Improving particle confinement in inertial electrostatic fusion for spacecraft power and propulsion

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2007.Includes bibliographical references (p. 216-244).Fusion energy is attractive for use in future spacecraft because of improved fuel energy density and reduced radioactivity compared with fission power. Unfortunately, the most promising means of generating fusion power on the ground (Tokamak based reactors like ITER and inertial confinement reactors like NIF) require very large and heavy structures for power supplies and magnets, in the case of magnetic confinement, or capacitors and lasers in the case of inertial confinement. The mass of these reactors and support equipment is sufficiently large that no existing or planned heavy-lift vehicle could launch such a reactor, thereby necessitating in-space construction which would substantially increase the cost of the endeavor. The scaling of Inertial Electrostatic Confinement (IEC) is such that high power densities might be achievable in small, light-weight reactors, potentially enabling more rapid, lower cost development of fusion power and propulsion systems for space applications. The primary focus of the research into improving particle and energy confinement in IEC systems is based on the idea of electrostatic ion focusing in a spherically symmetric gridded IEC system.(cont.) Improved ion confinement in this system is achieved by the insertion of multiple concentric grids with appropriately tailored potentials to focus ion beams away from the grid wires. In order to reduce the occurrence of charge exchange and streaming electron power losses, the system is run at high vacuum. This modification to the usual approach was conceived of by Dr. Ray Sedwick and computational modeling has been conducted by Tom McGuire using a variety of custom and commercial codes. In this thesis, a semi-analytic model of the potential structure around a multi-grid IEC device is developed. A 1-D paraxial ray ion beam envelope approximation is then used along an equatorial beamline and the assumed beam density is gradually increased until an effective beam space charge limit is reached at which point the potential fusion output is calculated. Significant use of the commercial particle-in-cell code OOPIC was made, and its ability to predict multi-grid IEC confinement properties is evaluated. An experiment was built to confirm the effectiveness of the multiple-grid structure to improve ion confinement times. It is shown that the multi-grid IEC can improve ion confinement time over the conventional, 2-grid IEC device. The PIC predicted ion bunching mode is also seen in experiment.by Carl C. Dietrich.Ph.D

Theoretical analysis and experimental investigations of an expander-cycle centrifugal direct injection rocket engine

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2003.Includes bibliographical references (p. 103-104).by Carl Dietrich.S.M

Specific structural features of syndecans and heparan sulfate chains are needed for cell signaling

The syndecans, heparan sulfate proteoglycans, are abundant molecules associated with the cell surface and extracellular matrix and consist of a protein core to which heparan sulfate chains are covalently attached. Each of the syndecan core proteins has a short cytoplasmic domain that binds cytosolic regulatory factors. the syndecans also contain highly conserved transmembrane domains and extracellular domains for which important activities are becoming known. These protein domains locate the syndecan on cell surface sites during development and tumor formation where they interact with other receptors to regulate signaling and cytoskeletal organization. the functions of cell surface heparan sulfate proteoglycan have been centered on the role of heparan sulfate chains, located on the outer side of the cell surface, in the binding of a wide array of ligands, including extracellular matrix proteins and soluble growth factors. More recently, the core proteins of the syndecan family transmembrane proteoglycans have also been shown to be involved in cell signaling through interaction with integrins and tyrosine kinase receptors.Universidade Federal de São Paulo, Escola Paulista Med, Dept Bioquim, BR-04044020 São Paulo, BrazilUniversidade Federal de São Paulo, Escola Paulista Med, Dept Bioquim, BR-04044020 São Paulo, BrazilWeb of Scienc