Engineering topics

Lee, M. H.

Publications and source records attributed to Lee, M. H..

9 records

NASA NTRS2012

Measurement of the Cosmic-Ray Antiproton Spectrum at Solar Minimum with a Long-Duration Balloon Flight over Antarctica

The energy spectrum of cosmic-ray antiprotons (p-bar's) from 0.17 to 3.5 GeV has been measured using 7886 p-bar's detected by BESS-Polar II during a long-duration flight over Antarctica near solar minimum in December 2007 and January 2008. This shows good consistency with secondary p-bar calculations. Cosmologically primary p-bar's have been investigated by comparing measured and calculated p-bar spectra. BESS-Polar II data.show no evidence of primary p-bar's from the evaporation of primordial black holes.

Abe, K.↗

NASA NTRS2012

Search for Antihelium with the BESS-Polar Spectrometer

In two long-duration balloon flights over Antarctica, the BESS-Polar collaboration has searched for antihelium in the cosmic radiation with higher sensitivity than any reported investigation. BESSPolar I flew in 2004, observing for 8.5 days. BESS-Polar II flew in 2007-2008, observing for 24.5 days. No antihelium candidate was found in BESS-Polar I data among 8.4 x 10(exp 6) [Z] = 2 nuclei from 1.0 to 20 GV or in BESS-Polar II data among 4.0 x 10(exp 7) [Z] = 2 nuclei from 1.0 to 14 GV. Assuming antihelium to have the same spectral shape as helium, a 95% confidence upper limit of 6.9 x 10(exp -8) was determined by combining all the BESS data, including the two BESS-Polar flights. With no assumed antihelium spectrum and a weighted average of the lowest antihelium efficiencies from 1.6 to 14 GV, an upper limit of 1.0 x 10(exp -7) was determined for the combined BESS-Polar data. These are the most stringent limits obtained to date.

Sasaki, M.↗

NASA NTRS2011

Search for Cosmic-Ray Antiproton Origins and for Cosmological Antimatter with BESS

The balloon-borne experiment with a superconducting spectrometer (BESS) has performed cosmic-ray observations as a US-Japan cooperative space science program, and has provided fundamental data on cosmic rays to study elementary particle phenomena in the early Universe. The BESS experiment has measured the energy spectra of cosmic-ray antiprotons to investigate signatures of possible exotic origins such as dark matter candidates or primordial black holes. and searched for heavier antinuclei that might reach Earth from antimatter domains formed in the early Universe. The apex of the BESS program was reached with the Antarctic flight of BESS-Polar II, during the 2007- 2008 Austral Summer, that obtained over 4.7 billion cosmic-ray events from 24.5 days of observation. The flight took place at the expected solar minimum, when the sensitivity of the low-energy antiproton measurements to a primary source is greatest. Here, we report the scientific restults, focusing on the long-duration flights of BESS-Polar I (2004) and BESS-Polar II (2007-2008).

Yamamoto, A.↗

NASA NTRS2011

Measurement of Cosmic-Ray Antiproton Spectrum at Solar Minimum with a Long-Duration Balloon Flight in Antarctica

The energy spectrum of cosmic-ray antiprotons (p(raised bar)'s) collected by the BESS-Polar II instrument during a long-duration flight over Antarctica in the solar minimum period of December 2007 through January 2008. The p(raised bar) spectrum measured by BESS-Polar II shows good consistency with secondary p(raised bar) calculations. Cosmologically primary p(raised bar)'s have been searched for by comparing the observed and calculated p(raised bar) spectra. The BESSPolar II result shows no evidence of primary p(raised bar)'s originating from the evaporation of PBH.

Abe, K.↗

NASA NTRS2000

Laser Transmission Measurements of Soot Extinction Coefficients in the Exhaust Plume of the X-34 60K-lb Thrust Fastrac Rocket Engine

A four-channel laser transmissometer has been used to probe the soot content of the exhaust plume of the X-34 60k-lb thrust Fastrac rocket engine at NASA's Marshall Space Flight Center. The transmission measurements were made at an axial location approximately equal 1.65 nozzle diameters from the exit plane and are interpreted in terms of homogeneous radial zones to yield extinction coefficients from 0.5-8.4 per meter. The corresponding soot mass density, spatially averaged over the plume cross section, is, for Rayleigh particles, approximately equal 0.7 microgram/cc, and alternative particle distributions are briefly considered. Absolute plume radiance at the laser wavelength (515 nm) is estimated from the data at approximately equal 2,200 K equivalent blackbody temperature, and temporal correlations in emission from several spatial locations are noted.

Dobson, C. C.↗

NASA NTRS2000

Laser Transmission Measurements of Soot Extinction Coefficients in the Exhaust Plume of the X-34 60k-lb Thrust Fastrac Rocket Engine

A four-channel laser transmissometer has been used to probe the soot content of the exhaust plume of the X-34 60k-lb thrust Fastrac rocket engine at NASA's Marshall Space Flight Center. The transmission measurements were made at an axial location about equal 1.65 nozzle diameters from the exit plane and are interpreted in terms of homogeneous radial zones to yield extinction coefficients from 0.5-8.4 per meter. The corresponding soot mass density, spatially averaged over the plume cross section, is, for Rayleigh particles, approximately equal to 0.7 micrograms/cubic cm and alternative particle distributions are briefly considered. Absolute plume radiance at the laser wavelength (515 nm) is estimated from the data at approximately equal to 2.200 K equivalent blackbody temperature, and temporal correlations in emission from several spatial locations are noted.

Dobson, C. C.↗

NASA NTRS2000

New Submount Requirement of Conductively Cooled Laser Diodes for Lidar Applications

New submount technology is essential for the development of conductively cooled high power diode laser. The simulation and experimental results indicate that thermal conductivity of submount for high power laser-diode must be at least 600 W/m/k or higher for stable operation. We have simulated several theoretical thermal model based on new submount designs and characterized high power diode lasers to determine temperature effects on the performances of laser diodes. The characterization system measures the beam power, output beam profile, temperature distribution, and spectroscopic property of high power diode laser. The characterization system is composed of four main parts: an infrared imaging camera, a CCD camera, a monochromator, and a power meter. Thermal characteristics of two commercial-grade CW 20-W diode laser bars with open heat-sink type were determined with respect to the line shift of emission spectra and beam power stability. The center wavelength of laser emission has a tendency to shift toward longer wavelength as the driving current and heat sink temperature are increased. The increase of heat sink temperature decreases the output power of the laser bar too. Such results lay the guidelines for the design of new submount for high power laser-diodes.

Mo, S. Y.↗

NASA NTRS1986

A long-pulse amplifier for solar-pumped iodine lasers

The characteristics of a photodissociation iodine-laser amplifier pumped with a solar-simulating radiation were studied. Under long-pulse energy extraction, an energy amplification of about three and an energy storage time of longer than 500 microseconds were observed for a one meter long, 10 mm i.d. amplifier tube. The effects of elevated temperatures resulted in little reduction of the amplifier gain. These results confirm that developing an efficient chain of oscillator-amplifiers for a high-power solar-pumped iodine laser is indeed feasible.

Hwang, I. H.↗

NASA NTRS1986

Solar-pumped photodissociation iodine laser

The scientific feasibility of a solar-pumped iodine photodissociation laser for space applications is under investigation. Recently, a 2-W CW output for more than one hour was achieved using n-C3F7I vapor as the laser material and a vortex-stabilized argon arc as the light source.

Lee, J. H.↗