1. Compensating Parasitic Collisions using Electro-Magnetic Lenses
G. Burtin, J. Camas, G. de Rijk, G. Ferioli,
J.-J. Gras, S. Jackson, J.-P. Koutchouk, J. Wenninger,
F. Zimmermann, … with help from lots of groups!
Summary
Motivation
LHC & SPS Simulations
Scaling
MDs in 2002&2003
BCT, PMT
Future Devices
Summary again
J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

2. J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.
Summary
SPS BBLR Set Up models Long-Range Beam-Beam Collisions
in the LHC; so far 3+3 MDs performed in 2002 & 2003
Tune shift & orbit distortions well understood; they allow precise
determination of beam-wire distance
Beam lifetime and loss measurements indicate LHC parameters
at the edge (10% less crossing angle -> beam lifetime of 4 h)
Clear shrinkage of emittance due to BBLR & its dependence on
current and distance; using calibration by scraper, this was
converted into diffusive aperture (d.a.); Irwin’s scaling law
confirmed (d.a.~Sqrt(I)); d.a. might be only 2s in LHC?!
Direct diffusion measurements started (limited by PMT
signals, & by scraper speed & software), so far difficult
Further MDs (upgraded scraper) & analysis (e.g., 1000 turns)
foreseen
Two more devices in 2004 will demonstrate correction efficiency &
also allow comparison of various crossing schemes
J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

3. Long-Range Beam-Beam Collisions
perturb motion at large betatron amplitudes, where particles come close to opposing beam
cause ‘diffusive aperture’ (Irwin), high background, poor beam lifetime
increasing problem for SPS, Tevatron, LHC,...
that is for operation with larger # of bunches
#LR encounters
SPS 9
Tevatron Run-II 70
LHC
120
J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

4. J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.
LHC: 4 primary IPs
and
30 long-range collisions per IP
120 in total
partial mitigation by alternating planes of crossing at IP1 & 5 etc.
J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

5. Simulations of the LR B-B in LHC
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 .
J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

6. J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.
result of weak-strong simulations for LHC
center
of other
beam
Y. Papaphilippou
& F.Z., LHC 99
‘diffusive aperture’
J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

7. Long-Range Beam-Beam Compensation for the LHC
To correct all non-linear effects correction must be local.
Layout: 41 m upstream of D2, both sides of IP1/IP5
Phase difference between BBLRC &
average LR collision is 2.6o
(Jean-Pierre Koutchouk)
J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

8. J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.
Scaling from LHC to SPS
perturbation by wire:
relative perturbation:
for constant normalized emittance the effect in units
of sigma is independent of energy and beta function!
J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

9. Experimental Set-Up in the SPS
Iwire=Nb e c #LR/lwire
Tech. Coord. J. Camas & G. Burtin/BDI
Help from many groups
wire current
wire length
two 60-cm long wires
with 267 A current
equivalent to 60 LHC LR
collisions (e.g., IP1 & 5)
J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

10. J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.
nominal
distance
19 mm
(in the
shadow
of the arc
aperture)
water cooling
J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

11. J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.
LHC long-range collisions & SPS wire cause similar fast losses at large amplitudes in simulations
SPS wire
‘diffusive
aperture’
LHC beam
1 mm/s
1 mm/s
‘diffusive aperture’
effect of the 1-m long wire at 9.5s from the beam
center, carrying 267 A current, resembles the
total number of long-range collisions in the LHC
J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

12. J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.
MDs in 2002 and 2003
20/08/2002, 26 GeV/c: IC and PMT reading vs. position (threshold!), tune A DQx,y=-/
10/09/2002, 26 GeV/c: commissioned new inductive coil, DT >18o at 275 A, blew up ey by damper chirps (WH), DQ & Dy vs. A & 267 A
23/09/2002, 55 GeV/c: blew up ey by damper, vertical aperture problem emittance shrinks for beam-wire distances <12 mm, beam losses & lifetime vs. separation
27/06/2003, 26 GeV/c: new dipole corrector, emittance shrinkage if BBLR is excited
04/07/2003, 26 GeV/c: blew up emittance by mismatch, emittance shrinkage vs. wire excitation
21/08/2003, 26 GeV/c: kick pencil beam, emittance shrinkage vs. separation, calibration by scraping, diffusion measurement
J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

13. J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.
linear optics perturbations:
orbit change Dd and tune shift DQ due
to wire (or due to other beam)
precise control of beam-wire separation!
J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

14. J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.MD
comparison with
MAD prediction
(J. Wenninger)
orbit kick Qy Qx
J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

15. J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.
MD : beam-wire distance derived from
tune shift and from orbit change versus prediction
prediction
J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

16. evidence for diffusion vs. beam-wire distance in SPS MD-2002-3
background up
lifetime drops
below 9s!
logarithmic scales!
LHC at
the edge of
lifetime
drop!
compare with
LHC simulation:
8 s
9.5 s
J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

17. J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.MD
final
emittance
reduced,
if wire is
excited
for large
initial
emittances
it may approach
a ~constant
value
dependence on initial emittance
J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

18. J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.
dependence of diffusive aperture on wire current
experiment of July 4, 2003, confirms Irwin’s scaling law;
beam shrinks since particles at large amplitude are lost
J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

19. J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.
Final emittance vs bump for
3 different BBLR excitations
Reduction in emittance of the left outermost point without excitation is consistent with scraping at an amplitude of ( )mm = 5.6 mm, corresponding to 2.4 times the rms beam size of 2.3 mm. This is also the dynamic aperture for 267 A w/o bump.
dependence on beam-wire separation
J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

20. J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.
Scraper at +3.05(+ 0.88)mm
gives eOUT=1.7 mm, no BBLR
IN Scan at
100 ms
OUT Scan at
3200 ms
Note: orbit bump and LRBB
excitation from 1500 ms
Bump –11.6 mm for A
gives eOUT=2.2 mm
Bump –9.4 mm for A
gives eOUT=1.15 mm
J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

21. J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.
Abel transformation of wire-scan data gives change in (norm.) amplitude distribution:
(Krempl, Chanel, Carli)
scraping at
3.06 mm,
eout=1.71 mm
BBLR 267 A,
bump –4.5 mm
eout=2.06 mm
scraping at
2.06 mm,
eout=1.31 mm
BBLR 267A
Bump –9.4 mm,
eout=1.15 mm
J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

22. J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.
Calibration: measured final
emittance vs. scraper position
Calibration curve of measured final emittance vs scraper position allows us to estimate effective aperture due to BBLR excitation
J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

23. J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.
scaling to the LHC – d.a. only 2-3 s?
J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

24. J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.
Example of BCT & PMT data
only BBLR (at ms),
w/o scraping
BBLR at ms,
scraping at ms
PMT
PMT
BCT
BCT
can we fit a
diffusion
constant?
on the right, scraper position is about 1s;
at larger amplitudes the diffusion seems
much faster than the speed of the scraper
J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

25. Extension 1: Compensation
Goal: demonstrate the correctability of the LR-BB effect for LHC conditions:
Betatron phase shift (~2 degrees)
Wire out of beam aperture (12  instead of 9.5 )
Excitation error: say 10%
Set-up: a second identical device in LLS5 about 2 m away + vertical motion: same quality (vacuum compatibility) + larger safety vs SPS aperture.
J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

26. Extension 2: Long-Distance Compensation & Crossing Schemes
compensation over long distance with variable phase advance and independent x&y orbit bumps at two wires [y wire];
this will confirm the practicability of the compensation scheme for the LHC with reduced systematic cancellations & explore tolerances
compare effects of alternating x-y crossings at two locations (LHC baseline) with 2 times stronger collision at 45 degrees - “inclined hybrid crossing” - and with pure vertical or pure horizontal crossing [other 2 wires]; this will probe the sensitivity to the LHC crossing scheme and assess present choice
J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

27. J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.
schematic of 2nd and 3rd device
clearance required to stay in the arc shadow:
19 mm (y), 51.5 mm (x), 26.5 mm (45 deg)
J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

28. J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.
2nd & 3rd devices will be mobile with
wires in different planes (G. Burtin)
J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.

29. J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.
Summary
SPS BBLR Set Up models Long-Range Beam-Beam Collisions
in the LHC; so far 3+3 MDs performed in 2002 & 2003
Tune shift & orbit distortions well understood; they allow precise
determination of beam-wire distance
Beam lifetime and loss measurements indicate LHC parameters
at the edge (10% less crossing angle -> beam lifetime of 4 h)
Clear shrinkage of emittance due to BBLR & its dependence on
current and distance; using calibration by scraper, this was
converted into diffusive aperture (d.a.); Irwin’s scaling law
confirmed (d.a.~Sqrt(I)); d.a. might be only 2s in LHC?!
Direct diffusion measurements started (limited by PMT
signals, & by scraper speed & software), so far difficult
Further MDs (upgraded scraper) & analysis (e.g., 1000 turns)
foreseen
Two more devices in 2004 will demonstrate correction efficiency &
also allow comparison of various crossing schemes
J.P. Koutchouk, J. Wenninger, F. Zimmermann, et al.