CRYSTAL

BASED COLLIMATION SYSTEM
AS AN ALTERNATIVE WAY TO SOLVE
THE COLLIMATION PROBLEM FOR
FUTURE HIGH ENERGY ACCELERATORS
ALEXEI SYTOV
Research Institute for Nuclear Problems,
Belarusian State University
The LHC
luminosity
upgrade
The beam luminosity will increase
with a factor
10
!
10
10
1
2
34
s
cm
L
Halo particles
can damage the LHC equipment
because of their large amplitude of
betatron
oscilla

tions
. So we should remove them using
collimation
system
:
Absorber
Absorber
new
collimation
system
Collimation system for removing halo particles
old
collimation
system
(after the LHC luminosity
upgrade becomes
insufficient
)
The remarkable feature of crystals in high energy
physics is very strong
electric
fields applied to
particle beam with accuracy of Angstrom.
How can we deflect high energy
particles using bent crystal?
Different effects in crystal
θ
L0
Channeling
Volume
reflection
Channeling in Bent crystals
─ large
deflection,
but small acceptance
VR
─
large acceptance,
but small deflection
Advantages and disadvantages of
different effects
Channeling in Bent crystals
─ large
deflection,
but small acceptance
VR
─
large acceptance,
but small deflection
MVR
─
large acceptance,
increased
deflection
MVR indeed increases reflection angle
5 times
in comparison with VR
Advantages and disadvantages of
different effects
Multiple Volume Reflection (MVR)*
X
Y
Z
Θ
y
Θ
x
Axes form
many
inclined
reflecting planes
*
V.
Tikhomirov,
PLB
655
(
2007)
217
;
V. Guidi, A. Mazzolari
and V. Tikhomirov,
JAP 107 (2010) 114908
A trajectory
θ
X
θ
Y
δθ
X,Y
,
μ
rad
*)
MVR orientation with Θ
X0
=

273
μ
rad, Θ
Y0
= 100
μ
rad and R=2m
Angular acceptance increase by MVR
*)
200
100
0
100
0
1
2
3
N
r
/N, %
cr
MVROC 1mm, Vx=273urad, Vy=100urad
Si
cut 2um, 8um
Channeling
VR
MVR
Crystal
with cut
Crystal
0
z
1
z
2
z
3
Beam
z
cut
A technique to improve crystal channeling
efficiency of charged particles till 99,9%
*
A narrow plane cut near the crystal surface
considerably increases the probability of capture into
the stable channeling motion of positively charged
particles.
z
c
*V.
Tikhomirov
. JINST, 2 P08006, 2007.
Conclusion 1.
MVR is very good for collimation because
of high collimation efficiency.
We can increase the collimation efficiency
by application of channeling regime if we
solve some additional problems.
Problems of the channeling effect
for the collimation
The UA9 experimental layout:
experiment
simulation
UA9
experiment at SPS (CERN)
*
Dependence of
inelastic
nuclear interaction
number
of protons
on the angular position of the crystal C1:
*W.Scandale et al.
Phys. Let.,
B692 78

82, 2010
.
Miscut
angle
First crystal hit
First crystal hit
UA9: more than
90
%
of particles
for both
miscut
cases
Probability of nuclear reactions in the crystal collimator
vs
miscut
angle at perfect crystal alignment*
*V.
Tikhomirov
, A.
Sytov
.
arXiv:1109.5051 [
physics.acc

ph
]
Probability of nuclear reactions in the crystal collimator
vs
miscut
angle at perfect crystal alignment*
*V.
Tikhomirov
, A.
Sytov
.
arXiv:1109.5051 [
physics.acc

ph
]
×
4,5
Probability of nuclear reactions in the crystal collimator
vs
miscut
angle at perfect crystal alignment*
*V.
Tikhomirov
, A.
Sytov
.
arXiv:1109.5051 [
physics.acc

ph
]
UA9
×
4,5
What is the
miscut
influence at the LHC?
miscut
influence
zone
miscut
influence
zone
Particle
distribution in
impact parameter
for
the UA9 (SPS
) and the LHC*
*V.
Tikhomirov
, A.
Sytov
. arXiv:1109.5051 [
physics.acc

ph
]
average
impact
parameter
average
impact
parameter
Both the
positive
and
negative
miscut
angles can be the reason of considerable
decreasing of the collimation efficiency.
The usual
miscut
angle
can increase
the
probability
of nuclear reactions
with a factor
4,5
for the UA9 case.
T
he
LHC
functioning
will not
be considerably disturbed
by
the
influence
of crystal
miscut
.
In
addition, the
performance of
the
crystal collimator can be
drastically
improved by the narrow plane cut.
Conclusion 2
Both the
positive
and
negative
miscut
angles can be the reason of considerable
decreasing of the collimation efficiency.
The usual
miscut
angle
can increase
the probability of nuclear reactions
with a factor
4,5
for the UA9 case.
T
he
LHC
functioning
will not
be considerably disturbed
by
the
influence
of crystal
miscut
.
In
addition, the
performance of
the
crystal collimator can be
drastically
improved by the narrow plane cut.
Conclusion 2
Both the
positive
and
negative
miscut
angles can be the reason of considerable
decreasing of the collimation efficiency.
The usual
miscut
angle
can increase
the probability of nuclear reactions
with a factor
4,5
for the UA9 case.
T
he
LHC
functioning
will not
be considerably disturbed
by
the
influence
of crystal
miscut
.
In
addition, the
performance of
the
crystal collimator can be
drastically
improved by the narrow plane cut.
Conclusion 2
Both the
positive
and
negative
miscut
angles can be the reason of considerable
decreasing of the collimation efficiency.
The usual
miscut
angle
can increase
the probability of nuclear reactions
with a factor
4,5
for the UA9 case.
T
he
LHC
functioning
will not
be considerably disturbed
by
the
influence
of crystal
miscut
.
In
addition, the
performance of
the
crystal collimator can be
drastically
improved by the narrow plane cut.
Conclusion 2
What is crystal application for the ILC?
What is crystal application for the ILC?
speeding
up of
the
electromagnetic
showers generation.
e
±
crystal collimation
decrease
of size of
electromagnetic calorimeters
polarization generation/measurement
positron source for ILC
Both the
MVR
and
channeling
phenomena
can be successfully used for the crystal
collimation at the
LHC
.
T
he
channeling
can provide better efficiency
than the
MVR
but the
MVR
is easier to use with
high efficiency.
There are many additional
crystal applications
for
the
ILC
.
Summary
Thank you for attention!
Particle
distribution in
deflection angle
for
the UA9 (SPS
) and the LHC*
*V.
Tikhomirov
, A.
Sytov
. arXiv:1109.5051 [
physics.acc

ph
]
Average
impact parameter
vs
average beam
diffusion step for the SPS UA9
and
the LHC*
*V.
Tikhomirov
, A.
Sytov
. arXiv:1109.5051 [
physics.acc

ph
]
Measured in
cm
average length
<
Δz
>
of scattering of particles
entering the crystal through the
lateral crystal
surface
vs
both
miscut
angle and diffusion
step at perfect
crystal
alignment*
Miscut
angle
~
95%
UA9:
~
92%
Uncaptured particles
after the first crystal passage:
First MVROC observation
W. Scandale et al, PLB
682(
2009)
274
MVROC indeed increases reflection angle
5 times
Phase space in accelerator at the crystal coordinate
Distribution of angle of deflection by crystal
after the first crystal passage








{
4
4
3
3
3
3
{
{
{
x', μrad
x, mm
θ
def
,
μ
rad
Count
0.05 mm
0.3 mm
0.5 mm
1.0 mm
0.05 mm
0.3 mm
0.5 mm
1.0 mm
0.05 mm
0.3 mm
0.5 mm
1.0 mm
Channeling
Crystal
Crystal
thickness
Crys
tal thick
ness
Crystal thickness choice
amorphous
Volume
reflection
Dcr, mm
Dependence of inelastic
nuclear interaction
fraction of protons
on the crystal thickness
fraction
Dcr=
∞
Absorber
Particles flowing from
the
opposite side
of the crystal
Secondary beam problem
Secondary
beam
the experimental equipment hit
W.Scandale et al. Phys. Let,
B692 78

82, 2010.
experiment
simulation
My simulation:
Miscut angle:
θ
mc
=+200
μ
rad
θ
mc
=0
μ
rad
θ
mc
=

200
μ
rad
θ
cr
,
μ
rad
*W.Scandale et al.
Phys. Let.,
B692 78

82, 2010.
θ
mc
=+200
μ
rad
(Crystal
width=2mm)
count
UA9 experiment interpretation
*
Phase space transformations
1
2
3
z=0
z=z
1
z=z
2
z=z
c
Without cut
x,
Å
x,
Å
4
2
'
x,
Å
θ
/
θ
ch
θ
/
θ
ch
θ
/
θ
ch
θ
/
θ
ch
θ
/
θ
ch
5
3
'
z>z
1
z>z
2
z=z
c
*V.V.
Tikhomirov
.
JINST, 2 P08006, 2007.
With cut
Dependence of the 7
TeV
proton
dechanneling
probability in a 1cm bent Si crystal on the
r.m.s
.
incidence angle
*
Without cut
With cut
*V.V.
Tikhomirov
. JINST, 2 P08006, 2007.
UA9 collaboration references:
•
V.V.
Tikhomirov.
Phys. Lett. B
655 (2007), 217
•
V.V.
Tikhomirov
. JINST, 2(2007), P08006
•
V. Guidi, A. Mazzolari, V. V. Tikhomirov. J. of Phys. D: Applied Physics, 42
(2009), 165301
•
W. Scandale, V.V.Tikhomirov. Phys. Lett. B. 682 (2009), 274
•
V. Guidi, A. Mazzolari, V.V. Tikhomirov. J. Appl. Phys. 107 (2010), 114908
•
W. Scandale
et al…
V. V. Tikhomirov
.
EPL, 93 (2011)
,
56002
V.V.Tikhomirov’s references:
•
W. Scandale et al. PRL 98, 154801 (2007)
•
W. Scandale et al. PRL 101, 234801 (2008)
•
W. Scandale et al. PRL 101, 164801 (2008)
•
W. Scandale et al. PRL 102, 084801 (2009)
•
W. Scandale et al. Phys. Let. B688, 284 (2010)
•
W. Scandale et al. Phys. Let., B692 78 (2010)
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