Part I An efficient ionizer designed for the ionization of a low intensity molecular beam has been developed. The ionizer will have an efficiency for an argon beam at room temperature and 0.8 amperes plate electron current of greater than 5.3% and for an helium 4 beam at room temperature and 0.8 amperes plate electron current of greater than 0.12%. The electron bombardment ionization occurs between two flat plates both of which are at 200 volts potential with respect to the cathode. The two plates are at a 2.5° angle to each other so that the ions once formed experience a field gradient produced by this angle which accelerates them out the open side of the ionizer 90° to the direction of the incident neutral beam. The electrons were emitted from 6, 0.030 x 0.004 inches, thoriated tungsten ribbon filaments heated by d.c. power. Successful activation of the filaments, however, was not achieved and so they were used as pure tungsten filaments. The ionizer ran at between 1900° Kelvin and 2600°Kelvin for about 8 hours without significant distortion, filament sag, or appreciable outgassing. Part II The design of a source of doubly charged helium ions was carried out to provide an helium beam of twice the terminal energy of the Van de Graafe Accelerator. The unit, to be installed in the top terminal of the Van de Graaffe, employs a radio frequency ion source followed by a double focusing magnet. The magnet has plane parallel pole pieces with a fringing field that produces focusing in a vertical plane. The unit is designed so that at 2.5 kilovolts extraction voltage a magnetic field of 3060 gauss is required to bend the He⁺⁺ through an angle of 90° and bring them to a focus at 5.8 cm. from the exit face of the magnet. The beam acceptance angle of the magnet is 10° at a source distance from the entrance face of 5 cm. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The conductance of a small electric probe has been determined for radial distances (2 - 15 cm) from a recovering spark gap as a function of time after discharge initiation. The times investigated were from 0.2 to 15 ms and the gas pressure was varied from 22 mmHg down to 0.1 mmHg. The voltage applied to the probes was a sawtooth pulse which rose to about 80 volts in 10 μs. It is shown theoretically that the probe conductance should be proportional to the three-halves power of the gas temperature. Prom a known value of the temperature, deduced from recovery measurements, and the known probe conductance the constant of proportionality was deduced. Hence it was possible to determine the temperature from the probe conductance. The probe conductance measurements show that at 200 mmHg pressure the spark channel is only 2 cm in radius and that there is no detectable ionization left 2 ms after the discharge. As the gas pressure decreases the spark channel increases in size and takes longer to deionize, until at 1 mmHg pressure the channel fills the whole spark chamber (spark channel radius is 15 cm) and requires almost 15 ms to deionize. At 1 mmHg gas pressure there is a radial temperature gradient, while at 0.1 mmHg pressure the gas everywhere in the channel recovers at the same rate. In this experiment it is theoretically predicted that volume recombination should be the dominant recovery method and this is experimentally verified. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

This thesis is concerned with a theoretical and experimental investigation of Alfvén waves in an ionized medium, and magnetic interaction effects between a moving plasma and a magnetic coil external to the plasma. Methods for generating Alfvén disturbances for varying conditions of gas density and magnetic fields are considered and various means for measuring any effects that may be produced. It will be seen that for propagation of m.h.d. waves, extremely strong coupling between the plasma and field is necessary with consequent necessary high fields and Alfvén speeds. The effect of an axial magnetic field modifying the shock speed in the plasma is investigated and also the effect of the field on incident and reflected shock speeds by placing a plain obstruction in the shock tube which blocks the plasma flow. A further study of magnetic interaction effects between a moving plasma and a localized radial field was undertaken with the desire of correlating mechanical momentum transfer with varying conditions of applied field and gas pressures in the plasma (hence conductivity, density, and shock speed variations). Mechanical and electrical measurements of momentum transfer are compared with theory, and it will be seen that the mechanical method offers a fairly reliable means of measurement. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

In the work described in this thesis attempts have been made to obtain information on three aspects of the behaviour of liquid argon as an ionization counter. Ionization was produced by alpha particles from a source deposited on the negative electrode of a small parallel-plate chamber in which pure argon was liquefied. The current pulses resulting from movement of the liberated electrons in the field applied to the plates were analysed electronically. Firstly, it was desired to determine the time taken by the electrons originating from distinct ionization events to traverse measured electrode separations and be collected by the positive electrode. These transit times depend upon the electron mobility in liquid argon, defined as the velocity of the electrons per unit field. From this mobility, the mean free path and collision cross-section of the electrons with respect to argon atoms can be calculated. Some estimates of transit times and mobilities, and resulting values of mean free path and cross-section are given. However, it appears that limitations of the electrode spacing and the applied field cause the transit time to be so short as to necessitate the use of wide band amplifiers with, consequently, high noise levels. Secondly, the causes of variation in size of current pulses with angle of emission of the initiating alpha particles were investigated. The effect of greatest interest was that, due to the geometry of the chamber, as from it a determination was made of the range of alpha particles in liquid argon. For 5.3 MeV alpha particles, the weighted centre of ionization was found to be 0.006 cms. from the source, implying a particle range of about 0.009 cms. The number of electrons contributing to current pulses was also found to be a function of the angle of emission, on account of a variable degree of recombination with the positive ion column. This number was determined, and even under the most advantageous conditions fell considerably short of the probable total number liberated. This fact imposes a serious limitation on the potentialities of liquid argon as a useful counter. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The dissociative ionization by electron impact of H₂, H₂O, and H₂S was investigated between the electron impact energies of 20 and 45 eV. Protons were the detected fragments, and a time-of-flight method was used to measure the proton kinetic energies. By also measuring the thresholds for the production of discrete energy groups of protons, it was possible to determine the dissociation limits and kinetic energy distributions for individual electronic states. It was found that autoionizing states that lead to dissociation were the major contributors of proton fragments for all of the molecules investigated. Some of the measurements are tabulated in the following table. (UNFORMATTED TABLE FOLLOWS) Molecule Threshold Dissociation Probable Probable (eV) limit (eV) state fragments H₂ 24.5±1.0 18.0±1.0 Q₁ ¹Σ(g)⁺ H⁺, H(1S) 30.5±1.0 18.0±1.0 Q₁ ¹Πᵤ H⁺, H(1S) 36.5±1.0 -- ²Πᵤ H⁺, H(2P) H₂O 24.5±1.0 19.5±1.0 -- H⁺, OH (X²Π) 29.5±1.0 23.0±1.0 -- H⁺,O(³P),H(1S) H₂S 25.5±1.0 18.0±1.0 -- H⁺, HS (X²Π) 32.0±1.0 -- -- H⁺, . . . 42.0±1.0 -- -- H⁺, . . . (TABLE ENDS)

Thesis (M.S.)--University of Wisconsin--Madison, 1982. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 122-127).

Thesis (Ph.D.)--University of California, Berkeley, 1961. / "UC-34 Physics" -t.p. "TID-4500 (16th Ed.)" -t.p. Includes bibliographical references (p. 67-68).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1982. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 159-165).

The greater part of the experimental research, described in this thesis, has been devoted to an investigation, by direct electrical methods, of the formation of ionised molecules in mercury vapour and helium. […] This thesis is divided into four parts. The first contains a brief outline of the quantum theory of the atom and the molecule, a summary of our present knowledge of the interchange of energy in various collision processes, and a discussion of the theory of the thermionic emission from a heated filament and its applications. Particular reference for the development of the experimental research described in Parts 2, 3 and 4.

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