1. Magnetic Compensation Issues
Eucard workshop: Search for the electron EDM in an electrostatic storage ring: September 2015
Dr. Helmut Soltner, ZEA-1

2. Magnetic Compensation Issues
Cancellation Techniques
Passive Magnetic Shielding
Active Magnetic Shielding
Differential Methods – Gradiometry
Summary

3. high-permeability materials: concentration of flux density
B. Meyer, Wikipedia

4. High-permeability materials: concentration of flux density vs
High-permeability materials: concentration of flux density vs. shielding
Shielding Factor S = (B field without shielding) / (B field with shielding)
Shielding by a hollow sphere
Simple reasoning
use high permeable material
use a thick wall
avoid holes
linear material
seamless (no feedthroughs etc.)
Use multiple shields
Source: J.D. Jackson: Classical Electrodynamics
Koski, A., and S. L. Wipf. "Magnetic shielding of an accelerator
beam using passive ferromagnetic material." Magnetics,
IEEE Transactions on 32.4 (1996):

5. High-permeability materials: concentration of flux density
Control the magnetic properties of the openings in your shield!
Rikitake, Tsuneji. "Magnetic shielding by a spherical shell having a hole (1).“
Journal of geomagnetism and geoelectricity (1990):

6. High-permeability materials: concentration of flux density
Real materials have a nonlinear B(H) relationship: µr decreases for higher fields

7. High-permeability materials: companies
Companies and their materials
Vacuumschmelze Hanau Germany µ-metal
Amuneal Manufacturing Company USA amumetal
IMEDCO AG Switzerland
Magnetic Shield Corp. USA Netic-Conetic
AK Steel GmbH Germany ARMCO®
Thyssen Krupp Germany Magnifer®
The MuShield Company USA
Magnetic Shield Limited GB
Holland Shielding Systems BV NL …
Treatment of metal sheets:
Anealing at higher temperatures at 800 °C to 1170 °C in vacuum or hydrogen
Slow cool down

8. High-permeability materials: properties
Material preparation and application ranges
Magnetic Shield Corporation

9. Shielding … of what (source or measurement device)
Shielding … of what (source or measurement device)? … against which type of fields? … for which application (to which level)?
Specifications:
type of field:
static (geomagnetic?)
dynamic (line frequency?)
gradient
field component
mirrored field
application:
MCG - MEG
NSE
electromagnetic compatibility (EMC)
EDM
Electric devices
(motors, photomultipliers etc.)
transformers

10. Spectral density of various magnetic fields
Malmivuo, J., et al. "Improvement of the properties of an eddy current magnetic
shield with active compensation." Journal of Physics E: Scientific Instruments 20.2 (1987): 151.

11. The geomagnetic field is not a truly static one.

12. Ultimate limitation: Noise by charge carriers in conductors
Flux noise due to proximity of metal sheet
A.Montsch,Diploma thesis, FZ Jülich, 1996
Varpula, Timo, and Torsti Poutanen. "Magnetic field fluctuations
arising from thermal motion of electric charge in conductors.“
Journal of applied physics (1984):

13. Shielding factor as a function of frequency for JMSR
Additional
aluminum layer! Al
µ-metal
µ-metal
Davidson, C. R., et al. "Design of a Magnetically Shielded Room for
Development of HTS SQUID Systems for Magnetocardiography."
Biomag 96. Springer New York,

14. Prof. Heil‘s group at JMSR – Xe EDM

15. Line frequency disturbances in the JMSR at PGI 8

16. MCG – MEG recorded in shielded rooms

17. BMSR-2: 7 layers of high-permeability material
Bork, J., et al. "The 8-layered magnetically shielded room of the PTB: Design and construction.
"Biomag2000, Proc. 12th Int. Conf. on Biomagnetism. Espoo, Finland, 2001.

18. A shielded room for nEDM reseach at TUM
Altarev, I., et al. "A magnetically shielded room with ultra low residual field and gradient.“
Review of scientific instruments 85.7 (2014):

19. A shielded room for nEDM reseach at TUM
7-layer BMSR
6-layer BMSR
Boston 3-layer MSR
Ak3b MSR by Vacuumschmelze
Degaussing with surrounding coils
Altarev, I., et al. "A magnetically shielded room with ultra low residual field and gradient.“
Review of scientific instruments 85.7 (2014):

20. Shielded room at SNS for neutron research
Double-layer µ-metal shield for NSE at SNS in Oak Ridge, TN
Soltner, Helmut, et al.
Nuclear Instruments and Methods in Physics Research Section A:
Accelerators, Spectrometers, Detectors and Associated Equipment (2011):

21. Shielded room at SNS for neutron research
Neutron spin echo spectrometer
Soltner, Helmut, et al.
Nuclear Instruments and Methods in Physics Research Section A:
Accelerators, Spectrometers, Detectors and Associated Equipment (2011):

22. Shielding of an accelerator beam
Combination of passive and active shielding for the HERA electron beam
Koski, A., and S. L. Wipf. "Magnetic shielding of an accelerator
beam using passive ferromagnetic material." Magnetics,
IEEE Transactions on 32.4 (1996):

23. Cancellation Techniques: active shielding
Coils and feed-back by reference sensor
Platzek, D., et al. "Active shielding to reduce low frequency disturbances in direct current
near biomagnetic measurements." Review of scientific instruments 70.5 (1999):

24. Cancellation Techniques: active shielding
Commercial systems are available

25. Cancellation Techniques: gradiometry
Careful adjustment of redundant sensors and signal filtering
can make shielding (ative or passive) obsolete
Tavrin, Y., et al. "A second-order SQUID gradiometer operating at 77 K." Superconductor Science and Technology 7.5 (1994): 265

26. Use superconductors as magnetic shielding?
Koike, Atsushi, et al. "Magnetic Shielding Effect of Bi Oxide Superconducting Vessels with a SQUID.“
Advances in Superconductivity III. Springer Japan,
Ishikawa, Yuuichi, et al. "Magnetic Shielding in High-Tc Bi-Pb-Sr-Ca-Cu-O
Superconducting Cylinder.“Advances in Superconductivity IV. Springer Japan,

27. Magnetic cancellation techniques: summary
Magnetic fields can be cancelled by several methods
passive shielding (high-permeability, high conductivity
materials surrounding the experiment)
active shielding (feed back to coils generating counter-fields)
differential methods

28. Thank you for listening!