AS AN ALTERNATIVE WAY TO SOLVE

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Nov 15, 2013 (3 years and 4 months ago)

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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)