35 research outputs found
Shielding superconductors with thin films
Determining the optimal arrangement of superconducting layers to withstand
large amplitude AC magnetic fields is important for certain applications such
as superconducting radiofrequency cavities. In this paper, we evaluate the
shielding potential of the superconducting film/insulating film/superconductor
(SIS') structure, a configuration that could provide benefits in screening
large AC magnetic fields. After establishing that for high frequency magnetic
fields, flux penetration must be avoided, the superheating field of the
structure is calculated in the London limit both numerically and, for thin
films, analytically. For intermediate film thicknesses and realistic material
parameters we also solve numerically the Ginzburg-Landau equations. It is shown
that a small enhancement of the superheating field is possible, on the order of
a few percent, for the SIS' structure relative to a bulk superconductor of the
film material, if the materials and thicknesses are chosen appropriately.Comment: 7 pages, 5 figure
Evaluation of predictive correlation between flux expulsion and grain growth for superconducting radio frequency cavities
A series of experiments were carried out in an effort to develop a simple
method for predicting magnetic flux expulsion behavior of high purity niobium
used to fabricate superconducting radio frequency (SRF) cavities. Using
conventional metallographic characterizations in conjunction with high spatial
resolution electron backscattered diffraction-orientation imaging microscopy
(EBSD-OIM), we found that the flux expulsion behavior of 1.3 GHz single cell
SRF Nb cavities is significantly associated with the grain growth of the Nb
material during heat treatment. Most of Nb grains rapidly grew during 900C heat
treatment, and likely full-recrystallized with 1000C HT. With comparison of the
magnetic flux expulsion ratio (Bsc/Bnc) at dT = 5 K, the flux expulsion
efficiency of the cavities increases along with increasing of grain size. Most
interestingly, 900C HT shows a roughly linear trend that suggests this
criterion could be used to predict appropriate heat treatment temperature for
sufficient flux expulsion behavior in SRF-grade Nb. This result would be used
to see if flux expulsion can be predicted by examining the materials coming
from the Nb vendor, prior to cavity fabrication
A Precision Gyroscope from the Spin of Light
We describe a gyroscope that measures rotation based on the effects of the
rotation on the polarization of light. Rotation induces a differential phase
shift in the propagation of left and right circularly polarized light and this
phase shift can be measured in suitably designed interferometric setups. The
signal in this setup is independent of the frequency of light, unlike various
sources of noise such as vibrations, which cause phase shifts that depend on
the frequency. Such vibrations are the practical limit on the sensitivity of
conventional Sagnac-style optical interferometers that are typically used as
gyroscopes. In the proposed setup, one can potentially mitigate this source of
noise by simultaneously using two (or more) sources of light that have
different frequencies. The signal in this setup scales with the total storage
time of the light. Due to its frequency independence, it is thus most optimal
to measure the signal using superconducting RF systems where the high finesse
of the available cavities enables considerably longer storage times than is
possible in an optical setup.Comment: 15 pages, 1 figur
Selective thermal evolution of native oxide layer in Nb and Nb3Sn-coated SRF grade Nb: An in-situ angular XPS study
This contribution discusses the results of an in-situ angular XPS study on
the thermal evolution of the native oxide layer on Nb3Sn and pure Nb. XPS data
were recorded with conventional spectrometers using an AlK(alpha) X-ray source
for spectra collected up to 600 C, and an MgK(Alpha) X-rays source for
temperatures above 600 C. The effect of the thickness, composition, and thermal
stability of that oxide layer is relevant to understanding the functional
properties of superconducting radiofrequency (SRF) cavities used in particle
accelerators. There is a consensus that oxide plays a role in surface
resistance (Rs). The focus of this study is Nb3Sn, which is a promising
material that is used in the manufacturing of superconducting radiofrequency
(SRF) cavities as well as in quantum sensing, and pure Nb, which was included
in the study for comparison. The thermal evolution of the oxide layer in these
two materials is found to be quite different, which is ascribed to the
influence of the Sn atom on the reactivity of the Nb atom in Nb3Sn films. Nb
and Sn atoms in this intermetallic solid have different electronegativity, and
the Sn atom can reduce electron density around neighbouring Nb atoms in the
solid, thus reducing their reactivity for oxygen. This is shown in the
thickness, composition, and thermal stability of the oxide layer formed on
Nb3Sn. The XPS spectra were complemented by grazing incident XRD patterns
collected using the ESRF synchrotron radiation facility. The results discussed
herein shed light on oxide evolution in the Nb3Sn compound and guide its
processing for potential applications of the Nb3Sn-based SRF cavities in
accelerators and other superconducting devices
Measuring axion gradients with photon interferometry (MAGPI)
We propose a novel search technique for axions with a -violating monopole
coupling to bulk Standard Model charges .
Gradients in the static axion field configurations sourced by matter induce
achromatic circular photon birefringence via the axion-photon coupling
. Circularly polarized light fed into an optical or (open)
radio-frequency (RF) Fabry-P\'erot (FP) cavity develops a phase shift that
accumulates up to the cavity finesse: the fixed axion spatial gradient prevents
a cancellation known to occur for an axion dark-matter search. The relative
phase shift between two FP cavities fed with opposite circular polarizations
can be detected interferometrically. This time-independent signal can be
modulated up to non-zero frequency by altering the cavity orientations with
respect to the field gradient. Multi-wavelength co-metrology techniques can be
used to address chromatic measurement systematics and noise sources. With Earth
as the axion source, we project reach beyond current constraints on the product
of couplings for axion masses . If shot-noise-limited sensitivity can be achieved, an
experiment using high-finesse RF FP cavities could reach a factor of into new parameter space for for masses
.Comment: 9 pages, 2 figures. Published versio
Phase-controlled improvement of photon lifetime in coupled superconducting cavities
High-quality cavities are crucial for various fundamental physical studies
and applications. Here we find that by coupling two cavities directly or via a
phase-tunable coupling channel, the photon lifetime of the local field can
exceed that of the bare cavities. The cavity photon lifetime is modified by the
phases of the initial states and the phase accumulation on the coupling channel
which affect the interference between cavities. In experiments, by coupling
superconducting radio-frequency cavities via phase-tunable cables, we realize a
factor of two improvement in the cavity photon lifetime. The results can bring
rich revenue to quantum information science, sensing, and high-energy physics.Comment: 6 pages, 4 figure