1. Efficiency studies for CRYSTAL experiment in SPS
Igor Yazynin
AB-ABP Collimation working group,
collaboration UA9.

2. Layout of system and principles of estimation efficiency
Iscr,% I1mm,% Icr% Ia_glob% Ich%
W coll
Absol. coll
At two stage collimation system
Losses defined 2 sources crystal and collimator
At optimal orientation, losses from crystal consist only 20%.
For 1 stage collimation system global inefficiency will be in 100time more.

3. Influence of amorphous layer
Losses on the crystal and channeling efficiency versus alignment with amorphous layers (R=12m, L=2.04mm).
Relation of losses n=I(am)/I(ch)
When thickness Sam=0, n=40. For Sam=10 n=8.
Channeling efficiency decrease from 96 to 94%
Losses at Sam=10um increase in ~3 times, Ig=0.0063

4. Influence of torsion (skew) parameter
Extraction efficiency and distributions on the TAL versus alignment with (skew of crystal) torsion.
Torsion Iscr,% I1mm,% Icr% Ia_glob% Ich%
Losses at torsion=0.02mrad/mm increase in 5 times, and channeling eff. decrease on 6%.

5. Influence of miscut parameter
Losses and extraction efficiency alignment of crystal with miscut.
Miscut(mrad) Iscr,% Iout,% I1mm,% Icr% Ia_glob% Ich%
Losses (global inefficiency) at negative miscut(-1mrad) increase only in 1.7 times,
And at positive (1mrad) increase in 6 times.
That explained increasing proton density at edge of collimator.

6. Influence of collimator’s offset
Losses on the crystal and efficiency versus alignment with any offsets.
Rcoll(mm)
5.2
5.7
6.7
7.7
I(chan)%
92.83
93.48
94.42
95.21
I(out)%
96.96
97.4
97.66
98.11
I(tar)%
0.125
0.15
0.165
0.19

7. Influence of crystal angle deviation
Distribution of scattering protons on the TAL with optimum orientation
Density at the edge of TAL practically the same for crystals with R=3m, and in 3 time smaller than for crystal with R=12m. Such as global losses proportional the density the efficiency of system increase in 3 time with use crystal with R=3m.
Optimal bend crystal: – 200 urad.

8. Interaction of protons with the crystal: channeling
Random flat angle x’ distribution between +- 10urad.
Angular beam distribution after interaction with the crystals for different bending radius
Bent angle = 150 urad, E=120 GeV, channeling case.
Image for collimator edge
A: offset 0.2 mm
B: offset 2 mm
1:R= m, 2: R=6.67m, 3:R= m

9. Orientation curves for two cristals
Losses on the crystal versus alignment for two crystals with amorphous layer.
For 1 case (R=12m) Imax/Imin ~ 10
For 2 case (R=3m) Imax/Imin ~ 40
In experiment Imax/Imin ~ 5-7
that can explain by added none ideality of crystal: twist,miscut,skew

10. Interaction of protons with the crystals Volume Reflection (multi- crystals)
Each crystal has: bent angle= 300 urad, length= 1mm, Rcurv= 3.33 m
Initial beam: angle average=-100urad, deviation 0urad
Angular beam distribution after interaction with the crystals for different number of crystals
E=120 GeV
Image for collimator edge
A: offset 0.2 mm
B: offset 2 mm
~ 8 crystals: optimal number

11. Conclusion and proposals:
With using crystal in channeling mode may increase may increase efficiency of collimation system (SPS) in 100 time.
Different bending angles have been investigated: our proposal is to use a larger bending angle (> 150 μrad, e.g μrad). No change in efficiency but larger impact parameter (2-5mm). This would allow to increase the offset of the collimator and the two RP to 2-3 mm.
We proposed to use more shot crystal with bend radius 3-4m for E=120GeV. In this case all none idealities of crystal will influence much smaller on the efficiency of system.
The optimum number of crystals for MVR is 7-8. We propose the use of crystalline target with quasi elastic technology (IHEP, INFN). Length of every crystal 1 mm, curve radius 3m.
It is very important not forget to use the monitoring of losses near crystal, because of inelastic losses in it will decrease in ~ 50 times for good alignment in channeling mode.