Physics – Condensed Matter – Superconductivity
Scientific paper
Jan 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993phdt........68c&link_type=abstract
PhD Dissertation, Harvard Univ. Cambridge, MA United States
Physics
Condensed Matter
Superconductivity
Superconductivity, Protostars, Receivers, Submillimeter Waves, Quantum Theory, Plasma Jets, Superconductors (Materials), Turbulent Mixing, Morphology, Frequency Converters
Scientific paper
This thesis consists of three parts: submillimeter wavelength receiver development, submillimeter observations and modeling of protostellar outflows. Experiments were conducted on a Pb/ln/Au superconductor insulator-normal metal tunnel junction mixer to investigate the performance of a submillimeter receiver and to make a comparison with the quantum mixer theory. The theory predicts an optimal mixer conversion of -20 dB, and the best receiver measurement was -28 dB, thus the input and and mismatch losses are 8 dB. The effects of junction quality, capacitance, tuning, bias voltage and frequency on the mixer conversion have also been studied in detail. The second part of this thesis consists of submillimeter observations of protostellar outflows and these are interpreted as evidence that outflows are driven by jets. Two cases that are studied are the HH 46/47 system which shows a morphological link between an outflow and a jet, and the NGC 2071 outflow which shows extremely high velocity (EHV) CO emission. It is shown that an alternative to a jet-driven outflow model such as a one with poorly collimated wind cannot account for the mass profiles of outflows. A simple analytic model of an outflow driven by a high velocity is presented, that shows a radiative bow shock at the head of a jet. The outflow is initially driven by the high thermal pressure in the post shock gas, but then as this gas rapidly cools, the outflow evolves in a momentum conserving snowplow fashion. Hydrodynamical simulations have been used to examine the physical properties of the shocked gas in more detail and to quantify the transfer of momentum from the jet to the outflow. It is shown that for low Mach number jets, M < 6 entrainment occurs through turbulent mixing at the sides of the jet. This jet model can reproduce many of the key features of outflows such as the increase of velocity with distance away from the source which is due to the density gradient in the ambient medium, the correct shape of the position-velocity diagram and the EHV features which arise in the jet's working surface.
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