switched off during cogging?  (Ldt)2 reduction
- Fatalities
- Aborted stores,
- Completely debunched beams,
- Lost beam synch clock, ...
-   (Ldt)3  – 15%  (educated guess)

## Longitudinal – debunching

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

## Transverse – luminosity lifetime

- Run 2001:
- Small tune changes (of order ~) could result in dramatic changes in beam lifetimewith *=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/1)exp(T2/2) ...  (Ldt)5  –10%
- Emittance growth from recogging,difficult to estimate  (Ldt)6  –5% (educated guess)

## Summary I

| Effect | (Ldt) |
| --- | --- |
| Cogging time | – 8% |
| Fatalities | – 15% |
| Debunching | – 5% |
| Beam lifetime | – 10% |
| Emittance growth | – 5% |
| Total | – 65% |

**(********Ldt)****tot**** = ******** [1 – (********Ldt)****i****]**
**Not considered:**
**- Additional experiments dead time for cogging****- Loss in polarization**

## 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