This page collects the simulations results performed for collimation
studies and provides data on primary protons
· undergone
to inelastic scattering (absorbed) at collimators
·
undergone
to Single Diffractive scattering (SD) at collimators
· lost
from the machine aperture
These data can be used also for studies of machine induced
background to the experiments.
Foreword
Collimation and beam cleaning
studies are carried out with the well established
SixTrack [1] code, extended for tracking large numbers
of halo particles, and to take into account halo interaction with
arbitrarily placed collimators.
Particles are transported through the lattice element by element and their
phase space coordinates are transformed according to the type of element.
When a particle hits a collimator jaw, it is randomly scattered through
matter.
The effect of collimator scattering is
modeled using
COLLTRACK/K2
[2, 3] routines.
The main characteristics of the SixTrack used
for collimations studies are:
· Proton scattering in various collimator materials, including
□
Multiple Coulomb scattering,
□
Ionization of the collimator material,
□
Elastic protonproton (pp) scattering, and inelastic diffractive
pp scattering
(single diffractive scattering),
□
Inelastic protonnucleon
scattering,
□
Elastic and inelastic protonnucleus scattering,
□
Rutherford scattering.
· Various
types of
halo and
possibility of including
diffusion.
· Tracking of large particle ensembles (~10^{6}
protons)
over hundreds of turns.
· Multiple imperfections on the beam and the
collimator properties (setting errors, tilts, orbit, beta beat, …)
MADX is used to generate the LHC lattice, the
optics and eventual orbit and focusing errors.
[1]
F. Schmidt: ”SixTrack,
User’s Reference Manual”, CERN SL/9456 (AP), 1994 (Update July 2008).
[2] T. Trenkler, J.B. Jeanneret:
“K2, A software package evaluating collimation systems in circular colliders
(manual)”, CERN SL/94–105 (AP), 1994.
[3]
G. RobertDemolaize, R. Assmann, S. Redaelli, F. Schmidt, CERN, Geneva,
Switzerland: A new version of SixtTrack with collimation and aperture
interface (PAC 2005).
[4] R. Assmann, J.B.
Jeanneret, D. Kaltchev: “Status of Robustness Studies for the LHC
Collimation”, APAC 2001.


Simulations parameters (executable) 
Beam energy 
3.5TeV per beam 
Optics: 
LHC optics version V6.503 (twiss_file_beam1
and
twiss_file_beam2)

Crossing angles OFF

Separations ON

ALICE and LHCb spectrometers ON

ATLAS and CMS solenoids OFF

b*:
IP1&5 = 2m, IP2 = 10m, IP8 = 3m

Collimator
Settings:
intermediate settings (keeping same distance in mm
between collimator hierarchy as at injection) 

Family

setting 3.5 TeV
[s]

LSS7

TCP IR7

6.0

TCSG IR7

8.8

TCLA IR7

17.2

LSS6

TCDQ

11.6

TCS TCDQ

10.2

LSS3

TCP IR3

10.6

TCSG IR3

12.7

TCLA IR3

14.1

LSS1

TCTH

12.8

TCTV

12.8

TCL

13.7

LSS2

TCTH

30.2

TCTV

30.2

LSS5

TCTH

12.8

TCTV

12.8

TCL

13.7

LSS8

TCTH

15.3

TCTV

15.3


Initial halo distribution 
Figure 1: Impact Parameter (b) and
coordinate system at collimator jaw

Figure 2: Pencil beam distribution 

Results
Beam 1: horizontal
halo
Beam 1:
vertical
halo
Beam 1:
skew
halo
Beam 2: horizontal halo
Beam 2:
vertical
halo
Beam 2:
skew
halo

Below are inefficiency curves
corresponding to beam 1 (Figure 3 to 5) and beam 2 (Figure 6 to
8)with different initial halo distributions, calculated for the
ideal machine (no imperfections nor misalignments).
The equivalent quench limit for the real machine  estimated to
about 1/10 of the one for the ideal machine (see Chiara Bracco's
thesis)  is also shown in the pictures. The BLM threshold for beam
dump is set to 1/3 of the quench limit.
The results are divided in:
 summary of parameters
at collimators for the 2 beams:
......
collgap_beam1
......
collgap_beam2
 summary of
interactions at collimators (file coll_summary
[note1]);
 particles absorbed
(inelastic scattering, flag=1) or undergone to SD
scattering (flag=4) at collimators (file
FLUKA_impacts_real [note 2]);
 primary protons lost
from the aperture along the machine (file LPI
[note 3])
Figure 3: Initial halo distribution = pencil beam
with Gaussian distribution on TCP.C6L7.B1 (horizontal)
(picture in full size)
Results (beam 1, 3.5TeV per beam, V6.503 optics,
intermediate collimator settings, no imperfections, horizontal halo)

Total number of particle absorbed nabs_tot =5049273

interactions at collimators (file coll_summary)

absorptions or SD scattering at collimators (file
FLUKA_impacts_real)

loss maps (file LPI)
Figure 4: Initial halo distribution = pencil beam
with Gaussian distribution on TCP.D6L7.B1 (vertical)
(picture in full size)
Results (beam 1, 3.5TeV per beam, V6.503 optics,
intermediate collimator settings, no imperfections, vertical halo)

Total number of particle absorbed nabs_tot =5055916

interactions at collimators (file coll_summary)

absorptions or SD scattering at collimators (file
FLUKA_impacts_real)

loss maps (file LPI)
Figure 5: Initial halo distribution = pencil beam
with Gaussian distribution on TCP.B6L7.B1 (skew)
(picture in full size)
Results (beam 1, 3.5TeV per beam, V6.503 optics,
intermediate collimator settings, no imperfections, skew halo)

Total number of particle absorbed nabs_tot =5118428

interactions at collimators (file coll_summary)

absorptions or SD scattering at collimators (file
FLUKA_impacts_real)

loss maps (file LPI)
Figure 6: Initial halo distribution = pencil beam
with Gaussian distribution on TCP.C6R7.B2 (horizontal)
(picture in full size)
Results (beam 2, 3.5TeV per beam, V6.503 optics,
intermediate collimator settings, no imperfections, horizontal halo)
 Total
number of particle absorbed nabs_tot =5115634

interactions at collimators (file coll_summary)

absorptions or SD scattering at collimators (file
FLUKA_impacts_real)

loss maps (file
LPI)
Figure 7: Initial halo distribution = pencil beam
with Gaussian distribution on TCP.D6R7.B2 (vertical)
(picture in full size)
Results (beam 2, 3.5TeV per beam, V6.503 optics,
intermediate collimator settings, no imperfections, vertical halo)
 Total
number of particle absorbed nabs_tot =5119240

interactions at collimators (file coll_summary)

absorptions or SD scattering at collimators (file
FLUKA_impacts_real)

loss maps (file
LPI)
Figure 8: Initial halo distribution = pencil beam
with Gaussian distribution on TCP.B6R7.B2 (skew)
(picture in full size)
Results (beam 2, 3.5TeV per beam, V6.503 optics,
intermediate collimator settings, no imperfections, skew halo)
 Total
number of particle absorbed nabs_tot =5118301

interactions at collimators (file coll_summary)

absorptions or SD scattering at collimators (file
FLUKA_impacts_real)

loss maps (file
LPI)


coll_summary 
Column #1: Collimator ID number
#2:
Collimator name (in database)
#3:
Total number of impacts on collimators per batch of Np halo
protons (Np=1280)
#4:
Total number of protons undergone to inelastic interactions
(absorbed) at collimator
#5:
Average impact parameter
#6: RMS
impact parameter
#7:
Collimator jaw length [m].

FLUKA
_impacts_real 
Column #1: Collimator ID number
#2: Collimator rotation (0 for horizontal collimators)
[rad]
#3: Collimator longitudinal coordinate s[m]
along the LHC w.r.t. collimator jaw
#4: x[mm] impact
coordinate at collimator w.r.t. beam orbit
#5: xp[mrad]
impact angle at collimator
#6:
y[mm] impact
coordinate at collimator w.r.t. beam orbit
#7: yp[mrad]
impact angle at collimator
#8:
Type of interaction (1= inelastic scattering, 4= SD scattering)
#9:
Particle ID number (XXYY: with YY = 1 to 64 particle per run, XX = 1
to 50 runs)
#10:
Number of turn of interaction

LPI 
Column #1: Particle ID number (XXYY: with YY = 1 to 64 particle per
run, XX = 1 to 50 runs)
#2:
Number of turn (200 maximum)
#3:
Longitudinal coordinate s[m] along the LHC where particle
was lost w.r.t. IP1
#4:
x[m] x
coordinate at s w.r.t. beam orbit
#5:
xp[rad] angle at s
#6:
y[m] y
coordinate at s w.r.t. beam orbit
#7:
yp[rad] angle at s
#8:
Energy spread
#9:
Type of halo distribution
#10:
Number of turns before the particle is absorbed (number of survival
turns)
 

AR ,
Thursday, 10. June 2010 17:28 +0200 
