Magnetic Field Imaging using Polarized Pulsed Neutrons at J-PARC

J-PARC, JAEA Takenao Shinohara

JAEA　K. Sakai, T. Kai, M. Harada, K. Oikawa, M. Ohi, F. Maekawa,

J. Suzuki, S. Takata, K. Aizawa, M. Arai, M. Kureta, M. Segawa

Hokkaido Univ. Y. Kiyanagi

PNCMI 2010, 05-08 July 2010, Delft, The Netherlands

Neutron Imaging with Pulsed Neutrons

Origin of contrast Attenuation by Absorption or ScatteringChange in Polarization, ...

Neutron Imaging

neutron technique to observe the internal structure of materials in real space by taking an image of neutron transmission.

Imaging of magnetic field

“Energy-resolved neutron imaging”

Usage of pulsed neutrons

Energy dependence can be obtained efficiently and precisely by TOF method.

PNCMI 2010, 05-08 July 2010, Delft, The Netherlands

Wide energy range neutrons can be available.

Suitable for the

Magnetic Field Imaging

(Nature Physics, vol.4, pp399-403, (2008))

d

dtS!(t) =

gµN

h̄[S(t) ! B(t)]

!, ! = x, y, z

! = "Lt =#L

$

!path

Bds

!L =gµN

h̄B = "LB

Change of neutron spin direction in a magnetic field

Polarizer Analyser

RotationMagnetic Fieldneutron

Detector

Usage of polarized neutrons

A change in the neutron spin is detected as a change in polarization

HZB group

Spin rotation angle by Lamor precession

Rotation angle apparently depends on the neutron velocity.

Study of wavelength dependence gives more information.

PNCMI 2010, 05-08 July 2010, Delft, The Netherlands

Wavelength dependence can be obtained with good resolution and efficiency.

Usage of polarized pulsed neutrons

Pulsed neutrons are suitable for magnetic imaging technique.

Path integrals of magnetic field can be evaluated.

Short wavelength neutron is good for large magnetic field.

We performed magnetic field imaging experiments using polarized pulsed neutrons at J-PARC

Obtaining wavelength dependence of polarization with high efficiency

Magnetic Field Imaging with Pulsed Neutrons

Advantage 1.

Advantage 2. Wide wavelength range is available.

Long wavelength neutron is good for small magnetic field or sensitive measurements.

Quantitative treatment of magnetic field

PNCMI 2010, 05-08 July 2010, Delft, The Netherlands

Experimental Set Up

Beam Line：BL10

Polarizer/Analyzer：Stacked Bent Magnetic Super Mirrors

Spin Flipper：AFP type　　　　（RF field：173kHz, ~20G)

2D detector：5 inch-PSPMT(scintillator：ZnS(Ag)/6LiF 0.25mm-t)(Δx,Δy=~1mm, Δt=0.5msec)

(Beam Power：16kW, 120kW)

Beam Size：20mm(H) x 10mm(W)Exposure Time：~30 min. for one measurement (50,000 pulses)

Sample：Solenoid Coil (diameter : 5mm)

PNCMI 2010, 05-08 July 2010, Delft, The Netherlands

BL10 NOBORU as a Test Port

PNCMI 2010, 05-08 July 2010, Delft, The Netherlands

Obtained Polarization

Polarization degree : about 95% @λ>6Å

Oscillation is due to the inhomogeneity in efficiency of Spin Flipper.

K. Sakai

Neutron Intensity Distribution（S.F. = OFF）

Distribution of Polarization

P =NOFF ! NON

NOFF + NON

polarization was defined as

Neutron Intensity Distribution（S.F. = ON）

PNCMI 2010, 05-08 July 2010, Delft, The Netherlands

Solenoid coil

I=0.0A

I=1.8A

Decrease of polarization was seen at the position of the solenoid.

Visualization of magnetic field

We can know where the magnetic field is.

Neutron Intensity Distribution（S.F. = OFF）

Distribution of PolarizationNeutron Intensity Distribution（S.F. = ON）

PNCMI 2010, 05-08 July 2010, Delft, The Netherlands

Wavelength dependence

Using TOF method, we can get series of images by a couple of measurements (S.F. on/off).

PNCMI 2010, 05-08 July 2010, Delft, The Netherlands

Quantification of the magnetic field strength

Normalization by Polarization@I=0.0A

Pi/P0 ! cos !

! = "Bt = "BL#

3956

By fitting the wavelength dependence of polarization with sinusoidal function, the path integrals (BL) can be evaluated.

For I>0.6A, fitting by a sinusoidal function can be done successfully.

BLmin<4x10-6[Tm]

Polarized pulsed neutrons can be used for the quantification of magnetic field.

Sinusoidal oscillation

Β=2.2mT/A

PNCMI 2010, 05-08 July 2010, Delft, The Netherlands

Magnetic field directionMagnetic field direction can be also analyzed by the wavelength dependence of polarization.

Tilted solenoid coil was used as the sample

neutron

Applied Current I = 2.5A

Distribution of Polarization

Guide Field Direction

Guide Field Direction

|α| = 47.1±1.8deg.

|α| = 48.6±1.9 deg.

B

amplitude

offset

Tilt angle α of magnetic field can be evaluated from the oscillation amplitude and the offset of oscillation center.

α

PNCMI 2010, 05-08 July 2010, Delft, The Netherlands

3D magnetic field analysis

Tuning neutron spin direction tree-dimensionally by XY direction coils and solenoids (Z direction) and analyze it.

Combination with the CT techniqueThree-dimension for magnetic field vectorThree-dimension for spatial distribution

total analysis of magnetic field

PNCMI 2010, 05-08 July 2010, Delft, The Netherlands

Quantitative treatment of magnetic field strength was confirmed for a simple example.

To understand the magnetic field vectorially, neutron spin analysis is necessary.

Testing 2D magnetic field analysis

Setup for 2D analysis

guide field by permanent magnet

sample

PNCMI 2010, 05-08 July 2010, Delft, The Netherlands

New Imaging Beam Line at J-PARC

Evaluate the physical quantities of materials, and Visualize them in real space.stress, texture, microstructures, chemical composition, temperature, ...

Magnetic field in/outside of materials or space is also regarded as an important object for our pulsed neutron imaging study.

BL22

29m

15m

24m

BL22

A new beam line dedicated to the pulsed neutron imaging was proposed to J-PARC.“Energy-Resolved Neutron Imaging System (ERNIS)”

Neutron polarization/analysis is a key technique.

2nd experimental hall

PNCMI 2010, 05-08 July 2010, Delft, The Netherlands

Summary

We have performed magnetic field imaging experiments using polarized pulsed neutrons at BL10 of MLF in J-PARC.

The possibility of quantitative analysis of magnetic field using polarized pulsed neutrons was confirmed.

Detector selection is a difficult problem.

Introduction of the CT technique is planned.

Application to magnetic materials or super-conducting materials will start this year.

Sufficient resolutions both in spatial and time are necessary.

Three-dimensional full spin analysis for the reconstruction of magnetic field vector is under the test.

PNCMI 2010, 05-08 July 2010, Delft, The Netherlands

Thank you for your attention