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Southern Hemisphere Measurement of the Anisotropy in the CosmicMicrowave Background Radiation

Description: A recent measurement of the anisotropy in the Cosmic Background Radiation from the southern hemisphere (Lima, Peru) is essentially in agreement with previous measurements from the northern hemisphere. The net anisotropy can be described as a first order spherical harmonic (Doppler) anisotropy of amplitude 3.1 {+-} 0.4 m{sup o}K with a quadrupole anisotropy of less than 1 m{sup o}K. In addition, measurements of the linear polarization yield an upper limit of 1 m{sup o}K, or one part in 3000, at 95% C.L. for the amplitudes of any spherical harmonic through third order.
Date: June 1, 1979
Creator: Smoot, George F. & Lubin, Phil M.
Partner: UNT Libraries Government Documents Department

Constraints on the Topology of the Universe from the 2 Year COBEData

Description: The cosmic microwave background (CMB) is a unique probe of cosmological parameters and conditions. There is a connection between anisotropy in the CMB and the topology of the Universe. Adopting a universe with the topology of a 3-Torus, or a universe where only harmonics of the fundamental mode are allowed, and using 2-years of COBE/DMR data, we obtain constraints on the topology of the Universe. Previous work constrained the topology using the quadrupole component and the correlation function of the CMB. In this letter, we obtain more accurate results by using all multipole moments, avoiding approximations by computing their full covariance matrix. We obtain the best fit for a cubic toroidal universe of scale 7200h{sup -1} Mpc for n = 1. The data set a lower limit on the cell size of 4800h{sup -1} Mpc at 95% confidence and 6000h{sup -1} Mpc at 65% confidence. These results show that the most probable cell size would be around 1.2 times larger than the horizon scale, implying that the 3-Torus topology is no longer an interesting cosmological model.
Date: November 1, 1994
Creator: de Oliveira-Costa, A. & Smoot, George F.
Partner: UNT Libraries Government Documents Department

3 mm Anisotropy Measurement: On the Quadrupole Component in theCosmic Background Radiation

Description: We have mapped the large-scale anisotropy in the cosmic background radiation at 3 mm wavelength using a liquid-helium-cooled balloon-borne radiometer sensitive enough to detect the dipole in one gondola rotation (1 minute). Statistical errors on the dipole and quadrupole components are below 0.1 mK with less than 0.1 m K galactic contribution. We find a dipole consistent with previous measurements but disagree with recent quadrupole reports. The measurement is also useful in searching for spectral distortions.
Date: November 1, 1982
Creator: Lubin, Philip M.; Epstein, Gerald L. & Smoot, George F.
Partner: UNT Libraries Government Documents Department

The Astromag Superconducting Magnet Facility Configured for a FreeFlying Satellite

Description: ASTROMAG is a particle astrophysics facility that was originally configured for the Space Station. The heart of the ASTROMAG facility is a large superconducting magnet which is cooled using superfluid helium. The task of resizing the facility so that it will fly in a satellite in. a high angle of inclination orbit is driven by the launch weight capability of the launch rocket and the desire to be able to do nearly the same physics as the Space Station version of ASTROMAG. In order to reduce the launch weight, the magnet and its cryogenic system had to be downsized, yet the integrated field generated by the magnet in the particle detectors has to match the Space Station version of the magnet. The use of aluminum matrix superconductor and oriented composite materials in the magnet insulation permits one to achieve this goal. The net magnetic dipole moment from the ASTROMAG magnet must be small to minimize the torque due to interaction with the earth's magnetic field. The ASTROMAG magnet consists of identical two coils 1.67 meters apart. The two coils are connected in series in persistent mode. Each coil is designed to carry 2.34 million ampere turns. Both coils are mounted on the same magnetic axis and they operate at opposite polarity. This reduces the dipole moment by a factor of more than 1000. This is tolerable for the Space Station version of the magnet. A magnet operating on a free flying satellite requires additional compensation. This report presents the magnet parameters of a free flying version of ASTROMAG and the parameters of the space cryogenic system for the magnet.
Date: June 1, 1991
Creator: Green, M.A. & Smoot, George F.
Partner: UNT Libraries Government Documents Department

Polarization of the cosmic background radiation

Description: We discuss the technique and results of a measurement of the linear polarization of the Cosmic Background Radiation. Data taken between May 1978 and February 1980 from both the northern hemisphere (Berkeley Lat. 38{sup o}N) and the southern hemisphere (Lima Lat. 12{sup o}s) over 11 declinations from -37{sup o} to +63{sup o} show the radiation to be essentially unpolarized over all areas surveyed. Fitting all data gives the 95% confidence level limit on a linearly polarized component of 0.3 mK for spherical harmonics through third order. A fit of all data to the anisotropic axisymmetric model of Rees (1968) yields a 95% confidence level limit of 0.15 mK for the magnitude of the polarized component. Constraints on various cosmological models are discussed in light of these limits.
Date: August 1, 1980
Creator: Lubin, Philip M. & Smoot, George F.
Partner: UNT Libraries Government Documents Department

A Measurement of the Temperature of the Cosmic MicrowaveBackground at a Frequency of 7.5 GHz

Description: We have measured the intensity of the cosmic microwave background (CMB) at a frequency of 7.5 GHz (wavelength 4.0 cm) using a ground-based, total power radiometer calibrated at the horn aperture by an external cryogenic reference target. The radiometer measured the difference in antenna temperature between the reference target and the zenith sky from a dry, high-altitude site. Subtraction of foreground signals (primarily atmospheric and galactic emission) measured with the same instrument leaves the CMB as the residual. The radiometer measured the atmospheric antenna temperature by correlating the signal change with the airmass in the beam during tip scans. The small galactic signal was subtracted based on extrapolation from lower frequencies, and was checked by differential drift scans. The limiting uncertainty in the CMB measurement was the effect of ground radiation in the antenna sidelobes during atmospheric measurements. The thermodynamic temperature of the CMB at 7.5 GHz is 2.59 {+-} 0.07 K (68% confidence level).
Date: June 1, 1989
Creator: Kogut, A.; Bensadoun, M.; De Amici, Giovanni; Levin, S.; Smoot,George F. & Witebsky, C.
Partner: UNT Libraries Government Documents Department

Design and Testing of a Superfluid Liquid Helium CoolingLoop

Description: This paper describes the design and preliminary testing of a cryogenic cooling loop that uses a thermomechanical pump to circulate superfluid liquid helium. The cooling loop test apparatus is designed to prove forced liquid helium flow concepts that will be used on the Astromag superconducting magnet facility.
Date: July 24, 1989
Creator: Gavin, L.M.; Green, M.A.; Levin, S.M.; Smoot, George F. & Witebsky, C.
Partner: UNT Libraries Government Documents Department

Abundances and Spectra for Cosmic-Ray Nuclei from Li to Fe For 2to 150 GeV/n

Description: We report measurements of the absolute and relative abundances, differential energy spectra, and spectral indices for cosmic-ray nuclei from Li to Fe for 2 to 150 GeV/nucleon. These measurements were made using a balloon-borne superconducting magnetic spectrometer with scintillators and optical spark chambers. The abundances of Li, Be, and B for rigidities below 10 GV/c are consistent with an energy-independent mean interstellar pathlength of 4 1/2 {+-} 1/2 g cm{sup -2} for all propagation models. The abundances of all elements above 10 GV/c are consistent with an interstellar pathlength decreasing with rigidity as R{sup -n} with an index n = 0.6{sub -0.3}{sup +0.4}. All differential source spectra can be fitted by power laws in total energy per nucleon with the same spectral index, which is between 2.5 and 2.6 depending on n. If n is near 0.5 (as for simple diffusion), the source index is 2.54 {+-} 0.03. Relative abundances at the sources are thus energy-independent, and have ratios to solar abundances as a function of first ionization potential which indicate a source temperature between 10{sup 4} and 5 x 10{sup 4} K depending on the equilibrium nature of the injection environment.
Date: March 27, 1978
Creator: Orth, Chalres D.; Ruffington, Andrew; Smoot, George F. & Mast,Terry S.
Partner: UNT Libraries Government Documents Department

A Liquid-Helium-Cooled Absolute Reference Cold Load forLong-Wavelength Radiometric Calibration

Description: We describe a large (78-cm) diameter liquid-helium-cooled black-body absolute reference cold load for the calibration of microwave radiometers. The load provides an absolute calibration near the liquid helium (LHe) boiling point, accurate to better than 30 mK for wavelengths from 2.5 to 25 cm (12-1.2 GHz). The emission (from non-LHe temperature parts of the cold load) and reflection are small and well determined. Total corrections to the LHe boiling point temperature are {le} 50 mK over the operating range. This cold load has been used at several wavelengths at the South Pole and at the White Mountain Research Station. In operation, the average LHe loss rate was {le} 4.4 l/hr. Design considerations, radiometric and thermal performance and operational aspects are discussed. A comparison with other LHe-cooled reference loads including the predecessor of this cold load is given.
Date: May 1, 1990
Creator: Bensadoun, M.; Witebsky, C.; Smoot, George F.; De Amici,Giovanni; Kogut, A. & Levin, S.
Partner: UNT Libraries Government Documents Department

Radiometer System to Map the Cosmic Background Radiation

Description: We have developed a 33 GHz airborne radiometer system to map large-scale angular variations in the temperature of the 3 K cosmic background radiation. A ferrite circulator switches a room-temperature mixer between two antennas pointing 60{sup o} apart in the sky. In forty minutes of observing, the radiometer can measure the anisotropy of the microwave background with an accuracy of {+-} 1 m{sup o}K rms, or about one part in 3000 of 3 K. The apparatus is flown in a U-2 jet to 20 km altitude where 33 GHz thermal microwave emission from the atmosphere is at a low level. A second radiometer, tuned to 54 GHz near oxygen emission lines, monitors spurious signals from residual atmospheric radiation. The antennas, which have an extremely low side-lobe response of less than -65 dB past 60{sup o}, reject anisotropic radiation from the earth's surface. Periodic interchange of the antenna positions and reversal of the aircraft's flight direction cancel equipment-based imbalances. The system has been operated successfully in U-2 aircraft flown from NASA-Ames at Moffett Field, California.
Date: November 1, 1977
Creator: Gorenstein, Marc V.; Muller, Richard A.; Smoot, George F. & Tyson,J. Anthony
Partner: UNT Libraries Government Documents Department

A 2-GHz Rectangular Corrugated Horn

Description: We have designed, constructed and tested a large, rectangular horn antenna with a center frequency of 2.0 GHz, corrugated on the E-plane walls, made out of aluminum sheet. A new technique has been developed to solder thin aluminum strips onto the back plane to form the corrugations. The radiation beam pattern shows half-power beamwidths of 12{sup 0} and 14{sup 0} in the H and E planes respectively, and side lobe response below -40 dB at angles greater than 50{sup 0} from horn axis. The measured return loss is less than -20 dB (VSWR < 1.22) between 1.7 and 2.3 GHz; insertion loss is less than 0.15 dB.
Date: October 1, 1991
Creator: Bersanelli, M.; Bensadoun, M.; De Amici, Giovanni; Limon, M.; Smoot, George F.; Tanaka, S. et al.
Partner: UNT Libraries Government Documents Department

Low-Frequency Measurements of the CMB Spectrum

Description: As part of an extended program to characterize the spectrum of the cosmic microwave background (CMB) at low frequencies, we have performed multiple measurements from a high-altitude site in California. On average, these measurements suggest a CMB temperature slightly lower than measurements at higher frequencies. Atmospheric conditions and the encroachment of civilization are now significant limitations from our present observing site. In November 1989, we will make new measurements from the South Pole Amundsen-Scott Station at frequencies 0.82, 1.5, 2.5, 3.8, 7.5, and 90 GHz. We discuss recent measurements and indicate improvements possible from a polar observing site.
Date: October 1, 1989
Creator: Kogut, A.; Bensadoun, M.; De Amici, Giovanni; Levin, S.; Limon,M.; Smoot, George F. et al.
Partner: UNT Libraries Government Documents Department

The Temperature of the Cosmic Background Radiation: Results fromthe 1987 and 1988 Measurements at 3.8 GHz

Description: We have measured the temperature of the cosmic background radiation (CBR) at a frequency of 3.8 GHz (7.9 cm wavelength), during two consecutive summers, obtaining a brightness temperature, T{sub CBR}, of 2.56 {+-} 0.08 K in 1987 and 2.71 {+-} 0.07 K in 1988 (68% confidence level). The new results are in agreement with our previous measurement at 3.7 GHz obtained in 1986, and have smaller error bars. Combining measurements from all three years we obtain T{sub CBR} = 2.64 {+-} 0.07 K.
Date: November 10, 1989
Creator: De Amici, Giovanni; Bensadoun, M.; Bersanelli, M.; Kogut, A.; Levine, S.; Smoot, George F. et al.
Partner: UNT Libraries Government Documents Department

Measurements of Retractable Gas-Cooled 6061 Aluminum ElectricalLeads Operating in a Vacuum

Description: To charge and discharge the ASTROMAG superconducting magnet in space requires retractable gas-cooled leads which must operate in a vacuum. This report describes the design and test of 500 ampere retractable gas-cooled leads made from 6061-T4 aluminum tubes. Aluminum is attractive for gas-cooled electrical leads in space because of its low mass density and the desire for short leads. Initial tests showed that retractable gas-cooled leads could operate in a vacuum from a source of normal helium. The pressure drop through the leads was low enough to permit a superconducting magnet to be charged and discharged while the leads vent into space. The leads were stable at currents above 700 amperes. The voltage drop across the contact between the upper and lower leads was as low as 1.2 mV per lead out of a total voltage drop of 42 mV per lead when the leads carried 714 amperes. The gas required for cooling was comparable to the more conventional copper gas-cooled current leads. In a second test seven months later. The contact resistance between the lead sections had increased considerably. In the second test, the contact resistance was repeatable for one lead but not for the other.
Date: June 1, 1991
Creator: Green, M.A.; Aguiar, H.; Bensadoun, M.J.; Gibson, J.H.; Heine,D.L.; Levin, S. et al.
Partner: UNT Libraries Government Documents Department

Technology Development for a Neutrino AstrophysicalObservatory

Description: We propose a set of technology developments relevant to the design of an optimized Cerenkov detector for the study of neutrino interactions of astrophysical interest. Emphasis is placed on signal processing innovations that enhance significantly the quality of primary data. These technical advances, combined with field experience from a follow-on test deployment, are intended to provide a basis for the engineering design for a kilometer-scale Neutrino Astrophysical Observatory.
Date: February 1, 1996
Creator: Chaloupka, V.; Cole, T.; Crawford, H.J.; He, Y.D.; Jackson, S.; Kleinfelder, S. et al.
Partner: UNT Libraries Government Documents Department