FY2010 - Oak Ridge National Laboratory

Director’s R&D Fund—
Science for Extreme Environment: Advanced Materials and Interfacial Processes for Energy
known to have negligible EDM (e.g., 3 He). Next-generation experiments aim to improve our knowledge
of the neutron EDM by two orders of magnitude. One proposed technique utilizes a superthermal process
to generate UCNs in superfluid 4 He. Polarized 3 He is simultaneously introduced into the 4 He and serves as
a frequency monitor (through the spin-dependent cross section) and as a co-magnetometer. The 4 He also
serves as a scintillating medium, converting the neutron/ 3 He reaction products into a detectable light
signal, and is believed to have a very high dielectric strength. This technique has several challenges
directly related to the large-scale low-temperature requirements. We are preparing a series of
measurements and calculations designed to address these challenges.
Measure the dielectric breakdown strength of liquid helium
Demonstrate injection of polarized 3 He into a volume of 4 He
Demonstrate movement of 3 He between volumes using heat currents
Design thermally conductive links to allow a large-scale apparatus to be cooled down with a dilution
refrigerator and maintain appropriate temperature gradients
Mission Relevance
A significantly more precise measurement of the neutron EDM is a high priority for nuclear physics. This
is because such a measurement would greatly improve our understanding of the “Baryon Asymmetry of
the Universe,” the fundamental, yet unexplained observation that matter exists. The importance of
improving the measurement of the neutron electric dipole moment is documented in long-range plans for
the nuclear physics community issued by the Nuclear Science Advisory Committee, and in performance
milestones accepted by the DOE Office of Nuclear Physics. In addition, one of the primary motivations
for the construction of the Fundamental Neutron Physics Beamline at the Spallation Neutron Source was
that it would provide a source of neutrons necessary to carry out world-class measurement of the neutron
electric dipole moment.
Results and Accomplishments
In the last fiscal year, the author participated in the operation in combining a dilution refrigerator (DUC)
and a high-voltage (HV) test facility in order to measure the dielectric strength in superfuild 4 He at
temperatures below 1 K at Los Alamos National Laboratory. Several technical issues have been identified
on these systems. Meanwhile, the scope of the HV test was expanded substantially to include several
experiments such as testing the electrode coating, effect of leakage current, impact of dielectrics, and
SQUID effects in high electric field. The expanded HV tests require temperatures between 0.6 K to 1 K.
The Experiments 2 and 3 in the list above also require temperatures around 0.35 K to be facilitated by the
DUC. In order to move forward with these two experiments, which were originally planned to follow the
HV test, the author is constructing a second low-temperature system at the MIT Bates Laboratory, which
will be dedicated to HV tests in the near future.
During the last year the author also developed a unique design for a high-power dilution refrigerator that
can effectively cool a large volume of liquid helium to 0.3 K for generating 8.9 Å neutrons via
superthermal technique in the ultra cold neutron experiments.
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