Collimation

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15 Νοε 2013 (πριν από 3 χρόνια και 10 μήνες)

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Collimator Damage


Adriana Bungau


The University of Manchester



Collaboration between RAL, Manchester University and Daresbury Laboratory


Goal:

determine optimal material and geometry for ILC collimators in order to

maximize the collimation efficiency and minimize the wakefield effects



Investigate the heating effects caused by various patterns of energy deposit using

ANSYS

(G. Ellwood
-
RAL, G.Kourevlev

Manchester Univ.)



Simulate the energy deposition in a spoiler of specified geometry due to a beam
being mis
-
steered using
FLUKA
( L. Fernandez


Daresbury) and
Geant4

(A.Bungau


Manchester Univ. )


Cross
-
check these studies with Lewis Keller’s results on spoiler survival (SLAC)


Study a range of geometry/material combinations that allows low wakefields and
verify these experimentally

What we do:

Update report on material damage

Geant4/Fluka results:

Model of an isometric view of the collimator (geometry, material)

Simulations of the energy deposition along z at several depths; distributions in various
2D projections of the energy density

Calculations of the corresponding increase in temperature

Kinetic energy of the outgoing particles

Results passed on for ANSYS studies

ANSYS results:

Studies of steady state heating effects (3d isothermal contours
-
consistent)

Comparison between ANSYS simulations and analytic calculations (good agreement)

ANSYS used to predict stress induced in a 3d solid (apply to the collimator geometry)

Collimator geometry (modelled with Geant4)


Dimensions:




x = 38 mm


y = 17 mm


z = 21.4 mm


Z = 122.64 mm


θ

= 324 mrad



Material:


Ti alloy (Ti
-
6Al
-
4V)




=

4.42 g/cm
3


melting temperature 1649
C
°


c = 560 J/kg C
°

z

y

x

Beam profile


Ellipsoid with

x

=

111

m

y
= 9

m


Simulated particles: 10
4
electrons/bunch


E = 250 GeV


Energy cutoff:


e
-

kinetic energy cutoff = 2.0 MeV
-
>2.9 mm range in Ti alloy


e
+
kinetic energy cutoff = 2.0 MeV
-
>3.1 mm range in Ti alloy




energy cutoff =100.4 KeV
-
>6.18 cm attenuation length


in Ti alloy

Energy deposition in Ti alloy at 2 mm depth



the beam is sent through the collimator along z at 2 mm depth



E
dep

max in the second wedge at

14 mm



the mesh size should be smaller than the beam size for realistic results



at z
≈14 mm: max energy deposition is 3 GeV/2e
-
3 mm
3

-
>
∆T = 215 K


Energy deposition at 10
mm depth in Ti alloy



the beam goes through the
collimator at 10 mm depth



max E
dep

at 10 mm depth is at
≈35
mm along z (second wedge)



at z≈35 mm, the max E
dep
is 6.66
GeV/2e
-
3 mm
3

-
>
∆T = 430 K


e.m. shower for one 250
GeV e
-

at 2 mm depth


e.m. shower for one 250
GeV e
-

at 10 mm depth


Energy deposition at 16 mm depth in Ti alloy spoiler



the beam is sent through the collimator at 16 mm depth



max E
dep

is at
≈55 mm



max E
dep

= 8 GeV/2e
-
3 mm
3
-
>
∆T = 517 K

e.m. shower for one 250 GeV e
-

at 16 mm depth

Depth (mm)


T for Ti


T for Ti alloy

2

226

215

10

452

430

16

581

517

Summary


L.Keller:

e
+

: multiplicity
≈ 4

e
-


: multiplicity
≈ 4

e
-

: multiplicity


4

e
+
: multiplicity

3

Steering

Condition

Beam Size (
µm)


σ
x

σ
y

Max T

500 GeV
CM

Max T

1 TeV CM

Max T

500 GeV

CM

Max T

1 TeV

CM

0.6 rl Ti

spoiler


28 6

1020

2887

1380

2770

0.6 rl Ti

spoiler

111 9

302

761

290

560

1.0 rl Ti

Spoiler

104 15

295


-

260

720*

Direct Hits on Spoilers

L. Keller

Geant 4 simulation

Maximum
∆T/2x10
10

bunch at Hit
Location,
°
C/bunch

*with a spread in energy
∆E/E = 0.06 %

Conclusion

The instantaneous temperature rise at various depths were below the
melting temperature of the Ti alloy
-
>collimators are not in danger in case
of a direct hit from one bunch

Little energy deposition in the material


a large fraction of the energy
appears as photons emerging from the collimators

Future plans

Compare the Geant4 results with Fluka predictions

Carry out a survey of materials (so far only Ti and Ti
-
6Al
-
4V were used)

Pass on the energy deposits files for ANSYS studies ( RAL)