Claudia Tambasco Belen Salvachua Stefano R edaelli Roderik Bruce Daniele Mirarchi Collimation Working Group 31032014 Acknowledgements Thanks to whole the collimation team in particular to ID: 252669
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Slide1
Update of the Sixtrack scattering routine
Claudia Tambasco, Belen Salvachua, Stefano Redaelli, Roderik Bruce, Daniele Mirarchi
Collimation Working Group 31/03/2014 Slide2
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.pdfSlide3
Contents
SixTrack scattering routine updates:
Carbon densityIonization losses
Coulomb scattering correctionNuclear 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
ConclusionsSlide4
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
S
cattering routine
developed in 1990’s (by
T.
Tranker
and J.B
Jeanneret
)
Recent measurements of cross section processes
Better description of interaction with matterSlide5
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 interactionsscattering with the nucleons
Small angle:
Multiple Coulomb scattering
Large angle:
Rutherford Scattering
E
ffective number of nucleons Slide6
Proton-proton SD cross section
Proton-proton elastic cross sectionProton-proton total cross section
Proton-Nucleus inelastic cross sectionProton-Nucleus total cross section
Proton-Nucleus elastic cross section
Scattering routine changes:
u
pdated
according to recent experimental data
Nuclear Interactions:
Review of electromagnetic processes:
Ionization
Coulomb scattering
and Carbon density (see next slide for the value implemented)Slide7
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 collimators
Used as TCP/TCSG
Carbon jaw by default
C
Z
6
A
[g/
mol
]
12.01
Density [
g/
cm3
]
1.65
Rad
length
[m]
0.188
New!Slide8
Update of ionization energy loss
In 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 Slide9
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:
0.00292
RMS: 0.00242
Carbon 60 cm
New SixTrack
Old 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 distributionSlide10
Proton-proton scattering
E
xperimental data from LHC experiments are available for p-p total and elastic cross sections at 3.5 TeV and 4 TeV beam energyNew SixTrack version:
implemented recent parameterizations from COMPETE collaboration
New parameterizations:
New parameterization:
Differential
pp
ELASTIC cross-section
:
Slope Parameter
7 TeV
Before: linear fit usedSlide11
Single diffractive cross section
Old 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 1995New parameterization:
Larger momentum change w.r.t. elastic scatteringThe previous version underestimated the total proton-proton SD cross section
pp
SD cross sectionSlide12
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 sectionsSlide13
Results: Global losses at 3.5 TeV
New SixTrack 3.5 TeV
Old SixTrack 3.5 TeV
Cold
Magnet
Max loss/lossTCP
New
Routine
Max loss/lossTCP
Old Routine
Q8
3.073×10−5
1.725×10−5
Q9
6.260×10−5
3.558×10−5
Q10
7.967×10−6
2.156×10−6
Q11
3.870×10−5
1.833×10−5
Change on Cleaning Q8-Q11
Cold
Magnet
Integrated
loss/lossTCP
New
Routine
Integrated
loss/lossTCP
Old Routine
Q8
1.617×
10−3
8.217×10−4
Q9
4.454×10−3
2.255×10−3
Q10
5.691×10−5
1.617×10−5
Q11
3.910×10−3
2.096×10−3
Impacts at collimators and aperture
TCSG IP6
new:
~1.5 e-4
old:
~4 e-5Slide14
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
T
eV Experimental Data
vs
simulation
at TCTs
Thanks to R.Bruce
for experimental dataPerfect machine
By a factor of ≈3 closer to data w.r.t. the old routineThe 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 FLUKA
For BLM response factors
Only Sixtrack
FLUKA+SixtrackSlide15
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
IP1Slide16
New predictions
of the losses at 7 TeV
Beam 1 Horizontal halo distribution
New SixTrack at 7TeV
r
1
r
2Slide17
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:
r
1
=20270-20350
r
2
=20370-20450Slide18
Paper in preparation includes:
Description of all the updates
7 TeV predictions of the new simulationsParametric 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 PDGSlide19
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
:
Further comparisons with other codes (FLUKA/SixTrack/Merlin/
Geant
)Further physics model improvement (Bethe-Bloch/Landau tails)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)