1. Impact of synchrotron radiation in LEPTON COLLIDER arcs
Francesco Cerutti, Alfredo Ferrari, Luisella Lari*, Alessio Mereghetti
*BE department
Acknowledgments: B. Holzer, R. Kersevan, A. Milanese
FCC study kickoff meeting
Lepton collider design
University of Geneva, Feb 14, 2014

2. OUTLINE simulation of synchrotron radiation interaction
a (too?) much preliminary layout and the role of absorbers
power sharing
beam chamber and water heating
dose to hypothetical coils
ozone production
a shielded beam chamber
absorption and leakage
photoneutrons and activation

3. SYNCHROTRON RADIATION

4. SYNCHROTRON RADIATION
E>100 eV
% of the total power
95.75% of the photon amount
<E>=395 keV
E= 8.5 GeV/turn (dE/ds=1.375 keV/cm in the dipoles)
P = 8.5 x I[mA] MW = 8.5 x 10mA = 85 MW in the whole accelerator
(dP/ds= x I[mA] W/cm in the dipoles)

5. RELEVANT FLUKA CAPABILITIES
Sophisticated low energy photon transport including polarization effects for Compton, photoelectric and coherent scattering, and full account for bound electron effects: already available in FLUKA since several years
New: dedicated “generic” source for SR radiation accounting for:
Spectrum sampling
Polarization as a function of emitted photon energy
Angular distribution
Arbitrary orientation emitting particle vs magnetic field
Photon emission along arcs/helical paths

6. SYNCHROTRON RADIATION INTERCEPTIONℓ 𝑅
𝑅 accelerator bending radius
ℓ dipole length
𝑟 vacuum chamber radius
inside the same dipole only if ℓ > 2 𝑟 𝑅
for 𝑅= 9 km and 𝑟= 4.5 cm ℓ > 28.5 m
for 𝑅= 3.1 km and 𝑟= 6.5 cm (LEP2) ℓ > 20 m ℓ 𝑅
totally escaping for shorter dipoles
shielding in the interconnects ?

7. LAYOUT MODEL 1.5 m Q 10.5 m dipole 24 cm absorber 25 mm
Iron + plastic
25 mm
24 cm absorber
Copper (2mm tube)
water cooling
Lead

8. normalized to 10 mA beam current
TOTAL POWER
normalized to 10 mA beam current

9. normalized to 10 mA beam current
BEAM CHAMBER
normalized to 10 mA beam current

10. normalized to 10 mA beam current
WATER
normalized to 10 mA beam current
values averaged along the dipole length

11. normalized to 10 mA beam current over 116 days/year
DIPOLE COILS
normalized to 10 mA beam current over 116 days/year
front face masks ?

12. normalized to 10 mA beam current
DIPOLE COILS
normalized to 10 mA beam current
values averaged along the dipole length

13. OZONE
Adapted from NCRP Report 51 and LEP Note 379
(under the assumption of no O3 decomposition, yielding in the t expression a neglected term kPeV/V with k decomposition constant equal to cm3/eV)
For P=10 W in air, V108 cm3, vent10 h  at saturation CO31-2 ppm

14. SHIELDED BEAM CHAMBER Beam chamber: round IR = 4.5 cm
3 mrad
Scoring
surfaces
Beam chamber: round IR = 4.5 cm
Aluminum pipe: thickness = 0.5 cm
Lead shielding: thickness = 5.0 cm
9 km radius, Ec = 1.32 MeV

15. GRAZING INCIDENCE EFFECT
Radius or Depth  sin(3 mrad) (cm)
3 mrad incidence 

16. THE PHYSICAL EXPLANATION
The first scattering effect: after a Compton interaction the photon loses
“memory” of the initial grazing incidence because of the much larger scattering angle

17. BENDING (NO) EFFECT
Vacuum Al Pb

18. BENDING (NO) EFFECT
Vacuum Al Pb

19. SPECTRUM EVOLUTION
Al Kx lines
Pb Kx lines
Annihilation

20. REFLECTION INTO VACUUM

21. ESCAPING POWER
100%
10% 1% Al Pb
0.1%

22. ESCAPING RADIATION Pb Al

23. NEUTRON PRODUCTION AND ACTIVATION
 1.110-10 n/cm/e, 7105 n/s/cm/mA
Activity at saturation:
 170 kBq/cm/mA
(mostly 203Pbgs/m, 26Alm,205Pbm)
After 1 day:
 5.5 kBq/cm/mA
After 1 week:
 800 Bq/cm/mA
(almost only 203Pb)

24. OPENING CONCLUSIONS
extensive calculation of synchrotron radiation is possible with full generality
as expected the attenuation curve is insensitive to the incidence angle and (unfortunately) far from naïve line-of-sight approximations
localized absorbers look as an attractive option. More realistic shape is under way (possibly integrated inside the dipoles)
which magnets? Coils on the external side of the beam would be highly exposed

25. RESERVE
SLIDES

26. N=pair production, nuclear field e=pair production, electron field
PHOTON CROSS SECTION
Compton dominated
Photoelectric dominated
Pair dominated
p.e.=photoelectric incoh=Compton coherent=Rayleigh nuc=photonuclear
N=pair production, nuclear field e=pair production, electron field