Transcript hendrickson

Superconductivity
and the
Cosmic Microwave Background
Karl Franz Flasch Hendrickson
Truman State University
Kirksville, Missouri
REU 2003
Or
The Taming of the SQUID
The CMB: A Brief Review
What we’ve seen:
“What next?”
The Detection Method
Bolometric Detectors
Transition Edge Sensor (TES)
Bolometers
Two issues:
“Wait! Didn’t he say something
about superconductors?”
1) Stray Magnetic Fields
2) Readout
Those Mangy Magnetic Fields
Problem: Stray Magnetic Fields will produce too much current for the Superconductor
Sources:
•Earth’s Magnetic Field
•Detector wiring
•Refrigeration System
Solution?
The Meissner Effect:
A metal in the
superconducting state
never allows a magnetic
flux density to exist in
its interior.
“Theory Schmeory…”
Magnetic Shielding Test
“What inside
this Dewer
anyway?”
What’s in the Dewar?
“Cool!, how did it go?”
Magnetic Shielding Test Results
Hall Probe Shielding Test
0.075
T~35K
T~4K
T~210K
0.07
Linear (T~35K)
Linear (T~4K)
Hall Probe Voltage (V)
Linear (T~210K)
0.065
y = -0.0007x + 0.0649
y = -0.0007x + 0.0713
0.06
y = -0.00007x + 0.05718
0.055
0.05
0
5
10
15
20
Power Supply Voltage (V)
Strength of field shielded: 2.3 mT
Earth’s B-Field: 0.04 mT
SQUIDs:
Superconducting Quantum
Interference Devices
What is it?
•A ring of superconducting metal
•Total flux through loop stays constant
Advantages:
•Sensitive to magnetic fields
producing a change in one flux
quanta: F0
•Lowest noise Ammeter possible
“How does it work
with Bolometers?”
SQUIDs and Bolometers
Rs – Shunt Resistor
Rb – Bolometer
C – Capacitor Filter
Rs<<Rb
Vout = CsIext
Cs is SQUID specific
“So, how did it go?”
SQUIDs and Bolometers: Results
Rs=6.2±0.6[10%] m  Ω
Rb=24±2[10%] m 
Ω
After much struggle…
Trial Bolometer Resistance
A
B
C*
212[10%]m
242[10%]m
242[10%]m
“Now what?”
SQUIDs and Bolometers:
The Next Step
•Bias the bolometer with AC Voltage
•Use a lock-in amplifier to read
•Read multiple Bolometers with a single SQUID readout
“Did you do this all by yourself ?”
Acknowledgements
•Dr. Peter Timbie, Advisor
•Dr. Shafinaz Ali and Dr. Jean-Marc Duval, Post-Docs
•Peter, Seth and Ben
•The Rest of the Observational Cosmology Group
•Dr. Charlie Silver, former ObCos Post-Doc
References
•UW Observational Cosmology: http://cmb.physics.wisc.edu/
•Wayne Hu’s CMB Page: http://background.chicago.edu/~whu/
•UW X-Ray Lab’s TES page: http://wisp11.physics.wisc.edu/xray/
•Rose-Innes, A.C. and Rhoderick, E.H. Introduction to
Superconductivity. 2nd Ed. Pergamon:Oxford, 1978.
•Star Cryoelectronics – Mr. SQUID User’s Guide