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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

High Voltage Insulation and Gas Absorption of Polymers in High Pressure Argon and Xenon Gases

High pressure gas time projection chambers (HPGTPCs) are made with a variety of materials, many of which have not been well characterized in high pressure noble gas environments. As HPGTPCs are scaled up in size toward ton-scale detectors, assemblies become larger and more complex, creating a need for detailed understanding of how structural supports and high voltage insulators behave. This includes the identification of materials with predictable mechanical properties and without surface charge accumulation that may lead to field deformation or sparking. This paper explores the mechanical and electrical effects of high pressure gas environments on insulating polymers PTFE, HDPE, PEEK, POM and UHMW in Argon and Xenon, including studying absorption, swelling and high voltage insulation strength.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

High-voltage insulator having multiple materials

High-voltage insulators are disclosed that are capable of handling diverse requirements, such as providing high standoff voltages, high temperature cycling, and the ability to withstand flexural stress. One high-voltage insulator includes a first piece formed from a first material, a second piece formed from a second material, and an interface section where the first piece contacts with and forms a seal with the second piece. The interface includes a first groove located that accommodates a first gasket, sets of matching threads on the first and second pieces. The interface section further accommodates a second gasket. In this multi-piece high-voltage insulator, the first material can have a first set of flexural, heat resistance, and electrical standoff characteristics suitable for a first environment, and the second material can have a second set of flexural, heat resistance and electrical standoff characteristics suitable for a second environment.

Podpaly, Yuri Anatoly↗
DOE OSTI2023

High-voltage insulators having multiple materials

High-voltage insulators are disclosed that are capable of handling diverse requirements, such as providing high standoff voltages, high temperature cycling, and the ability to withstand flexural stress. One high-voltage insulator includes a first piece formed from a first material, a second piece formed from a second material, and an interface section where the first piece contacts with and forms a seal with the second piece. The interface includes a first groove located that accommodates a first gasket, sets of matching threads on the first and second pieces. The interface section further accommodates a second gasket. In this multi-piece high-voltage insulator, the first material can have a first set of flexural, heat resistance, and electrical standoff characteristics suitable for a first environment, and the second material can have a second set of flexural, heat resistance and electrical standoff characteristics suitable for a second environment.

Podpaly, Yuri Anatoly↗
DOE OSTI2020

Design Considerations for High-Voltage Insulated Gate Drive Power Supply for 10-kV SiC MOSFET Applied in Medium-Voltage Converter

High-performance gate drive power supply (GDPS) plays a crucial role in ensuring the reliability and safety of the gate driver for power semiconductor devices. This article focuses on the design of a high-voltage-insulated GDPS for the 10-kV silicon carbide MOSFET in medium-voltage (MV) application. Design considerations, including insulation scheme, high-voltage-insulated transformer design, and load voltage regulation scheme, are proposed. In addition, the performance of the secondary-side-regulated (SSR) GDPS and that of the primary-side-regulated (PSR) GDPS are compared for several aspects, including interwinding capacitance, load voltage regulation rate, conversion efficiency, and hardware complexity. Finally, an SSR GDPS and a PSR GDPS, with an insulation voltage of 20 kV, are built in the lab. Furthermore, the test results demonstrate that the PSR GDPS is more preferable because of lower interwinding capacitance, lower load voltage regulation rate, higher conversion efficiency, and simpler control circuit.

42 ENGINEERING↗
DOE OSTI2018

High Voltage Insulation and Gas Absorption of Polymers in High Pressure Argon and Xenon Gases

This work advances the development of the high-pressure xenon gas Time projection Chamber (TPC) concept in the search for neutrino-less double beta decay in Xenon136, a promising isotopic candidate. In particular, this work advances the use of electroluminescence (EL) as a nearly noiseless gain mechanism that preserves energy resolution in measurement of the visible energy in the decay—the two emitted electrons. Energy resolution of ~1% FWHM at the Q-value of the decay, 2458 kEV, allows complete separation of the much more copious 2-neutrino mode. The goal is to realize the EL mechanism in a very large parallel plane, nearly optically transparent mesh geometry, on the order of one meter diameter. Additional effort by collaborators at Argonne National Laboratory provide design solutions for the electrostatic boundary conditions of the active volume of the TPC. Solutions for the large mesh have been found in either electroformed grids or a more conventional woven mesh made from stainless steel wire. Posts to maintain approximate planarity are needed to minimize electrostatic deflection. The work has shown that these posts are feasible with certain plastics that can support the high electric field with out discharges.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Inverted Geometry Ceramic Insulators in High Voltage DC Electron Guns for Accelerators

A direct current (dc) high voltage photo-emission electron gun operating at 130 kV is utilized at the Jefferson Lab (JLab) Continuous Electron Beam Accelerator Facility to generate spin-polarized electrons for nuclear physics experiments. Over the past decade, JLab has tested and implemented inverted-geometry ceramic insulators in photoguns, connecting the cathode electrode in vacuum to the high voltage power supply using commercial high voltage cables. This contribution reports on tests performed up to 375 kV dc, implementation of inverted insulators in a 300 kV dc photogun generating magnetized electron beams, and describes plans to develop a reliable insulator-cable connector for applying 500 kV dc to a future polarized beam photogun operating reliably and without field emission at 350 kV.

Hernandez-Garcia, C.↗
DOE OSTI2017

High-Frequency Transformer Design for Modular Power Conversion From Medium-Voltage AC to 400 VDC

This paper presents a high-frequency modular medium-voltage AC (4160 VAC or 13.8 kVAC) to low-voltage DC (400 VDC) system that is scalable in order to be used for different scale microgrids. A 15 kW, 500 kHz DC/DC converter is demonstrated as the most important stage of the system overall, which can be scalable to a 225 kW 4160 VAC to 400 VDC system. Motivation of a CLLC resonant converter and its design parameters determination is carefully illustrated. The high-frequency transformer is the key element for the DC/DC converter. Then, the paper focuses on high-frequency transformer design to realize high-voltage insulation, high efficiency, and high density at the same time. Based on a split winding UU core transformer structure, transformer insulation materials and dimension parameters are determined referring to the IEEE insulation standard. The transformer magnetic loss model is reviewed based on which loss design tradeoff is carefully analyzed. Different working frequency impact on transformer design over three different core materials is also presented. Finally, a 500 kHz transformer prototype has been developed and demonstrated with the IEEE standard required insulation tests. A whole CLLC resonant converter is also present with experiments results. Here, the converter holds outstanding 98% efficiency and 2.9 kW/L power density.

42 ENGINEERING↗
DOE OSTI2010

SECONDARY ELECTRON TRAJECTORIES IN HIGH-GRADIENT VACUUM INSULATORS WITH FAST HIGH-VOLTAGE PULSES

Vacuum insulators composed of alternating layers of metal and dielectric, known as high-gradient insulators (HGIs), have been shown to withstand higher electric fields than conventional insulators. Primary or secondary electrons (emitted from the insulator surface) can be deflected by magnetic fields from external sources, the high-current electron beam, the conduction current in the transmission line, or the displacement current in the insulator. These electrons are deflected either toward or away from the insulator surface and this affects the performance of the vacuum insulator. This paper shows the effects of displacement current from short voltage pulses on the performance of high gradient insulators. Generally, vacuum insulator failure is due to surface flashover, initiated by electrons emitted from a triple junction. These electrons strike the insulator surface thus producing secondary electrons, and can lead to a subsequent electron cascade along the surface. The displacement current in the insulator can deflect electrons either toward or away from the insulator surface, and affects the performance of the vacuum insulator when the insulator is subjected to a fast high-voltage pulse. Vacuum insulators composed of alternating layers of metal and dielectric, known as high-gradient insulators (HGIs), have been shown to withstand higher electric fields than conventional insulators. HGIs, being tolerant of the direct view of high-current electron and ion beams, and having desirable RF properties for accelerators, are a key enabling technology for the dielectric-wall accelerators (DWA) being developed at Lawrence Livermore National Laboratory (LLNL). Characteristically, insulator surface breakdown thresholds go up as the applied voltage pulse width decreases. To attain the highest accelerating gradient in the DWA, short accelerating voltage pulses are only applied locally, along the HGI accelerator tube, in sync with the charged particle bunch, and the effects of displacement current on trajectories of electrons emitted from HGI surface are particularly interesting. This paper presents simulated electron trajectories experiencing either constant or short-duration applied voltage pulses. Comparisons of these trajectories clearly indicate the importance of the voltage pulse shape, especially the rise time, in the flashover initiation process for HGIs.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Using fiberglass volumes for VPI of superconductive magnetic systems’ insulation

The paper describes the method of manufacturing fiberglass molds for vacuum pressure impregnation (VPI) of high-voltage insulation of superconductive magnetic systems (SMS) with epoxidian hot-setting compounds. The basic advantages of using such vacuum volumes are improved quality of insulation impregnation in complex-shaped areas, and considerable cost-saving of preparing VPI of large-sized components due to dispensing with the stage of fabricating a metal impregnating volume. Such fiberglass vacuum molds were used for VPI of high-voltage insulation samples of an ITER reactor’s PF1 poloidal coil. Electric insulation of these samples has successfully undergone a wide range of high-voltage and mechanical tests at room and cryogenic temperatures. Some results of the tests are also given in this paper.

36 MATERIALS SCIENCE↗
DOE OSTI2020

HVDC Surface Flashover in Compressed Air for Various Dielectrics

Here, this study measures the voltage at which flashover occurs in compressed air for a variety of dielectric materials and lengths in a uniform field for DC voltages up to 100 kV. Statistical time lag is recorded and characterized, displaying a roughly exponential dependence on breakdown voltage. Of the materials tested, acrylic is observed to be the most resistant to flashover. These data are intended to facilitate the design of compressed-air insulated high voltage systems as an alternative to SF 6 insulated systems.

42 ENGINEERING↗
DOE OSTI2010

Analysis Code for High Gradient Dielectric Insulator Surface Breakdown

High voltage (HV) insulators are critical components in high-energy, accelerator and pulsed power systems that drive diverse applications in the national security, nuclear weapons science, defense and industrial arenas. In these systems, the insulator may separate vacuum/non-vacuum regions or conductors with high electrical field gradients. These insulators will often fail at electric fields over an order of magnitude lower than their intrinsic dielectric strength due to flashover at the dielectric interface. Decades of studies have produced a wealth of information on fundamental processes and mechanisms important for flashover initiation, but only for relatively simple insulator configurations in controlled environments. Accelerator and pulsed power system designers are faced with applying the fundamental knowledge to complex, operational devices with escalating HV requirements. Designers are forced to rely on “best practices” and expensive prototype testing, providing boundaries for successful operation. However, the safety margin is difficult to estimate, and system design must be very conservative for situations where testing is not practicable, or replacement of failed parts is disruptive or expensive. The Phase I program demonstrated the feasibility of developing an advanced code for modeling insulator breakdown. Such a code would be of great interest for a number of applications, including high energy physics, microwave source development, fusion sciences, and other research and industrial applications using high voltage devices.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2016

Multisource inverse-geometry CT. Part II. X-ray source design and prototype

Purpose: This paper summarizes the development of a high-power distributed x-ray source, or “multisource,” designed for inverse-geometry computed tomography (CT) applications [see B. De Man et al., “Multisource inverse-geometry CT. Part I. System concept and development,” Med. Phys. 43, 4607–4616 (2016)]. The paper presents the evolution of the source architecture, component design (anode, emitter, beam optics, control electronics, high voltage insulator), and experimental validation. Methods: Dispenser cathode emitters were chosen as electron sources. A modular design was adopted, with eight electron emitters (two rows of four emitters) per module, wherein tungsten targets were brazed onto copper anode blocks—one anode block per module. A specialized ceramic connector provided high voltage standoff capability and cooling oil flow to the anode. A matrix topology and low-noise electronic controls provided switching of the emitters. Results: Four modules (32 x-ray sources in two rows of 16) have been successfully integrated into a single vacuum vessel and operated on an inverse-geometry computed tomography system. Dispenser cathodes provided high beam current (>1000 mA) in pulse mode, and the electrostatic lenses focused the current beam to a small optical focal spot size (0.5 × 1.4 mm). Controlled emitter grid voltage allowed the beam current to be varied for each source, providing the ability to modulate beam current across the fan of the x-ray beam, denoted as a virtual bowtie filter. The custom designed controls achieved x-ray source switching in <1 μs. The cathode-grounded source was operated successfully up to 120 kV. Conclusions: A high-power, distributed x-ray source for inverse-geometry CT applications was successfully designed, fabricated, and operated. Future embodiments may increase the number of spots and utilize fast read out detectors to increase the x-ray flux magnitude further, while still staying within the stationary target inherent thermal limitations.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2021

Hardware Design of Medium Voltage SiC-Based Modular Multilevel Converters for Grid-Tied Applications

This paper presents a design of a 10 kV silicon carbide (SiC) MOSFET based modular multilevel converter (MMC). The MMC functions as the interconnection between a 24 kV dc bus and a 13. SkV distribution grid. This paper focuses on the hardware design of the MMC and its submodules. The gate driver, auxiliary power supply and bus bur in submodules are major components that need to meet high dv/dt immunity and high insulation voltage requirements. The gate driver achieves over 200 kV/us common mode transient immunity (CMTI). Its associated auxiliary power supply is based on an on-board transformer with over 30 kV insulation capability and 1.4 pF barrier capacitance. The busbar achieves less than 11 kV/cm electric field in the air to avoid partial discharges. Validation tests of the MMC submodule were performed by double pulse tests at 5 kV and buck converter tests at3 kV, 52A (peak). Reliable operations were achieved in validation tests.

auxiliary power supply↗
DOE OSTI2015

Development of a Time-tagged Neutron Source for SNM Detection

Associated particle imaging (API) is a powerful technique for special nuclear material (SNM) detection and characterization of fissile material configurations. A sealed-tube neutron generator has been under development by Lawrence Berkeley National Laboratory to reduce the beam spot size on the neutron production target to 1 mm in diameter for a several-fold increase in directional resolution and simultaneously increases the maximum attainable neutron flux. A permanent magnet 2.45 GHz microwave-driven ion source has been adopted in this time-tagged neutron source. This type of ion source provides a high plasma density that allows the use of a sub-millimeter aperture for the extraction of a sufficient ion beam current and lets us achieve a much reduced beam spot size on target without employing active focusing. The design of this API generator uses a custom-made radial high voltage insulator to minimize source to neutron production target distance and to provide for a simple ion source cooling arrangement. Preliminary experimental results showed that more than 100 µA of deuterium ions have been extracted, and the beam diameter on the neutron production target is around 1 mm.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Computer System for Unattended Control of Negative Ion Source

The computer system for control of cw surface-plasma source of negative ions is described. The system provides an automatic handling of source parameters by the specified scenario. It includes the automatic source start and long-term operation with switching and control of the power supplies blocks, setting and reading of source parameters like hydrogen feed, cesium seed, electrodes' temperature, checking of the protection and blockings elements like vacuum degradation, absence of cooling water, etc. The semi-automatic mode of control is also available, where the order of steps and magnitude of parameters, included to scenario, is corrected in situ by the operator. Control system includes the main controller and a set of peripheral local controllers. Commands execution is carried out by the main controller. Each peripheral controller is driven by the stand-alone program, stored in its ROM. Control system is handled from PC via Ethernet. The PC and controllers are connected by fiber optic lines, which provide the high voltage insulation and the stable system operation in spite the breakdowns and electromagnetic noise of cross-field discharge. The PC program for data setting and information display is developed under the LabView.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2018

300 kV DC High Voltage Photogun with Inverted Insulator Geometry and CsK2sb Photocathode

A compact DC high voltage photogun with inverted-insulator geometry was designed, built and operated reliably at 300 kV bias voltage using alkali-antimonide photocathodes. This presentation describes key electrostatic design features of the photogun with accompanying emittance measurements obtained across the entire photocathode surface that speak to field non-uniformity within the cathode/anode gap. A summary of initial photocathode lifetime measurements at beam currents up to 4.5 mA is also presented.

Wang, Yan↗