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Thin film cadmium telluride solar cells. Technical progress report No. 1, July 1-September 30, 1979

Description: The objectives of this contract are to investigate thin films of cadmium telluride on low cost substrates and to demonstrate the feasibility of producing thin film cells with a conversion efficiency of 10% or higher. Efforts during the first quarter have been direcrted to the construction of apparatus for the chemical vapor deposition of cadmium telluride films, the selection and preparation of substrates, and the deposition and characterization of cadmium telluride films. Cadmium telluride films have been deposited on a number of substrates by the direct combination of cadmium and tellurium on the substrate surface at 550 to 740/sup 0/C. At substrate temperatures below 550/sup 0/C, the deposit is non-adherent. In the temperature range 580 to 740/sup 0/C, the deposition rate is 0.5 to 1 ..mu..m/min, and the microstructure and crystallographic properties of deposited films have been investigated. Without intentional doping, cadmium telluride films deposited on mullite substrates have room temperature resistivities and carrier concentrations of (4-7) x 10/sup 4/ ohm-cm and (6-9) x 10/sup 12/ cm/sup -3/, respectively. Current-voltage measurements of Schottky barriers prepared from cadmium telluride films indicate the rectifying interface in CdTe/W/graphite, CdTe/graphite, CdTe/Al/graphite structures and the presence of pinholes in the films.
Date: October 1, 1979
Creator: Chu, T. L.
Partner: UNT Libraries Government Documents Department

Thin film cadmium telluride solar cells. Technical progress report No. 2, October 1-December 31, 1979

Description: The objectives of this contract are to investigate thin films of cadmium telluride on low cost substrates and to demonstrate the feasibility of producing thin film cells with a conversion efficiency of 10% or higher. The chemical vapor deposition of cadmium telluride films on foreign substrates by the direct combination of the elements has been further investigated. Inert substrates such as graphite and tungsten/graphite are not suitable for the deposition of device quality cadmium telluride films because of the rectifying interface and pinhole problems. Indium coated W/graphite forms an ohmic contact with n-type cadmium telluride, and the deposited films are essentially free of pinholes. The properties of Ag/n-CdTe/In/W/graphite structures, such as the current-voltage characteristics as a function of temperature, the barrier height, the photovoltaic properties, and the intragrain diffusion length in cadmium telluride, have been investigated. Preliminary work has also been carried out on the deposition of p-type cadmium telluride films on Sb/W/graphite substrates. The reaction between cadmium iodide and tellurium in a hydrogen atmosphere has been concluded to be unsuitable for the deposition of cadmium telluride films.
Date: January 1, 1980
Creator: Chu, T.L.
Partner: UNT Libraries Government Documents Department

Cyclotron radiation by a multi-group method

Description: A multi-energy group technique is developed to study conditions under which cyclotron radiation emission can shift a Maxwellian electron distribution into a non-Maxwellian; and if the electron distribution is non-Maxwellian, to study the rate of cyclotron radiation emission as compared to that emitted by a Maxwellian having the same mean electron density and energy. The assumptions in this study are: the electrons should be in an isotropic medium and the magnetic field should be uniform. The multi-group technique is coupled into a multi-group Fokker-Planck computer code to study electron behavior under the influence of cyclotron radiation emission in a self-consistent fashion. Several non-Maxwellian distributions were simulated to compare their cyclotron emissions with the corresponding energy and number density equivalent Maxwellian distribtions.
Date: January 1, 1980
Creator: Chu, T.C.
Partner: UNT Libraries Government Documents Department

Radiant heat evaluation of concrete: a study of the erosion of concrete due to surface heating

Description: Experiments were carried out to investigate the erosion of concrete under high surface heat flux in connection with the core-melt/concrete interaction studies. The dominate erosion mechanism was found to be melting at the surface accompanied by chemical decomposition of the concrete beneath the melt-solid interface. The erosion process reaches a steady state after an initial transient. The steady state is characterized by an essentially constant erosion rate at the surface and a nonvarying (with respect to the moving melt interface) temperature distribution within the concrete. For the range of incident heat flux 64 W/cm/sup 2/ to 118 W/cm/sup 2/, the corresponding steady state erosion rate varies from approximately 8 cm/hr to 23 cm/hr. A simple ablation/melting model is proposed for the erosion process. The model was found to be able to correlate all temperature responses at various depths from all tests at large times and for temperatures above approximately 250/sup 0/C.
Date: January 1, 1978
Creator: Chu, T.Y.
Partner: UNT Libraries Government Documents Department

Thin film cadmium telluride solar cells. Final technical report for period July 1, 1979-August 31, 1980

Description: The objectives of this contract are to investigate thin films of cadmium telluride on low cost substrates and to determine the feasibility of using these films for high efficiency solar cells. Efforts during this program have been directed to the construction of apparatus for the chemical vapor deposition of cadmium telluride films, the selection and preparation of substrates, the deposition and characterization of cadmium telluride films, and the fabrication and characterization of solar cells. Cadmium telluride films have been deposited on a number of substrates by the direct combination of cadmium and tellurium on the substrate surface at 500/sup 0/C or higher at rates of up to 0.6 ..mu..m/min. The structural, crystallographic, and electrical properties of cadmium telluride films deposited over a wide range of conditions have been evaluated. A series of doping experiments have been carried out using iodine and indium as the n-type dopant, and phosphorus, arsenic, and antimony as the p-type dopant. Low resistivity films have not been produced thus far. In/W/graphite substrates have been used for the deposition of n-type films with an ohmic interface. However, no suitable substrates have been found to form an ohmic interface with p-type films. Solar cells prepared from these films exhibit relatively good short-circuit current density, up to 15 mA/cm/sup 2/, but their conversion efficiencies are severely limited by the high series resistance of the devices.
Date: August 1, 1980
Creator: Chu, T.L.
Partner: UNT Libraries Government Documents Department

Thin film cadmium telluride solar cells. Final technical report, July 1, 1979-August 31, 1980

Description: Efforts during this program have been directed to the construction of apparatus for the chemical vapor deposition of cadmium telluride films, the selection and preparation of substrates, the deposition and characterization of cadmium telluride films, and the fabrication and characterization of solar cells. Cadmium telluride films have been deposited on a number of substrates by the direct combination of cadmium and tellurium on the substrate surface at 500/sup 0/C or higher at rates of up to 0.6 ..mu..m/min. The structural, crystallographic, and electrical properties of cadmium telluride films deposited over a wide range of conditions have been evaluated. A series of doping experiments have been carried out using iodine and indium as the n-type dopant, and phosphorus, arsenic, and antimony as the p-type dopant. Low resistivity films have not been produced thus far. In/W/graphite substrates have been used for the deposition of n-type films with an ohmic interface. However, no suitable substrates have been found to form an ohmic interface with p-type films. Solar cells prepared from these films exhibit relatively good short-circuit current density, up to 15 mA/cm/sup 2/, but their conversion efficiencies are severely limited by the high series resistance of the devices. It is believed that low resistivity cadmium telluride films can be prepared by optimizing the deposition conditions. In parallel with the search of substrates with low interface resistance, back wall cells, such as p-CdTe/n-CdS/ITO/glass(substrate), should be investigated.
Date: August 1, 1980
Creator: Chu, T.L.
Partner: UNT Libraries Government Documents Department

The effect of electron thermal conduction on plasma pressure gradient during reconnection of magnetic field lines

Description: The interplay of electron cross-field thermal conduction and the reconnection of magnetic field lines around an m = 1 magnetic island prior to a sawtooth crash can generate a large pressure gradient in a boundary layer adjacent to the reconnecting surface, leading to an enhanced gradient of poloidal beta to satisfy the threshold condition for ideal MHD modes. This narrow boundary layer and the short onset time of a sawtooth crash can be supported by fine-grained turbulent processes in a tokamak plasma. 11 refs.
Date: December 1, 1987
Creator: Chu, T.K.
Partner: UNT Libraries Government Documents Department

Fragmentation of molten core material by sodium. [LMFBR]

Description: A series of scoping experiments was performed to study the fragmentation of prototypic high temperature melts in sodium. The quantity of melt involved was at least one order of magnitude larger than previous experiments. Two modes of contact were used: melt streaming into sodium and sodium into melt. The average bulk fragment size distribution was found to be in the range of previous data and the average size distribution was found to be insensitive to mode of contact. SEM studies showed that the metal component typically fragmented in the molten phase while the oxide component fragmented in the solid phase. For UO/sub 2/-ZrO/sub 2//stainless steel melts no sigificant spatial separation of the metal and oxide was observed. The fragment size distribution was stratified vertically in the debris bed in all cases. While the bulk fragment size showed generally consistent trends, the individual experiments were sufficiently different to cause different degrees of stratification in the debris bed. For the highly stratified beds the permeability can decrease by as much as a factor of 20 from the bottom to the top of the bed.
Date: January 1, 1982
Creator: Chu, T.Y.
Partner: UNT Libraries Government Documents Department

Comments on experimental results of energy confinement of tokamak plasmas

Description: The results of energy-confinement experiments on steady-state tokamak plasmas are examined. For plasmas with auxiliary heating, an analysis based on the heat diffusion equation is used to define heat confinement time (the incremental energy confinement time). For ohmically sustained plasmas, experiments show that the onset of the saturation regime of energy confinement, marfeing, detachment, and disruption are marked by distinct values of the parameter /bar n//sub e///bar j/. The confinement results of the two types of experiments can be described by a single surface in 3-dimensional space spanned by the plasma energy, the heating power, and the plasma density: the incremental energy confinement time /tau//sub inc/ = ..delta..W/..delta..P is the correct concept for describing results of heat confinement in a heating experiment; the commonly used energy confinement time defined by /tau//sub E/ = W/P is not. A further examination shows that the change of edge parameters, as characterized by the change of the effective collision frequency ..nu../sub e/*, governs the change of confinement properties. The totality of the results of tokamak experiments on energy confinement appears to support a hypothesis that energy transport is determined by the preservation of the pressure gradient scale length. 70 refs., 6 figs., 1 tab.
Date: April 1, 1989
Creator: Chu, T.K.
Partner: UNT Libraries Government Documents Department

Nonthermal effects in two component DT fusion reactors

Description: Net energy generation rates and f-factors are calculated for a variety of two component DT reactor configurations using a computer code that follows the energy distributions of the reactants and products explicitly, utilizing the Fokker--Planck approximation for low-angle Coulomb scattering and a transfer matrix for high-angle Coulomb, nuclear, and radiative processes. The relative importance of such non-thermal effects as alpha particle deposition, non- Maxwellian energy distributions for the target tritons and electrons, and the influence of high-angle Coulomb and nuclear scattering on the energy loss rate of the injected deuterons is explicitly assessed. (auth)
Date: November 1, 1975
Creator: Weaver, T.A. & Chu, T.C.
Partner: UNT Libraries Government Documents Department

Theory and application of maximum magnetic energy in toroidal plasmas

Description: The magnetic energy in an inductively driven steady-state toroidal plasma is a maximum for a given rate of dissipation of energy (Poynting flux). A purely resistive steady state of the piecewise force-free configuration, however, cannot exist, as the periodic removal of the excess poloidal flux and pressure, due to heating, ruptures the static equilibrium of the partitioning rational surfaces intermittently. The rupture necessitates a plasma with a negative q{prime}/q (as in reverse field pinches and spheromaks) to have the same {alpha} in all its force-free regions and with a positive q{prime}/q (as in tokamaks) to have centrally peaked {alpha}'s.
Date: February 1, 1992
Creator: Chu, T.K.
Partner: UNT Libraries Government Documents Department

Energy confinement comparison of ohmically heated stellarators to tokamaks

Description: An empirical scaling prescribes that the energy confinement time in ohmically heated stellarators and tokamaks is proportional to the internal energy of the plasma and the minor radius, and inversely proportional to the current density. A thermal-conduction energy transport model, based on a heuristic assumption that the effective momentum transfer in the radial direction is proportional to the classical parallel momentum transfer which results in ohmic heating, is used to explain this scaling.
Date: December 1, 1979
Creator: Chu, T.K. & Lee, Y.C.
Partner: UNT Libraries Government Documents Department

Theory of minimum dissipation of energy for the steady state

Description: The magnetic configuration of an inductively driven steady-state plasma bounded by a surface (or two adjacent surfaces) on which B{center dot}n = 0 is force-free: {del}{times}B = 2{alpha}B, where {alpha} is a constant, in time and in space. {alpha} is the ratio of the Poynting flux to the magnetic helicity flux at the boundary. It is also the ratio of the dissipative rates of the magnetic energy to the magnetic helicity in the plasma. The spatial extent of the configuration is noninfinitesimal. This global constraint is a result of the requirement that, for a steady-state plasma, the rate of change of the vector potential, {partial derivative}A/{partial derivative}t, is constant in time and uniform in space.
Date: February 1, 1992
Creator: Chu, T.K.
Partner: UNT Libraries Government Documents Department

Thermal convection with large viscosity variation in an enclosure with localized heating

Description: The present study is undertaken in order to gain an understanding of convective transport in a magma chamber. We have chosen to represent the chamber by an enclosure with localized heating from below. Results of both laboratory experiments and computer modeling are reported. The experimental apparatus consists of a transparent enclosure with a square planform. An electrically heated strip, with a width equal to one-fourth of the length of a side of the enclosure, is centered on the lower inside surface of the enclosure. For the experiments reported here, the top of the fluid layer is maintained at a constant temperature and the depth of the layer is equal to the width of the heated strip. The large viscosity variation characteristic of magma convection is simulated by using corn syrup as the working fluid. Measured velocity and temperature distribution as well as overall heat transfer rates are presented. The experiment is numerically simulated through use of a finite element computer program. Numerically predicted streamlines, isotherms, and velocity distributions are presented for the transverse vertical midplane of the enclosure. Good agreement is demonstrated between predictions and measurements. 23 refs., 8 figs., 2 tabs.
Date: January 1, 1988
Creator: Chu, T.Y. & Hickox, C.E.
Partner: UNT Libraries Government Documents Department

An analysis of loss of offsite power with a PWR at shutdown

Description: In many Probabilistic Risk Assessments (PRAs), loss of offsite power (LOOP) when a nuclear power plant is operating was found to be a significant contributor to core damage. The purpose of this study is to provide an analysis of a loss of offsite power event that occurs while a PWR is shut down. The importance of such an analysis was recognized as part of a study to evaluate the core damage frequency due to a loss of decay heat removal capability during an outage. 5 refs., 1 fig.
Date: June 1, 1987
Creator: Chu, T.L.; Yoon, W.H. & Fitzpatrick, R.G.
Partner: UNT Libraries Government Documents Department

Estimation of initiating event distribution at nuclear power plants by Bayesian procedure

Description: Initiating events at nuclear power plants such as human errors or components failures may lead to a nuclear accident. The study of the frequency of these events or the distribution of the failure rate is necessary in probabilistic risk assessment for nuclear power plants. This paper presents Bayesian modelling methods for the analysis of the distribution of the failure rate. The method can also be utilized in other related fields especially where the data is sparse. An application of the Bayesian modelling in the analysis of distribution of the time to recover Loss of Off-Site Power ( LOSP) is discussed in the paper.
Date: December 31, 1995
Creator: Chen Guangming & Chu, T.L.
Partner: UNT Libraries Government Documents Department

Enhanced-confinement class of stellarators

Description: A class of stellarators has been found in which the transport is reduced by an order of magnitude from transport in conventional stellarators, by localizing the helical ripple to the inside of the torus. The reduction is observed in numerical experiments and explained theoretically.
Date: August 1, 1981
Creator: Mynick, H.E.; Chu, T.K. & Boozer, A.H.
Partner: UNT Libraries Government Documents Department

Measurements of the parametric decay of CO/sub 2/ laser radiation into plasma waves at quarter critical density using ruby laser Thomson scattering

Description: We report the results of small-angle ruby laser Thomson scattering measurements of the parametric excitation of plasma waves by CO/sub 2/ laser radiation at quarter-critical density in a laser-heated gas target plasma. From supplementary data obtained from interferometry and large-angle ruby laser scattering we infer that the threshold conditions for a convective decay are satisfied.
Date: November 1, 1977
Creator: Schuss, J.J.; Chu, T.K. & Johnson, L.C.
Partner: UNT Libraries Government Documents Department

Containment performance evaluation for the GESSAR-II plant for seismic initiating events

Description: As a part of the overall effort undertaken by Brookhaven National Laboratory (BNL) to review the GESSAR-II probabilistic risk assessment, an independent containment performance evaluation was performed using the containment event tree approach. This evaluation focused principally on those accident sequences which are initiated by seismic events. This paper reports the findings of this study. 1 ref.
Date: January 1, 1986
Creator: Shiu, K.K.; Chu, T.; Ludewig, H. & Pratt, W.T.
Partner: UNT Libraries Government Documents Department

Probabilistic analysis of allowed outage times relaxation at a PWR plant

Description: Technical Specifications (TS) in a nuclear power plant are specific requirements on its day-to-day operation, designed to protect public health and safety. Two primary aspects of the TS are (1) limiting conditions of operation (LCO) with allowed outage times (AOTs) and (2) surveillance testing intervals (STIs). In recent years, there has been growing interest in the nuclear community in reexamining the TS. One of the reasons is that a significant portion of reactor downtime (plant unavailability) is attributable to the strict TS. Existing TS were derived from engineering judgement based on deterministic review; they were not directly risk-based, and their efficacy in enhancing public safety is difficult to establish. This paper presents a summary of a critical review of the Westinghouse report which proposed that AOTs for a number of safety systems at the Byron Generating Station be increased from 3 to 7 days.
Date: January 1, 1986
Creator: Cho, N.; Chu, T.; Xue, D.; Bozoki, G. & Youngblood, R.
Partner: UNT Libraries Government Documents Department