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Cooling to a temperature of approximately liquid nitrogen or lower, reduces arcing, or high voltage breakdown, between two closely spaced electrodes operating in a vacuum. This cooling technique can be applied to electrodes having other than hemispherical shapes.
Our research uses the electron beam ion trap (EBIT) at the Lawrence Livermore National Laboratory to study X-ray emission from the charge exchange (CX) of highly charged ions with neutral gases. The resulting data help to fill a void in existing experimental and theoretical understanding of this atomic physics process, and are needed to explain all or part of the observed X-ray emission from the soft X-ray background, stellar winds, the Galactic Center and Galactic Ridge, supernova ejecta, and photoionized nebulae. Appreciation of the astrophysical relevance of our work continues to grow with the publication of roughly a dozen papers in the past four years describing Chandra and XMM observations of geocoronal and heliospheric CX emission, the temporal variation of such emission and correlation with X-ray emission enhancements observed by ROSAT, the theoretical spatial distribution of that emission, and CX emission around other stars. A similar number of papers were also published during that time describing CX emission from planets and comets. We expect that the launch of ASTRSE2, with its second-generation XRS microcalo- (with 6-eV resolution), will reveal even more clearly the contributions of CX to astrophysical emission. In our EBIT work we collected CX spectra from such ions as H-like and He-like Ne, Ar, and Fe. Our early measurements were made with a high-purity Ge detector, but during the second year we began operation of the first-generation XRS microcalorimeter (a twin of the XRS on ASTRO-E) and greatly improved the resolution of our measurements from roughly 150 eV (FWHM) with the Ge detectors to 10 eV with the XRS. We found that saturation of the XRS counting apparatus, which we described in our proposal as a potential concern, is not a problem for studying CX. During the course of our research, we expanded the number of injection gases permitted by the LLNL safety team, purchased and eventually operated an atomic H source, and clearly demonstrated the feasibility of our longer-range plan. For example, we successfully injected He into EBIT (not a small feat because of the difficulty of maintaining a good vacuum with He and avoiding electrical breakdown) to collect a H-like oxygen CX spectrum. The highest energy CX spectrum recorded with the XRS to date is that of the Ar K-shell emission. These measurements provided the first observation of the relative intensity ratios of resolved He-like singlet and triplet n=2->1 lines. We also carried out measurements of He-like Ne as a function of collision energy (i.e., ion temperature). Significant differences in the resulting x-ray spectra were noted. In all cases, the intensity of high-n H-like Lyman lines is significantly higher than current theoretical CX models predict.
Gas pressure effect on electrical breakdown and field emission, discussing ion bombardment and whisker formation
The experimental results are summarized that were obtained in the development of a Teflon solid propellant pulsed plasma thruster. The feasibility was established of storing and feeding solid propellant in the form of an open circular loop into an operational thruster. This technique was verified to be practical by feeding over 20 inches of Teflon into a micro-thruster over an accumulated life test of 1858 hours. High energy density capacitors were evaluated under vacuum conditions when the capacitor is coupled directly to a plasma thruster. Numerous early capacitor failures were encountered. It was concluded that essentially all of the failures encountered in a vacuum environment are due to an internal electrical breakdown that will occur inside a capacitor that is not truly hermetically sealed. A steady input power significantly in excess of 130 watts can safely be tolerated if heat conduction can be provided to a sink whose temperature is about 16 C. A vacuum life test of the capacitor bank was carried out while discharging into a milli-lb. (milli-Newton) type pulsed plasma thruster. More than 1500 hours of vacuum testing of this milli-Newton type system has been accumulated without any capacitor problems. Recommendations are made for future capacitor designs.
A coaxial cable connector is provided, which resists radio frequency breakdown in coaxial cables used in the vacuum of outer space. The connector body surrounds an insulator which includes an easily compressible elastomeric portion. An insulated coaxial cable is prepared so that its insulation projects beyond the outer conductor and compresses the elastomeric portion of the connector insulator.
Several dummy tubes imitating the IUE Camera System design were encapsulated with Solithane 2, Conathane EN-11, Green and Black Hysols and SMRD 432. Various flaws were purposefully placed in some of these. Partial discharge testing in vacuum under direct voltage conditions was carried once a week for 12 weeks, 15 kv dc being applied during normal working hours for 40 hours duration per week. None of the units showed much damage during this time judging by the P.D. energy histograms. A more complete mathematical presentation is given on diffusion and permeation than previously. Measurements of diffusion constants for various silicone rubbers are carried out by the Time-Lag method and compared to other determinations in the literature. Calculations of the time required for diffusion through a thick wall are demonstrated in the long time approximation and for dimensions pertaining to void and wall sizes of a delamination problem in the LANDSAT-C vidicon tubes. An actual delaminated LANDSAT-C tube and some facsimiles are immersed in vacuum for long periods and tested for catastrophic breakdown due to diffusion of gas, by application of high voltage.
The Electrostatics and Surface Physic Laboratory has devised a new method to determine the electromagnetic effects from precipitation static or p-static as its commonly called. P-static occurs as a result of triboelectric charging of granular materials or ice crystals bombarded onto the surfaces of air and/or space vehicles at high speeds. The electrostatic charge that builds up on the outer surface can have deleterious effects that arise during discharge events. These discharges can cause loss of communication to and from the vehicle from ground stations, EMI interference, radio frequency noise, etc… There are even cases of total loss of vehicles caused by p-static charging. We have developed a method to simulate the extensive tribocharging of insulating materials that occurs during p-static through the use of corona charging which allows testing to occur within a lab environment. These tests simulate the discharges that occur on rocket vehicles during ascent as a result of gas breakdown by performing the corona charging tests inside a vacuum chamber and subsequently removing the air. The simultaneous gas discharges emit electromagnetic interference (EMI) which can be captured and monitored.
Single-shot fs laser-induced breakdown spectroscopy (LIBS) has been used to interrogate low-density gases of H 2 , CH 4 , CO 2 , and H 2 O ranging from 0.5 × 10 15 to 9.1 × 10 15 cm −3 (15–275 mTorr). Strong spectral signatures were observed above the noise baseline for each test gas at all densities considered. Unique molecular signatures were observed for both CH 4 and CO 2 along with atomic features for each gas. The LIBS intensity response with respect to density was determined for each species using Voigt lineshape fitting or numerical integration. Finally, the collection and analysis of LIBS spectra of composite mixtures of CH 4 –CO 2 and CH 4 –H 2 demonstrates that the extraction of individual densities from gas mixtures is feasible at low densities.
A coaxial switch capable of operating in a vacuum with high RF power in the 1.2 GHz range without multipactor breakdown, and without relying on pressurization with an inert gas is described. The RF carrying conductors of the switch are surrounded with a high grade solid dielectric, thus eliminating any gaps in which electrons can accelerate.
In planetary exploration, in situ absolute geochronology is one of the main important measurements that needs to be accomplished. Until now, on Mars, the age of the surface is only determined by crater density counting, which gives relative ages. These ages can have a lot of uncertainty as they depend on many parameters. More than that, the curves must be ties to absolute ages. Thus far, only the lost lander Beagle 2 was designed to conduct absolute geochronology measurements, though some recent attempts using MSL Curiosity show that this investigation is feasible and should be strongly encouraged for future flight. Experimental: The Potassium (K)-Argon Laser Experiment (KArLE) is being developed at MSFC through the NASA Planetary Instrument Definition and Development Program (PIDDP). The goal of this experiment is to provide in situ geochronology based on the K-Ar method. A laser ablates a rock under high vacuum, creating a plasma which is sensed by an optical spectrometer to do Laser Induced Breakdown Spectroscopy (LIBS). The ablated material frees gases, including radiogenic 40Ar,which is measured by a mass spectrometer (MS). As the potassium is a content and the 40Ar is a quantity, the ablated mass needed in order to relate them. The mass is given by the product of the ablated volume by the density of this material. So we determine the mineralogy of the ablated material with the LIBS spectra and images and calculate its density. The volume of the pit is measured by using microscopy. LIBS measurement of K under high vacuum: Three independant projects [1, 2, 3] including KArLE, are developing geochronological instruments based on this LA-LIBS-MS method. Despite several differences in their setup, all of them have validated the methods with analyses and ages. However, they all described difficulties with the LIBS measurements of K [3,4]. At ambient pressure, the quantification of K by LIBS on geological materials can be accurate [5]. However the protocol of the LA-LIBS-MS experiment required hundreds of shots under high vacuum in order to free enough 40Ar* to be measured by the QMS. This long duration of ablation may induces significant changes in the LIBS spectra. The pressure may increases by orders of magnitudewithin the chamber and the laser pit geometry can change the effectiveness of ablation and intensity of plasma light received. These effects introduce variation between the first and last spectra and so the quantification of K is more complex. The ablation of one crater can give, depending on the protocol of acquisition, from tens to hundreds of spectra. Protocol and results: We are in the process of further characterizing the variation introduced into LIBS spectra by the use of hundreds of laser shots, and definining a protocol that can be used to ensure accuracy and reporoducibility in the results.We are using natural rock powder standards fused in a furnace, as well as mars analog samples with known K content. We will show the result of the calibration and some new statistical approaches in order to apprehend the effects of the long time ablation on rocks under high vacuum.
Low inductance three-electrode spark source for vacuum UV generating high degree ionization spectra
Ga 2 O 3 unipolar devices are of high interest due to their ~8 MV/cm predicted breakdown fields, which have not yet been achieved due to premature device failure. Pre- and post-failure defect analysis of Ni–Ga 2 O 3 Schottky diodes in ultrahigh vacuum (UHV) and air were performed using depth-resolved cathodoluminescence, high angle annular dark field scanning transmission electron microscopy, and energy dispersive x-ray analysis to understand the physical mechanisms that precede premature breakdown. The breakdown voltage in UHV was dramatically reduced by nearly 40% compared with the breakdown in air. This reduction in the breakdown voltage correlated with post-breakdown differences in Ni distribution, indicating that the coordination and bonding of Ni contribute strongly to electrical behavior in Ni–Ga 2 O 3 Schottky diodes. Breakdown studies in UHV revealed that Ni diffuses away more from the metal–semiconductor interface than with air breakdown, where Ni localizes more near the interface, indicative of the preferential formation of a Ni oxide under O-poor conditions. These measurements also identified the formation of divacancy-interstitial complexes and their characteristic luminescence signature ~150 nm from the interface, the densities of which correlated with breakdown fields. These findings show that electric-field-induced degradation occurs via the rearrangement of native point defects, which act as an additional precursor to device failure. Macroscopically, they show the impact of both vacuum conditions and metal reactivity on Ga 2 O 3 device fabrication.
This viewgraph presentation reviews exploration activities at JPL into various potting materials. Since high power space-borne microwave transmitters invariably use a vacuum tube as a final power amplifier, and this tube requires high electrode voltages for operation. The associated high voltage insulation typically represents a significant fraction of the mass of the transmitter. Since mass is always a premium resource on board spacecraft, we have been investigating materials with the potential to reduce the mass required for our applications here at JPL. This paper describes electrical breakdown results obtained with various potting materials. Conathane EN-11 (polyurethane) is the traditional HVPS encapsulant at JPL, but due to temperature limitations and durability issues it was deemed inappropriate for the particular application (i.e., CloudSat radar). The choices for the best available materials were epoxies, or silicones. Epoxies are too rigid, and were deemed inadvisable. Two silicones were further investigated (i.e.,ASTM E595- 93e2: GE RTV566(R) and Dow Corning 93-500X(R), another compound was considered (i.e., DC material, Sylgard 184(R)). "Loading" (adding filler materials) the potting compound will frequently alter the final material properties. Powdered alumina and borosilicate glass known as "microballoons" were investigated as possible loading materials. The testing of the materials is described. Each of the two loading materials offers advantages and disadvantages. The advantages and disadvantages are described.
The switching properties of power transistors are investigated. The devices studied were housed in IO-3 cases and were of an n(+)-p-n(-)-n(+) vertical dopant structure. The effects of the magnitude of the reverse-base current and temperature on the reverse-bias second breakdown characteristics are discussed. Brief discussions of device degradation due to second breakdown and of a constant voltage turn-off circuit are included. A description of a vacuum tube voltage clamp circuit which reduces clamped collector voltage overshoot is given.
This viewgraph presentation reviews the Argon Geochronology Experiment (AGE). Potassium-Argon dating is shown along with cosmic ray dating exposure. The contents include a flow diagram of the Argon Geochronology Experiment, and schematic diagrams of the mass spectrometer vacuum system, sample manipulation mechanism, mineral heater oven, and the quadrupole ion trap mass spectrometer. The Laser-Induced Breakdown Spectroscopy (LIBS) Operation with elemental abundances is also described.
Conductive polymer aluminum capacitor (PA capacitor) is an evolution of traditional wet electrolyte aluminum capacitors by replacing liquid electrolyte with a solid, highly conductive polymer. On the other hand, the cathode construction in polymer aluminum capacitors with coating of carbon and silver epoxy for terminal connection is more like a combination of the technique that solid tantalum capacitor utilizes. This evolution and combination result in the development of several competing capacitor construction technologies in manufacturing polymer aluminum capacitors. The driving force of this research on characterization of polymer aluminum capacitors is the rapid progress in IC technology. With the microprocessor speeds exceeding a gigahertz and CPU current demands of 80 amps and more, the demand for capacitors with higher peak current and faster repetition rates bring conducting polymer capacitors to the center o( focus. This is because this type of capacitors has been known for its ultra-low ESR and high capacitance. Polymer aluminum capacitors from several manufacturers with various combinations of capacitance, rated voltage, and ESR values were obtained and tested. The construction analysis of the capacitors revealed three different constructions: conventional rolled foil, the multilayer stacking V-shape, and a dual-layer sandwich structure. The capacitor structure and its impact on the electrical characteristics has been revealed and evaluated. A destructive test with massive current over stress to fail the polymer aluminum capacitors reveals that all polymer aluminum capacitors failed in a benign mode without ignition, combustion, or any other catastrophic failures. The extraordinary low ESR (as low as 3 mOMEGA), superior frequency independence reported for polymer aluminum capacitors have been confirmed. For the applications of polymer aluminum capacitors in space programs, a thermal vacuum cycle test was performed. The results, as expected, show no impact on the electrical characteristics of the capacitors. The breakdown voltage of polymer capacitors has been evaluated using a steady step surge test. Initial results show the uniform distribution in the breakdown voltage for polymer aluminum capacitors. Polymer aluminum capacitors with a combination of very high capacitance, extraordinary low ESR, excellent frequency stability, and non-ignite benign failure mode make it a niche fit in space applications for both today and future. Polymer capacitors are apparently also the best substitutes of the currently used MnO2-based tantalum capacitors in the low voltage range. However, some critical aspects are still to be addressed in the next phase of the investigation for PA capacitors. These include the long term reliability test of 125 C dry life and 85 C/85%RH humidity, the failure mechanism and de-rating, the radiation tolerance, and the high temperature performance. All of the above requires the continuous NEPP funding and support.
The phenomenon of pulsed surface flashover is studied using a fast image converter camera. A still photograph of a surface flashover for a TiO2 test piece reveals that the breakdown path is a straight line perpendicular to the streak direction. It is found that visible light is initially emitted from the cathode and that the light front propagates at a constant speed of about 1 x 10 to the 7th m/s. The low luminous light is emitted up to the point where the gap is bridged by the bright light.
Circuits are described that permit measurement of fast events occurring in power semiconductors. These circuits were developed for the dynamic characterization of transistors used in inductive-load switching applications. Fast voltage clamping using vacuum diodes is discussed, and reference is made to a unique circuit that was built for performing nondestructive, reverse-bias, second-breakdown tests on transistors.