1. CLIC Interaction Region when beams meet detectors
Barbara Dalena (CERN BE/ABP-CC3 )
LAL
25th January 2011

2. Outline Introduction Solenoid effects on beam dynamics
Interaction Region (IR) Solenoid
Solenoid effects on beam dynamics
Optical distortions
Compensation
Incoherent Synchrotron Radiation
Impact of IR magnet designs on luminosity loss
Beam-related backgrounds and luminosity measurement signal
25/1/2011
B. Dalena, LAL seminar

3. CLIC layout @ 3 TeV Drive beam Main beam Drive Beam Generation Complex
Main Beam Generation Complex
25/1/2011
B. Dalena, LAL seminar

4. Detector Solenoid

5. Solenoids Instrumented Return Yoke
Superconductive coils + instrumented
return yoke
Engineering based on CMS experience
Coil
6 m
B [T]
Rin [m]
ILD 4
3.395
SiD 5
2.684
25/1/2011
B. Dalena, LAL seminar

6. Why and which magnetic field ?
General considerations  PT
fit : Measurement errors in curvature and direction
MS : Multiple scattering errors
25/1/2011
B. Dalena, LAL seminar

7. Errors on track momentum and direction
Measurement errors
L’ : trajectory on the plane orthogonal to B
L : total trajectory
 : resolution in the plane orthogonal to B
z : resolution in the z direction
N + 1 : number of measurement points
Multiple scattering
Pagina e in poi della tesi di elena botta
where
X0 : radiation length of the scattering medium
LC-measurements require
25/1/2011
B. Dalena, LAL seminar

8. B-field and beam-beam background
Higher solenoid magnetic field confines more the beam-beam secondary particles
 reduce background in the detector
Takashi Maruyama
25/1/2011
B. Dalena, LAL seminar

9. Effects on the beams

10. Solenoid and beam crossing angle
Schematic view of the two beams colliding with a crossing angle in the detector solenoid.
Vertical orbit of e+ e- beams colliding with a crossing angle in the detector solenoid for different magnetic field.
25/1/2011
B. Dalena, LAL seminar

11. Solenoid beam dynamics
Orbit deviation : the beam is bent as it traverses the magnetic field
Weak focusing : in the two transverse planes
Coupling between x-y plane : the particle position in one plane depends on the position in the other plane
Dispersion : particles at lower energies experience a larger deflection than those at higher energies
The beam emits Incoherent Synchrotron Radiation (ISR) as it is deflected
Bxcosc and Bzsinc
act on the beam with opposite sign
Br  r
x’’  Br  y
y’’  Br  x
x’’  e/cp
y’’  e/cp
Ps  1/(m0c2)4  E4 / R2
25/1/2011
B. Dalena, LAL seminar

12. Detector Solenoid magnetic fieldsx s
θc/2 z
x, z solenoid axes
s beam line longitudinal axis
Different detector designs generate different field along the beamline
25/1/2011
B. Dalena, LAL seminar

13. Main field component acting on the beam
Mult
QD0 L* IP
BX component of solenoid fields in the beamline reference system
CLIC_SiD H. Gerwig (CERN)
CLIC_ILD D. Swoboda (CERN)
4th concept J. Hauptman (Iowa State University)
25/1/2011
B. Dalena, LAL seminar

14. Orbit deviations Mult QD0 IP
Vertical orbit deviations due to the detector solenoid field and its overlap with QD0 (and the other FF magnets)
25/1/2011
B. Dalena, LAL seminar

15. Vertical offset correction
QD0
Mult
Vertical offset at IP compensated by QD0 offset
25/1/2011
B. Dalena, LAL seminar

16. Distortions in the transverse plane
25/1/2011
B. Dalena, LAL seminar

17. IR coupling compensation
When detector solenoid overlaps QD0, coupling between y & x’ and y & E causes large (30 – 190 times) increase of IP size (green=detector solenoid OFF, red=ON)
without compensation sy/ sy(0)=32
Even though traditional use of skew quads could reduce the effect, the local compensation of the fringe field (with a little skew tuning) is the most efficient way to ensure correction over wide range of beam energies
antisolenoid
QD0
SD0
with compensation by antisolenoid sy/ sy(0)<1.01
25/1/2011
B. Dalena, LAL seminar
A.Seryi, ILC Accelerator School 2010

18. Compensation of the optical distortions
Bucking coils that cancel the main solenoid field in the magnets region
reduce the beam distortions at the IP
QD0 shielding from the main solenoid field
R  25 cm
LIP  3.5 m
CLIC_ILD
QD0
25/1/2011
B. Dalena, LAL seminar

19. Anti-solenoid design H. Gerwig CERN PH-CMX Anti-solenoid integration:
- 4 bucking coils of same length and equally spaced
CLIC_SiD
R 50 cm
LIP  3.8 m
CLIC
CLIC
CLIC
CLIC
CLIC
CLIC
CLIC
CLIC
QD0
25/1/2011
B. Dalena, LAL seminar

20. Anti-solenoids impact on the beams
25/1/2011
B. Dalena, LAL seminar

21. |corr(y,E)|/beam sizes |corr(y,x’)|/beam sizes
Optical compensation
|corr(y,E)|/beam sizes
ILD
SiD
|corr(y,x’)|/beam sizes
IP offset m
Main Solenoid
27.09
35.99
19.42
23.01
-4.421
-6.417
Solenoid +
Anti-solenoid
0.84
1.60
1.02
1.62
+0.069
-0.736
more than 90% of the distortions are corrected by the anti-solenoid
how much of residual distortions can be cancelled with other FFS magnets ?
ex: sextupoles knobs (constructed by E. Marin BE/ABP-CC3 )
sextupole offsets O(10) m
knobs
knobs
25/1/2011
B. Dalena, LAL seminar

22. Anti-solenoid optimization
To reach the QD0 gradient, external field should be low (due to permendur material)
optimize anti-solenoid bucking coils shape and/or adding ferromagnetic material
shift QD0 far from IP if first solution not feasible
insure it still reduces up to 90% the optical distortions of the beam at the IP
Work in progress
A. Bartalesi CERN TE-MSC
25/1/2011
B. Dalena, LAL seminar

23. Incoherent Synchrotron radiation

24. Incoherent Synchrotron Radiation sources in the BDS
Bending magnets in the FFS
about 10% luminosity loss in CLIC 3 TeV CM
vg = c
ve < c
A.Seryi, ILC Accelerator School 2010
Strong focusing in the final doublet (Oide effect)
about 10% of luminosity loss in CLIC 3 TeV CM
Final quad R L L* IP
25/1/2011
B. Dalena, LAL seminar

25. Effect on the beam sizes
Beam size increase at the IP due to Incoherent synchrotron radiation
FFS
Bend
Final Doublet
Solenoid
25/1/2011
B. Dalena, LAL seminar

26. Luminosity Loss due to incoherent synchrotron radiation
Field Map
Bz [T]
Lumi loss [%]
CLIC(ILC)_SiD 5
~(3)14.0
CLIC_SiD + Antisolenoid
~10.0
CLIC(ILC)_ILD 4
~(4)10.0
CLIC_ILD + Antisolenoid
4th concept at 3TeV
3.5
~20.0
ILC_ILD at 3 TeV + AntiDiD
~25.0
Luminosity calculation by GUINEA-PIG
CLIC half horizontal crossing angle 10 mrad
CLIC-BDS budget: 20% luminosity loss
25/1/2011
B. Dalena, LAL seminar

27. DiD - AntiDiD Bx DiD θc/2 AntiDiD θc/2
Coil wound on detector solenoid giving transverse field (Bx)
It can zero y and y’ at IP
But the field acting on the outgoing beam is bigger than solenoid detector alone  pairs diffuse in the detector
AntiDiD
Reversing DiD’s polarity and optimizing the strength, more than 50% of the pairs are redirected to the extraction apertures
θc/2
θc/2
25/1/2011
B. Dalena, LAL seminar

28. Position of emitted photons
Mean energy of emitted photons ~ 20 MeV,
peak at very low energy (< 1 MeV)
max photon energy ( < 200 MeV)
25/1/2011
B. Dalena, LAL seminar

29. Photon fans at the IP Collimation depths : x = 15x , y = 55y
Maximum photon cone for an envelope covering 15x and 55y
25/1/2011
B. Dalena, LAL seminar

30. Luminosity measurements

31. FFS luminosity optimization
Static imperfections
luminosity optimization only: 55% of the seeds reach 100% of nominal luminosity.
after 2 iterations of H and V knobs: 90% of the seed reach 90% of nominal luminosity (identical machines)
luminosity optimization needs O( ) luminosity measurements
Knobs tuning points  8 knobs  2 iter = 320 luminosity measurements
25/1/2011
B. Dalena, LAL seminar

32. Luminosity measurement signal
radiative bhabha :
high counting rate but not really visible in the spent beam spectrum
low angle bhabha
7-70 minutes for 1% luminosity measurement according to the  cut
long term luminosity stability due to dynamic imperfections minutes
we need a luminosity measurement signal  1 min
25/1/2011
B. Dalena, LAL seminar

33. Knobs vs luminosity and background (H)
25/1/2011
B. Dalena, LAL seminar

34. Knobs vs luminosity and background (V)
Incoherent pairs & hadronic events  luminosity
25/1/2011
B. Dalena, LAL seminar

35. Hadronic events multiplicity
No Pt cut applied
Nhadron per bx are ~3.21
Which particles are visible in the detector ?
25/1/2011
B. Dalena, LAL seminar

36. Multiplicity per train (example: +/-)
3 train : Mult rms ~ 7% 1 <  < 1.57 rad)
how much of this multiplicity is visible ?
25/1/2011
B. Dalena, LAL seminar

37. Summary & Conclusions
Detector solenoid design and related IR magnets can have a strong impact on the CLIC achievable luminosity
Anti-solenoid can reduce up to > 90% the optical distortions due to the interaction region solenoid and QD0 overlap
First look at the hadrons as potential fast luminosity measurement signal
25/1/2011
B. Dalena, LAL seminar

38. References Acknowledgement
R.L. Gluckstern Nucl. Instrument and Methods 24 (1963)
R. Tomás et al., « Summary of the BDS and MDI CLIC08 Working group »
CLIC-Note-776
B. Dalena et al., « Solenoid and Synchrotron Radiation Effects in CLIC »
PAC’09-TH6PFP074 and CLIC-Note-786
D. Swodoba, B. Dalena and R. Tomás « CLIC spectrometer magnet interference computation of transversal B-field on primary beam »
CLIC-Note-815
B. Dalena et al., « Impact of the Experimental Solenoid on the CLIC luminosity » IPAC’10-WEPE029 and CLIC-Note-831
J. Resta Lopez et al., « Optimization of the CLIC Baseline Collimation System » IPAC’10-WEPE046
B. Dalena and D. Schulte << Beam-Beam background in CLIC in presence of imperfections >> IPAC’10-WEPE025
Acknowledgement
Many thanks to D. Schulte, K. Elsener and André Sailer for useful discussions.
25/1/2011
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39. spares

40. Energy distribution
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41. Hadronic events multiplicity
Mult (rms) (0<<1.57 rad)
Mult (rms) (0<<0.5 rad)
Mult (rms) (0.5<<1 rad)
Mult (rms) (1<<1.57 rad)
e+/-
0.0967(0.4405)
(0.3689)
(0.1612)
(0.1443)
+/-
( )
( )
( )
( ) 
7.429 (8.648)
5.271(6.64)
1.193(1.859)
0.9651(1.562)
+/-
6.584(6.858)
4.919(5.409)
0.946(1.441)
0.7191(1.173)
K+/-
0.7285(1.247)
0.5797(1.076)
(0.3259)
(0.2656)
KoL
0.3525(0.7278)
0.2794(0.634)
(0.2155)
(0.176) p
0.42(0.907)
0.3462(0.8011)
(0.2276)
(0.1795) n
0.3975(0.8763)
0.3267(0.7719)
(0.2225)
(0.1754)
incoh. pairs*
(1292)
(1289)
(64.29)
(14.43)
* incoherent pairs are per bx, hadronic events are per  collision
(Nhadron are ~3.21 per bx)
25/1/2011
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42. CLIC crossing angle 10 mrad half crossing angle 25/1/2011
B. Dalena, LAL seminar

43. Incoherent pairs diffusion in ILC
Solenoid only
DID
anti-DID
A. Seryi et al., SLAC-PUB-11662
25/1/2011
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44. Incoherent pairs diffusion in CLIC
deposited energy ~ 27 TeV per bx
A. Sailer CERN PH-LCD
25/1/2011
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45. Backscattered particles
A. Sailer CERN PH-LCD
25/1/2011
B. Dalena, LAL seminar