No description available.

No description available.

No description available.

Two-dimensional numerical simulations of ablatively accelerated thin-shells subject to Rayleigh-Taylor instability are presented. Results for both single wavelength and multiwavelength perturbations show that the nonlinear effects of the instability are evident mainly in the "bubble" rather than the "spike." Approximate roles for predicting the dominant nonlinear mode-mode interactions, which limit shell performance, are also discussed. The work concludes with a discussion of recommendations for future work in this area.

A transient code (TFETC) for calculating the temperature distribution throughout the radial and axial positions of a thermionic fuel element (TFE) has been successfully developed. It accommodates the variations of temperatures, thermal power, electrical power, voltage, and current density throughout the TFE as a function of time as well as the variations of heat fluxes arising from radiation, conduction, electron cooling, and collector heating. The thermionic fuel element transient code (TFETC) is designed to calculate all the above variables for three different cases namely: 1) Start-up; 2) Loss of flow accident; and 3) Shut down. The results show that this design is suitable for space applications and does not show any deficiency in the performance. It enhances the safety factor in the case of a loss of flow accident (LOFA). In LOFA, it has been found that if the mass flow rate decreases exponentially by a -0.033t, where t is a reactor transient time in seconds, the fuel temperature does not exceed the melting point right after the complete pump failures but rather allows some time, about 34 seconds, before taking an action. If the reactor is not shut down within 34 seconds, the fuel temperature may keep increasing until the melting point of the fuel is attained. On the other hand, the coolant temperature attains its boiling point, 1057 ��K, in the case of a complete pump failure and may exceed it unless a proper action to trip the reactor is taken. For 1/2, 1/3, and 1/4 pump failures, the coolant temperatures are below the boiling point of the coolant. / Graduation date: 1994

Į kieto kūno paviršių krentant jonų srautui, jo paviršiuje vyksta procesai, keičiantys medžiagos elementinę sudėtį. Todėl medžiagos paviršiuje susidaro pakeistasis sluoksnis, kuris gali turėti didelę įtaką paviršiaus erozijai. Pavyzdžiui, termobranduolinės energetikos srityje, tokių elementų kaip volframas, anglis ir berilis maišymasis yra svarbūs procesai įtakojantys pirmosios sienelės eroziją, vandenilio išlaikymą ir prasiskverbimą su plazma sąveikaujančioje medžiagoje bei pirmosios sienelės degradaciją. Fizikiniai procesai sukeliantys šiuos pokyčius nėra pilnai suprasti. Darbe pristatomas fenomenologinis plazmos sąveikos su pirmąją sienele modelis. Modelyje atsižvelgiama į keletą galimų vienalaikių plazmos – paviršiaus sąveikos procesų: joninį dulkėjimą, dalelių iš plazmos adsorbciją ant paviršiaus, nudulkėjusių dalelių resorbciją, terminę difuziją, plazmos dalelių implantaciją sienelėje ir jų sukeltą kaskadinį maišymąsi. Taip pat į modelį yra įtraukta pasirinkta cheminė reakcija. Pateikiami modelio taikymo mažų energijų vandenilio plazmos su 0,1 ir 0,8% anglies priemaišų sąveikos su volframo sienele skaičiavimams rezultatai. Gauti modeliavimo rezultatai yra palyginami su eksperimentų duomenimis. Skaičiavimų rezultatai parodo kaskadinio maišymosi svarbą anglies atomų pernašai taikinyje. / If a material is subjected to an ion flux, atomic composition of the material surface layer (first wall) can be modified by various plasma – first wall interaction processes. Therefore, a modified surface layer of the material is formed due to the plasma – first wall interaction. Effects of mixed materials can be a serious concern for the surface erosion. E.g., mixing of materials such as tungsten, carbon and beryllium in the fusion devices can influence important wall parameters such as a wall life time and hydrogen retention and permeation. Physical processes, which cause this modification, are not completely understood. A phenomenological model of plasma – first wall interaction is presented in the paper. Several possible simultaneous processes of plasma – first wall interaction are considered in the model: ion sputtering, adsorption of plasma particles on the surface, resorption of sputtered particles, thermal diffusion, implantation of plasma particles into the wall and cascade mixing. Selected chemical reaction is included in the model as well. Results of the simulation of low energy hydrogen plasma with 0.1% and 0.8% of carbon impurities interaction with tungsten surface are presented. Obtained results of the simulation are compared to the experimental results. Results of the calculation show importance of cascade mixing to the transport of carbon atoms in the target.

Thesis--University of Illinois at Urbana-Champaign, 1977. / Includes bibliographical references (p. 126-128).

No description available.

This is Part A. / <p> Effects in 19 element CANDU fuel bundles containing ThO2 and UO2, located in thermonuclear reactor blankets, have been examined for a variety of blanket designs. The buildup in time of nuclides derived from Th232 by neutron capture was studied. The essential CTR (Controlled Thermonuclear Reactor) blanket features that were examined were tritium breeding in the blanket (the fusion reaction of interest was the DT reaction resulting in the production of a 14.1 MeV neutron and a 3.5 MeV alpha particle), neutron multiplication in the blanket and the U233 production. Means of optimizing these features were also examined. Some conclusions concerning the use and influence of the CANDU bundle are made.</p> <p> It is of interest to study the details of the buildup of U233 in the bundles with the view of perhaps transferring bundles directly from the CTR blanket into a core of a fission power reactor. As such, it would be necessary to convert approximately 3% of the initial thorium present to U233 before transferral. This report examines time steps over which this could be achieved and looks at the performance of the blanket as a whole when such changes occur. The production of unwanted radioactive isotopes is looked at with suggestions of how to minimize this production without harming the rest of the blanket's basic functions.</p> <p> Procedures outlined in the preliminary report "Bench-Mark Neutronic Calculations for Fusion Reactor Designs" by S.A. Kushneriuk and P.Y. Wong form a basis for all of the calculations made in this report. Based on the findings of that report, it is expected that values presented here do reflect, to a fair degree of accuracy, conditions encountered in the CTR blankets studied.</p> / Thesis / Master of Engineering (MEngr)

Fast magnetosonic waves in the ion cyclotron range of frequencies have the potential to heat plasma and drive current in a thermonuclear fusion reactor. A code, SELFO-light, has been developed to study the physics of ion cyclotron resonantheating and current drive in thermonuclear fusion reactors. It uses a global full wave solver LION and a new 1D Fokker-Planck solver for the self-consistent calculations of the wave field and the distribution function of ions.In present day tokamak experiments like DIII-D and JET, fast wave damping by ions at higher harmonic cyclotron frequencies is weak compared to future thermonuclear tokamak reactors like DEMO. The strong damping by deuterium, tritium and thermonuclear alpha-particles and the large Doppler width of fast alpha-particles in DEMO makes it difficult to drive the current when harmonic resonance layers of these ionspecies are located at low field side of the magnetic axis. At higher harmonic frequencies the possibility of fast wave current drive diminishes due to the overlapping of alpha-particle harmonic resonance layers. Narrow frequency bands suitable for the fast wave current drive in DEMO have been identified at lower harmonics of the alpha-particles. For these frequencies the effect of formation of high-energy tails in the distribution function of majority and minority ion species on the current drive have been studied. Some of these frequencies are found to provide efficient ion heating in the start up phase of DEMO. The spectrum where efficient current drive can be obtained is restricted due to weak electron damping at lower toroidal mode numbers and strong trapped electron damping at higher toroidal mode numbers. The width of toroidal mode spectra for which efficient current drive can be obtained have been identified, which has important implications for the antenna design. / <p>QC 20130327</p>