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Polarized Neutron Technique Network in NMI3 Larmor precession devices M. Janoschek, S. Klimko, H. Lauter, R. Gähler, ILL Grenoble L.P. Regnault, CEA Grenoble. MUPAD  3D polarization analysis bunching of continuous polychromatic beams Larmor precession and reflectometry.
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Larmor precession devices
M. Janoschek, S. Klimko, H. Lauter, R. Gähler, ILL Grenoble
L.P. Regnault, CEA Grenoble
Intensities from nuclear Bragg peaks: Inuclear N*k Nk; NkFT{nuclear(r)};
Intensities from magnetic Bragg peaks: ImagneticM*k Mk; M k k s(k) k ;
s(k) FT{magnetic(r)};
magnetic structure factor
Iinter[N*k Mk+ M*k Nk] Pi;
Higher visibility of magnetic(r) by nucl.magn. Interf.:
Iinter depends on direction of incom. Polarisation Pi to magn. interaction vector Mk
The component of Mkalong Pi is measured.
Blume (1963) : calculation of polarisation Pf(Pi) for magnetic + nuclear scattering:
Pf= N*k NkPi  M*k Mk Pi + M*k ( Pi Mk ) + ( Pi M*k ) M k +
N*k Mk+ M*k Nk  i [ N*k Mk Nk M*k] Pi
Measuring direction and magnitude of Pf for few reflexes as function of of Pi
is avery efficient way to determine magnitude and direction of Mk .
This method requires B = 0 at the sample!
In practice, complete information on Mk is obtained from measuring
3 orthogonal components of Pffor 3 orthogonal components of Pi
top view
field free area
B 5 mG
two Meissner shields
nutator
ki
precession fields
nutator
secondary coil
primary coil
kf
zi
couplingcoil in
zi
i
yi
icoil
xi
zi
yi
i
sample
the action of each coil is
shown downstream of it !
No spin turn on scattering is assumed in the drawing !
xi
i coil
Field free area
2
zf
f = i  2
yf
xf
f
f
f coil
fcoil
zi zf
couplingcoil out
field direction
yf
zf
Neutron spin
Assume spin turns on scattering:
by s in the scattering plane set f coil to f = i  s+2
by s with respect to zaxis set fcoil to f =  i  s
yf
xf
side view
top view
opening for
cryostat
mumetal links
between cylinders
and coupling screens
outer mumetalscreen
inner mumetal
screen;optional;
B 5 mG
ki
B 5 mG
coil
mumetal shield
around all coils
to guide return fields
in lowfield region
coil;
DCcompensation of mean
vertical component of earth field;
likely superfluous
kf
couplingcoil;
How to avoid field from current Iz?
Al frame anodized
Cu contacts for return field
Iret
Open area 40 x 40
Al foil for
return current
Al wire 1
Iz
Mu metal yoke
Mu metal screen
Outer dimensions: 118 x 118 x 60
demagnetisation coils for all mumetal screens!
top view
He3 spin filter
in coil
coil
in coil
coil
ki
cryostat
 coil;
return field
for coil
couplingcoil
kf
kf
Mu metal for return field
L1
L2
Coherent
frequency splitting
Coherent reversal
of frequency splitting
d
0 + (s  e)
e
s
total energy
k + e/v;
0 + e
+ s
+ e
plane of detection
E0
i(kx  0t)
e
0 =
 e
k0  e/v;
0  e
0  (s  e)
+i(keL1  ksL2)
i(s  e)t
ke = e/v;
e
e
0
i(keL1  ksL2)
+i(s  e)t
ks = (s e)/v;
e
e
=
For eL1 = (s e)L2 , gets independent from v. beats in time with d= (s e)
detector
detector
L1
L2
Ce
Cs
Bfield
spin down
A
B = 0
P
d
fast
detectors
d
e
analyzer
s
spin up
B
coupling coil
Idet
IB
IA
1
IA = 1/2[cos d·td +1],
IB = 1/2[cos (d·td +)+1],
with IB + IA = 1;
td: time of arrival at A
d = 2(s  e).
time
T
replace analyzing mirror by RFcoil (resonance frequency F=2B; condition )
E T/2 in arrival time for spin up and spin down at the detector.
E = E·T/t v3 ·T(like in spin echo); T is fairly constant for a velocity band of 510%.
+
+

L1
L2
fast
detector
Ce
Cs
Bfield
P
B = 0
d
s
e
RFfield; F
Signal function after bunching
buncher: sequence of highfieldRFflippers
Idet
1
EF = 8B
EF = 8B
T
time
Intensity
Signal function after bunching
Necessary condition for overlap of both signals:
= f L2 / (mv3) with /4 = D
1
f : change of energy by the bunching flipper
For L=10m; =10Å; D = 2 1 MHz:
f = 0.8 108 eV;
f = 2 B; = 6.8 108 eV/T
T
time
I = cos2Dt
I = sin2Dt
I = cos2(Dt  /4) = sin2(Dt + /4)
The variation of k = k1  k2 due to f is not cancelled
by the MIEZE condition and leads to an extra phase
difference d between both waves at the detector.
2+f
1+f
f
2
1
f
This determines f as before.
2f
1f
State behind the bunching flipper: [ = (s  e)t]
sin (+d)
k1
k2
k
cos (d)
k1  k2 depends on f !
using ZETA at IN3
A) Offspecular scattering from polymermultilayer
B) Larmor pseudoprecession in reflection
Lf
ki
= 2.44 Å
Li Lfr Lfy
Lenghts Lf depend to first
order on scattering angle;
‘angular encoding’
Rf flippers arranged symmetrically w.r.t. ki