Kyriacos Skoufaris, Stephane Fartoukh, Yannis Papaphilippou, Axel Poyet, Adriana Rossi and Guido Sterbini

ABP Group Information Meeting - 9th April 2020

Simulations of BBLR Wire Compensation for the HL-LHC

09/04/2020 Kyriacos Skoufaris | Simulations of BBLR wire compensation for the HL-LHC 1

I. Introduction– DA degradation and proposed solution

II. Numerical simulations– Nominal scenario– Ultimate scenario– Improved Ultimate scenario– Luminosity improvement

III. Conclusions

09/04/2020 Outline | Simulations of BBLR wire compensation for the HL-LHC 2

Outline

09/04/2020 Introduction | Simulations of BBLR wire compensation for the HL-LHC 3

For the nominal scenario with optimized working point [1] the DAmin at the end of leveling is 6.17 [σ] (no IP2&8)

The long range beam beam (BBLR) interactions are stronger at the end of luminosity levelling, where β* is minimum, than at the start of collisions (for a constant X-ing angle).

DA degradation and proposed solution

[1] Beam-beam simulations for optimizing the performance of the High-Luminosity Large Hadron Collider Proton Physics

5.5 [σ]

09/04/2020 Introduction | Simulations of BBLR wire compensation for the HL-LHC 4

For the nominal scenario with optimized working point [1] the DAmin at the end of leveling is 6.17 [σ] (no IP2&8)

The long range beam beam (BBLR) interactions are stronger at the end of luminosity levelling, where β* is minimum, than at the start of collisions (for a constant X-ing angle).

DA degradation and proposed solution

No margin for any unexpected detrimental effect on lifetime (like e-cloud ; significantly present at the last run of the LHC)

Not enough margin for X-ing anglereduction or bunch intensity increment(triplet protection from irradiation, crabcavities operation at lower voltage, extend the luminosity leveling)[1] Beam-beam simulations for optimizing the performance

of the High-Luminosity Large Hadron Collider Proton Physics

09/04/2020 Introduction | Simulations of BBLR wire compensation for the HL-LHC 5

The use of DC wires is an effective and simple solution for the BBLR compensation.

DA degradation and proposed solution

[2] DOI:10.1103/PhysRevSTAB.18.121001

➔ 4 wires, 1 per IP per side

➔ longitudinal position ±195 [m] from IP1&5 (beta ratio 0.5 or 2 [2] )

➔ free parameters is the current (Iw) while the transverse distance from the weak beam (Dw) should be Dw>10.4 [σ] (behind tertiaries)

09/04/2020 Numerical simulations | Simulations of BBLR wire compensation for the HL-LHC 6

Nominal scenario

➔ Different wire configurations with Dw>10.4 [σ] improve the DAmin up to ~1 [σ] on top of the well optimized nominal scenario (DA min = 6.17 [σ]) - Best conditional DAmin.

➔ The existing LHC wire (green square) is not ideal even for the HL-LHC nominal scenario.

09/04/2020 Numerical simulations | Simulations of BBLR wire compensation for the HL-LHC 7

Ultimate scenario➔ Even with assisting octupole current (negative polarity for partial BBLR compensation)

there is no tune configuration above the diagonal with DAmin 6 [σ]≥ .

➔ With wire compensators (using one of the best DA configuration) a large set of good WPs (DAmin 6 [σ])≥ can be used. The WP could remain constant during levelling.

09/04/2020 Numerical simulations | Simulations of BBLR wire compensation for the HL-LHC 8

Ultimate scenario➔ The wire compensators guarantee best conditional DAmin up to 7.6 [σ] (2.8 [σ]

improvement) even with zero Landau octupole.

➔ The DA gain along the different angles is even more significant.

09/04/2020 Numerical simulations | Simulations of BBLR wire compensation for the HL-LHC 9

Improved Ultimate scenario➔ Even with Φ15/2=200 [μrad], the DC wire can improve the DAmin up to ~6 [σ] with Dw 10.4 [σ].≥

➔ With the aid of Landau octupoles, different DC wire configurations with Dw=12 [σ] and Iw<400 [Am] can guaranty DAmin 6 [σ]≥ .

09/04/2020 Numerical simulations | Simulations of BBLR wire compensation for the HL-LHC 10

Improved Ultimate scenario

➔ The wire compensator is not needed at the start of collision, since the min(DAIw=0) 6 [σ]. ≥

➔ However, almost all the configurations above 18 [σ] (position of the tertiary collimators at the start of leveling) improve the DAmin.

➔ The x-ing angle at the start of collisions can be further reduced with DC wire.

09/04/2020 Numerical simulations | Simulations of BBLR wire compensation for the HL-LHC 11

Luminosity improvement

* The Luminosity values are kindly provided by R. Tomas

09/04/2020 Conclusions | Simulations of BBLR wire compensation for the HL-LHC 12

ConclusionsThe wire compensator guarantees DAmin 6 [σ] for all the studied scenarios≈≥ , respecting the machine protection restrictions and without degrading PACMAN bunches lifetime (see appendix).

➔ The wire guarantees 6 [σ] for the ultimate, which is not the case in the present scenario (without wire).

➔ The lifetime gained makes the machine more tolerant (flexible) at any unexpected destructive effect.

➔ With all the good wire configurations the area of the good working points (WPs) is enlarged thus the WP can be kept constant during the levelling.

➔ With the reduction of the crossing angle without sacrificing the lifetime (DAmin>6σ):

● the crab cavities can be operated at lower voltage● the irradiation of the triplets can be reduced● the integrated luminosity can be increased

➔ With the wire, the β* levelling could be extended up 13 [cm].WP2/WP13 HL-LHC Satellite Meeting, Fermilab 2019 - Wire Compensation

09/04/2020 Thanks | Simulations of BBLR wire compensation for the HL-LHC 13

thank you for your time!

09/04/2020 Backup | Simulations of BBLR wire compensation for the HL-LHC 14

Backup

09/04/2020 Backup | Simulations of BBLR wire compensation for the HL-LHC 15

Multipolar field of infinity long DC wire

B y+i B x∝∑u=0

∞

[cu(x+i y)u] cu=

(−1)u

~x+i~y

➔ With exactly the same optical functions at the IRs and a 90o rotation between the X-ing plain of the two IPs, the tune shift and the tune spread with amplitude from the wire/wire-like multipoles with u = 4m + 1 and m = 0, 1, 2, . . . are selfcompensated (the quadrupolar, decapolar, etc. components of the wire)

09/04/2020 Backup | Simulations of BBLR wire compensation for the HL-LHC 16

Nominal scenario - PACMAN➔ The configurations indicated with green

asterisks are the ones that give the best conditional DAmin for a non-pacman bunch. With these wire configuration the DAmin is up to 7.1 σ (0.5 σ improvement over the case without wire).

➔ Even for the extreme PACMAN bunches ( first bunch of the first train after the abort gap and the last bunch of the last train before the abort gap) , the DAmin is not degraded by the DC wire.

09/04/2020 Numerical simulations | Simulations of BBLR wire compensation for the HL-LHC 17

Improved Nominal scenario➔ Even with Φ15/2=190 [μrad], the DC wire can improve the DAmin up to ~6 [σ] with Dw 10.4 [σ].≥➔ The wire compensator is not needed at the start of collision, since the min(DAIw=0) 6 [σ]. ≥➔ Almost all the configurations above 18 [σ] (position of the tertiary collimators at the start of leveling)

improve the DAmin.➔ The x-ing angle at the start of collisions can be further reduced with DC wire.