1. HL-LHC operations with LHCb at high luminosity
R. De Maria, N. Karastathis
Thanks to G. Arduini, F. Cerutti, I. Efthymiopoulos, S. Fartoukh, M. Giovannozzi
LHCb Meeting 21/3/2018

2. Peak luminosity Minimum β* is constrained by optics flexibility.
𝐿= 𝑁 𝑏 2 𝑓 𝑟𝑒𝑣 𝑘 𝑏 4𝜋𝜖 𝛽 × ∗ 𝛽 ∥ ∗ ⋅ Φ 𝑝 2
Protons per bunch
𝑁 𝑏
Number of Bunches
𝑘 𝑏
2572(2374)
R.M.S. bunch length
𝜎 𝑠
7.61(9.0) cm
+/- Polarity
By<0 / By>0
Φ 𝑝 = 𝜎 𝑠 𝜎 × ⋅ 𝜃 × 2 = 𝜎 𝑠 𝛽 × ∗ ⋅ bb sep 2
𝜃 external , 𝛽* at constant luminosity
𝜃 × = 𝜃 external ± 𝜃 spectrometer cos 𝛼 plane
cm-2s-1
baseline
Minimum β* is constrained by optics flexibility.
Maximum crossing angle limited by orbit corrector strength
For a given β*:
Aperture constrains maximum crossing angle.
Beam-beam effects (i.e. beam lifetime) constrains minimum crossing angle.
Beam-beam effects
Orbit corrector limitations
Aperture limitations
cm-2s-1
Optics limitations

3. Beam-beam limitations at collision
DA margins at the end of Atlas/CMS levelling as a function of IR8 horizontal half external angle
for a scenario with cm-2s-1.
-250 μrad, Neg.
-200 μrad, Neg.
-180 μrad, Neg.
-150 μrad, Neg.
N. Karastathis

4. Beam-beam limitations at collision
DA margins at the end of Atlas/CMS levelling as a function of IR8 horizontal half external angle
for a scenario with cm-2s-1.
-200 μrad
“Bad”(Neg) Polarity
-150 μrad
“Good”(Pos.) Polarity
N. Karastathis
Spectrometer polarity has an impact of minimum external crossing angle.
Tentative IR8 external half crossing angle with horizontal crossing:
-200 μrad with Neg. polarity (-65 μrad half crossing angle)
-150 μrad with Pos. polarity (-285 μrad half crossing angle)
Not fully validated, full cycle simulation needed.
A vertical external half crossing angle of 160 μrad is expected to behave in between the two horizontal options (210 μrad half crossing angle)

5. Aperture limitations in collision
Maximum half external crossing angle as function of β*
β* [m]
H1 [µrad]
H2 [µrad]
V3 [µrad]
V1,4 [µrad] 1
-165
-220
±115
±220
1.5
-225
-275
±165
±235 2
-265
-310
±205
±270 3
±250
±310
1 with present TCDDM
2 without present TCDDM
3 crossing plane can be rotated during the ramp (difficult to setup)
4 if beam screen is rotated, introducing strong limitations during the ramp
Aperture in the triplet is not symmetric (H=57.8 mm, V=48 mm) and cannot be rotated easily.
TCDDM needed for D1 protection
Present aperture bottleneck for Beam 2 H and Beam 1 V.
H crossing
V crossing
H crossing
V crossing
Compatible with previous scenarios and still aperture margin for β*//.
Beam screen rotation not needed so far in V crossing, and, if it would, the issues are at injection…

6. Constraints at injection
Baseline Horizontal crossing.
Pos. Spec., 450 GeV
-170 µrad, +3.5 mm
As the LHC, but with double the intensity in HL-LHC.
This needs to be still validated, no margin expected.

7. Constraints at injection
Baseline Horizontal crossing.
Neg. Spec., 450 GeV
-170 µrad, +3.5 mm
As the LHC, but with double the intensity in HL-LHC.
This needs to be still validated, no margins expected.

8. Constraints at injection
Vertical crossing and rotated beam screen with critical issues
Neg. Spec., 450 GeV
-170 µrad, +3.5 mm 2σ
Additional close encounters, in particular close to the IP.
Not compatible with different ion species runs (e.g. p – lead).
Not compatible with present orbit tolerance specifications for p-p.

9. Constraints at injection
Horizontal crossing and rotated beam screen with critical issues
Neg. Spec., 450 GeV
-170 µrad, +3.5 mm 2σ
Not enough aperture for the crossing angle in the H plane.
Reducing crossing angle and increasing parallel separation not trivial.

10. Tentative scenarios β* [m] Ext. Crossing /Spec. Polarity
Peak Luminosity
[1034]
1.5
H/±200 /-
2.16
H/±150/+
1.59 (implies operation overhead)
V/±160/+ or -
1.8 (not simulated with DA)
β* [m] X
Int. Lumi
[1034/year]
1.5 H 43 52 V 51
Assuming same ∫L in both polarities, to be verified with more realistic luminosity models
Not significant advantage of designing the detector for cm-2s-1.
43 fb-1 sufficient to reach a target of 300fb-1 (triplet lifetime) in RunV, RunVI (~6 years of operations).
Beam screen rotation not needed for these configurations, small crossing angle also better for dose at constant luminosity.

11. Example of Luminosity evolution
Case with LHCb virtual luminosity of cm-2s-1
with three levelling scenarios.
Simple model used for illustration only and not for quantitative estimates.
Atlas/CMS
Atlas/CMS
LHCb
LHCb
Atlas/CMS
Machine
LHCb

12. Example of Luminosity evolution
Case with LHCb virtual luminosity of cm-2s-1
with three levelling scenarios.
Simple model used for illustration only and not for quantitative estimates.
Atlas/CMS
Atlas/CMS
LHCb
LHCb
Atlas/CMS
Machine
LHCb

13. Example of Luminosity evolution
Case with LHCb virtual luminosity of cm-2s-1
with three levelling scenarios.
Simple model used for illustration only and not for quantitative estimates.
Atlas/CMS
Atlas/CMS
LHCb
LHCb
Atlas/CMS
Machine
LHCb

14. Open points
Validate the new tentative configurations for LHCb at high luminosity:
Evaluate commissioning overhead of two external crossing angles depending on the polarity.
Complete beam-beam simulations, in particular for the whole cycle and with vertical crossing (ongoing).
Perform energy deposition studies for the cycle for different crossing scenarios.
Assess feasibility and cost of protecting devices such as: TAS, TAN, TCDDM, TCL.
A study group is going to be put in place to provide information concerning the impact on HW and costs.
Asses realistic dose considering no TAS before RunIV and large crossing angle.
If operational margins exist one can consider the options:
Flat beams (e.g. β*// < β*X) which gives more luminosity at constant aperture but with additional beam-beam effects to be evaluated.
In H crossing smaller β*X for Pos. Polarity at the cost of additional operational overhead to be quantified.
In parallel one would need to state what performance impact is acceptable for Atlas and CMS.

15. Conclusion
Tentative scenarios identified with levelled luminosity of 1·1034 cm-2s-1 and similar performance:
Horizontal crossing with two external angles
Time lost at each polarity change
Vertical crossing with rotation of the crossing plane at flat top
Time lost in commissioning the crossing plane rotations (it gave several problems during Run I)
Beam screen rotation:
is not needed in the present scenarios taking into account
triplet lifetime, present options and further optimizations that could be attempted
is not feasible option unless:
it is possible to reduce orbit tolerances AND disable LHCb during p-Ion runs OR it is possible inject with very large separation.
proven feasible for radiation issues.
compatible with cost and schedule (in-situ coating developed to avoid intervening on the triplet).
Flat beams in LHCb:
Can improve luminosity at constant aperture and beam-beam separation in the triplet,
with potential detrimental effects on lifetime compared to round at constant aperture (e.g. beam-beam effects).
Will be explored after round scenarios are fully validated.

16. Backup

17. Flat optics

18. Constraints at injection
Vertical crossing with critical issues
Neg. Spec., 1000 GeV
Rotated beam screen
-170 µrad, +3.5 mm
Close encounter moves with energy and needs strict control of the orbit during the ramp.

19. Constraints at injection
Vertical crossing with critical issues
Neg. Spec., 1000 GeV
Rotated beam screen
-200 µrad, +2.0 mm
Close encounter moves with energy and needs strict control of the orbit during the ramp.

20. Constraints at injection
Vertical crossing with critical issues
Neg. Spec., 3000 GeV
Rotated beam screen
-200 µrad, +1 mm
Close encounter moves with energy and needs strict control of the orbit during the ramp.

21. Constraints at injection
Vertical crossing with ramped spectrometer
Neg. Spec., 450 GeV
Rotated beam screen
and ramped spectrometer
Vertical crossing is straightforward if spectrometer could be ramped with energy.

22. Constraints at injection
Horizontal crossing with extreme conditions
Pos. spec., 450 GeV
Rotated beam screen
-120 µrad, +7.0 mm
80 µrad (bias)
1.5 mm offset
This solution is more robust at injection, but uses about 3 times the typical orbit corrector at injection. As energy increase separation, offset and bias would need to be reduced quickly. Needs validation from injection protection issues.

23. Constraints at injection
Baseline Horizontal crossing.
Pos. Spec., 450 GeV
-170 µrad, +3.5 mm
As the LHC, but with double the intensity in HL-LHC
This needs to be still validated.

24. Constraints at injection
Baseline Horizontal crossing.
Neg. Spec., 450 GeV
-170 µrad, +3.5 mm
As the LHC, but with double the intensity in HL-LHC
This needs to be still validated.

25. Constraints at injection
Vertical crossing with critical issues
Neg. Spec., 450 GeV
Rotated beam screen
-170 µrad, +3.5 mm
Additional close encounters, in particular close to the IP.
Not compatible with different ion species runs (e.g. Lead – Ion).
Not compatible with present orbit tolerance specifications for p-p.

26. Constraints at injection
Vertical crossing with critical issues
Neg. Spec., 1000 GeV
Rotated beam screen
-170 µrad, +3.5 mm
Close encounter moves with energy and needs strict control of the orbit during the ramp.

27. Constraints at injection
Vertical crossing with critical issues
Neg. Spec., 1000 GeV
Rotated beam screen
-200 µrad, +1 mm
Close encounter moves with energy and needs strict control of the orbit during the ramp.

28. Constraints at injection
Vertical crossing with critical issues
Neg. Spec., 3000 GeV
Rotated beam screen
-200 µrad, +1 mm
Close encounter moves with energy and needs strict control of the orbit during the ramp.

29. Constraints at injection
Vertical crossing with ramped spectrometer
Vertical crossing, -
450 GeV
Rotated beam screen
and ramped spectrometer
Vertical crossing is straightforward if spectrometer could be ramped with energy.

30. Constraints at injection
Horizontal crossing with extreme conditions
Neg. Spec., 450 GeV
Rotated beam screen
-120 µrad, +7.0 mm
80 µrad (bias)
1.5 mm offset
This solution is more robust at injection, but uses about 3 times the typical orbit corrector at injection. As energy increase separation, offset and bias would need to be reduced quickly. Do we need this?