75 research outputs found
A low-noise ferrite magnetic shield
Ferrite materials provide magnetic shielding performance similar to commonly
used high permeability metals but have lower intrinsic magnetic noise generated
by thermal Johnson currents due to their high electrical resistivity.
Measurements inside a ferrite shield with a spin-exchange relaxation-free
atomic magnetometer reveal a noise level of 0.75 fT Hz^(-1/2), 25 times lower
than what would be expected in a comparable mu-metal shield. The authors
identify a 1/f component of the magnetic noise due to magnetization
fluctuations and derive general relationships for the Johnson current noise and
magnetization noise in cylindrical ferromagnetic shields in terms of their
conductivity and complex magnetic permeability.Comment: 4 pages, 3 figures. Published in Appl. Phys. Lett.; replacement
reflects published wor
Constance mirror program: Progress and plans
The current state of the mechanics of the Constance II experiment, the physics results gathered, the motivation background, and future plans for the Constance II experiment are reviewed. Several improvements have been made and several experimental investigations have been completed. These include the construction/installation/testing of: (1) liquid-nitrogen cooled, Ioffe bars installed, (2) a diverter coil (3) the 100 kW ICRF generator, (4) the data acquisition system, and (5) the optimum hot-iron operation of the machine with Titanium and pulsed-gas plasma guns. Measurements were made of the density, temperature, and radius of the plasma. Ion-cyclotron fluctuations were observed, their bandwidth measured, and data collected demonstrating resonance heating. New X-ray diagnostics were designed and purchased, and progress on the Thomson scattering was made. Finally, a new hot cathode gun was designed and constructed
New Experimental Constraints on Non-Newtonian Forces below 100 microns
We have searched for large deviations from Newtonian gravity by means of a
microcantilever-based Cavendish-style experiment. Our data eliminate from
consideration mechanisms of deviation that posit strengths ~10^4 times
Newtonian gravity at length scales of 20 microns. This measurement is 3 orders
of magnitude more sensitive than others that provide constraints at similar
length scales.Comment: 4 pages, 4 figure
Analysis and design of a high tip speed, low noise aircraft fan incorporating swept leading edge rotor and stator blades
A Low-Noise High-Density Alkali Metal Scalar Magnetometer
We present an experimental and theoretical study of a scalar atomic
magnetometer using an oscillating field-driven Zeeman resonance in a
high-density optically-pumped potassium vapor. We describe an experimental
implementation of an atomic gradiometer with a noise level below 10
fT/Hz^{1/2}, fractional field sensitivity below 10^{-9}/Hz^{1/2}, and an active
measurement volume of about 1.5 cm^3. We show that the fundamental field
sensitivity of a scalar magnetometer is determined by the rate of alkali-metal
spin-exchange collisions even though the resonance linewidth can be made much
smaller than the spin-exchange rate by pumping most atoms into a stretched spin
state.Comment: 10 pages, 7 figures. Version 2 is longer, with more complete
description of theoretical analysis and comparison between analytical and
experimental result
Microwave Electronics
Contains reports on three research projects.Department of the NavyDepartment of the Air Force under Contract AF 19(122)-458Office of Naval Research under contract Nonr 1841 (05), NR 373-043Department of the ArmyLincoln Laboratory, Purchase Order DDL-B15
Radio Astronomy
Contains reports on four research projects.National Science Foundation (Grant G-13904)National Aeronautics and Space Administration (Contract NaSr-101)National Aeronautics and Space Administration (Grant NsG-250-62
Microwave Electronics
Contains research objectives and reports on three research projects.Department of the ArmyDepartment of the NavyDepartment of the Air Force under Contract AF19(122)-458U. S. Navy (Office of Naval Research) under Contract Nonr-1841(49)Lincoln Laboratory, Purchase Order DDL-B22
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