EM FIELD SIMULATIONS FOR - indico.slac.stanford.edu
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EM FIELD SIMULATIONS FOR Chiara Salemi, MIT DM Radio + ABRACADABRA First Collaboration Meeting 24 Jan 2020 +
Transcript of EM FIELD SIMULATIONS FOR - indico.slac.stanford.edu
EM FIELD SIMULATIONS FOR
Chiara Salemi, MITDM Radio + ABRACADABRA First Collaboration Meeting24 Jan 2020
+
OUTLINE
WHY— the need for field simulations
WHAT— an assortment of calculations
HOW— EM simulation software
2
WHY
the need for field simulations
3
UNDERSTANDING OUR SENSITIVITY
4
DAQ
Axion Effective Current Pickup
SQUID Magnetometer
UNDERSTANDING OUR SENSITIVITY
5
DAQ
Axion Effective Current Pickup
SQUID Magnetometer
SQUID response
UNDERSTANDING OUR SENSITIVITY
6
DAQ
Axion Effective Current Pickup
SQUID Magnetometer
Axion interactions in magnetic field
UNDERSTANDING OUR SENSITIVITY
7
DAQ
Axion Effective Current Pickup
SQUID Magnetometer
Coupling between axion current and pickup circuit
UNDERSTANDING OUR SENSITIVITY
8
DAQ
Axion Effective Current Pickup
SQUID Magnetometer
Impedance in pickup circuit
WHAT
an assortment of calculations
9
WHAT CAN WE MEASURE?
C. Salemi 10
axion effective current in toroid
induced real current in pickup
norm
(cur
rent
)
WHAT CAN WE MEASURE?
§ Coupling between axion effective current and pickup
§ Self inductance of pickup
§ Parasitic impedance in wiring
§ …
C. Salemi 11
axion effective current in toroid
induced real current in pickup
norm
(cur
rent
)
BASICS OF HOW TO CALCULATE
• Mutual inductance (current ratio)
• Enforce current through magnet volume (proportional to B field)
• Measure current in pickup
• Self inductance
• Enforce current through pickup
• Use
12
L = 2
ZWm
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WIRE LOOP(ABRA RUN 1)
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• Current ratio ~ 0.11
• Self inductance ~ 100 nH
• Calculable analytically
• Confirms COMSOL calculation
B z
pickup wire
superconducting shield
magnet toroid
CYLINDER(ABRA RUN 2)
14
• Coupling ~7x higher than with wire loop
• Current ratio ~ 0.74
• Reduces inductance in pickup circuit by ~5x
• Self inductance ~ 20 nH
B z
pickup cylinder
SHEATH(FUTURE)
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• Optimal coupling between axion effective current and pickup (current ratio = 1)
• 10x better than wire loop!
• Difficult engineering
• Construction
• Access
B z
pickup sheath
HOW
EM simulation software
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HOW DO FINITE ELEMENT SOLVERS WORK?
COMSOL MULTIPHYSICS
• Commercial finite element modeling software
• $$$, but UNC has licenses
• Helpful support team
• Can link together various physics modules (EM, mechanical, CAD imports, …)
• Include vibration?
• Automatic meshing
• Allows precise field modeling for complex geometries, but…
• Not good at large aspect ratios/large scale differences: wire windings are hard
• Complex 3D systems are hard/slow
18
axion effective current in ABRACADABRA-10cm toroid
THERE ARE MANY OTHER OPTIONS
• ANSYS HFSS• Designed for high frequency antenna design
• Only EM
• Kassiopeia• Designed for particle tracking in EM fields for Project 8 experiment
• Doesn’t really do AC
• Boundary element method (BEM)
• Opera• Primary applications are magnets, motors, etc.
• EM and electromechanical in 2D and 3D
• ANSYS Maxwell, FastHenry, …
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(that I don’t know as much about)
probably not
maybe!
SUMMARY
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To determine our sensitivity we
must fully understand the effective circuit from axions to
DAQ
DAQ
SUMMARY
21
To determine our sensitivity we
must fully understand the effective circuit from axions to
DAQ
This can be achieved with finite element
modeling of the system’s EM fields
SUMMARY
22
To determine our sensitivity we
must fully understand the effective circuit from axions to
DAQ
This can be achieved with finite element
modeling of the system’s EM fields
We have modeled and tested the ABRA-10cm setups and
demonstrated the usefulness of this
method
SUMMARY
23
To determine our sensitivity we
must fully understand the effective circuit from axions to
DAQ
This can be achieved with finite element
modeling of the system’s EM fields
We have modeled and tested the ABRA-10cm setups and
demonstrated the usefulness of this
method
Simulations will continue to be necessary to optimize the sensitivity of
future generations
BACKUP
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ERROR AND CHECKS
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• Is this even right?
• Compare to analytic calculations where possible (e.g. twisted pair, simple wire pickup loop, …)
• How precise is COMSOL anyway?
• Vary parameters to see effects (e.g. conductivity, geometry, boundary conditions, …)
Wire Diameter (mm)
COMSOL inductance,
surface current (nH)
Analytical inductance,
surface current (nH)
COMSOL inductance,
volume current (nH)
Analytical inductance,
volume current (nH)
0.5 112.5 112.8 118.8 119.1
1 95.0 95.3 101.3 101.6
2 77.5 77.8 83.8 84.1
Example: Simple pickup loop geometry self inductance
PARASITIC IMPEDANCE
§ Must particularly consider the parasitic inductance in the system
§ Twisted pair wire between pickup and SQUID input a major contributor
C. Salemi 26
superconducting shielding
NbTi wires
PARASITIC IMPEDANCE
• For a realistic configuration, simulations give 0.48 µH/m and 29 pF/m
• Wire diameter: 0.075 mm
• Insulation thickness: 0.08 mm
• Shield inner radius: 0.5 mm
• Conductivity: varied [107,1025]
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