Engineering topics

Lesyna, L.

Publications and source records attributed to Lesyna, L..

6 records

NASA NTRS1989

A progress report on using bolometers cooled by adiabatic demagnetization refrigeration

For sensitive detection of astronomical continuum radiation in the 200 micron to 3 mm wavelength range, bolometers are presently the detectors of choice. In order to approach the limits imposed by photon noise in a cryogenically cooled telescope in space, bolometers must be operated at temperatures near 0.1 K. Researchers report progress in building and using bolometers that operate at these temperatures. The most sensitive bolometer had an estimated noise equivalent power (NEP) of 7 x 10(exp 017) W Hz(exp -1/2). Researchers also briefly discuss the durability of paramagnetic salts used to cool the bolometers.

Lesyna, L.↗

NASA NTRS1988

An adiabatic demagnetization cooled bolometer system

An adiabatic demagnetization refrigeration (ADR) system suitable for cooling bolometers for use at infrared and submillimeter wavelengths is constructed. Because it does not rely on a gravitational field for operation, this refrigeration method has been proposed to cool bolometers intended for NASA's Space Infrared Telescope Facility. To explore the use of ADR in this manner, a portable instrument that has been used successfully for ground-based astronomical observations was constructed. By employing chromic potassium sulfate as a paramagnetic cooling material, bolometers were cooled to temperatures of 0.1 K with a cryogenic hold time of greater than nine hours.

Lesyna, L.↗

NASA NTRS1986

A progress report on bolometers operating at 0.1 K using adiabatic demagnetization refrigeration

Bolometers are still the detectors of choice for low background infrared observations at wavelengths longer than 200 microns. In the low background limit, bolometers become more sensitive as their operating temperature decreases, due to fundamental thermodynamic laws. The adiabatic demagnetization technique was evaluated by building a bolometer detection system operating at a wavelength of 1 millimeter for use at a ground based telescope. The system was fit checked at the telescope and is expected to take its first data in November, 1985.

Roellig, T.↗

NASA NTRS1984

Bolometers operated at 0.1 K and 0.2 K cooled by adiabatic demagnetization

The construction of bolometers operating at temperatures of 0.1 K and 0.2 K and cooled by adiabatic demagnetization is reported. The electrical noise-equivalent power (NEP) of the bolometers was found to be 1.8 and 6.6 x 10 to the -16th W/sq rt Hz, respectively. These values are within a factor of two of the expected performance based upon bolometer theory. The thermistor material used was gallium-doped single-crystal germanium, for which a resistivity temperature dependence is found.

Lesyna, L.↗

NASA NTRS1983

The 0.1K bolometers cooled by adiabatic demagnetization

The most straightforward way of reducing the noise equivalent power of bolometers is to lower their operating temperature. We have been exploring the possibility of using conventionally constructed bolometers at ultra-low temperatures to achieve NEP's suitable to the background environment of cooled space telescopes. We have chosen the technique of adiabatic demagnetization of a paramagnetic salt as a gravity independent, compact, and low power way to achieve temperatures below pumped He-3 (0.3 K). The demagnetization cryostat we used was capable of reaching temperatures below 0.08 K using Chromium Potassium Alum as a salt from a starting temperature of 1.5 K and a starting magnetic field of 30,000 gauss. Computer control of the magnetic field decay allowed a temperature of 0.2 K to be maintained to within 0.5 mK over a time period exceeding 14 hours. The refrigerator duty cycle was over 90 percent at this temperature. The success of these tests has motivated us to construct a more compact portable adiabatic demagnetization cryostat capable of bolometer optical tests and use at the 5m Hale telescope at 1mm wavelengths.

Roellig, T.↗

NASA NTRS1982

Recent SETI observations at Arecibo

Preliminary results are presented for a high-resolution search for narrowband signals from the direction of 210 nearby solar-type stars and five OH masers. The 305-m Arecibo radio telescope was used to seek narrowband radio emission at frequencies surrounding the 21-cm H I line and/or the 18-cm OH lines; the observations were made in right and left circular polarizations simultaneously. At the 98% level, 291 'birdies' were found, of which six sources at 18 cm and eight at 21 cm are considered potential candidates for reobservation and further study to identify the nature of the signals. It is noted that: (1) five of the 21-cm 'birdies' are probably H I clouds along the line of sight; (2) some of the 18-cm 'birdies' are associated with the extreme 13 frequency bands bordering unprotected bands above and below the established radio astronomy band; and (3) one of the 21-cm 'birdies' is distinctly narrowband and has no signal detected in the 'off' source.

Tarter, J. C.↗