Polarized Neutron Technique Network in NMI3 Larmor precession devices

1. 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

2. A) Conventional magnetic scattering: Intensities from nuclear Bragg peaks: Inuclear N*k Nk; NkFT{nuclear(r)}; Intensities from magnetic Bragg peaks: ImagneticM*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.

3. B) Spherical neutron polarimetry Blume (1963) : calculation of polarisation Pf(Pi) for magnetic + nuclear scattering: Pf= N*k NkPi - 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

4. Cryopad principle top view field free area B  5 mG two Meissner shields nutator ki precession fields nutator secondary coil primary coil kf

5. Eddy’s D3

7. Mupad, 3-coil version zi coupling-coil in zi i yi  i-coil 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  f-coil zi  zf coupling-coil 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 z-axis  set  f-coil to  f = - i -  s yf xf

8. MUPAD: general setup side view top view opening for cryostat mu-metal links between cylinders and coupling screens outer mu-metal-screen inner mu-metal -screen;optional; B  5 mG ki B  5 mG -coil mu-metal shield around all coils to guide return fields in low-field region  -coil; DC-compensation of mean vertical component of earth field; likely superfluous kf coupling-coil;

11. Design of new coils, goal: outer field integral < 1/1000 of inner field integral 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 mu-metal screens!

16. Mupad for 2D- analysis top view He3 spin filter in -coil  -coil in -coil -coil ki cryostat - -coil; return field for -coil coupling-coil kf kf Mu metal for return field

17. Bunching of continuous polychromatic polarized beams without loss of intensity

18. MIEZE - Principle 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

19. MIEZE (without bunching!) using transmitted and reflected beam after analyser L1 L2 Ce Cs B-field  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

20. II) MIEZE setup with bunching using the full beam replace analyzing mirror by RF-coil (resonance frequency F=2B;  -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 5-10%. + + - L1 L2   fast detector Ce Cs B-field   P B = 0 d s e RF-field; F Signal function after bunching buncher: sequence of high-field-RF-flippers Idet 1 EF = 8B EF = -8B T time

21. Estimate of the necessary energy chances ffor bunching: 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 10-8 eV; f = 2 B;  = 6.8 10-8 eV/T T time I = cos2Dt I = sin2Dt I = cos2(Dt - /4) = sin2(Dt + /4)

22. Quantum-mechanical view of bunching; there is no classical view of it!  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. 2-f 1-f State behind the bunching flipper: [ = (s - e)t]  sin (+d) k1 k2 k  cos (-d) k1 - k2 depends on f !

23. Application of bunching • MIEZE at SANS instruments (no analyzer near sample) • SPAN-like NRSE spectrometer with very high resolution?

24. 3) Larmor precession and reflectometry using ZETA at IN3 A) Off-specular scattering from polymer-multilayer B) Larmor pseudo-precession in reflection

25. Mono SEU1 sample* SEU2 Ana Det (CCD camera) 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