2,657 research outputs found
The bolometric focal plane array of the Polarbear CMB experiment
The Polarbear Cosmic Microwave Background (CMB) polarization experiment is
currently observing from the Atacama Desert in Northern Chile. It will
characterize the expected B-mode polarization due to gravitational lensing of
the CMB, and search for the possible B-mode signature of inflationary
gravitational waves. Its 250 mK focal plane detector array consists of 1,274
polarization-sensitive antenna-coupled bolometers, each with an associated
lithographed band-defining filter. Each detector's planar antenna structure is
coupled to the telescope's optical system through a contacting dielectric
lenslet, an architecture unique in current CMB experiments. We present the
initial characterization of this focal plane
Electron cloud buildup and impedance effects on beam dynamics in the future circular e+e− collider and experimental characterization of thin TiZrV vacuum chamber coatings
The Future Circular Collider FCC-ee is a study toward a high luminosity electron-positron collider with a centre-of-mass energy from 91 GeV to 365 GeV. Due to the beam parameters and pipe dimensions, collective effects and electron cloud can be very critical aspects for the machine and can represent the main limitations to its performance. An estimation of the electron cloud build up in the main machine components and an impedance model are required to analyze the induced instabilities and to find solutions for their mitigation. Special attention has been given to the resistive wall impedance associated with a layer of nonevaporable getter (NEG) coating on the vacuum chamber required for electron cloud mitigation. The studies presented in this paper will show that minimizing the thickness of this coating layer is mandatory to increase the single bunch instability thresholds in the proposed lepton collider at 45.6 GeV. For this reason, NEG thin films with thicknesses below 250 nm have been investigated by means of numerical simulations to minimize the resistive wall impedance. In parallel, an extensive measurement campaign was performed at CERN to characterize these thin films, with the purpose of finding the minimum effective thickness satisfying vacuum and electron cloud requirements
Silicon-Based Antenna-Coupled Polarization-Sensitive Millimeter-Wave Bolometer Arrays for Cosmic Microwave Background Instruments
We describe feedhorn-coupled polarization-sensitive detector arrays that
utilize monocrystalline silicon as the dielectric substrate material.
Monocrystalline silicon has a low-loss tangent and repeatable dielectric
constant, characteristics that are critical for realizing efficient and uniform
superconducting microwave circuits. An additional advantage of this material is
its low specific heat. In a detector pixel, two Transition-Edge Sensor (TES)
bolometers are antenna-coupled to in-band radiation via a symmetric planar
orthomode transducer (OMT). Each orthogonal linear polarization is coupled to a
separate superconducting microstrip transmission line circuit. On-chip
filtering is employed to both reject out-of-band radiation from the upper band
edge to the gap frequency of the niobium superconductor, and to flexibly define
the bandwidth for each TES to meet the requirements of the application. The
microwave circuit is compatible with multi-chroic operation. Metalized silicon
platelets are used to define the backshort for the waveguide probes. This
micro-machined structure is also used to mitigate the coupling of out-of-band
radiation to the microwave circuit. At 40 GHz, the detectors have a measured
efficiency of 90%. In this paper, we describe the development of the 90 GHz
detector arrays that will be demonstrated using the Cosmology Large Angular
Scale Surveyor (CLASS) ground-based telescope
Bolometric technique for high-resolution broadband microwave spectroscopy of ultra-low-loss samples
A novel low temperature bolometric method has been devised and implemented
for high-precision measurements of the microwave surface resistance of small
single-crystal platelet samples having very low absorption, as a continuous
function of frequency. The key to the success of this non-resonant method is
the in-situ use of a normal metal reference sample that calibrates the absolute
rf field strength. The sample temperature can be controlled independently of
the 1.2 K liquid helium bath, allowing for measurements of the temperature
evolution of the absorption. However, the instrument's sensitivity decreases at
higher temperatures, placing a limit on the useful temperature range. Using
this method, the minimum detectable power at 1.3 K is 1.5 pW, corresponding to
a surface resistance sensitivity of 1 for a typical 1
mm1 mm platelet sample.Comment: 13 pages, 12 figures, submitted to Review of Scientific Instrument
Electrochemical characterization of nanoporous nickel oxide thin films spray-deposited onto indium-doped tin oxide for solar conversion scopes
Nonstoichiometric nickel oxide (NiOx) has been deposited as thin film utilizing indium-doped tin oxide as transparent and electrically conductive substrate. Spray deposition of a suspension of nanoparticles in alcoholic medium allowed the preparation of uniform coatings. Sintering of the coatings was conducted at temperatures below 500°C for few minutes. This scalable procedure allowed the attainment of films with mesoporous morphology and reticulated structure. The electrochemical characterization showed that electrodes possess large surface area (about 1000 times larger than their geometrical area). Due to the openness of the morphology, the underlying conductive substrate can be contacted by the electrolyte and undergo redox processes within the potential range in which is electroactive. This requires careful control of the conditions of polarization in order to prevent the simultaneous occurrence of reduction/oxidation processes in both components of the multilayered electrode. The combination of the open structure with optical transparency and elevated electroactivity in organic electrolytes motivated us to analyze the potential of the spray-deposited films as semiconducting cathodes of dye-sensitized solar cells of p-type when erythrosine B was the sensitizer
Ferromagnetic Wires Composite Media with Tunable Scattering Spectra at Microwaves
We demonstrate composite media with ferromagnetic wires that exhibit a
frequency region at the microwave regime with scattering spectra strongly
dependent on an external magnetic field or stress. These tunable composite
materials have recently been proposed theoretically; however, no direct
experimental verification has been reported. We used composite materials with
predominantly oriented CoFeCrSiB glass-coated amorphous wires having large
magnetoimpedance at GHz frequencies. The free space measurements of reflection
and transmission coefficients were conducted in the frequency range 1-8 GHz in
the presence of an external static magnetic field or stress applied to the
whole sample. In general, the transmission spectra show greater changes in the
range of 10dB for a relatively small magnetic field of few Oe or stress of 0.1
MPa. The obtained results are quantitatively consistent with the analytical
expressions predicted by the effective medium arguments. The incident
electromagnetic wave induces an electrical dipole moment in each wire, the
aggregate of which forms the effective dipole response of the whole composite
structure in the radiative near or far field region. The field and stress
dependences of the effective response arise from a field or tensile stress
sensitivity of the ac surface impedance of a ferromagnetic wire. In the
vicinity of the antenna resonance the variations in the magneto-impedance of
the wire inclusions result in large changes of the total effective response. A
number of applications of proposed materials is discussed including the field
tunable microwave surfaces and the self-sensing media for the remote
non-destructive evaluation of structural materials
Application of Microwave Methods for Characterization of NEG Coatings and Obstacle Detection in Accelerator Beam-pipes
In many particle accelerators, including the LHC at the European Organization for Nuclear Research CERN, NEG coatings are used to improve vacuum performance. In other particle accelerators there have been hints that those coatings could have a relevant impact on the beam coupling impedance, however the data available is contradictory. To clarify the possible impact of NEG coatings the electromagnetic properties have been measured. The measurements have been carried out by means of cavity perturbation method. The second part of this thesis deals with the microwave waveguide reflectometer developed at CERN several years ago, which is used as part of the quality assurance test program for the LHC assembly. To ensure optimum operation and to avoid an expensive removal of any foreign object from inside the LHC beam-screen after its completion, microwave reflectometry is performed. Until now several objects have been found by means of reflectometry, but so far neither precise data about the reflections of different foreign objects, nor the precise limits of the system are known
Real-time visualisation of antenna radiation patterns
Projecte final de carrera fet en col.laboració amb el Department of Electrical and Information Technology. Lund UniversityIn this project the real-time visualisation of antenna radiation patterns through in-
frared thermography is studied. This technique allows for a 2-dimensional imaging
of incident power levels on the surface of a detector screen, through their temper-
ature signature, thus revealing a region of the radiation pattern of the emitting
antenna when placed at a distance.
Based on previous experiences, the design parameters of the resistive screen
on which to observe the heat signature of incident microwave radiation have been
studied in detail and di®erent possible implementations have been discussed. Mod-
els of the coating for the resistive screen have been made in order to test their
validity for the technique under study
Calibration and First light of the Diabolo photometer at the Millimetre and Infrared Testa Grigia Observatory
We have designed and built a large-throughput dual channel photometer,
Diabolo. This photometer is dedicated to the observation of millimetre
continuum diffuse sources, and in particular, of the Sunyaev-Zel'dovich effect
and of anisotropies of the 3K background. We describe the optical layout and
filtering system of the instrument, which uses two bolometric detectors for
simultaneous observations in two frequency channels at 1.2 and 2.1 mm. The
bolometers are cooled to a working temperature of 0.1 K provided by a compact
dilution cryostat. The photometric and angular responses of the instrument are
measured in the laboratory. First astronomical light was detected in March 1995
at the focus of the new Millimetre and Infrared Testa Grigia Observatory (MITO)
Telescope. The established sensitivity of the system is of 7 mK_RJ s^1/2$. For
a typical map of at least 10 beams, with one hour of integration per beam, one
can achieve the rms values of y_SZ ~ 7 10^-5 and the 3K background anisotropy
Delta T/T ~ 7 10^-5, in winter conditions. We also report on a novel bolometer
AC readout circuit which allows for the first time total power measurements on
the sky. This technique alleviates (but does not forbid) the use of chopping
with a secondary mirror. This technique and the dilution fridge concept will be
used in future scan--modulated space instrument like the ESA Planck mission
project.Comment: 10 pages, LaTeX, 12 figures, accepted for publication in Astronomy
and Astrophysics Supplement Serie
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