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Crystal tests in AB/ATB/EA
(previously SL-EA)
H.W.Atherton,C.Biino, M.Clément, N.Doble, K.Elsener,
L.Gatignon, P.Grafstrom, J.B.Jeanneret, U.Uggerhoj,
In close collaboration with many others, in particular
friends from Aarhus, CERN, Darmstadt, Dubna, Grenoble,
Johannesburg, Strassburg, Stuttgart
presented by L.Gatignon / AB-ATB-EA
Studies of proton channeling
 Radiation hardness for protons
 Studies of ion channeling
 NA48 application

Incentive:
Application of a bent crystal to provide simultaneous and collinear
KS and KL beams for the NA48 CP-violation experiment
Approach:
Started cooperation with E.Uggerhoj and S.P.Moller and their
NA43 colleagues to gain experience with bent crystals.
• Study performance and limitations of bent crystals
• Prepare the specific application for NA48
• Investigate long-term stability – radiation hardness
As the opportunity presented itself, some of these studies were
extended to Pb and In beams
Few 1012 ppp
> Few 104 ppp
STUDIES WITH PROTON BEAMS
• Try to understand bending phenomenology
• Measure limits
• Work towards design of crystal holders
Use mainly H8 beam
Initial attempt:
H8 microbeam, 450 GeV/c protons
Horizontal divergence 3 microrad
Spot size 2Hx 1V mm2 FWHM
Intensity at the 104 – 106 level
<110> Silicon crystal, 10x50x0.9 mm3
Front and back ends 3x8 mm2 fully
depleted solid state detectors
Note: outgoing beam: sq=2Yp = 15 mrad
Non-uniform
radius
of curvature
≈ 10% fully bent
through 7 mrad
Ball bearings (“fluid”)
Too much material
(bkgd into detectors)
to remove variation in Rcurv
over length of crystal
Crystal deformation
due to balls
1992: Next H8 test
<111> Si crystal, 52x9x0.9 mm3
Incident beam badly tuned:
divergence 35 mrad
Causes “foot”
More uniform bending radius
but curvature not monitored
Bending efficiency:
1993: Comparison of 450 and 200 GeV/c
(110) Si crystal, 50x10x0.9 mm3
4 solid state detectors
Classical 3-point bender
450 GeV/c microbeam:
3 mrad bend
450 GeV/c: microbeam (sq = 3 mrad)
200 GeV/c: secondary beam (larger sq)
Preliminary results for axial channeling:
In a p- (negative beam):
(111) Si crystal,
Bending angle is 3.1 mrad (to the left of the plots), hence Rcurv = 6 m
(i.e. cannot expect 3.1 mrad bending)
Axial channeling:
some clear deflection seen
but no particles are bent by more
than 0.5 mrad
Planar channeling:
even weaker, but significact
planar deflection effect is seen
1996-1997: Germanium crystal
(110) Ge crystal:50x10x1 mm3
bent over 30 mm of its length
Beam divergence:
450 GeV/c microbeam: 3 mrad
200 GeV/c sec beam:
7 mrad
(approx. 60% p, 40% p+)
Results for bending efficiency of Ge: up to 60%
450 GeV/c protons
200 GeV/c hadrons
Good agreement with theoretical expectations
Radiation hardness
A crystal has been irradiated in the T6 primary target for a full year with a
450 GeV/c slow-extracted proton beam of 5 1012 ppp over 2.4 s every 14.4 s.
The crystal was not aligned, the beam divergence was 0.2 mrad RMS.
Total flux: 2.4 1020 p/cm2 over an area of 0.8 x 0.3 mm2
The bending efficiency was measured before and after the irradiation
Contact radiography:
The measurement was done with a classical 3-point bender.
Deflection efficiency before irradiation: 50%
Unfortunately the crystal broke
into 2 pieces after the irradiation.
Hence the distance between
the two outer pins had to be reduced
from 30 to 25 mm. This lead to a smaller
radius of curvature and a correspondingly
reduced channeling efficiency.
Nevertheless the channeling and bending
efficiency could be measured as a
function of efficiency
C.Biino et al., CERN-SL-96-30-EA,
published as EPAC 96:2385-2387
Deflection efficiency measurement after irradiation
2.4 1020 p/cm2
FOR NA48
Crystal serves to
• bend beam back over 7.2 mrad
• attenuate proton beam by large factor
It replaces:
• a 5 m long dipole magnet
• a very small diameter pinhole
It avoids muons to be bent back
into the experiment
MECHANICAL DESIGN OF CRYSTAL HOLDER:
Reduce transmission by using coupling between H and V planes:
Transmission
through the
crystal :
≈ 2 10-5
NA48 experience
 Never had to replace a crystal
 Never had to retune the crystal during a run
 Very stable element in the beam
 We consider it a very successful application
 A crystal was also used as a photon converter
to enhance photon conversion efficiency for a
given thickness of the KS anti counter (C.Biino)
STUDIES WITH ION BEAMS
Tests were performed with fully stripped Pb82+ beams at 400- GeV/c (33 TeV)
Theoretical expectations:
 Yp = 7 mrad, like for protons
 Ions steered away from nuclei
hence reduced nuclear interactiuons
and reduced Weiszaecker-Williams
break-up
 Fraction channeled driven by beam
divergence and dechanneling
as for protons
 Expect 16.8±2.5% deflection efficiency
for a 4 mrad bend over 50 mm Si
First attempt (1996):
Achieved 14±2%,
consistent with theory
1999 (H4 beam):
105 ions per SPS cycle
60x18x1.5 mm (110) Si crystal,
bent over 55 mm with the 3-point
bender also used in H8
Beam divergence 43 mrad FWHM, measured by goniometer scan and
double scan with two steering magnets (change only angle at crystal)
Dechanneling due to 3-point bender
Hodoscope scans
2001: Study of background and dechanneling (H4)
60x60 mm scintillator,
operated at different HV
but fixed threshold:
sensitive to different
charge states
Ions interact at
rate much lower
than in
amorphous Silicon
Indications that
most of the lead
comes out as
Pb82+
But cannot exclude
e.m. dissociation
Very recent results from 2003 Indium run (H2 beam):
MUSIC – MUltiple Sampling Ionisation Chamber
Si crystal, 60 mm long, bent over 56 mm
Scan of S2.S3 coincidence
MUSIC output:
Bent beam
Direct beam
Evidence of strong reduction
(by factor ≈20) of nuclear
charge changing interactions
Fig. 5. The fragmentation probability suppression η versus charge number in
the upper region of Z for the bent beam for angles 7.5 mrad (filled squares:
perfect alignment, open triangles: aligned at Yp/2), 11.9 mrad (open circles)
and 19.8 mrad (filled triangles).
A list of papers (1)
 S.P. Møller et al., High efficiency bending of 450 GeV/c protons using channeling,
Phys. Lett. B256 (1991) 91
 B.N. Jensen et al., Deflection of 450 GeV/c protons by planar channeling in a bent silicon
crystal, Nucl.Instr. and Methods B71 (1992) 155–160
Proton channeling
 K.Elsener et al., Deflection of high energy beams by channeling in bent Silicon crystals,
CERN SL/94-26 (EA)
 S.P. Møller et al., Observation of high deflection efficiency and narrow energy loss
distributions for 450 GeV/c protons channeled in a bent silicon crystal,
Nucl. Instr. and Methods B84 (1994) 434
 Baurichter et al., New results from the CERN-SPS beam deflection experiments with bent
crystals, Nucl. Instr. and Methods B 119 (1996) 172-180.
 C. Biino et al., Deflection of 200 GeV/c and 450 GeV/c positively charged particles in a bent
Germanium crystal, Phys. Lett. B403 (1997) 163-167.
 C.Biino et al., Record deflection efficiencies measured for high energy protons in a bent Germanium
crystal, CERN SL-97-028-EA, June 1997, Published in Vancouver 1997, Particle Accelerator vol1*
80-82.
 A.Baurichter et al., Channeling of high-energy particles in bent crystals – Experiments at
the CERN SPS, Nucl.Instr.and Methods in Physics Research B164-165 (2000) 27-43.
Radiation
Hardness
A list of papers (2)
 C.Biino et al., The influence of radiation damage on the deflection of high-energy beams in bent
Silcon crystals, CERN-SL-96-30-EA, published as EPAC 96:2385-2387
 G.Arduini et al., Deflection and extraction of Pb ions up to 33 TeV/c by a bent Silicon crystal,
Phys. Rev.Lett. 79 (1997) 4182-4185
LHC
NA48
Ions
 C.Biino et al., Deflection of 32.8 TeV/c fully stripped Pb ions by means of a bent Si crystal,
May 1999, Nucl.Instr.and Methods Phys.res.B 160 (2000) 536-543.
 U.Uggerhoj et al., On the reduced interaction probability for fully stripped 33 TeV/c Pb ions
channeled in a bent Si crystal, Nucl.Instr. and Methods Phys.Res. B194 (2002) 417-424.
 U.Uggerhoj et al., Strong suppression of nuclear-charge changing interactions for
18 TeV/c ions channeled through a bent crystal, Phys.Lett.B619 (2005) 240-246.
 N. Doble et al., A novel application of bent crystal channeling to the production of
simultaneous particle beams, Nucl. Instr. and Methods B 119 (1996) 181.
 C.Biino et al., The simultaneous and nearly-collinear Ko beams for experiment NA48,
Proceedings EPAC (Stockholm) 1998.
 H.W.Atherton et al., Crystal Channeling at the LHC, SL/EA/Note 90-06
Final remarks and conclusions
 The H8 beam line is an excellent tool for crystal studies and qualification
Its intrinsic divergence can be much smaller than the critical angle Yp
 Detailed studies of proton channeling could be done successfully in H8
with nice results and record deflection efficiencies for the full beam !
 A crystal has been irradiated in the T6 target to a beam of 5 1012 ppp
with a 0.8x0.3 mm2 FWHM spot size over a full SPS year.
A 31% loss of deflection efficiency was observed for 2.4 1020 p/cm2
 The H8 tests contributed to the development of a successful application
of a bent crystal in the simultaneous Ko beams for NA48.
The crystal performed very well over many years and has been
extremely stable. It never needed to be replaced.
 Ion channeling has been studied in H4 (could have been done in H8).
The channeling efficiency for Pb is similar as for protons, the outcoming
particles are mostly of the same species as the incoming beam.