Work on film flow in liquid helium II is not new, but very little has been done in the temperature region below 1 degree. The present work describes a method of extending these measurements down to the very low temperature range. After a brief introduction laying the foundation of the problem in its proper framework in the field of low temperatures, the experiments and results obtained by other workers in film flow and associated phenomena are reviewed. Then the author proceeds to the development of experimental techniques used in attempting to seal gaseous helium at high pressures in glass capsules. Chapter II terminates with a full description of the so-called Heater Method with which helium 'bombs' were sealed at pressures ranging from 750 to 1100 psi. One of these capsules containing a capillary beaker, and partially filled with manganous ammonium sulfate, was used in determining film flow rates at temperatures ranging from approximately 2° to 0.6°K, The lower temperatures were obtained by adiabatic demagnetization techniques. Chapter III is a report of such experimentation. The results obtained are much like those of Ambler and Kurti, 1952, and support their contention that film flow rates do increase with decreasing temperatures in the region below one degree absolute. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The profiles of the He I lines with forbidden components in plasmas with electron densities below 10¹⁵ electrons per cc. are of astro-physical interest. A pulsed-arc plasma device has been constructed and operated at such initial conditions that in the afterglow (i.e. up to 200 μsec after breakdown), the steadily decreasing electron density passes through the range of interest. The plasma was observed end-on with a monochromator at a wavelength near 4471 angstroms for each discharge, and the intensity recorded as a functions of time. Good shot-to-shot reproducibility of the plasma permitted the line profile to be reconstructed for different times by repeating the measurements at different wavelengths spanning the line. The profile of He I 4471 has been measured for 10¹⁵ cm ̄³ and agreement has been found with the results of Burgess and Cairns (1971) and recent calculations of Barnard and Cooper (to be published). / Science, Faculty of / Physics and Astronomy, Department of / Graduate

A beam of polarized ³He⁺ ions has been produced using atomic beam method techniques. This method has the attraction of being capable of producing an ion beam with polarizations up to 100%. The polarization of ³He beams presently produced by optical pumping techniques is of the order of 5%. The apparatus is composed of three main sections, the atomic beam source consisting of a supersonic nozzle cooled to liquid helium temperatures to produce a low velocity atomic beam, the tapered hexapole magnet to spatially separate the particles in the two magnetic spin substates, and the electron bombardment ionizer to produce ³He⁺ ions from the neutral ³He atomic beam. The low velocity beam is required because the nuclear magnetic moment of ³He is of the order of 1000 times smaller than the electronic magnetic moment used to separate beams in conventional Stern-Gerlach magnets and to achieve a high ionization efficiency. The measured intensity of the beam produced by the atomic beam source cooled to liquid helium temperature was 1 x 10¹⁸ atoms/sr-sec, the most probable velocity was 310 m/sec, and the velocity full width at half maximum was 50 m/sec. The beam flux through the ionizer increases by a factor of 1.3 when the hexapole field is turned on, in good agreement with the theoretically expected increase. This increase corresponds to a polarization of 65% of the atomic beam. A 12nA³He⁺ ion beam was obtained corresponding to an ionization efficiency of approximately 0.15%. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

A model - of which a similar type was found applicable to an argon plasma jet - is developed and applied to a laminar helium jet operated at atmospheric pressure with a current of 185 amps. The results are used to investigate the equilibrium properties of the plasma. It was found that the helium plasma was not in a state of Local Thermodynamic Equilibrium but that the neutral atoms were considerably colder than the electrons. (Te ≈ 17,000°K; To≈5,700°K) Instructions are given in the thesis on the construction, operation and properties of a d.c. plasma jet. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The structure in the collapse stage of a linear Z-pinch discharge in helium has been studied by optical methods. Observations with a framing camera, rotating mirror spectrograph, and monochromator have been correlated with magnetic field and current distributions determined by Tam (1967). The luminous regions in a helium pinch are very faint. Therefore, up to twenty exposures have to be superimposed on the same framing camera or rotating mirror record. This requires a high degree of reproducibility in the initiation of the discharge. At high initial pressures, a non-luminous shock wave at the inner edge of the collapsing current shell precedes the luminous plasma layer towards the centre of the discharge vessel. This shock front is followed by a region of predominantly Hel emission, while most of the Hell radiation occurs in the outer regions of the collapsing plasma shell. The separation into Hel and Hell radiating regions is consistent with spectroscopic measurements of temperature: higher temperatures occur at larger radii. Pressure and density in the non-radiating shock wave region are determined by calculations based on a simple model. At low filling pressures, the Hel and Hell regions coincide. The position of maximum luminosity is observed to correspond with the position of maximum current density. The luminosity and current shells coincide with no shock wave preceding the luminous front. Strong continuum radiation is emitted from the centre of the discharge tube as soon as the leading edge of the current shell reaches the axis. This leading edge is luminous at low initial pressures, but becomes a non-radiating shock front at higher filling pressures. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The formation of a molecular beam using a miniature supersonic nozzle source is discussed. The results of operation at room, liquid nitrogen and liquid helium temperatures of a supersonic nozzle system designed for use in a polarized helium³ ion source are presented. It is shown that helium⁴ beam intensities at 4.2ºK are approximately 1/8 of those at 300ºK. Factors upon which the beam intensity depend have been investigated experimentally and it is found that at room temperature and a distance of 16cm from the skimmer a heliun⁴ beam intensity of 3x10¹⁶ molecules/cm²/sec is attainable under certain circumstances. This beam intensity is an improvement by a factor of 10 over the original performance of the nozzle source. Assuming a 40% transmission through the magnet and a 0.25% ionization efficiency an ion current of 0.02 microamperes is estimated for the polarized helium³ ion source. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

While endeavouring to produce macroscopic vortex rings in liquid helium by a drop method, a general study of the formation of vortex rings when a liquid drop falls into a stationary bath of the same liquid was made. Preliminary investigations were made using room temperature liquids with a wide range of surface tensions, densities and viscosities. A cryostat was designed to study vortex ring formation in liquid nitrogen, liquid helium I, and liquid helium II. A numerical method, involving vorticity and Stokes stream function as parameters, for the solution of non-steady, rotational, viscous flows is outlined. Experimental results confirm the reported existence of optimum dropping heights from which the drop develops into a superior vortex ring. These optimum heights are analysed, by a photographic study, in terms of the liquid drop oscillation. It is found that optimum vortex rings are formed, if the drop is spherical at the moment of contact with the bath, and is changing from an oblate spheroid to a prolate spheroid. Vortex rings were detected in liquid nitrogen but not in liquid helium. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The temperature of a Helium plasma produced in a shock tube has been determined from absolute intensity measurements. The plasma was considered to be homogeneous, transparent and in local thermodynamic equilibrium. The emissivity of the plasma has been measured by comparing the plasma radiation to the radiation from a carbon arc through a simple optical system. The influence of errors in measured parameters and the presence of impurities is discussed. Temperatures which depend on large exponential terms are relatively insensitive to both errors in measurement and the impurity content of the plasma. The accuracy of absolute intensity measurements is at best comparable to relative intensity measurements. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The polarization of light from helium atoms excited by the impact of low energy electrons has been measured for the spectral lines 2³P - 2³S (10,829 Å) and 3³P - 2³S (3889 Å). An electron beam carrying a current of 10μA was directed into helium gas at a pressure of 4 x 10⁻³ torr or less. Polarization was measured as a function of electron energy in a range from the excitation threshold (approximately 23 electron volts) to 50 e.v. For the 2³T - 2³S line, this work represents the first reported measurement of this type. There is special interest in the value of polarization near the excitation threshold. The theoretical threshold polarization for both lines studied in this thesis is 36.6%. In the experiment of this thesis, the observed polarization of the 2³P line rises to 21% near threshold, and by means of a curve fitting procedure may be extrapolated to 32 ± 6%. The polarization of the 3³P - 2³S line rises to 11% and may be extrapolated to 15 ± 3%. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

An experimental investigation of the absorption reaction ⁴He(π⁺,ppp) has been undertaken on the M11 beamline at the TRIUMF cyclotron. Positive pions at an average kinetic energy of 165 MeV were directed onto a cylindrical liquid 4He target and the outgoing protons were measured by a combination of two time-of-flight arrays and two plastic scintillator telescopes. A description of the apparatus, experimental technique and calibration is presented. Results from triple proton coincidences at a single orientation of three of the detectors are discussed. Their angular settings with respect to the pion beam were 40°, 136° and —55°. Comparisons are made with Monte-Carlo simulations of three and four body phase spaces. Identification of a quasi-free three nucleon absorption mode is made for the first time at this energy. An integrated cross-section for this process is determined (σQ₃N = 4.4 ± 0.6mb). The quantitative agreement between these results and those of another recent experiment¹ indicate that a small fraction(≈10%) of the coincidences could be due to a two step absorption mechanism. ¹Backenstoss et al. Phys. Rev. Lett 61:923(1988) / Science, Faculty of / Physics and Astronomy, Department of / Graduate