Open Issues from theSPS Long-Range Experiments

Frank ZimmermannUS-LARP Beam-Beam Workshop

SLAC, 2007

Gerard Burtin, Ulrich Dorda, Gijs de Rijk, Jean-Pierre Koutchouk, Yannis Papaphilippou, Tannaji Sen,

Vladimir Shiltsev, Jorg Wenninger, + many others

outline

• motivation & scaling• single wire as LHC LR simulator

(2002-2004)• two wire compensation (2004)• test of crossing schemes (2004)• open questions and 2007 plan

APC meeting, 19.09.03, LRBB J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

• To correct all non-linear effects correction must be local.• Layout: 41 m upstream of D2, both sides of IP1/IP5

(Jean-Pierre Koutchouk)

Motivation: Long-Range Beam-Beam Compensation for the LHC

Phase difference between BBLRC & average LR collision is 2.6o

1st Wire “BBLR” in the SPS

Tech. Coord. J. Camas &

G. Burtin/BDI

Help from many groups

two 60-cm long wireswith 267 A currentequivalent to 60 LHC LR collisions (e.g., IP1 & 5)

Iwire=Nb e c #LR/lwire

wire lengthwire current

nominaldistance19 mm(in theshadow of the arc aperture)

water cooling

each BBLR consists of 2 units, total length:2x0.8+0.25=1.85 m

Scaling from LHC to SPS

)(2'

dyecIlr

y wwp

−=Δγ

⎟⎟⎠

⎞⎜⎜⎝

⎛⎟⎟⎠

⎞⎜⎜⎝

⎛=

Δ

da

wwp

y nI

eclry

~)(2

'

'

γεσ

relative perturbation:

for constant normalized emittance the effect in units of sigma is independent of energy and beta function!

perturbation by wire:

in simulations LHC long-range collisions & SPS wire cause similar fast losses at large amplitudes

LHC beam

SPS wire

1 mm/s1 mm/s

diffusive aperture

simulation with WSDIFF simulation with WSDIFF

dedicated ion chambers and PMTsinductive coil to suppress wire ripplewire heating computed and verifiedemittance blow up by damper or injection mismatch

to reproduce LHC or to increase sensitivitywire scanners, scrapersdedicated dipole corrector to correct orbit change

locallyalways correct tune

a few technical issues

( )2,

,1

2 ddeclIr

Q wwyxpyx Δ+=Δ

πγβ

m

( ) ( )( )yy

pwwy

QQddecrlI

dΔ+Δ+

=Δπγ

βtan

changes in orbit & tunes (2002)→ precise measure of beam-wire distance

y orbit change

y tune change

x tune changeJ. Wenninger

non-linear optics

• turn-by-turn BPM data after kicks of various amplitude

→ reduced decoherence time due to wire→ tune shift with amplitude, roughly

consistent with

24 ˆ

43 y

decrlI

Q xpwwx

βγ

≈Δ 24 ˆ

83 y

decrlI

Q xpwwy

βγ

−≈Δ

measuring the “diffusive” or dynamic aperture

three types of signals:• lifetime and background• final emittance• scraper-retraction

lifetime vs. separation beam loss vs. separation

drop in the lifetime and increased losses for separations less than 9σ; at 7-8σ separation lifetime decreases to 1-5 h

lifetime and background

initial & final profile

initial/final emittance = 3.40/1.15 μm

Abel transformation of wire-scan data gives change in (norm.) amplitude distribution:

∫−

−=R

A AgdAA

22

' )(2)(η

ηηρ

wire scans

(Krempl, Chanel, Carli)

final emittance

mechanical scraping by edge of wire

calibration of final emittance by scraper

Calibration curve of measured final emittance vs scraper position allows us to estimate effective aperture due to BBLR excitation

scaling to LHC – d.a. only 2-3σ?

larger emittancevariation whenwire is excited?!

effect of wire current on SPS dyn.ap.

linear dependence consistent with Irwin scaling law;measured dynamic aperture is smaller than the simulated

BBLR at 12725 ms, scraping at 13225 ms

only BBLR (at 12725 ms), w/o scraping

BCTPMT PMT

BCT

can we fit adiffusionconstant?

on the right, scraper position is about 1σ; at larger amplitudes the diffusion seemsmuch faster than the speed of the scraper

scraper retraction attempt

scraper moving to target positionalready intercepts halo

5d ms 5 ⎟⎠⎞

⎜⎝⎛≈σ

τ

extrapolation to LHC beam-beam distance, ~9.5σ, wouldpredict 6 minutes lifetime

5th power!

effect of beam-wire distance on lifetime

BBLR logbook 4 July 2003“…We bumped exactly –8.2 mm at the BBLR from cycle# 330616 (this would give 12.1 mm separation between wire center and beam [~5σ], corresponding to the latest simulations). The interpolated position with wire off was –8.6 mm. The spread in the BPM readings was about +/-0.2 mm. … The wire current was only -10 A [~2 LR collisions in LHC]. Nevertheless, the losses were high, about 3x106 at the 3rd PMT (last year we had about 106 as the maximum integrated reading). “

effect at low wire excitation

for 2004 two novel 3-wire BBLRs were built;separated from 1-wire BBLR by about 2.6o

(average LR-BBLR phase advance in LHC)

G. Burtin

remotelymovablein Y by 5 mm!

3rd

10th

7th4th

nearly perfect compensationwhat happens here?

Qx=0.31

1 wire

2 wires

no wire

vertical tune

beam lifetime

lifetime is recovered over a large tune range, except for Qy<0.285

two-wire compensation: tune scan

two-wire compensation: distance scan

BBSIM (T. Sen): No compensation beyond ~3mmMeasurement: Compensation lost beyond ~2.5mm from optimum

“scaled” experimentsnatural SPS beam lifetime ~30 h at 55 GeV/c~5-10 min at 26 GeV/c

(physical aperture ~4 σ)

to improve beam lifetime at 26 GeV/c, emittance can be reduced by scraping;

lifetime for εN~1.5 μm improves to ~1 h

ε

ε

~

,~

d

Iw

178390 178400 178410 178420 178430 178440 178450cycle number

1000

2000

3000

4000

5000

6000

7000

emitefilni

sLifetime versus cycle number

compensation

excitation

no beam - beam

LHC tunes

~61 min.

~36 min.

~69 min.

scaled two-wire compensation: lifetime

J.-P. Koutchouk

crossing schemes

diffusive aperturewith alternating crossing

diffusive aperturewith xx or yycrossing

centreof otherbeam

comparing xy, xx and yy crossing for two working points

crossing schemes – motivation 1

simulation

LHC

here tunes w/o beam-beam wereheld constant

EPAC’04

xx yy

xysimulations for different latticetunes, located along red line:

8σ 8.5σ

6.5σcrossing schemes – motivation 2

tune evolution for three trajectories without folding;the motion remains bounded

tune evolution for three trajectories with folding;the resonance 1:1 is a direction of fast escape(J. Laskar, PAC2003)

bounded

fast escape

schematic of folded frequency map(J. Laskar)

det(M)>0 det(M)<0 modelsystem

⎟⎟⎠

⎞⎜⎜⎝

⎛

∂

∂=

⎟⎟⎠

⎞⎜⎜⎝

⎛

∂

∂=

2,

2

,

,

yx

yx

yx

IH

IQ

M

EPAC’04crossing schemes – motivation 3

sample trajectories projected on amplitude plane

nonlinear ‘coupling’ betweenthe planes? but stable

little motion at small amplitudes but particleloss at 6 σ

tune spread gives incomplete characterization of the dynamics;experimental simulations of the two crossing schemes can be compared at the SPS EPAC’04crossing schemes – motivation 4

xx xy

yyfrequency mapsfor nominalLHC tunes

thanks toYannisPapaphilippoufor his help incalculating frequency maps!

simulations

crossing schemes – motivation 5

in most cases simulated diffusive aperture along diagonal x=y larger for equal-plane crossing than for alternating crossing*, sensitivity to IP-IP phase advance

possible explanations:(1) different ‘folding’ since xy crossing cancels

dodecapole and 20-pole terms in addition to linear tune shift;

(2) twice the number of resonances for xycrossing

*(similar result for y=0 – to be revisited)

crossing schemes – motivation 6

x bump -23 mm

BBLR1 on

BBLR2x on beam

“xy”

x bump -23 mm

BBLR1 off

BBLR2x on(strength x2)beam

xx

x bump -23 mm

BBLR2x off

BBLR1 on(strength x2)

beam

“yy”(strength x2)“xy-2”&

crossing scheme test – configuration 1

simulated diffusive aperture for XX crossing is 10% larger than for ‘quasi-XY’ or ‘quasi-YY’ crossing

simulation

xx

yyxy(x2)

xy

experiment

measured beam lifetime is best for XX crossing, second best for ‘quasi-YY’ crossing, lowest for ‘quasi-XY’ crossing

xx

yyxy(x2)

xy

lifetime without wire excitation was comparable to xy case

BBLR1 (rotated) & BBLR2 (45 degrees)

beam

J.-P. Koutchouk

x bump -8.9 mmy bump +11.4 mm

“45o135o”

beamx bump -8.9 mmy bump +11.4 mm

“45o45o”BBLR1 on (strength x2)

BBLR2x-45 offBBLR1 on

BBLR2-45 on

beam

x bump 0 mmy bump +8.5 mm

“yy”BBLR1 on (strength x2)

BBLR2x-45 off

crossing scheme test – configuration 2

reduced emittance“scaled” experiment

simulation

45o135o

45o45o

yy

simulated diffusive aperture for ‘45o45o’ crossing is worst; at tunes below 0.29 it is best for YY crossing & above 0.30 for ‘45o135o’

experimentw/o BBLR

45o135o

45o45o

yy

measured beam lifetime is worst for ‘45o45o’ crossing, and at tunes above 0.3 best for ‘45o135o’ crossing

relative beam lifetimes consistent with simulations

• scaling from SPS to LHC• strong emittance dependence of lifetime (c.f.Tevatron pbar) • discrepancies between measured & simulated dynamic aperture• breakdown of 2-wire compensation for Qy<0.285 • why 5th power law? (Tevatron: 3rd power, RHIC: 2nd and 4th power); why

different & why not higher power?? • some effect observed at very low wire excitation• amplitude-dependent diffusion rate• study sensitivity of final emittance to tune with and without BBLR• discrepancies between simulated and measured lifetime (improved at higher

beam energy?)• understand parameters which are out of control or introduce intentional large

perturbation (excite sextupoles, octupoles) to reconcile experiments and measurements

• wire compensation test with colliding beams (at RHIC) (essential?)• common observable in experiments & simulations? – dynamic aperture!

lifetime?• demonstrate that 10-4 stability of pulsed wire can be achieved • crossing scheme conclusions?

some open questions

lifetime/emittance growth vs beam-wire distance at different wire currents

tune scan of wire compensation at higher energy with longer unperturbed lifetimes

study compromise between nominal and PACMAN bunches by partial compensation

use both wires as exciters at different beam-wire separation to mimic LRBB at different beam-beam separation (crucial issue for the early separation upgrade scheme)

beam lifetime vs. beam-wire distance for different tunes to see (understand) whether different power laws found at SPS (^5), Tevatron (^3) and RHIC (^2) and (^4) are tune related

noise studies (if more than 2 MDs) to experimentally verify thesimulated precision requirements on a pulsed device

experiments will be performed at two different energies(26 GeV and 55 GeV) to confirm the theoretical scaling law

2007 SPS MD plan

for future wire beam-beam compensators - “BBLRs” -, 3-m long sections have been reserved in LHC at 104.93 m(center position)on either side of IP1 & IP5

referencesJ.-P. Koutchouk, Principle of a Correction of the Long-Range Beam-Beam Effect in LHC using

Electromagnetic Lenses, LHC Project Note 223, 2000J.-P. Koutchouk, Correction of the Long-Range Beam-Beam Effect in LHC using Electromagnetic Lenses,

SL Report 2001-048, 2001F. Zimmermann, Weak-Strong Simulation Studies for the LHC Long-Range Beam-Beam Compensation,

presented at Beam-Beam Workshop 2001 FNAL; LHC Project Report 502 (2001)J. Lin, J. Shi, W. Herr, Study of the Wire Compensation of Long-Range Beam-Beam Interactions in LHC

with a Strong-Strong Beam-Beam Simulation, EPAC 2002, Paris (2002)J.-P. Koutchouk, J. Wenninger, F. Zimmermann, Compensating Parasitic Collisions using Electromagnetic

Lenses, presented at ICFA Beam Dynamics Workshop on High-Luminosity e+e- Factories ("Factories'03") SLAC; in CERN-AB-2004-011-ABP (2004)

J.-P. Koutchouk, J. Wenninger, F. Zimmermann, Experiments on LHC Long-Range Beam-Beam Compensation in the SPS, EPAC'04 Lucerne (2004)

F. Zimmermann, Beam-Beam Compensation Schemes, Proc. First CARE-HHH-APD Workshop on Beam Dynamics in Future Hadron Colliders and Rapidly Cycling High-Intensity Synchrotrons (HHH-2004), CERN, Geneva, Switzerland, CERN-2005-006, p. 101 (2005)

F. Zimmermann, J.-P. Koutchouk, F. Roncarolo, J. Wenninger, T. Sen, V. Shiltsev, Y. Papaphilippou, Experiments on LHC Long-Range Beam-Beam Compensation and Crossing Schemes at the CERN SPS in 2004, PAC'05 Knoxville (2005)

F. Zimmermann and U. Dorda, Progress of Beam-Beam Compensation Schemes, Proc. CARE-HHH-APD Workshop on Scenarios for the LHC Luminosity Upgrade (LHC-LUMI-05), Arcidosso, Italy (2005)

U. Dorda and F. Zimmermann, Simulation of LHC Long-Range Beam-Beam Compensation with DC and Pulsed Wires (Talk), RPIA2006 workshop, KEK, Tsukuba, 07-10.03.2006 (2006)

F. Zimmermann, Possible Uses of Rapid Switching Devices and Induction RF for an LHC Upgrade (Talk),RPIA2006 workshop, KEK, Tsukuba, 07-10.03.2006 (2006)

U. Dorda, F. Zimmermann et al, Assessment of the Wire Lens at LHC from the current Pulse Power Technology Point of View (Talk), RPIA2006 workshop, KEK, Tsukuba, 07-10.03.2006 (2006)