The HiLumi LHC Design Study is included in the High Luminosity LHC project and is partly funded by the European Commission within the Framework Programme 7 Capacities Specific Programme, Grant Agreement 284404.

US2: HL-LHC alternatives – first ideas (under construction)

R. Tomàs, O. Dominguez, S. WhiteReported by G. Arduini

Thanks to P. Baudrenghien, H. Bartosik, O. Bruning, X. Buffat, R. Calaga, E. Shaposhnikova, H. Damerau, S. Fartoukh, R. Garoby, R. de Maria, V. Litvinenko and G.

Rumolo

2

8b+4e scheme as a possible 25 ns-like back-up in case of e-cloud issues• Double splitting instead of triple splitting in the PS for 3/2

bunch charge and 2/3 bunches (H. Damerau):1. Inject 4+2 bunches in h=7 (as usual).2. Double splitting from h=7 directly to h=21, consequently leaving

every third bucket empty. Filling pattern: 6*(2b+1e).3. Quadruple splitting of each bunch in 4 as usual. The empty bucket

is virtually also split in 4. Final filling pattern: 6*(8b+4e).

• Filling scheme to be finalized. Tentatively 1832 bunches or more12-25 ns slots (4 empty)

X 6 = 48 bunches out of 72 25ns slots

3

8b+4e scheme as a possible 25 ns-like back-up in case of e-cloud issues•Merit: Significantly lower e-cloud, no cost

4

Performance (preliminary)• This could also be beneficial for earlier stages if

electron cloud is an issue

• To be compared with 50 ns case (Verena)

Scheme Nb coll

[1011]e*coll

[mm]Min b*

(xing/sep)[cm]

CollidingBunches

IP1-5

Machine eff. opt. fill length

[%]

Opt. Fill length

[h]

Avg. Peak-pile-up density[ev./mm]

Target int.Lumi

[fb-1/year]

PIC 1.38 1.8 40/20 2760 30 5.8 1.3 70

PIC – 8b+4e 1.85 2.2 40/20 1840 31 6.3 1.5 70

US1 1.9 2.62 40/20 2592 46 6.1 1.5 170

US1 – 8b+4e 2.85 2.62 40/20 1840 48 10 1.6 170

US2 2.2 2.5 15/15 2760 51 9.3 1.2 270

US2 – 8b+4e 2.85 2.62 15/15 1840 60 12 1.2 270

5

SC 200 MHz cavities in the LHC•Motivation:• One of the main limitations for the bunch population in the

SPS is related to the maximum longitudinal emittance that can be injected in the LHC.

• Installation of 200 MHz cavities in the LHC would allow to accept larger longitudinal emittance and longer bunches:• With 3 MV at 200 MHz in the LHC at injection: bunches with long.

emit. of 1.5 eVs, 4 sigma bunch length 3.1 ns and sigma dp/p = 3.6 E-4.

• Acceleration with 200/400 MHz needs SC technology. This was initially discarded for beam loading considerations for the 200 MHz copper capture cavities

6

SC 200 MHz cavities in the LHC• Motivation:• Capture and acceleration of

longer bunches will help in reducing the electron cloud effects and possibly IBS, heating• 200 MHz cavities allow

additional margin for levelling in the longitudinal plane by varying the bunch length

7

SC 200 MHz cavities with 400 MHz CC• Full crabbing to

provide head-on collisions for the core of the beam.

• Assumed a linear bunch shortening in time from 13-15 cm to 7.5 cm.

8

Performance (preliminary)Scheme Nb coll

[1011]e*coll

[mm]Min b*

(xing/sep)[cm]

CollidingBunches

IP1-5

Machine eff. opt. fill length

[%]

Opt. Fill length

[h]

Avg. Peak-pile-up density[ev./mm]

Target int.Lumi

[fb-1/year]

US2 2.2 2.5 15/15 2760 51 9.3 1.2 270

US2- 200 MHz – CC -

BBLR

2.56 3 50/10 2760 49 9.5 1.2 270

9

Others to be added (not presented today)

• Crab kissing scheme proposed by Stephane

• Exotic:• coherent electron cooling to reduce the beam

emittance• Electron lens to reduce/compensate beam-

beam head on?