3/7/2002 SLTC 1

An LHC Beam-Beam Long-Range Simulator for the SPS

Miniteam: J-P Koutchouk/BI, G. de Rijk/MS, F. Zimmermann/AP

Tech. Coordination: J. Camas/BI

+ much help

3/7/2002 SLTC 2

Motivations

• The Long-Range Beam-Beam effect has been identified as being the primary limit of LHC performance

• The nominal LHC parameters might not be consistent (intensity, Xing angle, luminosity)

• A proposal for an accurate compensation of this effect was devised and checked successfully in simulation both at Cern and elsewhere

• The design of such a compensator is challenging

3/7/2002 SLTC 3

Simulations of the LR B-B

1) Sen et al./1999: amplitude growth above 7 ; sharp threshold for the Xing angle at 300 urad.

2) Papaphilippou & Zimmermann/1999: strong amplitude diffusion above 5.5 Sqrt(2) [4D tracking]. Study of the parameter dependence.

3) Schmidt (6D): dynap decreases with increasing number of turns. At 10^6, min dynap is 6 ; onset of chaos detected around 4 . At injection, in spite of large separation, the dynap is about 7 .

3/7/2002 SLTC 4

Simulations of the Correction

1) JPK/2000: principle of a correction reducing by 10 the tune

footprint, large reduction of other non-linear terms and cancellation of the beam separation at the IP’s

2) FZ/2001: confirmation by independent tracking: diffusive aperture increases from 5.5 to 7 . The correction is robust.

The noise on the excitor current < .1%

3)J. Shi/U. Kansas/2002: confirmation in the strong-strong case with a very large number of particles and very large (LHC upgrade), including robustness. The noise shall be less than 0.5%.

3/7/2002 SLTC 5

An example of simulation results (FZ)

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Aim of the SPS experiment

1) Investigate the effect on the beam of the LR BB effect expected in LHC (lifetime vs intensity, separation). Investigate scaling. Compare with simulations and Tevatron observations (FNAL staff will join).

2) If a strong effect is confirmed, deduce a consistent set of LHC parameters and a new estimate of the nominal luminosity (without BBLR correction).

3) If …, prepare the design and installation of a compensation system in the SPS to study the efficiency of the correction in presence of imperfections.

3/7/2002 SLTC 7

Principle of the SPS experiment

1) Install a wire along the SPS beam which gives the same effect as the 60 long range interactions in IR1 and IR5 of LHC: equal beta’s, 320 A.m.

2) Simple set-up: the wire shall be fixed and the beam is moved towards the wire (energy issue). DC excitation current still allows the study of the PACMAN bunches.

3) Cheap implementation: use/modify existing equipment: existing couplers, cables, power converter, coil.

4) Compatibility with normal running: install the set-up in the shadow of the SPS aperture, V plane, BPM & BLM.

3/7/2002 SLTC 8

Diagram of the SPS experiment at 51760 & 51771

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Modified BCPL coupler(s)

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Wire excitor

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Main Parameters

Materials Cu OFHC, Al2O3,stainless steel

m

Active length 2* 0.6 m

Outer/Inner diameters 2.54 (r=1.25)/1.54 mm

Intensity 0 to 267 ACurrent density 81 A/mm^2

Power 760 WWater flow 0.36 l/mnPressure drop 2.5 bar

Max Pressure 4+2.5=6.5 bar

Pressure of service 60 bar

3/7/2002 SLTC 12

Machine Aperture IssuesTo minimize the risks,• the wire excitor is placed in the lower half of the

vertical plane,• it is positioned in the shadow of the global primary

aperture limit (TIDV)• and in the shadow of the distributed secondary

aperture limit (dipoles)… at 19mm from axis.

Reference absolute worst case: 26 GeV/c, En=13.8 10^-6

TIDV: 3.04, MBB: 3.39, BBLR: 3.80, =5mm

3/7/2002 SLTC 13

Machine Aperture Issues

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Machine Aperture Issues

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Machine Aperture Issues

3/7/2002 SLTC 16

Planning and InstallationA fast and safe installation/removal was prepared by

cutting the vac. chamber in April and putting in place a section of the BBLR length.

All other aspects are moving on. It seems today that we can be just ready by 24th July for installation if every thing goes well (crash programme).

This would leave a debugging period in 2002.

2003: experimentation and decision by summer on a corrector.

2004: installation of the corrector iff manpower.

3/7/2002 SLTC 17

Help and Collaborations Implementation

– Projeteur: R. Perret/EST

– Advising on brazing issues: S. Mathot/EST, J. Benoit/BT

– Advising on cooling in thin tubes and overall design: W. Weterings/BT, B. Goddard/BT

– Help on lab tests: BI + MS

– Power supply: M. Royer, A. Rubbio/PC

– Inductance, interlocks: G. de Rijk et al./MS

– Vacuum issues: N. Hilleret/VA consulted,

– + cables, water cooling,…

3/7/2002 SLTC 18

Help and Collaborations

Scientific (External)

– FNAL : T. Sen, Y. Alexahin, (SPS MD’s + wire modeling), A. Shiltsev (?)

– U. of Kansas: J. Shi et al.: Effect of the compensation in strong-strong beam-beam simulations

3/7/2002 SLTC 19

Conclusions

An important open question on the LHC performance can find an answer in a SPS experiment. This issue is also relevant for the Tevatron (collab.), the LHC upgrade, the VLHC,…

All efforts are made to design and install a b-b simulator on a time scale which should allow in-time information of more realistic performance prediction for the LHC and decision on whether to correct.

Care has been taken to minimize any risk to normal operation.

A correction in LHC being technically challenging, it is necessary to move on to be in time, say in 2009.