Update of the Sixtrack scattering

routine

Claudia Tambasco, Belen Salvachua, Stefano Redaelli, Roderik Bruce, Daniele Mirarchi

Collimation Working Group 31/03/2014

Acknowledgements

Thanks to whole the collimation team, in particular to L.Lari, A.Marsili, G.Cavoto.

Thanks to A. Lechner and the FLUKA team:

Providing FLUKA cross sections:

Ionization losses:Implementation of the Landau tail for the Ionization energy loss (D.Mirarchi et al.)

Comparison FLUKA/Sixtrack cross sections will continue (R.Bruce et al.)

Thesis on Cern Library at: https://cds.cern.ch/record/1690529/files/CERN-THESIS-2014-014.pdf

Contents

• SixTrack scattering routine updates: Carbon density Ionization losses Coulomb scattering correction Nuclear interactions

• Results: 3.5 TeV global losses 3.5 TeV data/simulations comparison at TCTs 7 TeV impacts at collimators 7 TeV Cleaning Efficiency

• Ongoing work• Conclusions

Higher Luminosity and Energy

More beam losses, more energy deposition on the machine equipment

quench of the superconducting magnets

Even more important Collimation System:More accurate prediction of the Cleaning efficiency

Why do we need to update the SixTrack scattering routine?

After the long shutdown, LHC will reach the designed proton energy of 7 TeV and the luminosity peak of 10^34 [cm-2 s-1] :

Improving the physics model of the scattering routine allows to increase the power of predictions for higher energy simulations

• Scattering routine developed in 1990’s (by T. Tranker and J.B Jeanneret)

• Recent measurements of cross section processes Better description of interaction with matter

SixTrack scattering routine Simulates scattering mechanisms of the protons within the collimator jaws developed in 1990’s (by T. Tranker and J.B Jeanneret)

Electromagnetic processes

Ionization (Bethe-Bloch equation)

Coulomb scattering:

Nuclear interactions

scattering with the nucleons

Small angle:Multiple Coulomb scatteringLarge angle: Rutherford Scattering

Effective number of nucleons

• Proton-proton SD cross section• Proton-proton elastic cross section• Proton-proton total cross section• Proton-Nucleus inelastic cross section• Proton-Nucleus total cross section• Proton-Nucleus elastic cross section

Scattering routine changes:

updated according to recent experimental data

Nuclear Interactions:

Review of electromagnetic processes:

• Ionization• Coulomb scattering

and Carbon density (see next slide for the value implemented)

Update Carbon density

Previous Carbon in SixTrack AC150K Carbon

C Z 6

A [g/mol] 12.01

Density [g/cm3] 2.26

Rad length [m] 0.188

Graphitic carbon, but its compaction rate is far from full so its nominal density is significantly lower, i.e. 1.65 g/cm^3.

TCP and TCSP collimatorsUsed as TCP/TCSGCarbon jaw by default

C Z 6

A [g/mol] 12.01

Density [g/cm3] 1.65

Rad length [m] 0.188

New!

Update of ionization energy lossIn many Monte Carlo programs the ionization energy loss is simulated by implementing a continue loss that is described by the Bethe-Bloch equation:

• Previous SixTrack version: used a constant value to describe the energy lost by ionization which was an approximation of the Bethe-Bloch.

• New SixTrack version: implemented the Bethe-Bloch equation for the complete list of collimator materials.

Used before for simulations at all energies

Multilple Coulomb Scattering: added logarithmic part in rms angle formula:

Multiple Coulomb Scattering correction

• Old SixTrack version: the logarithm part in the rms angle formula was missing• New SixTrack version: added missing logarithmic part

RMS: 0.00292RMS: 0.00242

Carbon 60 cmNew SixTrackOld SixTrack

With the new implementation the difference on the rms reaches up 20% for Tungsten

Adding the logarithmic part increases the rms of the scattered angle distribution

Proton-proton scatteringExperimental data from LHC experiments are available for p-p total and elastic cross sections at 3.5 TeV and 4 TeV beam energy• New SixTrack version: implemented recent parameterizations from COMPETE

collaboration

New parameterizations:

New parameterization:

Differential pp ELASTIC cross-section:Slope Parameter

7 TeV

Before: linear fit used

Single diffractive cross sectionOld SixTrack version: implementation from an old theory of K. Goulianos (1983) Further experimental data showed the necessity to develop a new theory New SixTrack version: implementation from updated theory from same author

“Renormalization of hadronic diffraction and the structure of the pomeron”, K. Goulianos Physic Letters B 358 1995

New parameterization:

Larger momentum change w.r.t. elastic scattering

The previous version underestimated the total proton-proton SD cross section

pp SD cross section

Proton-Nucleus total cross section: • new collision length from PDG (max variation ~2% )

Proton-Nucleus inelastic cross section:• new interaction length from PDG (max variation ~3% )

Proton-Nucleus elastic cross section: automatically updated since it is calculated by subtracting the other contributions

Minor Updates: p-Nucleus cross sections

Results: Global losses at 3.5 TeV

New SixTrack 3.5 TeV

Old SixTrack 3.5 TeV

Cold Magnet

Max loss/lossTCPNew Routine

Max loss/lossTCPOld Routine

Q8 3.073×10−5 1.725×10−5Q9 6.260×10−5 3.558×10−5

Q10 7.967×10−6 2.156×10−6Q11 3.870×10−5 1.833×10−5

Change on Cleaning Q8-Q11Cold

MagnetIntegrated

loss/lossTCPNew Routine

Integrated loss/lossTCPOld Routine

Q8 1.617×10−3 8.217×10−4Q9 4.454×10−3 2.255×10−3

Q10 5.691×10−5 1.617×10−5Q11 3.910×10−3 2.096×10−3

Impacts at collimators and aperture

TCSG IP6 new: ~1.5 e-4

old: ~4 e-5

Results: Check improvement with data Look at the TCT losses in IP1 and IP5 SixTrack gives the primary impacts at collimators, then BLM response factors from FLUKA

are needed [E.Skordis, R.Bruce]

3.5 TeV Experimental Data vs simulation at TCTs

Thanks to R.Brucefor experimental data

Perfect machine

By a factor of ≈3 closer to data w.r.t. the old routine

The new SixTrack version provides a better agreement with the experimental dataA new estimation of the cleaning inefficiency at 7 TeV has been carried out

Thanks to FLUKAFor BLM response factors

Only Sixtrack

FLUKA+Sixtrack

New predictions of the losses at 7 TeV: impacts at collimators

B1 horizontal halo case

~by a factor 4 more losses in TCSG in IP6

TCTH-V IP5 TCTH-V IP1

New predictions of the losses at 7 TeVBeam 1 Horizontal halo distributionNew SixTrack at 7TeV

r1 r2

New predictions of the losses at 7 TeV (DS region)

More losses on the cold magnets by a factor of≈ 1.8 w.r.t. the previous routine

DS regions:r1=20270-20350r2=20370-20450

Paper in preparation includes:• Description of all the updates• 7 TeV predictions of the new simulations• Parametric study of cleaning and impacts at TCTs and TCSG in IP6 for:

Ionization energy Bethe-Bloch vs most probable value of the Landau Distribution and the tails

Singe Diffractive cross section variation: ±10%, ±20, …, ±90%

Ongoing work

Preliminary!From PDG

Conclusions

3 times closer to the data w.r.t. the old SixTrack version

A study on the cleaning inefficiency prediction at 7 TeV has been carried out

1.8 times more losses on the cold magnets w.r.t. the old SixTrack version

Follow up of the work in the team:1. Further comparisons with other codes (FLUKA/SixTrack/Merlin/Geant)2. Further physics model improvement (Bethe-Bloch/Landau tails)3. New SixTrack release contains already the presented changes (R.Bruce, D.Mirarchi, A.Rossi)

The physics model of the SixTrack scattering routine has been updated and improved

The effects of the new SixTrack version has been studied by data-simulation comparison at 3.5 TeV

Data-simulations comparison at 3.5 TeV in the imperfect machine case

further agreement expected (see R. Bruce talk)