Nuclear Fusion Reaction Kinetics and Ignition Processes in Z Pinches

This thesis presents work on two topics related to nuclear fusion in plasmas. The first topic is the energy spectrum of products of fusion reactions in plasmas, called the production spectrum. The second is an investigation of the fusion reaction processes in high energy density Z pinch plasmas and the feasibility of ignition of such plasmas. A method is presented for the derivation of production spectra for plasmas with various distributions of ion velocities. The method is exact, requiring the solution of a 5 dimensional integral and is suitable for both isotropic and anisotropic distributions. It is shown that many of the integrals can be solved analytically. The solutions are used to study the spectra of neutron energies produced by deuterium-deuterium and deuterium-tritium reactions. It is found that for maxwellian distributions of ions the neutron spectrum is asymmetric with a longer high energy tail when compared with gaussian approximations of the spectrum. Deuterium and deuterium-tritium Z pinch plasmas are studied computationally using a hybrid code in which the fuel is modelled as a magnetohydrodynamic (MHD) fluid and fast ions are modelled as discrete particle-in-cell (PIC) particles. Using a Z pinch model in which the magnetic and thermal pressures are in equilibrium it is found that significant energy gain can be achieved for currents greater than 50MA. Deuterium gas puff experiments with a 15MA current are also analysed computationally in order to determine the reaction mechanism. The results of MHD simulations in 3 dimensions are post-processed with a PIC code to model reactions occurring due to the acceleration of deuterium ions by large electric fields. It is found that reactions due to this beam-target mechanism represent a small fraction (0.0001) of the number of thermonuclear reactions

High performance extendable instruction set computing

In this paper, a new architecture called the extendable instruction set computer (EISC) is introduced that addresses the issues of memory size and performance in embedded microprocessor systems. The architecture exhibits an efficient fixed length 16-bit instruction set with short length offset and immediate operands. The offset and immediate operands can be extended to 32 bits via the operation of an extension flag. The code density of the EISC instruction set and its memory transfer erformance is shown to be significantly higher than current architectures making it a suitable candidate for the next generation of embedded computer systems. The compact EISC instruction set introduces data dependencies that seemingly limit deep pipeline and superscalar implementations. This paper suggests a mechanism by which these dependencies might be removed in hardware

Rotating nuclei at extreme conditions: Cranked Relativistic Mean Field Description

The cranked relativistic mean field (CRMF) theory is applied for the description of superdeformed (SD) rotational bands observed in $^{153}$Ho. The question of the structure of the so-called SD band in $^{154}$Er is also addressed and a brief overview of applications of CRMF theory to the description of rotating nuclei at extreme conditions is presented.Comment: 4 pages, 1 PostScript figure, LaTex, uses 'espcrc1.sty', to be published in Proceedings of International Nuclear Physics Conference, Paris, 1998 which will appear in Nuclear Physic

Rotating Leaks in the Stadium Billiard

The open stadium billiard has a survival probability, $P(t)$, that depends on the rate of escape of particles through the leak. It is known that the decay of $P(t)$ is exponential early in time while for long times the decay follows a power law. In this work we investigate an open stadium billiard in which the leak is free to rotate around the boundary of the stadium at a constant velocity, $\omega$. It is found that $P(t)$ is very sensitive to $\omega$. For certain $\omega$ values $P(t)$ is purely exponential while for other values the power law behaviour at long times persists. We identify three ranges of $\omega$ values corresponding to three different responses of $P(t)$. It is shown that these variations in $P(t)$ are due to the interaction of the moving leak with Marginally Unstable Periodic Orbits (MUPOs)

Modification of classical electron transport due to collisions between electrons and fast ions

A Fokker-Planck model for the interaction of fast ions with the thermal electrons in a quasi-neutral plasma is developed. When the fast ion population has a net flux (i.e. the distribution of the fast ions is anisotropic in velocity space) the electron distribution function is significantly perturbed from Maxwellian by collisions with the fast ions, even if the fast ion density is orders of magnitude smaller than the electron density. The Fokker-Planck model is used to derive classical electron transport equations (a generalized Ohm's law and a heat flow equation) that include the effects of the electron-fast ion collisions. It is found that these collisions result in a current term in the transport equations which can be significant even when total current is zero. The new transport equations are analyzed in the context of a number of scenarios including $\alpha$ particle heating in ICF and MIF plasmas and ion beam heating of dense plasmas

Back-traced Garbage Collection

This disclosure describes back-traced garbage collection in a computer. A back-traced garbage collector searches backwards from an object in an object graph, until a root node is encountered, or until there are no further objects to search. If a root node is not encountered, the searched objects are unreachable and are deleted. The garbage collector can run incrementally, process portions of the object graph, and determine reachability of individual objects without examining the entire object graph. The garbage collector has low latency. The garbage collector is tunable, for example, in response to program characteristics and performance requirements

Large scale shell model calculations for odd-odd 58−62^{58-62}Mn isotopes

Large scale shell model calculations have been carried out for odd-odd $^{58-62}$Mn isotopes in two different model spaces. First set of calculations have been carried out in full $\it{fp}$ shell valence space with two recently derived $\it{fp}$ shell interactions namely GXPF1A and KB3G treating $^{40}$Ca as core. The second set of calculations have been performed in ${fpg_{9/2}}$ valence space with the $fpg$ interaction treating $^{48}$Ca as core and imposing a truncation by allowing up to a total of six particle excitations from the 0f$_{7/2}$ orbital to the upper $\it{fp}$ orbitals for protons and from the upper $\it{fp}$ orbitals to the 0g$_{9/2}$ orbital for neutron. For low-lying states in $^{58}$Mn, the KB3G and GXPF1A both predicts good results and for $^{60}$Mn, KB3G is much better than GXPF1A. For negative parity and high-spin positive parity states in both isotopes $fpg$ interaction is required. Experimental data on $^{62}$Mn is sparse and therefore it is not possible to make any definite conclusions. More experimental data on negative parity states is needed to ascertain the importance of 0g$_{9/2}$ and higher orbitals in neutron rich Mn isotopes.Comment: 5 pages, 4 figures, Submitted to Eur. Phys. J.

The GREAT triggerless total data readout method

Recoil decay tagging (RDT) is a very powerful method for the spectroscopy of exotic nuclei. RDT is a delayed coincidence technique between detectors usually at the target position and at the focal plane of a spectrometer. Such measurements are often limited by dead time. This paper describes a novel triggerless data acquisition method, which is being developed for the Gamma Recoil Electron Alpha Tagging (GREAT) spectrometer, that overcomes this limitation by virtually eliminating dead time. Our solution is a total data readout (TDR) method where all channels run independently and are associated in software to reconstruct events. The TDR method allows all the data from both target position and focal plane to be collected with practically no dead-time losses. Each data word is associated with a timestamp generated from a global 100-MHz clock. Events are then reconstructed in real time in the event builder using temporal and spatial associations defined by the physics of the experimen