victor tikhomirov institute for nuclear problems minsk, republic of belarus new approaches to the...

Victor Tikhomirov

Institute for Nuclear Problems Minsk, Republic of Belarus

New Approaches

to the Crystal Collimation

UA9 Workshop, Roma, 23-25 February 2011

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

-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

Crystals improve collimation efficiency

Crystals are used in either channeling

or volume reflection regimes

First results on the SPS beam collimation with bent crystals

W. Scandale et al, PLB 692(2010)78

New effects

allowing to facilitate

crystal collimation

Multiple Volume

Reflection from

different inclined

planes of One Crystal

(MVROC)

Multiple Volume Reflection in One Crystal (MVROC)V.V. Tikhomirov, PLB 655(2007)217

Axes form many inclined reflecting planes

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.

Protons are reflected from many different crystal plane sets in one crystal

Proton motion in comoving reference plane

Reflection from different crystal planesincreases VR angle about 5 times

Reflection angles from planes of one crystal vs bending radius

First MVROC observationW. Scandale et al, PLB 682(2009)274

MVROC indeed increases reflection angle 5 times

Channeling fraction increase

by crystal cut

or buried amorphous layer

The capture probability increase by crystal cut V.V.Tikhomirov, JINST, 2(2007)P08006

beam

cut

crystalz1

z2

z3

0

x

y z

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

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

-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

Channeling fraction increase by the cut

The cut increases channeling fraction from 85 to 99%

Crystal cut can be produced by anisotropic etching

Cut formation method

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.

BOX layer

“focuses”

protons

like a cut

diminishing

their

transverse

energy

MeVE

mz

nmz

nmz

p 7

,1

,80

,20

3

2

1

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)

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)

Crystal cut and MVROC application to crystal collimation

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

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

Rotation of the crystal with cut allows to use it at various energies

*) 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

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

First MVROC observationW. Scandale et al, PLB 682(2009)274

MVROC indeed increases reflection angle 5 times

Improvement of the cut action in Ge

Ge widens the cut acceptance by 40%

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

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%

-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

− 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

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