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Wire z-pinch experiments at the University of Michigan are in progress to test potential spectral lines for use as a local magnetic field diagnostic in dense plasmas driven by high currents. The goal of these experiments is to determine several spectral lines that can be used to reliably characterize the magnetic field and current density profiles of high energy density plasmas. Initial feasibility...
Recent research on the 1-MA Michigan Linear Transformer Driver, MAIZE, has focused on the Magneto Rayleigh-Taylor (MRT) instability and validation of analytic theory, developed at UM [1,2]. MRT is a concern to all forms of magnetically imploding experiments, most recently with the imploding liners anticipated in the MagLIF geometry.[3] Eliminating or mitigating MRT is crucial to success of these programs.
Most of the modern high-current high-voltage pulsed power generators require several stages of pulse conditioning (pulse forming) to convert the multi-microsecond pulses of the Marx generator output to the 40-300 ns pulse required by a number of applications including x-ray radiography, pulsed high current linear accelerators, Z-pinch, isentropic compression (ICE), and inertial fusion energy (IFE)...
Surface roughness plays an important role in a cavity or slow wave structure. It may cause enhanced RF power absorption. It may lead to excessive local electric field enhancement that triggers RF breakdown. In a superconducting cavity, surface roughness may also cause local magnetic field enhancement that leads to abrupt quenching, i.e., rapid loss of superconductivity. In this work, we analytically...
The UM/L-3 relativistic magnetron operates at -300 kV, 2-5 kA, for durations of 500 ns and is capable of generating microwave pulses of 100's MW output power at 1 GHz for 100's ns. Previous research at UM utilized Metal-Oxide- Junction (MOJ) cathodes to exploit triple point field enhancement to stimulate electron emission. These MOJ cathodes generated fast current turn-on, however, the lifetime of...
Summary form only given. Experiments are underway at UM on the first 1-MA LTD to be operated in the USA following its development at the Institute of High Current Electronics in Tomsk, Russia. This LTD employs 80 capacitors and 40 spark-gap switches arranged in 40 "bricks" that each generate 25 kA when charged to +-100 kV. Initial experiments at UM generated nearly 1-MA into resistive loads...
Summary form only given. While not widely used, thin foils as Z-pinch loads may soon become necessary to achieve the required mass for higher current-driven X-ray sources, and they may also offer useful options for X-ray pulse shaping (T.J. Nash et.al., 2004). This paper reports our latest design and experimental progress on the study of the dominant instability, the magneto-Rayleigh-Taylor instability...
Summary form only given. Electrical contact is an important issue for high power microwave sources, wire-array Z pinches, field emitters, and metal-insulator-vacuum junctions. Because of the surface roughness on a microscopic scale, true contact between two pieces of metal occurs only on the asperities of the two contacting surfaces. Current flows only through these asperities, which occupy a small...
Summary form only given. Post-hole convolutes are commonly used in large scale pulsed power devices to combine the current from several sources. The primary examples of convolute use are Load Current Multipliers (LCMs) and current combination from multiple Self-Magnetically Insulated Transmission Lines (MITLs). Sandia National Laboratory's Z-Machine utilizes a double post-hole convolute to combine...
From a circuit model for an oscillator, an equation was developed to describe the beam loaded admittance. The equation, which is presented in this paper suggests that the instantaneous beam loaded admittance, may be extracted from the output signal of the oscillator once the cold tube frequency and damping rates have been determined. This technique is used to analyze the behavior of a relativistic...
Summary form only given. The viability of coherent power combination of multiple high-efficiency, moderate power magnetrons requires a thorough understanding of frequency and phase control. Injection locking of conventional magnetrons, and other types of oscillators, employing a master-to-slave configuration has been studied theoretically and experimentally. We focus on peer-to-peer locking between...
Summary form only given.Nonlinear transmission lines have been demonstrated to be an effective technique for generating high power ultrawideband or mesoband radiation without the need for a vacuum system, electron beam, or magnet. Preliminary experiments have been performed at AFRL and UM on a discrete element nonlinear transmission line with nonlinear capacitance. Depending on the injected pulse,...
Cell electroporation using fields radiated or broadcast from an antenna is very attractive for both clinical and research applications. Experiments were performed to establish the basics of coupling a radiated field capacitively to a sample of cells in order to determine if electroporation can occur. Experiments have been performed using sub-nanosecond rise time pulses. Cells immobilized in agarose...
In this work, we analytically compute the power absorption due to a hemispherical protrusion on a resonant cavity's surface. The permittivity, conductivity, and permeability of the protrusion may assume arbitrary values. The local field enhancement factors of both electric field and magnetic field on the protrusion are also calculated analytically. These calculations have been spot-checked against...
We present experimental and simulation results from research on the 6-cavity, UM/L-3 relativistic magnetron, focusing on techniques to improve mode selection, power, and pulselength. Performance enhancements utilize magnetic priming, triple-point cathodes and mitigation of window flashover.
We evaluate the effects of small random fabrication errors on the small signal characteristics of a traveling wave tube.The classical ID small signal theory of Pierce, is applied. Random, axially varying perturbations are introduced in the circuit phase velocity mismatch the gain parameter and cold tube circuit loss in Pierce notation. First order perturbation analysis of the small signal equations...
Experiments have been performed testing magnetic priming at the cathode of a relativistic magnetron to study the effects on high power microwave performance. Three high permeability wires were embedded beneath the emission region of a 1.27 cm diameter cathode, spaced 120 degrees apart (for pi-mode symmetry in an 6 vane magnetron) to perturb both the axial and radial magnetic fields near the emission...
Electrical contact is an important issue for wafer evaluation of manufactured integrated circuits. It has also repeatedly surfaced in our ongoing studies of high power microwave sources, wire-array Z pinches, field emitters, and metal- insulator-vacuum junctions. Because of the surface roughness on a microscopic scale, true contact between two pieces of metal occurs only on the asperities of the two...
Summary form only given. Recent experiments at the University of Michigan have explored the mechanism of electron emission from triple points (vacuum-conductor-dielectric interface) for application to high current cathodes. Metal-oxide junction (MOJ) cathodes have been developed and tested; these consist of hafnium oxide (HfO2) or magnesium oxide (MgO) coatings over metal (#304 stainless steel) substrates...
We present designs, resistive-load test results and experimental plans of the first 1 MA z-pinch in the USA to be driven by a Linear Transformer Driver (LTD). The Michigan Accelerator for Inductive Z-pinch Experiments, (MAIZE), is based on the LTD developed at the Institute for High Current Electronics in collaboration with Sandia National Labs. This LTD utilizes 80 capacitors and 40 spark gap switches...
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