Tracking Code for Collimation Studies - Results
extended version of SixTrack for collimation
November 2009 update

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 proton-proton (pp) scattering, and inelastic diffractive pp scattering (single diffractive scattering),
□   Inelastic proton-nucleon scattering,
□   Elastic and inelastic proton-nucleus scattering,
□   Rutherford scattering.

· Various types of halo and possibility of including diffusion.

· Tracking of large particle ensembles (~10⁶ protons) over hundreds of turns.

· Multiple imperfections on the beam and the collimator properties (setting errors, tilts, orbit, beta beat, …)

MAD-X 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/94-56 (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. Robert-Demolaize, 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
LSS6	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
LSS2	TCTV	30.2
LSS5	TCTH	12.8
	TCTV	12.8
	TCL	13.7
LSS8	TCTH	15.3
LSS8	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