2,162 research outputs found
Demonstration experiments for solid state physics using a table top mechanical Stirling refrigerator
Liquid free cryogenic devices are acquiring importance in basic science and
engineering. But they can also lead to improvements in teaching low temperature
an solid state physics to graduate students and specialists. Most of the
devices are relatively expensive, but small sized equipment is slowly becoming
available. Here, we have designed several simple experiments which can be
performed using a small Stirling refrigerator. We discuss the measurement of
the critical current and temperature of a bulk YBa2Cu3O(7-d) (YBCO) sample, the
observation of the levitation of a magnet over a YBCO disk when cooled below
the critical temperature and the observation of a phase transition using ac
calorimetry. The equipment can be easily handled by students, and also used to
teach the principles of liquid free cooling
Magnetic field dependence of the internal quality factor and noise performance of lumped-element kinetic inductance detectors
We present a technique for increasing the internal quality factor of kinetic
inductance detectors (KIDs) by nulling ambient magnetic fields with a properly
applied magnetic field. The KIDs used in this study are made from thin-film
aluminum, they are mounted inside a light-tight package made from bulk
aluminum, and they are operated near . Since the thin-film
aluminum has a slightly elevated critical temperature (), it therefore transitions before the package (), which also serves as a magnetic shield. On cooldown, ambient
magnetic fields as small as approximately can produce
vortices in the thin-film aluminum as it transitions because the bulk aluminum
package has not yet transitioned and therefore is not yet shielding. These
vortices become trapped inside the aluminum package below
and ultimately produce low internal quality factors in the thin-film
superconducting resonators. We show that by controlling the strength of the
magnetic field present when the thin film transitions, we can control the
internal quality factor of the resonators. We also compare the noise
performance with and without vortices present, and find no evidence for excess
noise beyond the increase in amplifier noise, which is expected with increasing
loss.Comment: 5 pages, 4 figure
Determining the minimum mass and cost of a magnetic refrigerator
An expression is determined for the mass of the magnet and magnetocaloric
material needed for a magnetic refrigerator and these are determined using
numerical modeling for both parallel plate and packed sphere bed regenerators
as function of temperature span and cooling power. As magnetocaloric material
Gd or a model material with a constant adiabatic temperature change,
representing a infinitely linearly graded refrigeration device, is used. For
the magnet a maximum figure of merit magnet or a Halbach cylinder is used. For
a cost of \$40 and \$20 per kg for the magnet and magnetocaloric material,
respectively, the cheapest 100 W parallel plate refrigerator with a temperature
span of 20 K using Gd and a Halbach magnet has 0.8 kg of magnet, 0.3 kg of Gd
and a cost of \$35. Using the constant material reduces this cost to \$25. A
packed sphere bed refrigerator with the constant material costs \$7. It is also
shown that increasing the operation frequency reduces the cost. Finally, the
lowest cost is also found as a function of the cost of the magnet and
magnetocaloric material.Comment: 12 pages, 10 figure
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