Student Abstracts: Physics at ORNL

Partial Discharge in Spherical Voids in Epoxy Insulation at Room and Cryogenic Temperatures . DON BURDETTE (Indiana University of Pennsylvania, Indiana, PA 15701) ISIDOR SAUERS (Oak Ridge National Laboratory, Oak Ridge, TN 37831) .
Partial discharge, small bursts of current released in a dielectric material under an applied electric field, is a source of degradation and eventual failure in conventional equipment and cryogenic dielectric insulation for super-conducting power cables and transformers. Understanding the partial discharge (PD) patterns of typical defects will aid in the diagnosis of the remaining life-span of the insulation. One such defect is a spherical void or bubble created during the curing process of epoxy. In this work, various electric fields are applied across a spherical air-filled void inserted into epoxy to study the PD pattern produced in terms of charge magnitude q and the ac power supply phase angle N. PD patterns of epoxy samples with and without a void are compared in both oil at room temperature and liquid nitrogen at cryogenic temperature. A difference in the observed PD patterns at room and cryogenic temperatures is distinct. It has also been observed that the PD pattern associated with the void is dependent on how long the sample is aged. In order to clarify the PD signals originating from the samples, PD noise from other sources and their associated patterns are discussed along with noise reduction techniques. The electric field in the void and the solid sample is modeled using Ansoft software to gain an understanding of the physical mechanisms at work inside the two samples.

Derivation of an Optical Filter to Optimally Combine Solar and Electric Light Using Computational Modeling. TIMOTHY MOWRER (North Carolina State University, Raleigh, NC 27607) JEFF MUHS (Oak Ridge National Laboratory, Oak Ridge, TN 37831) .
Combining collected solar light with conventional electric lighting could drastically reduce energy consumption in buildings. Because the luminosity of solar light fluctuates from hour to hour and generally does not match the color values of conventional electric lights, such a hybrid lighting fixture would require a filter to optimize the appearance of the incoming solar light. The solar spectrum data is acquired via a computer algorithm written by the National Renewable Energy Laboratories (NREL). This data is further manipulated by an algorithm to simulate the effect of the fiber optic cable that will carry the light to the fixture. This data is generated for an entire year in thirty-minute increments. A genetic algorithm is then employed to determine an appropriate filter. Concentrating on the visible spectrum only, the filter is designed to optimize luminosity, chromaticity coordinates (color values), efficiency, and operation time (after sunrise and before sunset). All of these algorithms are combined into a single, customizable program with a Windows Graphical User Interface written in Borland C++. The program is designed to keep the color difference within a 1-step MacAdam ellipse, the minimum amount of color difference perceivable by the human eye. The use of a genetic algorithm will also allow future researchers to easily redefine the criteria for determining the optimal filter.

Electron cyclotron emission diagnostics of the VASIMR plasma rocket concept. RYAN MUNDEN (Stetson University, DeLand, FL 32720) D.A. RASMUSSEN (Oak Ridge National Laboratory, Oak Ridge, TN 37831) .
Advances in space exploration and sciences have led to great benefits for humankind. To continually enjoy those benefits and advances, it becomes necessary to improve the basic tool of space exploration, the rocket. Current chemical burn rockets are very useful for near-earth tasks and for breaking free of the Earth's gravitational field. The next step in space propulsion is a continuous burn, variable impulse rocket, which may be acheived through the VASIMR plasma rocket. The plasma rocket enables variable throttling of the propellant to maximize fuel efficiency. The plasma, an ionized gas, is created and accelerated by radio frequency (RF) fields launched with a helicon antenna. It attains much higher exhaust velocities enabling very rapid transit through space. By measuring the intensity and frequency of electron cyclotron emission in the plasma, a correlation to the electron temperature can be found. Preliminary tests with a helicon plasma source at Johnson Space Center showed promise that emission was in accordance with the predicted values based on the applied magnetic fields in the system. Continued tests on the Mini-RFTF helicon plasma system at ORNL have so far been inconclusive. Further testing with improved amplification and receivers is planned so that this diagnostic technique can be fruitfully applied to the VASIMR system. Determination of the electron temperature is important in developing models of the experiment.

An Algorithm to Control Decoherence in a Quantum Gate. JEFFREY SCHMULEN (Texas A&M University, College Station, TX 77840) VLADIMIR PROTOPOPESCU (Oak Ridge National Laboratory, Oak Ridge, TN 37831) .
Quantum computation relies on the laws of quantum mechanics to operate on quantum bits (qubits) and thereby process information faster than classical computing. Each qubit is realized in a two-level quantum system (e.g. a two level atom, a spin, a photon, etc.). Due to inherent interactions with the environmental noise, the two-level quantum system loses its initial/desired configuration; this process is called decoherence. Thus, to maintain the qubit in the state needed for quantum computation (i.e. prevent it from decohering), suitable control algorithms must be implemented. This report outlines a Matlab/Maple program that calculates these controls. A two by two density matrix yields eight real quantities that describe the two level quantum system. From the general theory, these quantities are calculated for an ideal (unitary) situation and realistic (decohered/controlled) situation. At each time step, the unitary and the decohered/controlled quantities are equated to find the control value that restores the decohered state to the unitary state. Application of the calculated controls shows an almost perfect restoration of unitarity.

Construction and Calibration of a Tri-Directional Magnetic Probe for Investigation of Field Structure in the VASIMR Helicon Plasma Source. HANNA SMITH (Smith College, Northampton, MA 01063) RICHARD H. GOULDING (Oak Ridge National Laboratory, Oak Ridge, TN 37831) .
The performance of a helicon plasma source as a propulsion device depends upon the structure of the magnetic fields generated by the rf antenna that ignites and maintains the plasma. The EMIR2 code predicts the configuration of these fields in three dimensions for the helicon plasma source on mini-RFTF. Due to a lack of appropriate diagnostics, however, the theoretical results from EMIR2 still await experimental confirmation. Inductive loop probes provide a convenient means of investigating magnetic fields inside experimental plasmas of moderate energy density. Conventional single loop probes sample one component of dB/dt, the time-rate-of-change of the magnetic field. Acquisition of data in three dimensions for comparison with EMIR2 results demands the use of three mutually perpendicular (and physically proximate) loops. Moreover, mapping the fields associated with the helicon source on mini-RFTF requires a small probe of high frequency response. This paper details the design, construction and calibration of a tri-directional magnetic probe for the VASIMR experiment on mini-RFTF.

Designing a LabVIEW Program to Determine the Electrical Properties of New Superconducting Materials. . JENNIFER TOBIN (Albion College, Albion, MI 49224) DAVID K. CHRISTEN (Oak Ridge National Laboratory, Oak Ridge, TN 37831) .
Superconductivity has the ability to revolutionize the distribution of energy in the form of electrical power. The negligible resistance in superconductive materials makes them much more efficient than existent materials as carriers of electricity. Presently materials found to be superconductive do so at low temperatures (near or below the boiling temperature of liquid nitrogen, 77K). A cryocooler is a mechanical device with the ability to reach and maintain these low temperatures using compressed helium gas. In a cryocooler, superconductivity was measured through a four terminal reading on the sample (current, voltage, voltage, current). LabVIEW (a graphical programming language) was used to develop a program to control the temperature, evaluate the amount of current applied to and forced through the superconductive film sample and measure the voltage across the sample. These values were stored in LabVIEW, were transformed into resistance readings and stored in data files. The program was customized to provide a sufficient density of recorded and plotted values during the abrupt resistance decrease that occurs at the superconducting transition temperature, Tc, below which the resistance is zero. Data were taken for a thin film sample of irradiated Hg1212/LaAlO3 that yielded a Tc of 113.142 K when cooling and a Tc of 114.015 when warming due to thermal hysteresis. When compared to data of the sample before radiation, it was found that resistance had increased in the irradiated sample at comparable temperatures. The Tc was lowered after radiation from 117.55 to 113.142.

Simulation Studies of High Intensity Proton Accumulator Rings. KATHERINE WOODY (Tennessee Technolgical University, Cookeville, TN 38505) JEFF HOLMES (Oak Ridge National Laboratory, Oak Ridge, TN 37831) .
The Spallation Neutron Source (SNS) will have the highest intensity proton beam to date. Because of this high intensity, SNS will also have unprecedented low beam loss requirements and an array of physics concerns impacting the beam dynamics. Computer simulation proves to be the most productive method for investigating the SNS beam dynamics, and the computer code, ORBIT, is at the forefront of these studies. The present work involves a novel study using the ORBIT code: new three-dimensional space charge and transverse impedance models that will allow the investigation of a whole new range of phenomena have been developed. These models increase the amount of computational work by one three orders of magnitude, even with the use of fast solution algorithms. It is therefore important to benchmark these methods both for accuracy and computer time. This is carried out here.

Investigation of Rotating Arc Spark Plugs. JACOB YODER (Case Western Reserve University, Cleveland, OH 44106) JOHN WHEALTON (Oak Ridge National Laboratory, Oak Ridge, TN 37831) .
The fuel to air ratio in an internal combustion engine piston is an important factor in the fuel efficiency of automobiles. A lower fuel to air ratio can yield greater fuel efficiency, but the rate of misfires increases. A rotating arc spark plug can allow leaner ratios without the misfire problem. An axial magnetic field is applied on the spark gap, and the spark rotates. Because the spark effectively occupies more volume, it is hoped that the ignition probability will remain high in the lean burning scenario. In addition to occupying more volume, rotating sparks tend to have a higher electron temperature. The temperature of the sparks from Capacitive Discharge, Inductive, and Multiple Spark Discharge ignition systems were investigated with a spectrometer. It was found for each system, applying an axial magnetic field resulted in higher electron temperatures (i.e., a preponderance in the lower wavelength bands). When the arc lasted for more than 100 ms, a noticeable rotation of the spark occurred, in accordance with the Lorenz force, measured via digital photography. Implementation of the rotating arc spark plug in an engine is currently in progress, as well as a study of electrode erosion using spectroscopic techniques.