Rozprawy doktorskie na temat „Ion”
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Hughes, Ian G. "Electron ion and ion-ion collisions". Thesis, Queen's University Belfast, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.335410.
Pełny tekst źródłaPickles, Raymond J. "Intracellular calcium ions in epithelial ion transport". Thesis, University of Cambridge, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.307103.
Pełny tekst źródłaUribe, Cristina Jarque. "Ion-ioin interaction in a polarizable medium". Thesis, University of Cambridge, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.386158.
Pełny tekst źródłaXu, Yaodong. "Applications of mass spectrometric techniques to charge-transfer processes and cluster ion reactions". Diss., Georgia Institute of Technology, 1991. http://hdl.handle.net/1853/26208.
Pełny tekst źródłaIsildak, Ibrahim. "Ion selective electrodes in ion chromatography". Thesis, University of Newcastle Upon Tyne, 1992. http://hdl.handle.net/10443/859.
Pełny tekst źródłaAdelhelm, Philipp. "From Lithium-Ion to Sodium-Ion Batteries". Diffusion fundamentals 21 (2014) 5, S.1, 2014. https://ul.qucosa.de/id/qucosa%3A32397.
Pełny tekst źródłaEbanezar, John Angelin [Verfasser]. "Negative Ion formation in Ion-Molecule and Ion-Surface collisions / Angelin Ebanezar John". Greifswald : Universitätsbibliothek Greifswald, 2014. http://d-nb.info/1061064654/34.
Pełny tekst źródłaShen, Kuan-Hsuan. "Modeling ion conduction through salt-doped polymers: Morphology, ion solvation, and ion correlations". The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1595422569403378.
Pełny tekst źródłaOrban, Istvan. "Electron - Ion Recombination Studies of Astrophysically Relevant Ions : Storage Ring and Electron Beam Ion Trap Based Measurements /". Stockholm : Department of Physics, Stockholm University, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-33254.
Pełny tekst źródłaAt the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 6: Submitted. Paper 7: Submitted. Härtill 7 uppsatser.
Bissonnette, Martine C. "Ion/radical and ion/molecule complexes and ion structure assignments in the gas phase". Thesis, University of Ottawa (Canada), 1991. http://hdl.handle.net/10393/7731.
Pełny tekst źródłaLi, Libing. "Strategies for secondary ion yield enhancements in focused ion beam secondary ion mass spectrometry". Thesis, Imperial College London, 2010. http://hdl.handle.net/10044/1/11806.
Pełny tekst źródłaSoyk, Matthew W. "Instrumentation development for coupling ion/ion reactions and ion mobility in biological mass spectrometry". [Ames, Iowa : Iowa State University], 2008.
Znajdź pełny tekst źródłaBozkurt, Bilge. "Dynamic Ion Behavior In Plasma Source Ion Implantation". Master's thesis, METU, 2006. http://etd.lib.metu.edu.tr/upload/12607025/index.pdf.
Pełny tekst źródłaAllan, Scott Young. "Ion Energy Measurements in Plasma Immersion Ion Implantation". Thesis, The University of Sydney, 2009. http://hdl.handle.net/2123/5338.
Pełny tekst źródłaAllan, Scott Young. "Ion Energy Measurements in Plasma Immersion Ion Implantation". The School of Physics. The Faculty of Science, 2009. http://hdl.handle.net/2123/5338.
Pełny tekst źródłaThis thesis investigates ion energy distributions (IEDs) during plasma immersion ion implantation (PIII). PIII is a surface modification technique where an object is placed in a plasma and pulse biased with large negative voltages. The energy distribution of implanted ions is important in determining the extent of surface modifications. IED measurements were made during PIII using a pulse biased retarding field energy analyser (RFEA) in a capacitive RF plasma. Experimental results were compared with those obtained from a two dimensional numerical simulation to help explain the origins of features in the IEDs. Time resolved IED measurements were made during PIII of metal and insulator materials and investigated the effects of the use of a metal mesh over the surface and the effects of insulator surface charging. When the pulse was applied to the RFEA, the ion flux rapidly increased above the pulse-off value and then slowly decreased during the pulse. The ion density during the pulse decreased below values measured when no pulse was applied to the RFEA. This indicates that the depletion of ions by the pulsed RFEA is greater than the generation of ions in the plasma. IEDs measured during pulse biasing showed a peak close to the maximum sheath potential energy and a spread of ions with energies between zero and the maximum ion energy. Simulations showed that the peak is produced by ions from the sheath edge directly above the RFEA inlet and that the spread of ions is produced by ions which collide in the sheath and/or arrive at the RFEA with trajectories not perpendicular to the RFEA front surface. The RFEA discriminates ions based only on the component of their velocity perpendicular to the RFEA front surface. To minimise the effects of surface charging during PIII of an insulator, a metal mesh can be placed over the insulator and pulse biased together with the object. Measurements were made with metal mesh cylinders fixed to the metal RFEA front surface. The use of a mesh gave a larger ion flux compared to the use of no mesh. The larger ion flux is attributed to the larger plasma-sheath surface area around the mesh. The measured IEDs showed a low, medium and high energy peak. Simulation results show that the high energy peak is produced by ions from the sheath above the mesh top. The low energy peak is produced by ions trapped by the space charge potential hump which forms inside the mesh. The medium energy peak is produced by ions from the sheath above the mesh corners. Simulations showed that the IED is dependent on measurement position under the mesh. To investigate the effects of insulator surface charging during PIII, IED measurements were made through an orifice cut into a Mylar insulator on the RFEA front surface. With no mesh, during the pulse, an increasing number of lower energy ions were measured. Simulation results show that this is due to the increase in the curvature of the sheath over the orifice region as the insulator potential increases due to surface charging. The surface charging observed at the insulator would reduce the average energy of ions implanted into the insulator during the pulse. Compared to the case with no mesh, the use of a mesh increases the total ion flux and the ion flux during the early stages of the pulse but does not eliminate surface charging. During the pulse, compared to the no mesh case, a larger number of lower energy ions are measured. Simulation results show that this is caused by the potential in the mesh region which affects the trajectories of ions from the sheaths above the mesh top and corners and results in more ions being measured with trajectories less than ninety degrees to the RFEA front surface.
Choi, Jong-Ho Okumura Mitchio Okumura Mitchio. "Infrared spectroscopy of molecular ions and ion-solvent clusters /". Diss., Pasadena, Calif. : California Institute of Technology, 1995. http://resolver.caltech.edu/CaltechETD:etd-09252007-09111.
Pełny tekst źródłaWhitlow, Harry James. "Ion-materials interactions and their application". Thesis, University of Bath, 1998. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.285272.
Pełny tekst źródłaMcVeigh, Ryan. "Biologically enhanced ion exchange of ammonium ion using clinoptilolite". Thesis, Queen's University Belfast, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.247390.
Pełny tekst źródłaSterling, Robin C. "Ytterbium ion trapping and microfabrication of ion trap arrays". Thesis, University of Sussex, 2012. http://sro.sussex.ac.uk/id/eprint/39684/.
Pełny tekst źródłaRosenberg, Ron S. M. Massachusetts Institute of Technology. "Screen-printed ion selective electrodes for soil ion detection". Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/110884.
Pełny tekst źródłaCataloged from PDF version of thesis.
Includes bibliographical references (pages 187-192).
Rural Indian farmers lack an available, affordable, usable, and actionable means to diagnose soil health, which is a prerequisite for judicious application of fertilizer. Although government labs and mobile kits are available, these fail to meet the aforementioned qualities; as a result fewer than 5% of rural Indian farmers have ever performed a soil test. This thesis details the design and characterization of a point-of- use soil testing device, comprising a set of disposable ion-selective electrode (ISE) strips and a handheld electrochemical reader, which together transduce soil analyte concentrations into a numeric input for a mobile-phone based fertilizer recommendation engine. As a proof-of-concept, potassium (K+) selective electrodes are studied, because K+ is essential to plant growth and reproduction. The strips employ a simple two electrode system, wherein carbon nanotube and silver chloride inks are the electrode contacts, plasticizer-free butyl acrylate ion selective membranes are located on the working electrodes, and sodium-chloride doped polyvinyl butyral membranes provide stable reference potentials. The electrodes were fabricated by a combined screen printing and drop casting process, and the protocol, extraction solution, and reference potential stability were tuned to maximize ISE performance and repeatability. Using a mathematical model and supporting experiments, we verified that hydrogen selectivity determines the detection limit, and furthermore, that scientists can tune the ionophore-ionic site ratio to minimize this effect. Using the final electrode fabrication process, a set of 20 full ISE devices in the presence of 0.02M SrCl2 extraction solution were shown to have sub-uM detection limits and near-Nernstian average sensitivity (61 mV/decade). When compared to ICP data for a set of 30 soil samples using the final reader, the sensors demonstrated a 0.898 correlation factor. Workshops in India were conducted to determine user needs and corresponding product attributes, as well as a "usability index" for the system assessed across farmer demographics. The favorable system performance proves that solid-state ISEs are a promising technology for soil diagnostics in resource-constrained environments.
by Ron Rosenberg.
S.M.
Perez, Martinez Carla S. (Carla Sofia). "Engineering ionic liquid ion sources for ion beam applications". Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/105605.
Pełny tekst źródłaCataloged from PDF version of thesis.
Includes bibliographical references (pages 177-186).
Ionic liquid ion sources (ILIS) are devices capable of producing positive and negative molecular ion beams through field evaporation from room-temperature molten salts. If sufficiently high hydraulic impedance from the liquid-supporting emitter is provided such that the ratio of flow rate Q to liquid's electrical conductivity K is sufficiently small, a pure ionic regime (PIR) can be achieved, in contrast with traditional electrosprays that produce charged droplets, or mixtures of droplets and ions. The PIR provides high current density from a point source, making ionic liquid ion beams suitable for use in focused ion beam (FIB) applications. The use of ionic liquids in focused ion beams could allow the production of sub-100 nm beams of up to kiloDalton organic ions as well as reactive species, with the possibility of engineering ionic liquid properties for a specific application. In addition, using micro-fabricated and nano-structured emitter arrays operating in the PIR can give access to efficient and compact positive or negative ion sources, for applications from spacecraft thrusters to deep reactive ion etchers (DRIE). There is a need for novel tip geometries and materials that favor the stable formation of a single emission site on the liquid supporting structure, while providing a continuous liquid supply compatible with the PIR. In this thesis, porous carbon based on resorcinol-formaldehyde xerogels is introduced as an emitter substrate. The target pore sizes and emitter geometries to attain the PIR are obtained through analytical estimates. The carbon xerogel can be shaped to the required micron-sized geometry through mechanical polishing. Time-of-flight mass (TOF) spectrometry is used to verify that charged particle beams produced from the mechanically polished carbon xerogel source, infused with the ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI-BF₄), contain solvated ions exclusively. In the case of the liquid 1-ethyl-3-methylimidazolium bis(trifluorometrylsulfonyl)imide (EMI-Im), mixed ion-drop operation is obtained. Laser micro-machining has been validated as a manufacturing technique to shape carbon xerogel into emitters. This technique should allow the production of emitter arrays for DRIE or propulsion applications, and allow the reproducible fabrication of emitters for FIB. Stable emission has been obtained from a laser micromachined tip infused with the ionic liquid EMI-BF₄ . The results of TOF and retarding potential analysis (RPA) experiments indicate that the emission consists mostly of monomers and dimers, and that a small fraction (< 5%) of the beam might be composed of cluster ions with greater degrees of solvation. To conclude, the thesis reports on the etching properties of the beams obtained from ILIS, both in the case of traditional externally wetted tungsten sources and with the novel carbon xerogel emitter technology. The W ILIS etches silicon with sputtering rates between 6 and 35 atoms of silicon removed per incident ion at 15 keV irradiation energies, whereas the carbon xerogel ILIS has been used to etch gold, silicon and gallium nitride with sputtering rates in the order of 10 for irradiation energies between 2 and 7 keV.
by Carla S. Perez Martinez.
Ph. D.
Kuzema, O. S., i P. O. Kuzema. "Ion Probe with Primary ion Beam Prism Mass Separator". Thesis, Sumy State University, 2013. http://essuir.sumdu.edu.ua/handle/123456789/35627.
Pełny tekst źródłaShi, Yu. "Single-ion Hydration and Ion Association in Aqueous Solutions". University of Cincinnati / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1439310243.
Pełny tekst źródłaKellerbauer, Alban. "Production of a cooled ion beam by manipulation of 60-keV ions into a radio-frequency quadrupole ion guide". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape9/PQDD_0025/MQ50804.pdf.
Pełny tekst źródłaHohenschutz, Max. "Nano-ions in interaction with non-ionic surfactant self-assemblies". Thesis, Montpellier, 2020. http://www.theses.fr/2020MONTS064.
Pełny tekst źródłaNanometer-sized ions (nano-ions), such as ionic boron clusters, polyoxometalates (POMs) and large organic ions, have spawned remarkable interest in recent years due to their ability to adsorb or bind to electrically neutral chemical systems, such as macrocyclic host molecules, colloidal nano-particles, surfactants and polymers etc. The underlying adsorption or binding processes were shown to be driven by a solvent-mediated phenomenon, the chaotropic effect, which drives the nano-ion from the water bulk towards an interface. Thus, hydration water of the ion and the interface is released into the bulk resulting in a bulk water structure recovery. This effect is particularly strong for nano-ions. Therefore, they were termed superchaotropic or hydrophobic ions as an extension to classical (weakly) chaotropic ions such as SCN-. All commonly studied superchaotropes, though chemically diverse, share physical characteristics such as low charge density and high polarizability. Herein, the effects of nano-ions on ethoxylated non-ionic surfactant self-assemblies, micellar and bilayer phases, are elucidated to draw conclusions on their chaotropic and/or hydrophobic nature. By combining small angle scattering of neutrons and x-rays (SANS and SAXS), and phase diagrams, non-ionic surfactant/nano-ion systems are examined and compared, from the nanometer to the macroscopic scale. Thus, all studied nano-ions are found to induce a charging of the surfactant assemblies along with a dehydration of the non-ionic surfactant head groups. Furthermore, chaotropic and hydrophobic ions differ in their effects on the micellar shape. Superchaotropic ions drive the elongated non-ionic surfactant micelles towards spherical micelles (increase in curvature), whereas hydrophobic ions cause a transition towards bilayer phases (decrease in curvature). It is concluded that superchaotropic nano-ions act like ionic surfactants because their addition to non-ionic surfactant systems causes a charging effect. However, nano-ions and ionic surfactants are fundamentally different by their association with the non-ionic surfactant assembly. The nano-ion adsorbs to the non-ionic surfactant heads by the chaotropic effect, while the ionic surfactant anchors into the micelles between the non-ionic surfactant tails by the hydrophobic effect. The comparison of the effects of adding nano-ions or ionic surfactant to non-ionic surfactant was further investigated on foams. The foams were investigated regarding foam film thickness, drainage over time and stability, respectively using SANS, image analysis and conductometry. The tested superchaotropic POM (SiW12O404-, SiW) does not foam in water in contrast to the classical ionic surfactant SDS. Nevertheless, addition of small amounts of SiW or SDS to a non-ionic surfactant foaming solution resulted in wetter foams with longer lifetimes. Meanwhile, the foam film thickness (determined in SANS) is increased due to the electric charging of the non-ionic surfactant monolayers in the foam film. It is concluded that the remarkable behavior of nano-ions – herein on non-ionic surfactant systems – can be extended to colloidal systems, such as foams, polymers, proteins or nanoparticles. This thesis demonstrates that the superchaotropic behavior of nano-ions is a versatile tool to be used in novel formulations of soft matter materials and applications
Marto, Jarrod A. "External Ion Injection and Applications of Ion Axialization in Fourier Transform Ion Cyclotron Resonance Mass Spectrometry /". The Ohio State University, 1995. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487868114113087.
Pełny tekst źródłaTorres, Theresa Ann. "Development of Fourier transform ion cyclotron resonance mass spectrometry for the study of ion-ion reactions /". Digital version accessible at:, 1998. http://wwwlib.umi.com/cr/utexas/main.
Pełny tekst źródłaLi, Ailin. "Miniaturization of Linear Ion Traps and Ion Motion Study in a Toroidal Ion Trap Mass Analyzer". BYU ScholarsArchive, 2017. https://scholarsarchive.byu.edu/etd/6503.
Pełny tekst źródłaFowles, Jonathon Richard. "Characterization of the skeletal muscle sodium ion-potassium ion-ATPase, and the acute effects of exercise on sodium ion-potassium ion-ATPase activity". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/NQ65239.pdf.
Pełny tekst źródłaBäckström, Erik. "LIfetimes measurement states in ions at an ion storage ring". Licentiate thesis, Stockholms universitet, Fysikum, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-67024.
Pełny tekst źródłaRussell, Elspeth. "Ions and ion transport mechanisms in the developing chick embryo". Thesis, University of Newcastle Upon Tyne, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.287301.
Pełny tekst źródłaFisher, Zachary (Zachary Kenneth). "Shuttling of ions for characterization of a microfabricated ion trap". Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/78510.
Pełny tekst źródłaCataloged from PDF version of thesis.
Includes bibliographical references (p. 65-67).
In this thesis, I present experimental results demonstrating the characterization of a planar Paul trap. I discuss the theory of ion trapping and analyze the voltages required for shuttling. Next, the characteristics of a digital-to-analog converter (DAC) are calibrated, and this instrument is integrated into trapping experiments to test the viability of the analytic model. Combining theory with the capabilities of the DAC, I calculate that the new experimental system is capable of 3 nm-precision control of the ion. Taking advantage of this ion control, I present initial results for a lock-in micromotion detection method which minimizes stray fields around an ⁸⁸Sr+ ion using Fourier analysis on the ion fluorescence to detect resonance at the secular frequencies. This method drives the ion oscillator across resonance using a superimposed radiofrequency electric field, which allows for off-axis field measurements as well as trap characterization. With this method, the secular frequencies of the trap are measured and are observed to fall within 3.50[sigma] of the analytic prediction.
by Zachary Fisher.
S.B.
Ali, Safdar. "Electron - Ion Recombination Data for Plasma Applications : Results from Electron Beam Ion Trap and Ion Storage Ring". Doctoral thesis, Stockholms universitet, Fysikum, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-75311.
Pełny tekst źródłaAt the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: Accepted. Paper 5: Accepted. Paper 6: Manuscript. Paper 7: Manuscript.
Zhao, Qin. "Development of ion mobility mass spectrometry coupled with ion/ion reactions instrumentation and applications for protein analysis /". [Ames, Iowa : Iowa State University], 2009.
Znajdź pełny tekst źródłaHornsey, Richard Ian. "Factors affecting ion energy distributions in liquid metal ion sources". Thesis, University of Oxford, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.236154.
Pełny tekst źródłaPapadopoulos, S. "Atomic and cluster ion emission from liquid metal ion sources". Thesis, University of Oxford, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.375310.
Pełny tekst źródłaScrivens, R. M. "Extraction of an ion beam from a laser ion source". Thesis, Swansea University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.638785.
Pełny tekst źródłaScott, Graham Bruce Ian. "Experimental studies of astrochemical ion-atom and ion-molecule reactions". Thesis, University of Canterbury. Chemistry, 1997. http://hdl.handle.net/10092/7813.
Pełny tekst źródłaLambrecht, Alexander [Verfasser], i Tobias [Akademischer Betreuer] Schätz. "Optical ion trapping with regard to ultracold atom-ion experiments". Freiburg : Universität, 2017. http://d-nb.info/1136567089/34.
Pełny tekst źródłaMurrell, Jason. "Some studies in ion/molecule reactions on ion trapping instruments". Thesis, University of Kent, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.319223.
Pełny tekst źródłaBahaffi, Saleh Omar Saeed. "An investigation of ion-exchangers for ion chromatography of anions". Thesis, University of Kent, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.328170.
Pełny tekst źródłaFranklin, A. M. "Computational applications and ion behaviour in ion trap mass spectrometer". Thesis, University of Kent, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.294313.
Pełny tekst źródłaPearson, C. H. G. "New ion exchange resins for ion chromatography applied to anions". Thesis, University of Kent, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.372771.
Pełny tekst źródłaOrrman-Rossiter, Kevin G. "Ion scattering analysis of low energy ion bombarded GaAS(001)". Thesis, University of Salford, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.327940.
Pełny tekst źródłaHolden, Nicola Kathleen. "Atmospheric ion measurements using novel high resolution ion mobility spectrometers". Thesis, University of the West of England, Bristol, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.288184.
Pełny tekst źródłaGallen, Niall Anthony. "Ion implantation waveguide formation in transition metal ion doped insulators". Thesis, University of Sussex, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.310665.
Pełny tekst źródłaDobie, Paul J. "Microwave excitation of argon ion and helium-krypton ion lasers". Thesis, University of St Andrews, 1989. http://hdl.handle.net/10023/14163.
Pełny tekst źródłaPollum, Laura L. "Digital ion trap mass spectrometry for cold ion-molecule chemistry". Thesis, University of Oxford, 2015. http://ora.ox.ac.uk/objects/uuid:18c6451d-d247-4384-9257-f8864e038343.
Pełny tekst źródłaSteele, Adam V. "Barium ion cavity qed and triply ionized thorium ion trapping". Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/26530.
Pełny tekst źródłaCommittee Chair: Michael Chapman; Committee Member: Alex Kuzmich; Committee Member: Brian Kennedy; Committee Member: Chandra Raman; Committee Member: Kenneth Brown. Part of the SMARTech Electronic Thesis and Dissertation Collection.
Miller, Catherine Elizabeth. "Characterization of ion Cluster fragmentation in ionic liquid ion sources". Thesis, Massachusetts Institute of Technology, 2019. https://hdl.handle.net/1721.1/122372.
Pełny tekst źródłaThesis: Ph. D., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2019
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 273-281).
Ion electrospray propulsion is a cutting-edge micropropulsion technology that could revolutionize the capabilities of microsatellites. Ion electrospray thrusters could also be used on large spacecraft for precision attitude control applications such as gravity wave detection and exoplanet imaging. Novel room temperature molten salts, called ionic liquids, are used as propellant, which are composed purely of positive and negative molecular ions. When exposed to strong electric fields, ions and metastable clusters of ions are evaporated from the bulk liquid surface. The free ions and ion clusters can be accelerated to high velocities, producing thrust at high specific impulse. The performance of ion electrospray thrusters is affected by the composition of the ion beam and the amount of ion clusters that break apart during the acceleration phase. To improve thruster performance, a better understanding of the fundamental physics of ion evaporation and cluster break-up is needed.
The break-up of ion clusters, also called fragmentation, is not a well understood phenomenon. It has been observed in past experiments, but the rates of break-up have not been measured. The focus of this work is to experimentally investigate fragmentation more deeply than ever before. To accomplish this, a specialized instrumentation suite has been designed, built, and tested to measure fragmentation characteristics in unprecedented detail. A full-beam, spherical geometry retarding potential analyzer is used to measure the rates of fragmentation of ion clusters both outside the thruster and within the acceleration region for the first time. A narrow-beam, high time-resolution time of flight mass spectrometer is used to measure the beam composition. Single emitters based on resorcinol formaldehyde carbon xerogels were used as ion sources. Four ionic liquids spanning a wide range of liquid properties were characterized: EMI-FAP, EMI-Im, EMI-BF4, and BMI-I.
Analytical models were also developed to enhance the interpretation of the experimental results. The experimental measurements show that the amount of fragmentation increases with distance from the thruster and follows a constant rate equation. The mean lifetimes of ion clusters outside of the thruster range from 1-6 [mu]s, indicating that these clusters are quite unstable. It is observed that the fragmentation throughout most of the acceleration region is linear with respect to electric potential, which can be understood using analytical models. Rapid fragmentation likely occurs immediately after evaporation due to the strong electric fields near the emission site, which has significant implications for thruster performance. It is also observed that clusters of complex molecular ions which consist of many atoms tend to be the most stable. The initial temperature of ion clusters, which range from 520 K - 790 K, were estimated using analytical methods.
The effect of liquid temperature on the rates of fragmentation was also investigated. In conclusion, the work in this thesis provides a greatly enhanced understanding of ion cluster fragmentation, particularly how it is affected by ionic liquid properties, liquid temperature, and electric fields.
This research was supported by a NASA Space Technology Research Fellowship
by Catherine Elizabeth Miller.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Aeronautics and Astronautics