victor tikhomirov institute for nuclear problems minsk, republic of belarus new approaches to the...
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Victor Tikhomirov
Institute for Nuclear Problems Minsk, Republic of Belarus
New Approaches
to the Crystal Collimation
UA9 Workshop, Roma, 23-25 February 2011
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Outline
Beam collimation by crystals
MVROC – Multiple Volume Reflection in One crystal (VR amplification by crystal axes)
Channeling fraction increase by the crystal cut
Crystal cut and MVROC application to crystal collimation
Conclusions
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-8 -4 0 4 8
-8
-4
0
4
8
y/ y
x/x
The planned LHC luminosity upgrade will intensify the beam halo formation
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Crystals improve collimation efficiency
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Crystals are used in either channeling
or volume reflection regimes
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First results on the SPS beam collimation with bent crystals
W. Scandale et al, PLB 692(2010)78
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New effects
allowing to facilitate
crystal collimation
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Multiple Volume
Reflection from
different inclined
planes of One Crystal
(MVROC)
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Multiple Volume Reflection in One Crystal (MVROC)V.V. Tikhomirov, PLB 655(2007)217
Axes form many inclined reflecting planes
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Comoving reference frame rYz rotates with the normal bent axis direction when a particle moves through the crystal.
Horizon projections of the angles of reflection from different skew planes sum up giving rise to the MVROC effect while the vertical angles of reflection from symmetric skew planes, like (-101) and (0-11), mutually compensate.
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Protons are reflected from many different crystal plane sets in one crystal
Proton motion in comoving reference plane
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Reflection from different crystal planesincreases VR angle about 5 times
Reflection angles from planes of one crystal vs bending radius
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First MVROC observationW. Scandale et al, PLB 682(2009)274
MVROC indeed increases reflection angle 5 times
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Channeling fraction increase
by crystal cut
or buried amorphous layer
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The capture probability increase by crystal cut V.V.Tikhomirov, JINST, 2(2007)P08006
beam
cut
crystalz1
z2
z3
0
x
y z
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V, , eVe
x, A
e
x1x2
V(x )2
V(x )1
. . ..
Vmax
d
v1
v2
v0
e
x0
The cut diminishes the potential energy conserving the transverse kinetic one
Transverse energy reduction by the cut - 1
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0 1 20
5
10
15
20
25
ch
x0, Å
ε ,
eVε
,
xp
d
0
0 1 2
ch
= 0.25 ch
= 0.320 0
0 1 2
xp
d dxp
ch
= 0.10
Transverse energy reduction by the cut - 2
Only 1-2% of protons avoid drastic transverse energy reduction by the cut
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-0,5
0,0
0,5
1,0a
0,5 1,0 1,5
b
c
0,0 0,5 1,0 1,5
-1,0
-0,5
0,0
0,5
1,0
dd
dx, Å
0,0 0,5 1,0 1,5
-1,0
-0,5
0,0
0,5
1,0
x, Åx, Å
e ch
/ ch
/ ch
/ ch
/
Protons cease to reach the high nuclear density regions
Phase space transformation by the cut
plane crystal crystal with cut
z1
z20
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Channeling fraction increase by the cut
The cut increases channeling fraction from 85 to 99%
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Crystal cut can be produced by anisotropic etching
Cut formation method
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SIMOX Buried Oxide Layer can be used instead of crystal cut
V. Guidi, A. Mazzolari and V.V. Tikhomirov, J. Phys. D: Appl. Phys. 42(2009) 165301
• Thermal annealing restores silicon cristalline quality and creates a buried SiO2 layer,
• Interfaces between Si and SiO2 are well terminated,
• Misalignment between silicon layers in available SIMOX structures: less than 0.7 Å/mm.
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BOX layer
“focuses”
protons
like a cut
diminishing
their
transverse
energy
MeVE
mz
nmz
nmz
p 7
,1
,80
,20
3
2
1
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0 2 4 6 8 10 12 14 16 180,0
0,2
0,4
0,6
0,8
1,0
SiP110 - simulations SiMoxP110 - simulations Si, simulations SIMOX, z
1=20nm, z
2=60nm, simulations
Rutherford Backscattering allows to observe
the channeling eficiency increase at low energies (6.1 MeV Legnaro)
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Grazing proton incidence allows to abserve the channeling eficiency increase
at SPS energy of 400 GeV (H8 line)
Beam
Θ (mrad)
dN
/dΘ
(m
rad)
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Crystal cut and MVROC application to crystal collimation
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Inelastic loss fraction as a function of the crystal orientation
in the usual crystal, crystal with cut and a crystal in MVROC orientation*)
-200 -100 0 100
0
1
2
3
Nr/N
, %
cr
MVROC 1mm, Vx=-273urad, Vy=100urad Si cut 2um, 8um
-30 -15 0 15 3010-3
10-2
10-1
100
Nr/N
, %
cr
cut, z1=2m, z
2=8m
crystal MVROC
Crystal cut decreases inelastic losses MVROC increases angular acceptance
*) MVROC orientation with ΘX0 = -273urad, ΘY0 = 100urad and R=2m
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0.0 0.2 0.4 0.6 0.8 1.0
0.1
1
10
x, cm
(1/N
)dN
/dx,
cm
-1
120 GeV 1mm 6.67m crystal cut
0 5 10 15 201
10
100
1000
10000
Npass
N
120 GeV 1mm 6.67m crystal cut
*) cut is between 2 and 8 μm. R=6.67m, l=1mm
Distributions of the impact parameter and number of the crystal transversals
in usual Si crystal and crystal with cut*)
at perfect alignment
The cut both increases the impact parameter and decreases the crystal transversals number at perfect alignment
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Rotation of the crystal with cut allows to use it at various energies
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*) ΘX0 = -70urad! +) ΘX0 = -250urad, ΘY0 = 100urad and R=2m
0.0 0.2 0.4 0.6 0.8 1.00
3
6
9
12
(1/N
)dN
/dx,
cm
-1
x, cm
120 GeV 104p Channeling
x0=-70rad 1mm 6.67m 0.787%
MVROC x0
=-250rad, y0
=100rad 1mm 2m
0 5 10 15 20 250.0
2.0k
4.0k
6.0k
8.0k
N
Npass
120 GeV 104p Channeling
x0=-70rad 1mm 6.67m 0.787%
MVROC x0
=-250rad, y0
=100rad 1mm 2m
Distributions of the impact parameter and number of the crystal transversals
in usual Si crystal *) and crystal in MVROC orientation+)
at rough alignment
MVROC both increases the impact parameter and decreases the crystal transversals number at rough alignment
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CONCLUSIONS
Crystal collimation can be drastically facilitated by both crystal cut and MVROC process, namely:
both the impact parameter can be increased and the crystal transversals number can be decreased
– by crystal cut at perfect alignment
– by MVROC process at rough alignment
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First MVROC observationW. Scandale et al, PLB 682(2009)274
MVROC indeed increases reflection angle 5 times
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Improvement of the cut action in Ge
Ge widens the cut acceptance by 40%
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0.0 0.5 1.0 1.50
10G
20G
30G
40G
50G
60G
70G
Axial Electric Field
E, V
/cm
Si Ge
o
, A0.0 0.5 1.0 1.5
0
50
100
150
200
Axial Potential
V(
), e
V
, A
Si Ge
o
Comparison of axial potential and field strength in Si and Ge
Both potential and field strength are nearly twice as larger in Si than in Ge
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Comparison averaged potentials and field strengths of Ge and Si planes and axes
u(293K)=0.085Å, u(100K)=0.054Å, u(0K)=0.036Å
Ge cooling is very productive!
Si(293K) Ge(293K) Ge(100K)
<110> V0, eV 133 229 172% 309 232%
<110> Emax,GV/cm 46 78 170% 144 313%
Si(293K) Ge(293K) Ge(0K)
(110) V0, eV 21.5 37.7 175% 44.0 205%
(110) Emax,GV/cm 5.7 9.9 1.74 14.9 261%
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-200 -100 0 100 2000.000
0.005
0.010
0.015
0.020
Ge
Si
(1/N
) dN
/d x
, ra
d-1
x, rad
Ge <111> 400 GeV 4mm 11.43/1.35m Vx=195*1.35 Vy=85*1.35dvx=11, dvy=9.13б 77.07/51.9
Si <111> 400 GeV Gaussian asymmetric, x=11rad,
Y=9.13rad,
x=195rad,
y=85rad
Volume reflection angle increase in Ge
0 50 100 1500.000
0.005
0.010
0.015
0.020
Si
Ge
x, rad
(1/N
) dN
/d x
, ra
d-1
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− the main parameter of quantum electrodynamics
Investigating Strong Field QED effects
Si(293K) Ge(293K) Ge(100K)
<110>Emax,GV/cm 46 78 170% 144 313%
χ(120GeV) 0.82 1.39 2.56
3/2
2
)1(
,)1~(
,)1(
EI
EI
EI
216 /1032.1 mccmeV
E
Radiation intensity will grow like 2EE
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v
0 20 40 60 80 100 1200
1
2
3
4
Ge
Si
dN
/d
, GeV
120GeV, (1-10), 2mm, ||160urad Ge _|_ 26urad Si _|_ 20urad
Increase of radiated photon number in Germanium
The increase exceeds two