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Recent experiments on the Mercury pulsed power accelerator were performed with a large-area bremsstrahlung diode operated at 5 MV. Extensive measurements of the x-ray dose distribution were made using TLDs, both in the near field and far field of the x-ray beam. In order to understand the operation of the diode and the properties of the x-ray beam, numerical simulations of the diode and beam were performed. Particle-in-cell simulations of the diode were driven using the measured currents from the experiment in order to simulate the electron beam produced by the accelerator. These beam electrons were then used as a source in Monte Carlo simulations of the bremsstrahlung converter to compute the generated x-ray beam. The photons from this simulation were then transported to the near- and far-field TLD locations and doses were computed. The dose predictions were compared to measurements, showing reasonably good agreement.

The reliable detection of special nuclear materials continues to be a primary goal of national security programs conducted by Defense Nuclear Nonproliferation agencies. While these programs are diverse, many share a core need for a small, robust pulsed neutron generator. This project addresses this need by building a portable dense plasma focus (DPF) neutron source. DPF technology offers many benefits that are infeasible using conventional neutron sources: it can generate intense neutron pulses, operate at relatively low voltage, and be scaled to a lightweight form factor. Large-scale DPF sources produce prolific neutron radiation but require heavy machinery for transport and are therefore not ideal for mobile applications. Alternatively, compact DPF systems can be fabricated that are easily transported by human operators and generate sufficient neutron output to accomplish mobile active interrogation missions. Recently, researchers at Mission Support and Test Services (MSTS) have constructed a bench-top DPF system to produce neutron radiation. The system comprises commercially available high voltage power supplies, capacitors, and cold-cathode thyratron switches and weighs approximately 25 kg. The system draws approximately 750 Wand can be powered using lithium-ion battery packs. A custom plasma process chamber was designed using hybrid PIC-MHD modeling software and constructed using off-the-shelf components. A control system was implemented on a microcontroller platform to discharge the DPF source with a repetition rate up to 0.2 Hz. A suite of neutron yield and time-of- flight diagnostics was used to measure the radiation output of the portable DPF source.

SIRIUS is a state-of-the-art detector system for nuclear decay spectroscopy that will be mounted at the focal plane of S3 (Super Separator Spectrometer), which is part of the new SPIRAL2 facility at GANIL, Caen in France. Such a system requires high performance as it is dedicated to the study of very exotic nuclei. It is the result of collaboration between GANIL CSNSM, IRFU, and IPHC It is composed of a succession of detectors (Trackers, Silicon detector DSSD and Tunnel plus an array of five clover Germanium detectors). This set-up is mounted in a compact geometry. The energy measurement varies from 50 keV to over 500 MeV with high precision (2 × 10−3) at low energies and 1 % for the detection of heavy ions. A major challenge has been the development of new electronics with a very large dynamic range maintaining an adequate energy resolution for the measured particles (with energies from a few hundred keV up to 500 MeV).

Piezoelectric transformers (PTs) are capable of generating the high accelerating potentials required for many charged-particle beam applications. However, the PTs need to be characterized during operation as an accelerator for such beam loads. PT characteristics such as internal stress, electric field, and electric potential can provide insight into the optimal operating conditions for a given application. Measurement of internal stress can be used to ensure that the single-crystal lithium niobate (LiNbO 3 ) PT does not exceed the fracture limit. Internal electric field and potential can be used to determine the accelerating potential created by the PT. Internal parameters such as these have been measured using an optical diagnostic that relies on the inherent photoelastic and electro-optic properties of lithium niobate. Beam currents have been determined using least-squares curve fitting with experimental and modeled results. Further characterization of the beam interactions with the PT was done by examining the direct bremsstrahlung x-ray spectra that were produced and the x-ray fluorescence peaks excited by the source. This paper presents a variety of PT characterization results under varied PT operating conditions.

Summary form only given. A compact neutron source based on a piezoelectric transformer has been developed as part of an on-going research effort into radioisotope source replacements for oil-well logging and non-destructive testing applications. One of the key features that will dictate the viability of the device is the effective neutron yield produced during operation. A proportional counter that uses helium-3 as the active sensing material was used for the purpose of detecting neutrons. The detector response to neutrons depends upon the efficiency of the helium-3 proportional counter tube in conjunction with the solid angle subtended by the source and the detector, as well as the material system that surrounds the proportional counter. The coupled geometry effect and energy dependence of the detector efficiency make an analytical solution prone to error. Additionally, obtaining a calibrated neutron source that mimics the size and desired activity of the piezoelectric transformer-based source was not in the scope of the research. Consequently, a numerical model of the neutron source and detector was developed and subjected to Monte Carlo analysis using MCNPX using neutrons as the source particles. A sensitivity analysis of the detector position and orientation was used to determine the optimal location for high-sensitivity neutron counting.

Summary form only given. A piezoelectric transformer plasma source (PTPS) is being developed as a plasma ion source for D(d, n)3 He neutron production. The PTPS consists of a lithium niobate piezoelectric disc in a differentially pumped chamber with controlled gas flow from an external source. The PTPS was previously characterized using a range of gas flows, extraction voltages, and aperture geometries. This ion source has been used for preliminary neutron production measurements using a target at high voltage. Ion current measurements are presented for deuterium gas at PTPS internal pressures from 0.5 to 4 Torr, extraction voltages up to 1.5 kV, and a range of duty cycles and operating times. Ion current yields on the order of 10 μA are presented. The PTPS was also operated with a high voltage dc source coupled with a deuterium impregnated palladium foil. Preliminary neutron yields are presented.

Piezoelectric transformers (PTs) are currently being used to accelerate charged-particle beams for various applications [1, 2]. Beam interactions at the output of the PT can be treated as a parallel RC electrical load. The impedance of the load can affect the output voltage due to the small, finite amount of charge available in the PT. High output voltages necessary for beam acceleration cannot be achieved if the current output from the PT is too high. A thermionic electron emitter was used to provide a controllable beam current for testing the effects of electrical loading on the PT. The electron beam was operated in vacuum pressures of approximately 10-5 Torr. Variations in the electron beam current were used to vary the resistive portion of the load while beam distance was used to vary capacitance. The effects of such variations were measured via bremsstrahlung interactions at the output electrode of the PT to determine output voltage and optical techniques for finding internal operating parameters such as electric field. This paper focuses on determining an optimal beam current and PT placement such that high output voltages are still achieved.

Full characterization of a piezoelectric transformer (PT) requires knowledge of internal operating parameters such as electric field, stress, and strain. Finite-element numerical models can determine these parameters with respect to the geometry of the PT and input conditions. However, experimental verification of these parameters for a resonating PT are challenging due to the mechanical vibration and electrical loading effects. An optical measurement has been designed to measure internal electric field by taking advantage of the electro-optic and photoelastic effects that also occur in lithium niobate (LiNbO3). The optical measurement can probe the PT without influencing its operation. A linearly polarized helium-neon laser beam was used to transversely probe a PT with respect to the input and output electric fields. As the piezoelectric effect caused variations in the internal electric field and strain, the superposition of the photoelastic and electro-optic effects resulted in a relative phase shift in the linearly polarized beam. The resultant phase shift was measured via intensity variations at a photodiode following a second linear polarizer. Internal parameters such as stress, strain, and electric field were calculated based on the coupled piezoelectric, photoelastic, and electro-optic equations. These results are presented for varying positions along the output section of a resonating LiNbO3 length-extensional PT.

Compact electrical neutron generators are a desirable alternative to radioisotope neutron sources. A piezoelectric transformer system is presented which has been used to achieve neutron production. The two primary components of the system include a piezoelectric transformer plasma source (PTPS), which produced a deuterium plasma for ion extraction, and a high voltage piezoelectric transformer (HVPT), which generated an accelerating potential in excess of 100 k V. The system was operated at a pressure of 700 μTorr with an external gas supply providing controlled deuterium flow to the differentially pumped PTPS. Synchronized AC signals were used to independently drive each of the piezoelectric devices in burst mode with a 1 Hz rep-rate and 10% duty factor. A timing offset between the two signals was used to decrease electrical loading effects and increase neutron flux. The mechanism for neutron production was the D(d, n)3 He nuclear reaction, occurring when deuterium ions from the PTPS accelerated toward and impacted a deuterium-impregnated Pd or Ti target adhered to the output terminal of the HVPT.

Summary form only given. A compact electron beam accelerator driven by a lithium niobate piezoelectric transformer was used to produce beams with energies greater than 100 keV. Charge was directly extracted from the transformer output using field-electron emitters. Electric fields generated by the transformer accelerated the charge into a grounded metallic target. The resultant bremsstrahlung radiation was used as a direct measurement of beam voltage. Time-dependent analysis of the x-ray spectra showed that electron beam production was limited to approximately one-minute intervals. This limitation was attributed to the accumulation of surface charge at the transformer output.

Summary form only given. A lithium niobate piezoelectric transformer was used to generate neutrons using a deuterium-deuterium (D-D) nuclear reaction. Deuterium gas was flowed into a vacuum chamber at pressures between 10−4 and 10−3 Torr. The deuterium gas was ionized and electric fields generated by the transformer accelerated deuterons into a grounded, deuterium impregnated target. A suite of diagnostics, including a bremsstrahlung x-ray measurement, electrooptic probe, and helium-3 neutron detector were used to evaluate the generator voltage, electric fields, and neutron production rates.

Piezoelectric transformers (PTs) can be useful as compact, high-voltage supplies. However, PTs cannot be fully utilized if the associated circuitry does not allow for the desired transformation ratio to be maintained. The effects of adding capacitive and/or resistive loads to a PT are being studied. Experiments and modeling suggest that the highest transformation ratios are achieved when both the resistive and reactive load elements are optimized, rather than only the magnitude of the impedance. Specifically, these effects are being studied to modularize the PT as a compact, high-voltage power supply for a variety of applications. This paper will analyze these loading effects and suggest a coupling method for maintaining high transformation ratios from Rosen-type PTs comprised of rotated y-cut lithium niobate.

Research and development are being conducted into the production of neutrons from a piezoelectric transformer power source. The neutrons generated by the piezoelectric transformer (PT) may eventually be used for portable active interrogation technologies or gas and oil well diagnostics. The University of Missouri program ties together several independent areas of focus, including ion source development, PT characterization and optimization, and PT-compatible high voltage diagnostics. The neutron source was based on the well known D-D collision interaction, during which free energy and a neutron are released. An ion source is under development that optimizes ion emission current through structural changes in the emission surface characteristics. A PT-based accelerator is under development to evaluate ion beam characteristics and circuit dynamics under resonant operating conditions. A suite of diagnostics are under development to directly and indirectly measure circuit parameters including voltage and current, as well as parameters accessible using optical techniques.

A new LINAG accelerator is developed for production of high intensity deuteron beam for the SPIRAL2 project. It will also deliver unprecedented high intensity stable beams that can be used for direct reactions on a target. The Super Separator Spectrometer (S3) is designed to open with these beams new horizons for the physics of rare nuclei and low production cross-section nuclei at the extreme limits of the nuclear chart. The S3 focal-plane detection is one of the major equipments in this framework. A research and development program has been launched in order to get the best setup according to the three main physics cases: Synthesis of new Super Heavy Elements, Spectroscopy of Very and Super Heavy Elements and Spectroscopy of neutron-deficient nuclei around 100Sn.

Piezoelectric transformers have been used to generate high voltage and are used to drive a compact electron accelerator in order to produce x-rays. Presented is an analysis of the electrostatic optics used to the increase maximum current density of the accelerator. Fowler-Nordheim analysis suggests that an electron beam produced by this accelerator reaches currents of 30 µA. This beam then impinges onto a high-z target where it is converted to x-rays via bremsstrahlung interactions. In order to maximize x-ray production, charged particle optics have been designed to focus the beam and increase current collected at the target. The target is then placed in the focus of the beam causing the number of incident electrons on its surface to increase as compared to the unfocused case. The electron beam is generated using a variety of cathodes on the output terminal of the piezoelectric transformer. A combination of finite-element simulations and experiments will be used to show how piezoelectric transformers perform as compact high-voltage electron beam accelerators and x-ray generators.

Piezoelectric transformers can be useful as compact, high-voltage supplies. At the University of Missouri, the effect of adding output circuits to bipolar piezoelectric transformers is being studied. These piezoelectric transformers produce output voltages in excess of 25 kV from medium-voltage, radio frequency inputs. However, the high output voltage and low output current of these devices can make it difficult to acquire an accurate electrical measurement of the output voltage without affecting the transformer ratio or resonance of the device. This paper will analyze capacitive voltage dividers as a means of diagnostic measurement and Cockcroft-Walton type circuits to increase the voltage multiplication beyond that of the piezoelectric transformer alone.

Ion generation can be accomplished in a number of ways including through field ion desorption and surface flashover. Both of these methods hold promise as exceptionally compact ion sources for numerous applications.

Compact ion and electron beam sources are potentially useful for many applications. Compact beam generators require both compact charged particle diodes and compact high voltage generators. Piezoelectric transformers are currently being developed at the University of Missouri to convert medium voltage at radio frequency to high voltages. Piezoelectric transformer geometries, including tapered and wedge shaped crystals operated in bipolar output mode, are being studied. Results demonstrating resonant properties of these crystals will be presented. High voltage operation, in excess of 25 kV peak voltage, will also be presented. Additionally, various voltage multiplying circuit topologies and crystal geometries are being studied to maximize the voltage output from piezoelectric transformer systems.

The ISOIMPEG standard for video and audio compressed bit streams has become industry standard for broadcasting and non-broadcasting applications. The MPEG Audio standard combines superior performance with future proofing, both in encoder improvements and compatible multi-channel extension at the lowest cost of implementation. FUTURE-PROOF WORLD STANDARD The ISO/MPEG group is now acknowledged world-wide as the standardization forum for low bit-rate audio-visual coding. In the first phase of work, the MPEG Audio group developed a gcncric standard for high-quality coding of mono and stereo audio signals. The standard allows a trade-off between audio quality, compression factor and encoder complexity. The flexible encoder concept guarantees that future results from psychoacoustic research can be applied to improved encoders without the need to update existing decoders. The formal name for this International Standard is ISO/IEC 11 172-3, but it is better known as the MPEG Audio standard.