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Simulation of Neutron Backgrounds in the ILC Extraction Line Beam Dump. Siva Darbha University of Toronto SLAC, ILC BDS Supervisors: Lewis Keller and Takashi Maruyama. The International Linear Collider (ILC). 500 GeV center of mass energy Precision measurements Clean signal to noise ratio. - PowerPoint PPT Presentation
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Thursday, August 16, 2007
SULI Presentation 1
Simulation of Neutron Backgrounds in the ILC
Extraction Line Beam Dump
Siva DarbhaUniversity of Toronto
SLAC, ILC BDSSupervisors: Lewis Keller and Takashi Maruyama
Thursday, August 16, 2007
SULI Presentation 2
The International Linear Collider (ILC)
• 500 GeV center of mass energy• Precision measurements• Clean signal to noise ratio
Thursday, August 16, 2007
SULI Presentation 3
Extraction Line and Water Dump
z (cm)
x (cm)
e-
n
e-
H2O
Concrete Tunnel
Concrete Collimator
e+ 40 cm A
A’
Most n are directed forward
FLUKA was used for all simulations, ROOT for analysis and some particle generation
250 GeV
Thursday, August 16, 2007
SULI Presentation 4
Fluence at IP
• Flux was treated as isotropic from -1 < cosθ < -0.99
• Flux for 1.5 cm radius scoring plane at z=0 was found from flux in 2 m radius scoring plane
x (cm)
y (cm)
Scoring plane at z=0
At A-A’ (on the surface of the dump)
Tunnel Wall
Quadrupole aperture
Thursday, August 16, 2007
SULI Presentation 5
1. Leading particle biasing
• simulating a full EM shower requires long
CPU time
• to save time, take only the most energetic
secondary and remove all others
• applied to e+,e-, and γ’s < 2.5 GeV
2. Photonuclear interaction length
• #n produced proportional to σ
• σ was increased by a factor of 50
• ‘weight’ associated with each n produced from this was decreased by a factor of 50 to compensate
Particle Biasing
• Three types of biasing were used:
γ A → n + X (σ, )
Thursday, August 16, 2007
SULI Presentation 6
Particle Biasing (continued)
3. Splitting/Russian roulette• Dump divided into 10
regions• Each region given a
factor of 2 larger importance
• As e+, e-, or γ crosses a boundary, their number is increased or decreased on average by the ratio of importances on either side of the boundary
• ‘weight’ is adjusted accordingly
1248…
e-
x (cm)
z (cm)
Thursday, August 16, 2007
SULI Presentation 7
Cutoffs
• Production– e+, e- > 50 MeV– photons > 10 keV
• Transport– e+, e- > 50 MeV– photons > 10 keV– neutrons > 10 keV (group number < 48)
Thursday, August 16, 2007
SULI Presentation 8
Computation Time
6000 incident e- n total ‘weight’ n total number
Run # Type of Bias
CPU time
At z=300m
At z=0 At z=300m
At z=0
1 None 23 h 35 min
82 2 82 2
2 LPB 1 h 36 min
103. 0 87 0
3 Interaction length
6 h 46 min
103. 0.781 5008 49
4 Splitting/RR 6 h 22 min
96.4 1.09 16619 117
Thursday, August 16, 2007
SULI Presentation 9
Fluence at IP
n’s/cm2/year at IP (z=0)
Mean (10 runs) RMS
No tunnel or collimator
8.33*1010 1.50*1010
Collimator 3.73*1010 3.34*1010
Tunnel and Collimator
3.65*1010 2.34*1010
1010 n/cm2 at the VXD would cause displacement damage to CCD Si detectors
However, not all neutrons that reach the IP will hit the inner detector
Thursday, August 16, 2007
SULI Presentation 10
Neutron Energy Distribution
• Information was gathered on the neutron distribution in the backward direction and was used to generate 106 neutrons to study the real flux at the VXD
10 MeV bins
In first 10 MeV bin
Thursday, August 16, 2007
SULI Presentation 11
Detector
C’
C
7 mrad
n
Be Si VXD
x (cm)
z (cm)
quadrupole2.4 cm
3.0 cm
All n’s were given a 7 mrad trajectory towards the detector
W BeamCal
2.4 cm
Thursday, August 16, 2007
SULI Presentation 12
Initial position of n’s• n’s randomly
and uniformly distributed within the quadrupole bore
C-C’
Thursday, August 16, 2007
SULI Presentation 13
CCD Si VXD with Be beampipe
A’
A
B’
B
A-A’B-B’ z (cm)
x (cm) x (cm)
y (cm)
Thursday, August 16, 2007
SULI Presentation 14
Results: Fluence at VXD
• The BeamCal acts as a collimator for neutron backscattering from dump
• With the W BeamCal, the nominal fluence at Layer 1 of VXD is: 4.28*108 n/cm2/year
No BeamCal
W BeamCal
Black BeamCal
Thursday, August 16, 2007
SULI Presentation 15
1 MeV Neutron Equivalent Fluence• However, the amount of displacement
damage done to CCD Si detector by neutrons is a function of neutron energy
• When relative damage to Si is considered, normalized to 1 MeV, the fluence is: 9.27*108 n/cm2/year
• When e+ beam is considered also, value is doubled to 1.85*109 n/cm2/year
• A value of 1010 n/cm2 would damage the CCD Si detector by this measure
1 MeV
T. M. Flanders and M. H. Sparks, “Monte Carlo calculations of the neutron environment produced by the White Sands Missile Range Fast Burst Reactor,” Nuclear Science and Engineering, vol. 103, pp. 265 – 275, 1989.
Thursday, August 16, 2007
SULI Presentation 16
BeamCal Radius Dependence
• Values are not normalized to 1 MeV fluence
• Values should be doubled to incorporate positron beam
Thursday, August 16, 2007
SULI Presentation 17
Acknowledgements
• Takashi Maruyama and Lewis Keller• Tom Markiewicz• Nan Phinney• Mario Santana• Nicholas Arias• SLAC• ILC BDS Group• DOE, Office of Science
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