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A Low-Noise Current Supply for an Electron Electric Dipole
Moment Experiment
APPROVED BY:
_______________________________
Daniel J. Heinzen, Supervisor
_______________________________
Melvin E. L. Oakes, Honors Advisor
A Low-Noise Current Supply for an Electron Electric Dipole
Moment Experiment
by
Daniel Borrero Echeverry
UNDERGRADUATE HONORS THESIS
Presented to the Faculty of the Department of Physics of
The University of Texas at Austin
in Partial Fulfillment
of the Requirements
for
SPECIAL DEPARTAMENTAL HONORS
THE UNIVERSITY OF TEXAS AT AUSTIN
May 2005
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A Low-Noise Current Supply for an Electron Electric Dipole
Moment Experiment
Daniel Borrero Echeverry
The University of Texas at Austin, 2005
Supervisor: Daniel J. Heinzen
We designed and built a custom current supply for use in an electron electric
dipole moment experiment. This supply will be used to drive a set of magnetic field coils
in the experimental apparatus. Based on a design used at the University of California,
Berkeley in earlier electron EDM measurements, our supply sources 140mA of current
with a measured noise level of 16 nA Hz at 0.05 Hz, although this measurement may
be too high due to the limitations of the measurement equipment. This noise level is
consistent the desired level of precision ( 10 -29 e cm ) in the electron EDM measurement,
but we believe that this noise level could be improved with further work.
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Table of Contents
Title Page ........................................................................................................................ 2
Abstract ........................................................................................................................... 3
Table of Contents ............................................................................................................ 4
List of Figures ................................................................................................................. 5
Background ..................................................................................................................... 6
Why an Electron EDM implies T-violation ................................................................ 6
T-Violation Experiment at UT .................................................................................... 7
Magnetic Field Noise .................................................................................................. 9
Design ........................................................................................................................... 12
Current Source .......................................................................................................... 12
Vishay VHP-3 Bulk Metal Foil Current Sensing Resistor ....................................... 14
Linear Technology LTZ1000 Ultra-Precision Reference ......................................... 16
Construction .................................................................................................................. 19
Noise Measurement ...................................................................................................... 20
Results ........................................................................................................................... 22
Summary ....................................................................................................................... 24
References ..................................................................................................................... 25
Appendix A: Final Construction Notes..........................................................................27
Appendix B: Operation ................................................................................................. 29
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List of Figures
1 The electron EDM in various unified theories ........................................................ 7
2 An electron with an EDM in magnetic and electric fields ...................................... 8
3 Line splitting of an electron with an EDM ............................................................. 8
4 An electron with an EDM under time reversal ....................................................... 8
5 Line splitting of an electron with an EDM under time reversal ............................. 8
6 Experimental test chamber ...................................................................................... 9
7 Current supply circuit diagram ............................................................................. 13
8 Voltage reference circuit diagram ......................................................................... 17
9 Temperature control circuit diagram .................................................................... 18
10 Temperature compensated voltage reference circuit diagram .............................. 19
11 Complete current supply circuit diagram .............................................................. 20
12 Measurement setup ............................................................................................... 21
13 Labview data acquisition and processing script.................................................... 22
14 LTZ1000 noise signature ...................................................................................... 23
15 LTZ1000 noise spectrum ...................................................................................... 24
16 Current supply noise spectrum.............................................................................. 24
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Background
The Standard Model is perhaps the greatest triumph of modern physics. It
accounts for all observed phenomena and has been tested to great levels of accuracy. The
Standard Model even accounts for certain time reversal asymmetries like those found in
kaon decays 1. In doing so, it puts a bound on other T-violating phenomena, one of which
is the T-violating electric dipole moment (EDM) of the electron de. The Standard Model
predicts an electron EDM of the order of 10-38 e