1. Septum protection challenges by LIU beams in the SPS
Matteo Marzo EN-STI-FDA
Students' coffee

2. Overview LSS4-TPSG4 and the TT40 extraction line
LHC Injectors Upgrade (LIU) in view of the HL-LHC
FLUKA simulations: LIU beam parameters and loss scenarios
Conclusions

3. Overview LSS4-TPSG4 and the TT40 extraction line
LHC Injectors Upgrade (LIU) in view of the HL-LHC
FLUKA simulations: LIU beam parameters and loss scenarios
Conclusions

4. LSS4 and the TT40-TI8 extraction line to LHC (1)
SPS-LSS4 418 period

5. LSS4 and the TT40-TI8 extraction line to LHC (2)
SPS MSE septum
In LSS4 6 electromagnetic septa are used to extract the beam
They bend the SPS proton beam, driving it towards TT40 and TI8, to finally deliver it to the LHC

6. LSS4 and the TT40-TI8 extraction line to LHC (3)
The septa are characterized by a constant dipolar magnetic field able to bend and consequently extract the beam (right hand rule)
As the name suggests, they allow the presence of both circulating and extracted beams
Those septa have to be protected in case of beam losses: if they are damaged, the SPS beam cannot be properly injected in the LHC
Image courtesy of M.Fraser

7. LSS4 and the TT40-TI8 extraction line to LHC (4)
TPSG4 located downstream the QFA.418 quadrupole and upstream the first septum…
In 2003 the TPSG4 beam diluter was firstly installed in LSS4
It is used to protect the septa and prevent direct impacts of the beam on the septa
It should absorbs energetic particles in case of mis- steering beams

8. Overview LSS4-TPSG4 and the TT40 extraction line
LHC Injectors Upgrade (LIU) in view of the HL-LHC
FLUKA simulations: LIU beam parameters and loss scenarios
Conclusions

9. A jump to the future…the HL-LHC!

10. LHC Injectors Upgrade (LIU)
Run1
Run2
Run3
Run4
Run5
Run6
LIU present status
L = 1.5×1034 cm-2s-1
Lint = ~70 fb-1
HL TARGET
L = 5.0×1034 cm-2s-1
Lint = ~3000 fb-1

11. LHC Injectors Upgrade (LIU)
Run1
Run2
Run3
Run4
Run5
Run6
LIU present status
L = 1.5×1034 cm-2s-1
Lint = ~70 fb-1
HL TARGET
L = 5.0×1034 cm-2s-1
Lint = ~3000 fb-1
But… what do we mean by luminosity?!?

12. A bit of math: how to increase the luminosity? (1)
Nev : number of events
R: event rate
σev : cross-section (m2, 1b = cm2)
L(t) : luminosity (cm-2s-1)
: int. luminosity (fb-1 = 1039 cm-2)

13. A bit of math: how to increase the luminosity? (1)
Nev : number of events
R: event rate
σev : cross-section (m2, 1b = cm2)
L(t) : luminosity (cm-2s-1)
: int. luminosity (fb-1 = 1039 cm-2)
With the HL-LHC we want to maximize the (integrated) luminosity in order to maximize total number collisions!

14. A bit of math: how to increase the luminosity? (2)
Introducing a series of approximations (*) to express the luminosity in a closed-form expression:
Nb1, Nb2: bunch populations for the 2 beams
nb: number of colliding bunches at the interaction point IP(*)
σx*, σy*: transverse beam size at the interaction point IP(*)
β: beta function (m)
ε : emittance (μm rad)
γ: relativistic gamma
(*) G.Papotti, “Luminosity and Beam-Beam at the LHC”, CAS Chevannes-de-Bogis,

15. A bit of math: how to increase the luminosity? (2)
Introducing a series of approximations (*) to express the luminosity in a closed-form expression:
Nb1, Nb2: bunch populations for the 2 beams
nb: number of colliding bunches at the interaction point IP(*)
σx*, σy*: transverse beam size at the interaction point IP(*)
β: beta function (m)
ε : emittance (μm rad)
γ: relativistic gamma
In order to maximize the (integrated) luminosity we can increase the number of protons per bunches of the colliding beams and reduce the beam size (smaller σ, that is to say smaller emittance and/or smaller beta function- not concerning the injectors upgrade-)!
Higher number of p/b
Smaller σ
Overall higher beam density

16. How is then the LIU project related to the HL-LHC?

17. LHC Injectors Upgrade (LIU): the SPS
“The LHC Injectors Upgrade (LIU) project has the ultimate goal of making the injectors capable of delivering reliably the beams required by the HL-LHC” LIU Technical Design Report – Volume I: Protons - 15 Dec 2014
Achieved
LIU target
N [1011 p/b]
1.20
2.32 ε
2.60
2.08
p [GeV/c]
450
Bunches
288
Total energy [MJ]
2.49
4.82
It’s worth noticing that:
The increase of N implies a larger amount of energy involved in LIU (luminosity increases)
The decrease of ε means that the beam is more focused (luminosity increases)
Are the injectors (Linac3, Linac4, LEIR, PSB, PS, SPS) in the present configuration able to sustain potential beam losses, given the change of the beam parameters, in the LIU phase?

18. Let’s rewind and go back to LSS4
Let’s rewind and go back to LSS4...what about the septa we were talking about, in the LIU phase? Are they still safe?

19. In other words, is the TPSG4 still capable of protecting the septa, given the new LIU beam parameters?
The answer is obviously “NO!”
Different solutions have been studied to protect the TPSG4 from direct impact of the LIU beam
The most suitable option seemed to be the installation of an additional carbon- carbon absorber upstream the QFA.418
8 quadrupole
PRESENT LIU

20. Overview LSS4-TPSG4 and the TT40 extraction line
LHC Injectors Upgrade (LIU) in view of the HL-LHC
FLUKA simulations: LIU beam parameters and loss scenarios
Conclusions

21. FLUKA geometry model
The FLUKA model has been built taking into account the presence of the TPSC4, for the LIU project
TPSC4
TPSG4
MDH
BPCE
QFA
MSE.x
QDA
418
419
TPSC4: carbon-carbon 20x20x1350 mm3 parallelepiped
TPSG4: carbon-carbon, Titanium, INCONEL
LIU beam parameter
Value
N [1011 p/b]
2.32 ε
2.08
p [GeV/c]
450
Bunches
288
Total energy [MJ]
4.82

22. How to find the most critical impact condition
How to find the most critical impact condition? Sensitivity analysis changing the impact parameter and FLUKA results…

23. Impact parameters and FLUKA trajectory check
The geometry has been built using the LineBuilder and the TPSC4, TPSG4 and the septa are oriented according to the beam extraction
The FLUKA trajectory has been checked to verify that magnetic fields were properly loaded in the FLUKA model
0σ, ±1σ and ±5σ impacts on the upstream end of the TPSC4, from both side, have been simulated to see how the energy deposition on the downstream elements changes
BPCE
0σ / +1σ / +5σ
-1σ / -5σ
QFA
MSE.x
TPSC4
TPSG4
MDH

24. LIU beam, Fluka simulations: sensitivity analysis
Most heavily loaded object
~1/3 of total energy

25. Energy peak profile on the TPSC4 (diluter upstream the QFA.418 quad)
TPSC characteristics
Dimensions: 20x20x1350 mm3
Material: carbon composite
Material density: ρ = 1.75 g/cm3
Specific heat: cp ~ 1.90 ~1000oC
Peak: ~3.3kJ/cm3
Peak location, as a function of the beam position
We simulated a 3.3 kJ/cm3 peak, corresponding to ~1300 oC.
This is well below the limit, as this material can survive up to ~2800 oC in vacuum

26. Dose peak profile on the QFA.418 (quadrupole)
QFA beam pipe characteristics
Material: 316LN stainless steel
Material density: ρ = 8.03 g/cm3
Specific heat: cp ~ 0.48 J/g/K

27. Dose peak profile on the QFA.418 (quadrupole)
Peak of ΔT ~170 oC
QFA beam pipe characteristics
Material: 316LN stainless steel
Material density: ρ = 8.03 g/cm3
Specific heat: cp ~ 0.48 J/g/K
Peak location
Localized energy deposition on the vacuum chamber
Worst +1s case scenario 90J/g  ~170 oC

28. Dose peak profile on the QFA.418 (quadrupole)
Peak of ΔT ~170 oC
Peak location
The QFA.418 is a focusing quadrupole (focusing on the horizontal plane and defocusing on the vertical plane for positive particles, vice versa for negative ones)

29. Dose peak profile on the QFA.418 (quadrupole)
Peak of ΔT ~170 oC
Peak spots
The peak is clearly due to low energy positive particles defocused by the quadrupole’s magnetic field, in the vertical plane

30. Dose peak profile on the QFA.418 (quadrupole)
Peak spots
Since in the original mesh a few bins were shared between air and stainless steel (artificial increase of dose!), we decided to refine the binning
Worst +1s case scenario 65J/g  ~120 oC, it does not pose any issue from a thermo-mechanical point of view, even if we have high ΔT gradient in the region of the maximum!

31. Dose peak profile on the TPSG4 (diluter downstream the QFA.418 quad)
TPSG characteristics
Dimensions: 25x50x3100 mm3
Design: 3 consecutive blocks
Materials: carbon composite, Ti alloy, INCONEL (Ni-based)
Materials densities: ρcc = 1.75 g/cm3, ρTi = g/cm3, ρIN = 8.19 g/cm3
Specific heat: cpcc ~ 1.20 J/g/K, cpTi ~ 0.52 J/g/K, cpIN ~ 0.44 J/g/K,
Hot spot on the INCONEL block of the TPSG4
(E=1130 J/cm3)
+1s impact parameter is the most critical,
TPSG4 dose: ~140 J/g (ΔT~305 oC, still acceptable thermo-mechanical stresses)
Peak mainly due to protons losing a bit of energy in the TPSC4, being over-focused by the quad and directly impacting the TPSG4!

32. How could we mitigate the energy peak on the TPSG, in case of +1σ impact?

33. Possible options
Titanium instead of INCONEL in the last 30cm of the TPSG4
3mm cut in the downstream block of the TPSG4 (INCONEL or Titanium)
We move the TPSC4 ~1m upstream the first quad?
3mm
Geometry of the 3mm cut in the TPSG4 downstream end

34. Dose on the TPSG4
Ti Vs INCONEL: dose reduction by a factor ~1.75, but peak still present in the TPSG4
3mm cut in the last block of the TPSG4: dose reduction by a factor ~7, in both the simulated cases!

35. But…
Where did the particles which were responsible for the dose peak in the downstream end of the TPSG4, in the +1σ configuration, end up, after the 3mm cut?
We decided to score proton fluence downstream the TPSG4 and this is the result ...

36. Protons fluence Summary: Simulated particles: 5.7x106
Recorded upstream QDA.419: 9.9x105
Recorded upstream QDA.419 above 449 GeV: 9.7x105 (17.0% of the total)
Protons (20% of the total)- the ones responsible for the dose peak in the downstream end of the TPSG4- follow the magnetic field in the septa, enter the quadrupole and go downstream the QDA.419 !

37. Dose and ΔT peak profile on the MSEx (electromagnetic septa)
Copper coil
Water pipes to cool down the coil

38. Dose and ΔT peak profile on the MSEx (electromagnetic septa)
Copper coil
Water pipes to cool down the coil
In the water pipes ΔT => Δp: pressures waves propagation through the pipe!
Operational limit ΔpH2O < 50bar ( =>ΔT ~7°C (*))
Water channels FLUKA simulated ΔT is ~4°C (cpH2O=4.187 J/g/K) => below the limit! (after the 3mm cut in the TPSG4, a decrease of ~1°C is seen in the cooling pipes)
(*) J.Borburgh, "MSE coil temperature rise with TPSC4” LIU-SPS BLPT meeting",
A 2 jaw TPSC4 would help in protecting the copper coil of MSEs

39. Dose and ΔT peak profile on the MSEx (electromagnetic septa)
Copper coil
Water pipes to cool down the coil
Longitudinal limit to thermal elongation for the coils body ΔT < 100°C (*)
Vertical limit: 7÷41μm between the coil’s body and the magnet’s yoke (*)
FLUKA simulated ΔT is ~170°C in the coils body:
Mechanical ~170°C to be quantified
What will happen to water in contact with ~170°C
(*) J.Borburgh, "MSE coil temperature rise with TPSC4” LIU-SPS BLPT meeting",
A 2 jaw TPSC4 would help in protecting the copper coil of MSEs

40. Overview LSS4-TPSG4 and the TT40 extraction line
LHC Injectors Upgrade (LIU) in view of the HL-LHC
FLUKA simulations: LIU beam parameters and loss scenarios
Conclusions

41. Results of the sensitivity analyses
The +1σ impact configuration is the most critical
A peak of 3.3 kJ/cm3 arises in the TPSC4 (below the limit for carbon carbon)
The QFA.418 quad gets ~1/3 of the total beam energy and a local peak of ~120°C in the quadrupole’s vacuum pipe that doesn’t pose any issue
The energy deposited in the TPSG4 downstream end (INCONEL) shows a peak ~140 J/g (ΔT~305 oC, acceptable thermo-mechanical stresses)
The increase of temperature in the septa cooling pipes is ~3÷4°C (within the limits) and for the copper coils ~170°C (still under study)
3mm cut in the INCONEL block to lower the dose peak in the TPSG4: dose reduction of a factor ~7 in the TPSG4 itself and ΔT decrease of ~1°C in the MSE’s cooling pipes… but 20% of protons are lost downstream the QDA.419

42. Many thanks!