Relaxation-time approximation for the mobility of electrons in helium.
Electron mobility in He, using irreversible quantum statistics theory to obtain momentum dependent relaxation time
QUANTUM THEORY↗
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Mobilities of uranium and mercury ions in helium
The mobilities of mass-identified U(+) and Hg (+) ions in helium were determined in a drift tube-mass spectrometer. For uranium ions, a reduced mobility value is obtained at 305 K and a standard gas density of 2.69 x 10 to the 19th power/cu cm. The mobility of mercury ions is in agreement with two previous determinations. The effect of fast ion injection in drift mobility measurements is discussed, and a technique to circumvent these problems is described. The results are compared with existing theories of ion mobilities.
Johnsen, R.↗
Miniature GC-Minicell Ion Mobility Spectrometer (IMS) for In Situ Measurements in Astrobiology Planetary Missions
Astrobiology flight experiments require highly sensitive instrumentation for in situ analysis of volatile chemical species and minerals present in the atmospheres and surfaces of planets, moons, and asteroids. The complex mixtures encountered place a heavy burden on the analytical instrumentation to detect and identify all species present. The use of land rovers and balloon aero-rovers place additional emphasis on miniaturization of the analytical instrumentation. In addition, smaller instruments, using tiny amounts of consumables, allow the use of more instrumentation and/or ionger mission life for stationary landers/laboratories. The miniCometary Ice and Dust Experiment (miniCIDEX), which combined Gas Chromatography (GC) with helium Ion Mobility Spectrometry (IMS), was capable of providing the wide range of analytical information required for Astrobiology missions. The IMS used here was based on the PCP model 111 IMS. A similar system, the Titan Ice and Dust Experiment (TIDE), was proposed as part of the Titan Orbiter Aerorover Mission (TOAM). Newer GC systems employing Micro Electro- Mechanical System (MEMS) based technology have greatly reduced both the size and resource requirements for space GCs. These smaller GCs, as well as the continuing miniaturization of Astrobiology analytical instruments in general, has highlighted the need for smaller, dry helium IMS systems. We describe here the development of a miniature, MEMS GC-IMS system (MEMS GC developed by Thorleaf Research Inc.), employing the MiniCell Ion Mobility Spectrometer (IMS), from Ion Applications Inc., developed through NASA's Astrobiology Science and Technology Instrument Development (ASTID) Program and NASA s Small Business Innovative Research (SBIR) Program.
Kojiro, Daniel R.↗
Analytical/Operational Requirements for the In Situ Chemical Analysis of Cometary and Planetary Environments Using GC-IMS
Exobiology flight experiments require highly sensitive instrumentation for the in situ analysis of the volatile chemical species that occur in the atmospheres and surfaces of various bodies within the solar system. The complex mixtures encountered place a heavy burden on the analytical instrumentation to detect and identify all species present. The minimal resources available onboard for such missions mandate that the instruments provide maximum analytical capabilities with minimal requirements of volume, weight and consumables. The miniCIDEX instrument was developed for the chemical analysis of a cemetery environment. It combined a Gas Chromatograph (GC) with a helium based Ion Mobility Spectrometer (IMS) to fulfill the analytical requirements of a cemetery exobiology mission: universal response; ppb sensitivity; low mass, volume and consumable MiniCIDEX is now a candidate for the chemical analysis instrument of a Titan Aero-rover Mission. The complexity of the analyses will be similar to the comet application with a heavier emphasis on organic molecules. Because the Titan Aero-Rover will be a balloon powered rover, much more attention is placed on the total mass of the instrument package. The GC will likely be a Micro-Electro-Mechanical-System (MEMS) design, smaller than the initial miniCIDEX GC by a factor of ten (with a similar reduction in consumable use). Similar miniaturization of the helium-based IMS will be necessary while maintaining the analytical capabilities. The two mission applications, the analytical requirements, and the evolution of the IMS design to accommodate these requirements will be presented.
Kojiro, Daniel R.↗
Analytical Instrument for Determining the Composition of Surface Materials and Ices in the Solar System: Mini-CIDEX to TIDE
Exobiology experiments onboard spacecraft or space probes often require the detection and identification of a wide range of chemical species over vast concentration ranges. These experiments must be carried out under severely limited conditions utilizing minimal resources. The mini-Cometary Ice and Dust Experiment (mini-CIDEX) instrument was developed for the chemical analysis of a cometary environment. It combined a Gas Chromatograph (GC) with a helium-based Ion Mobility Spectrometer (IMS) to fulfill the analytical requirements of a cometary exobiology mission: universal response; ppb sensitivity; low mass, volume, and consumables. Mini-CIDEX has evolved into the Titan Ice and Dust Experiment (TIDE) for the chemical analysis of the surface (liquid and solid) and lower atmosphere of Titan. The complexity of the analyses will be similar to the comet application with a heavier emphasis on organic molecules. TIDE is a component of the Titan Orbiter Aero-Rover Mission (TOAM) proposed to NASA's New Visions Program. Advances to the Mini-CIDEX technology for the Titan application and the analytical capabilities of TIDE will be presented.
Kojiro, Daniel R.↗
Electron mobility in randomly located hard-core scatterers
Irreversible quantum statistics for electron mobility analysis in low temperature helium
Neustadter, H. E.↗
A Helium GC/IMS for the Analysis of Extraterrestrial Volatiles in Exobiology Flight Experiments
For exobiology experiments on board spacecraft or space probes, a wide range of chemical species often must be detected and identified. The limited amount of power and space available for flight instruments severely limits the number of instruments that can be flown on any given mission. It is important then, that these experiments utilize instrumentation with universal response, so that all species of interest can be analyzed. Instrumentation to fulfill the analytical requirements of exobiology experiments has been developed utilizing Gas Chromatography - Ion Mobility Spectrometry. The Gas Chromatograph (GC) combines columns developed specifically for the complex mixtures anticipated with highly sensitive Metastable Ionization Detectors (a type of Helium Ionization Detector). To satisfy the limitations placed on resources, the Ion Mobility Spectrometer (IMS) uses the same ultra high purity helium as the GC. This GC-MS provides the analytical capability to fulfill a wide range of exobiology flight experiment applications and has been included on a proposed Discovery Mission and proposals for both Lander and Orbiter of the European Space Agency's Rosetta Comet Mission. A data base of helium IMS spectra is now being built for these future applications.
Kojiro, Daniel R.↗
High Electron Mobility Transistor Structures on Sapphire Substrates Using CMOS Compatible Processing Techniques
System-on-a-chip (SOC) processes are under intense development for high-speed, high frequency transceiver circuitry. As frequencies, data rates, and circuit complexity increases, the need for substrates that enable high-speed analog operation, low-power digital circuitry, and excellent isolation between devices becomes increasingly critical. SiGe/Si modulation doped field effect transistors (MODFETs) with high carrier mobilities are currently under development to meet the active RF device needs. However, as the substrate normally used is Si, the low-to-modest substrate resistivity causes large losses in the passive elements required for a complete high frequency circuit. These losses are projected to become increasingly troublesome as device frequencies progress to the Ku-band (12 - 18 GHz) and beyond. Sapphire is an excellent substrate for high frequency SOC designs because it supports excellent both active and passive RF device performance, as well as low-power digital operations. We are developing high electron mobility SiGe/Si transistor structures on r-plane sapphire, using either in-situ grown n-MODFET structures or ion-implanted high electron mobility transistor (HEMT) structures. Advantages of the MODFET structures include high electron mobilities at all temperatures (relative to ion-implanted HEMT structures), with mobility continuously improving to cryogenic temperatures. We have measured electron mobilities over 1,200 and 13,000 sq cm/V-sec at room temperature and 0.25 K, respectively in MODFET structures. The electron carrier densities were 1.6 and 1.33 x 10(exp 12)/sq cm at room and liquid helium temperature, respectively, denoting excellent carrier confinement. Using this technique, we have observed electron mobilities as high as 900 sq cm/V-sec at room temperature at a carrier density of 1.3 x 10(exp 12)/sq cm. The temperature dependence of mobility for both the MODFET and HEMT structures provides insights into the mechanisms that allow for enhanced electron mobility as well as the processes that limit mobility, and will be presented.
Mueller, Carl↗
Properties of crystalline bismuth selenide and its use as a Hall effect magnetometer
Single crystals of n-type Bi2Se3 grown by the Bridgman technique are found to make excellent Hall effect magnetometers. Plots of Hall resistivity sub yx against magnetic field B to 10 tesla are linear to within 1 percent. Furthermore, the slope of the sub yx against B curve varies by about 1 percent in the region 1.1 to 35 K and by less than 20 percent in the region 1.1 to 300 K. Analysis of galvanomagnetic measurements indicate the samples have semimetallic densities of approximately 10 to the 25th power/cu cm, with two band conduction and near carrier compensation. Reflectivity measurements suggest a band gap of approximately 0.08 eV for the samples. The temperature dependence of mobility is also measured. A series of 50 direct immersions into liquid helium and liquid nitrogen demonstrate the reliability of Bi2Se3 magnetometers for cryogenic use.
Wollam, J. A.↗
Determination of C1-C4 alkanes by ion mobility spectrometry
Results are presented from a comparison between two ion-mobility-spectrometer (IMS) methods of sample ionisation: a conventional IMS with very dry helium and an IMS using metastable helium ionization. As one of the tests, a mixture of several hydrocarbons expected to be the components of Titan's atmosphere (made of ethane, ethylene, acetylene, propane, n-butane, isobutane, and propyne in concentrations from 20 to 200 ppm) was analyzed by both methods. Results from the dry-He IMS showed that the dry-helium approach was more adequate for the analysis of these gases than the metastable-helium IMS approach. In the metastable-He approach, in which several versions of He ionization reaction were tested, the spectra produced were not as clear as the conventional IMS spectra, due to the fact that the strong electric field introduced in the reaction region to generate metastable helium affected the gating, resolution, and collection of the ions.
Kojiro, Daniel R.↗
Calibrating the Helium Pressurization System for the Space Shuttle Liquid-Hydrogen Tank
Analysis of the results from the STS-114 tanking tests and subsequent launch called into question existing thermal and mass models of helium pressurization of the liquid hydrogen tank. This hydrogen tank, which makes up the bottom two-thirds of the External Tank, is pressurized prior to launch to avoid cavitation in the Shuttle Main Engine pumps. At about 2 minutes prior to launch, the main vent valve is closed, and pressurized helium flows into the tank ullage space to achieve set point pressure. As the helium gas cools, its pressure drops, calling for additional helium. Subsequent helium flows are provided in short, timed pulses. The number of pulses is taken as a rough leak indicator. An analysis of thermal models by Marshall Space Flight Center showed considerable uncertainty in the pressure-versus-time behavior of the helium ullage space and the ability to predict the number of pulses normally expected. Kennedy Space Center proposed to calibrate the dime-sized orifice, which together with valves, controls the helium flow quantity (Figure 1). Pressure and temperature sensors were installed to provide upstream and downstream measurements necessary to compute flow rate based on the orifice discharge coefficient. An assessment of flow testing with helium indicated an extremely costly use of this critical resource. In order to reduce costs, we proposed removing the orifices from each Mobile Launcher Platform (MLP) and asking Colorado Engineering Experiment Station Inc. (CEESI) to calibrate the flow. CEESI has a high-pressure air flow system with traceable flow meters capable of handling the large flow rates. However, literature research indicated that square-edged orifices of small diameters often exhibit significant hysteresis and nonrepeatability in the vicinity of choked or sonic flow. Fortunately, the MLP orifices behaved relatively well in testing (Figure 2). Using curve fitting of the air-flow data, in conjunction with ASME orifice modeling equations, a method of relating the helium mass flow to measured air flow data was obtained. This analysis showed that the highest uncertainty in flow occurred in the vicinity of the choking pressure ratio, as would be expected. In addition, analysis of typical flow pulses showed that most of the helium flow occurred either well below or well above this uncertain area. The final result is the ability to provide postlaunch estimates of helium mass flows that are within 1.5 percent of the actual value.
Source record↗
Room-Temperature Determination of Two-Dimensional Electron Gas Concentration and Mobility in Heterostructures
A technique for determination of room-temperature two-dimensional electron gas (2DEG) concentration and mobility in heterostructures is presented. Using simultaneous fits of the longitudinal and transverse voltages as a function of applied magnetic field, we were able to separate the parameters associated with the 2DEG from those of the parallel layer. Comparison with the Shubnikov-de Haas data derived from measurements at liquid helium temperatures proves that the analysis of the room-temperature data provides an excellent estimate of the 2DEG concentration. In addition we were able to obtain for the first time the room-temperature mobility of the 2DEG, an important parameter to device application. Both results are significantly different from those derived from conventional Hall analysis.
Schacham, S. E.↗
NASA Tech Briefs, October 2012
Topics discussed include: Detection of Chemical Precursors of Explosives; Detecting Methane From Leaking Pipelines and as Greenhouse Gas in the Atmosphere; Onboard Sensor Data Qualification in Human-Rated Launch Vehicles; Rugged, Portable, Real-Time Optical Gaseous Analyzer for Hydrogen Fluoride; A Probabilistic Mass Estimation Algorithm for a Novel 7-Channel Capacitive Sample Verification Sensor; Low-Power Architecture for an Optical Life Gas Analyzer; Online Cable Tester and Rerouter; A Three-Frequency Feed for Millimeter-Wave Radiometry; Capacitance Probe Resonator for Multichannel Electrometer; Inverted Three-Junction Tandem Thermophotovoltaic Modules; Fabrication of Single Crystal MgO Capsules; Inflatable Hangar for Assembly of Large Structures in Space; Mars Aqueous Processing System; Hybrid Filter Membrane; Design for the Structure and the Mechanics of Moballs; Pressure Dome for High-Pressure Electrolyzer; Cascading Tesla Oscillating Flow Diode for Stirling Engine Gas Bearings; Compact, Low-Force, Low-Noise Linear Actuator; Ultra-Compact Motor Controller; Extreme Ionizing-Radiation-Resistant Bacterium; Wideband Single-Crystal Transducer for Bone Characterization; Fluorescence-Activated Cell Sorting of Live Versus Dead Bacterial Cells and Spores; Nonhazardous Urine Pretreatment Method; Laser-Ranging Transponders for Science Investigations of the Moon and Mars; Ka-Band Waveguide Three-Way Serial Combiner for MMIC Amplifiers; Structural Health Monitoring with Fiber Bragg Grating and Piezo Arrays; Low-Gain Circularly Polarized Antenna with Torus-Shaped Pattern; Stereo and IMU- Assisted Visual Odometry for Small Robots; Global Swath and Gridded Data Tiling; GOES-R: Satellite Insight; Aquarius iPhone Application; Monitoring of International Space Station Telemetry Using Shewhart Control Charts; Theory of a Traveling Wave Feed for a Planar Slot Array Antenna; Time Manager Software for a Flight Processor; Simulation of Oxygen Disintegration and Mixing With Hydrogen or Helium at Supercritical Pressure; A Superfluid Pulse Tube Refrigerator Without Moving Parts for Sub-Kelvin Cooling; Sapphire Viewports for a Venus Probe; The Mobile Chamber; Electric Propulsion Induced Secondary Mass Spectroscopy; and Radiation-Tolerant DC-DC Converters.
Source record↗
Hazardous Gas Leak Analysis in the Space Shuttle
Helium tests of the main propulsion system in the Space Shuttle and on hydrogen leaks are examined. The hazardous gas detection system (HGDS) in the mobile launch pad uses mass spectrometers (MS) to monitor the shuttle environment for leaks. The mass spectrometers are fed by long tubes to sample gas from the payload bay, mid-body, aft engine compartment, and external tank. The purpose is to improve the HGDS, especially in its potential for locating cryogen leaks. Pre-existing leak data was analyzed for transient information to determine if the leak location could be pinpointed from test data. A rapid response leak detection experiment was designed, built, and tested. Large eddies and vortices were visually seen with Schlieren imaging, and they were detected in the time plots of the various instruments. The response time of the MS was found in the range of 0.05 to 0.1 sec. Pulsed concentration waves were clearly detected at 25 cycles per sec by spectral analysis of MS data. One conclusion is that the backup HGDS sampling frequency should be increased above the present rate of 1 sample per second.
Barile, Ronald G.↗
Hydrogen leak detection in the Space Shuttle
This study focuses on a helium gas jet flowing into room air. Measurements of helium concentration and velocity in the jet-air mixture are reported. The objective is to learn about jet characteristics so that dynamically similar hydrogen leaks may be located in the Space Shuttle. The hazardous gas detection system (HGDS) in the mobile launch pad uses mass spectrometers to monitor the shuttle environment for leaks. The mass spectrometers are fed by long sample tubes which draw gas from the payload bay, mid body, aft engine compartment and external tank. The overall purpose of this study is to improve the HGDS especially in its potential for locating hydrogen leaks. A rapid-response leak detection experiment was designed, built, and tested, following on the work done in this program last summer. The apparatus included a Perkin Elmer MGA-1200 mass spectrometer and air velocity transducer, both monitored by a Macintosh IIFX computer using LabVIEW software. A jet of helium flowing into the lab air simulated a gas leak. Steady helium or hydrogen-nitrogen jets were logged for concentration and velocity, and the power spectral density of each was computed. Last year, large eddies and vortices were visually seen with Schlieren imaging, and they were detected in the time plots of the various instruments. The response time of the MGA-1200 was found in the range of 0.05 to 0.1 sec. Pulsed concentration waves were clearly detected at 25 cycles per sec by spectral analysis of MGA data. No peaks were detected in the power spectrum, so in the present study, 10 Hz bandwidth-averaged power levels were examined at regular frequency intervals. The practical consequences of last year's study are as follows: sampling frequency should be increased above the present rate of 1 sample per second so that transients could be observed and analyzed with frequency response methods. Many more experiments and conditions were observed in this second summer, including the effects of orifice diameter, jet velocity, sample tube design, radial effects, vertical flow, and low hydrogen concentrations (1 percent). A frequent observation was that the power spectrum, calculated from the Fourier transform of concentration fluctuations, gives a separate piece of information from concentration. Many of the tests suggest that power is high where mixing occurs at the helium-air interface. This fact is apparently independent of the concentration level, which could be high or low, but depends on the sample location relative to the jet (leak) origin, whereas high concentration may be due to a strong leak far away or a small leak close to the sample tube. If the power is low for any concentration level, this would signify helium is arriving at the sample tube by diffusion, not chaotic mixing caused by the jet interaction with air. The practical result is to propose a modification of the HGDL mass spectrometer data sampling and software so that sampling rates could be capable of observing at least 25 Hz fluctuations.
Barile, Ronald G↗
Sample Delivery and Computer Control Systems for Detecting Leaks in the Main Engines of the Space Shuttle
The main engines of the Space Shuttle use hydrogen and oxygen as the fuel and oxidant. The explosive and fire hazards associated with these two components pose a serious danger to personnel and equipment. Therefore prior to use the main engines undergo extensive leak tests. Instead of using hazardous gases there tests utilize helium as the tracer element. This results in a need to monitor helium in the ppm level continuously for hours. The major challenge in developing such a low level gas monitor is the sample delivery system. This paper discuss a system developed to meet the requirements while also being mobile. Also shown is the calibration technique, stability, and accuracy results for the system.
Griffin, Timothy P.↗
Deep Space Network, Cryogenic HEMT LNAs
Exploration of the Solar System with automated spacecraft that are more than ten astronomical units (1 AU = 149,597,870.691 km) from earth requires very large antennae employing extremely sensitive receivers. A key figure of merit in the specification of the spacecraft-to-earth telecommunications link is the ratio of the antenna gain to operatio nal noise temperature (G/Top) of the system. The Deep Space Network (DSN) receivers are cryogenic, low-noise amplifiers (LNAs) which addres s the need to maintain Top as low as technology permits. Historicall y, the extra-ordinarily sensitive receive systems operated by the DSN have required ctyogenically cooled, ruby masers, operating at a physi cal temperature near the boiling point of helium, as the LNA. Althoug h masers continue to be used today, they are hand crafted at JPL and expensive to manufacture and maintain. Recent advances in the developm ent of indium phosphide (InP) based high electron mobility transistor s (HEMTs) combined with cryogenic cooling near the boiling point of h ydrogen have made this alternate technology comparable with and a fraction of the cost of maser technology. InP HEMT LNA modules are demons trating noise temperatures less than ten times the quantum noise limi t (10hf/k) from 1 to 100 GHz. To date, the lowest noise LNA modules developed for the DSN have demonstrated noise temperatures of 3.5 K and 8.5 K at 8.5 K at 32 GHz, respectively. Front-end receiver packages employing these modules have demonstrated operating system noise temperatures of 17 K at 8.4 GHz (on a 70m antenna at zenith) and 39 K at 3 2 GHz (on a 34m antenna at zenith). The development and demonstration of cryogenic, InP HEMT based front-end amplifiers for the DSN requir es accurate component and module characterization, and modeling from 1 to 100 GHz at physical temperatures down to 12 K. The characterizati on and modeling begins with the HEMT chip, proceeds to the multi-stag e HEMT LNA module, and culminates with the complete front-end cryogenic receiver package for the antenna. This presentation will provide a n overview of this development process. Examples will be shown for de vices, LNA modules, front-end receiver packages, antennae employing these packages and the improvements to the down-link capacity.
low-noise amplifiers (LNAs)↗
Titan Ice and Dust Experiment (TIDE): Detection and Analysis of Compounds of Interest to Astrobiology in the Lower Atmosphere and Surface of Titan
The Titan Orbiter Aerorover Mission (TOAM) is a proposed concept for the Solar System Exploration Visions Mission, Titan Explorer, a follow-on to the Cassini-Huygens mission. TOAM would use a Titan polar orbiter and a lighter-than-air aerorover to investigate the surface and atmosphere of Titan. Astrobiology issues will be addressed though TOAM investigations including, for example: Distribution and composition of organics (atmospheric, aerosol, surface); Organic chemical processes, their chemical context and energy sources; and Seasonal variations and interactions of the atmosphere and surface. The TIDE instrument will perform in-situ analyses to obtain comprehensive and sensitive molecular and elemental assays of volatile organics in the atmosphere, oceans and surface. TIDE chemical analyses are conducted by a Gas Chromatograph-Ion Mobility Spectrometer (GC-IMS). This TIDE GC-IMS was a component of the mini-Cometary Ice and Dust Experiment (mini-CIDEX) developed for the chemical analysis of a cometary environment. Both the GC and helium IMS of mini-CIDEX have been further developed to better meet the analytical and operational requirements of the TOAM. application. A Micro-ElectroMechanical System (MEMS) GC and Mini-Cell helium IMS are under development to replace their respective mini-CIDEX components, providing similar or advanced analytical capabilities.
Kojiro, Daniel R.↗