Research Magnets with High-Field Uniformity

Abstract

Magnets with good field uniformity in a good-field region (GFR) of a certain volume are of interest for various research and calibration applications. Due to their simplicity and relatively low cost, Helmholtz coils have been the preferred magnet system for such projects. With air cooling, the magnetic flux density possible with Helmholtz coils is limited to typically 1 mT or below, and field uniformity in the GFR is about one percent. A novel design based on Maxwell and patented double-helix (DH) or Constant-Cosine-Theta (CCT) winding configurations offer better field uniformity in the GFR (order of 1x10-4) and enable much higher levels of flux density due to a much higher transfer function. The novel systems can reach flux density levels of 10 mT with air cooling based on a cooling design in which all parts of the conductor are in direct contact with the airflow. The systems can be built with one, two or all three magnetic axes. The coil configurations and complete designs of such systems with superior performance than Helmholtz coils are presented.

Full text

Abstract
Magnets with good field uniformity in a good‐field region (GFR) of a certain volume are of interest for various research and calibration applications. Due to their simplicity and relatively low cost, Helmholtz coils have been the preferred
magnet system for such projects. With air cooling, the magnetic flux density possible with Helmholtz coils is limited to typically 1 mT or below, and field uniformity in the GFR is about one percent. A novel design based on Maxwell and
patented double‐helix (DH) or Constant‐Cosine‐Theta (CCT) winding configurations offer better field uniformity in the GFR (order of 1x10‐4) and enable much higher levels of flux density due to a much higher transfer function. The
novel systems can reach flux density levels of 10 mT with air cooling based on a cooling design in which all parts of the conductor are in direct contact with the airflow. The systems can be built with one, two or all three magnetic axes.
The coil configurations and complete designs of such systems with superior performance than Helmholtz coils are presented.
SpaceExploration,Multi‐AxesMaxwellCoilConfigurationSpaceExploration
AdvancedMagnetLab MT26
MEINKERainer,BAHADORIReza,ARAVINDAKSHANTa
Monte‐CarloParametricStudyonField
Uniformity
ConstantCosineTheta(CCT)CoilConfiguration
ContactInformation:
BAHADORI,RezaiswithiswiththeAMLSuperconductivityandMagnetics.(email:rbahadori2013@my.fit.edu).
MEINKE,RaineriswiththeAMLSuperconductivityandMagnetics. (e‐mail:rbmeinke@amlsm.com).
Aravindakshan,TAiswithFloridaInstituteofTechnology,UnitedStates(email:athirumalaia2015@my.fit.edu).
DesignVariables: Variable Range Length ofvariablerange
AWG ଵଵ
BigRadiusofEllipsoid ଶଶ
SmallRadiusofEllipsoid ଷଷ
NumberofTurnsRing1 ସସ
NumberofTurnsRing2 ହହ
NumberofTurnsRing3 ଺଺
XpositionofRing1 ଻଻
XpositionofRing2 ଻଼
XpositionofRing3 ଽଽ
NumberofLayersRing1 ଵ଴ ଵ଴
NumberofLayersRing2 ଵଵ ଵଵ
NumberofLayersRing3 ଵଶ ଵଶ
Totalnumberofconfigurations: ௜
௜ୀଵଶ
௜ୀଵ
Figure1.VariablesContributinginSpaceExplorationofAMaxwell
CoilSystem
The Maxwell equation suggest that best field uniformity appears in the center of a coil with ellipsoidal or spherical shape. An space
exploration a design study has been developed to calculate the field uniformity the center of a coil with spherical or cylindrical shape.
1stAxis‐‐‐ 6MaxwellRings
Specifications/DesignGoals
NumberofAxes DiameterofSphericalGFR FieldUniformity FieldStrength Lengthof Coil DiameterofCoil
3 50[mm] <1e‐4 10 [Gauss] <250[mm] <200[mm]
[mm]
[mm]
[mm]
[mm]
[mm]
[mm]
[mm]
[mm]
[mm]
Axis1 Axis2 Axis3
[mm]
[mm]
[mm]
[mm]
1st Axis
3rd Axis
2nd Axis
GFR
Specifications/DesignGoals
Number
ofAxes
Dimension of GFR Field
Uniformity
Field
Strength
Lengthof
Coil
Diameter
ofCoil
3 20x20x20[mm] <1e‐3 10 [Gauss] <250[mm] <90[mm]
•Constant‐Cosine‐Theta:
•Multi‐Axis,
•LargeAccessSize
SideView
Figure6.EffectofradiusofcylinderandlengthofcylinderinaCCTcoilconfigurationonthefielduniformitywith
20x20x20mmdimensionatthecenterofthecoil
Figure2.ThreeAxesMaxwellCoilSystem– DesignParametersforEachIndividualAxis
Figure3.ThreeAxesMaxwellCoilSystem– AssemblyConfigurationandMechanicalSupportDesign
Figure5.ThreeAxesCCT/SolenoidCoilSystem
Figure4.CCTCoilConfiguration
Emergingthe
CPU/GPUbased
parallelcomputing
machines.
Employing
probabilisticmethods
suchasMonte‐Carlo.
AMLhasdevelopeda
softwarecalled
“CoilCadTM”tomodel
varioustypesofcoil
systemsandperformall
calculationsrelatedto
Electromagnetsdesign
includingfielduniformity.
Monte‐CarloSpaceExploration
calculatefielduniformityinspecifiedGFRfora
randomlyuniformdistributionoutofallpossible
configurationsinareasonabletime
Obstacles:
•Large number of variables
contributing in the field
uniformity
•Difficult to find the best
possible combination of
variable by means of
experience.
•It is impractical to run all
possible configurations (Time‐
Consuming Simulation and
lack of memory)