1. Scenarios for 2017 and 2018
Thanks to Gianni, Fanouria, Gianluigi, Dario, Stephane, Elias, Michi, Jamie, Christoph, Rogelio, Mirko, Riccardo, Hannes, Roderick, Stefano, Xavier,Massimo,…

2. BCMS versus nominal – performance; x-­‐angle, LRBB, beta
BCMS versus nominal – performance; x-­‐angle, LRBB, beta*, intensity, emittance, octupole, chromaticity, TOTEM bump. Nominal optics Vs ATS.
Flat optics for 2018?

3. Reach in β*
Assuming as last time a 0.5 σ safety margin on top of calculated aperture
For BCMS: can go to β*=30 cm, 160 urad without CMS bump
Separation plane limiting
With CMS bump: limit goes up to 32 cm
For nominal: can go to β*=32 cm, 185 urad
Limitation is in crossing plane
Even with CMS bump, crossing plane is still limiting, so no change in reach
Caveats
Aperture not measured in predicted bottleneck with CMS bump
Large uncertainty applies!
R. Bruce, S. Redaelli

4. Dario

5. Dario

6. BCMS vs Standard
Smaller emittance comes with additional DA (beam sigma), by reducing the crossing angle we seem to pay some margin for chromaticity, with some extra margin required for the intensity increase.
The fluctuations of the bands show some uncertainty in the study (~2 units of chroma).
From experience: BCMS with reduced crossing caused comparable losses as Standard (slide 2).

7. Dario

8. Dario

10. If no non-colliding bunches
Stable beam
If no non-colliding bunches
Ioct => Any value should be possible due to BBHO. Could be 0 or < 0 to optimise the lifetime
Q’ => Should be possible to reduce it but it is limited by e-cloud effects… A goal of ~ 10 seems reasonable (after some time)
ADT => Higher gain (lower bandwidth) could help to mitigate the emittance blow-up => Should try and optimise it
If non-colliding bunches
Ioct => Should be limited to the single-beam limit (~ 250 A). However, with the observed nonlinearities in 2016 it should be also possible to reduce and optimize it for lifetime
Elias Métral, ABP discussions for Evian and Chamonix, CERN, 06/12/ /5

11. ATS vs nominal, intensity, Crossing angle
ATS seems the choice (some potential gain in chromaticity and octupole reach)
Nominal optics is able to reach the same beta* and potentially solve issues with CT-PPS
Crossing angle and intensity
For 1.25e11, 9σ seems aggressive limited by eventual need of high octupoles and chromaticity
10 σ is safe and maybe reduced during the run, when reduction of octupoles and chromaticity is proved possible (as in 2016)
Keep the same geometrical crossing angle for nominal
Maybe consider crossing angle levelling (2018?)

12. Nominal vs BCMS

13. Nominal vs BCMS

14. LHCb scenario Standard BCMS n1 7.02E+10 n2 f_rev 11270.3931578947
beta_x 5 7
beta_y
e_x
3.50E-06
2.50E-06
e_y
Energy
6500
s_z
0.08
Xing/2
2.50E-04
s_x
E-05
s_y S
Lb [Hz/cm^2]
E+029
Xsec [mB] 80
Xsec [cm2]
8E-26
Pile up
LHCb max
1.1

15. Standard vs BCMS
Nominal configuration will give us important answers for the long term strategy
Little conditioning observed in 2016  for HL-LHC we need to do better!
We need to see if a period of operation with long trains can achieve significant further conditioning (~2 months could be a reasonable request)
But it could take time (months) to fill the machine, especially if we stick to 1.25e11 288bpi, and S12 is slowing us down
Instabilities in stable beams cannot be excluded (can we still increase Q’ to 22 if needed, even having ~9s separation?)
BCMS provides better performance on the short-medium term (Run 2) – see Fanouria
Even in absence of heat load limitations, integrated luminosity is slightly better for BCMS
With the heat load limitations on number of bunches the difference becomes ~30%
The difference in luminosity per bunch (20 %) defines a lower bound for the performance loss
Intensity ramp-up will most likely be significantly faster (2016-like), and it will be easier to deal with S12 recovery if needed
But most likely we will not see more conditioning than in 2016  not much impact on Run 2 performance, but heat loads will come back as a performance limitation for Run 3 and HL-LHC

16. Overhead of changing between the two
Standard vs BCMS
Nominal configuration will give us important answers for the long term strategy
Little conditioning observed in 2016  for HL-LHC we need to do better!
We need to see if a period of operation with long trains can achieve significant further conditioning (~2 months could be a reasonable request)
But it could take time (months) to fill the machine, especially if we stick to 1.25e11 288bpi, and S12 is slowing us down
Instabilities in stable beams cannot be excluded (can we still increase Q’ to 22 if needed, even having ~9s separation?)
BCMS provides better performance on the short-medium term (Run 2) – see Fanouria
Even in absence of heat load limitations, integrated luminosity is slightly better for BCMS
With the heat load limitations on number of bunches the difference becomes ~30%
The difference in luminosity per bunch (20 %) defines a lower bound for the performance loss
Intensity ramp-up will most likely be significantly faster (2016-like), and it will be easier to deal with S12 recovery if needed
But most likely we will not see more conditioning than in 2016  not much impact on Run 2 performance, but heat loads will come back as a performance limitation for Run 3 and HL-LHC
Overhead of changing between the two
It would be ideal to be able to change from one to the other “on the fly”, and probe both regimes. What forbids us to do it?
Not the b* choice! (b*>=32 cm should be compatible with both, see Roderick)
Abort gap keeper and MKI pulse settings, due to this we cannot even have 288bpi at 450 GeV if we go for BCMS!  but in 2016 change required ~1 shift, and used MD block as validation (to my memory, tbc.)
Crossing angle setting  According to Jorg’s talk at LSWG “crossing angle knob” is proved in MD. The open question is whether we can have TCT settings compatible with both angle values? (e.g. 155 urad and 180 urad for b* = 33 cm)
As discussed many times, this has other advantages (loss management at start of collision, adiabatic exploration of beam-beam limits, anti-leveling…)
Did I forget something?

17. Scenario for 2018
Flat optics?
Levelling crossing angle