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Modification of mesospheric OH and O3 during a measured highly relativistic electron precipitation event
Highly relativistic electron precipitation events (HRE's) can provide a major source of energy affecting mesospheric constituents and ionization. Based on satellite data, these events are most pronounced near the minimum of the solar sunspot cycle, increasing in intensity, spectral hardness, and frequency of occurrence as the solar cycle declines. Since such events can be sustained up to several days, their integrated effect in the mesosphere can dominate over those of other energy sources such as relativistic electron precipitation events (REP's) and auroral precipitation. The energy deposition data to be discussed and analyzed were obtained by rocket at Poker Flat, Alaska, in May 1990 during a modest HRE observed at midday near the peak of the sunspot cycle. Using a NASA two dimensional model, significant enhancement of OH and depletion of O3 at 75 +/- 10 km altitude from the measured radiation are found. Estimates of enhanced effects were made for more intense HRE events, as might be expected during solar minimum. By causing O3 depletion, the electron precipitation can also regulate the penetration of solar UV radiation, which could affect the thermal properties of the mesosphere.
Laboratory Experimentation Model of the 270 Degree Electron Tophat Analyzer
One of the most important space plasma measurements is that of a well-resolved low-energy (approximately 1 eV to 1 keV) electron spectrum. This range includes the regime where photoelectron and Auger processes are important as well as the very low energy range (down to 1 eV) where electron distributions of temperature 11,000 K are measurable. Knowledge of the structure (approx. eV scale) of the photoelectron spectrum can provide information on the composition of a planetary or cometary atmosphere. As evidence, scientists developing the Analyzer of Space Plasma and Energetic Atoms (ASPERA-3) Electron Spectrometer (ELS) flying on the European Space Agency (ESA) Mars Express Mission have adapted their electron instrument to increase energy resolution in the photoelectron energy region as a means of remotely sensing the Martian atmosphere; the idea being that the Martian magnetic field is so weak that electron interaction between the source and point of detection is nonexistent; the measured electrons are therefore reflective of the processes occurring in the Martian atmosphere.
Laboratory Experimentation Model of the 270 Degree Electron Tophat Analyzer
One of the most important space plasma measurements is that of a well-resolved low-energy (approx.1 eV to 1 keV) electron spectrum. This range includes the regime where photoelectron and Auger processes are important [Winningham et at., 1989] as well as the very low-energy range (down to 1 eV) where electron distributions of temperature 11,000 K are measurable. Knowledge of the structure (approx. eV scale) of the photoelectron spectrum can provide information on the composition of a planetary or cometary atmosphere. As evidence, scientists developing the Analyzer of Space Plasma and Energetic Atoms (ASPERA-3) Electron Spectrometer (ELS) flying on the European Space Agency (ESA) Mars Express Mission have adapted their electron instrument to increase energy resolution in the photoelectron energy region as a means of remotely sensing the Martian atmosphere; the idea being that the Martian magnetic field is so weak that electron interaction between the source and point of detection is nonexistent; the measured electrons are therefore reflective of the processes occurring in the Martian atmosphere.
First Measurements of Jovian Electrons by Parker Solar Probe/ISʘIS Within 0.5 AU of the Sun
Energetic electrons of Jovian origin have been observed for decades throughout the heliosphere, as far as 11 astronomical units (au), and as close as 0.5 au, from the Sun. The treatment of Jupiter as a continuously emitting point source of energetic electrons has made Jovian electrons a valuable tool in the study of energetic electron transport within the heliosphere. We present observations of Jovian electrons measured by the EPI-Hi instrument in the Integrated Science Investigation of the Sun (IS ʘ IS) instrument suite on Parker Solar Probe at distances within 0.5 au of the Sun. These are the closest measurements of Jovian electrons to the Sun, providing a new opportunity to study the propagation and transport of energetic electrons to the inner heliosphere. We also find periods of nominal connection between the spacecraft and Jupiter in which expected Jovian electron enhancements are absent. Several explanations for these absent events are explored, including stream interaction regions (SIRs) between Jupiter and Parker Solar Probe and the spacecraft lying on the opposite side of the heliospheric current sheet from Jupiter, both of which could impede the flow of the electrons. These observations provide an opportunity to gain a greater insight into electron transport through a previously unexplored region of the inner heliosphere.
Controllable Bidirectional dc Power Sources For Large Loads
System redesigned for greater efficiency, durability, and controllability. Modern electronically controlled dc power sources proposed to supply currents to six electromagnets used to position aerodynamic test model in wind tunnel. Six-phase bridge rectifier supplies load with large current at voltage of commanded magnitude and polarity. Current-feedback circuit includes current-limiting feature giving some protection against overload.
On the transport and propagation of relativistic electrons in galaxies
Analytic solutions to the time-dependent equation describing the transport of relativistic electrons that are being convected and diffused, and may be either gaining or losing energy, are described. The calculations yield a body of solutions from which specific ones can be chosen for the modelling of synchrotron radiation in the Galaxy and in other galaxies. The solutions allow for (1) spatially varying convection velocity; (2) an energy and spatially dependent diffusion coefficient; (3) adiabatic acceleration effects; (4) a term describing spatially dependent synchrotron loss and/or Fermi acceleration; (5) an injection source for the electrons that may be impulsive, steady-state, or variable-injection; (6) a spatial injection or spatially more diffuse source; (7) arbitrary energy dependence of the injection source; and (8) spatial and energy boundaries where the spatial or energy form of the convection, diffusion, and energy supply terms in the basic equation can change character.
Reliable Transport over SpaceWire for James Webb Space Telescope (JWST) Focal Plane Electronics (FPE) Network
NASA's James Webb Space Telescope (JWST) faces difficult technical and budgetary challenges to overcome before it is scheduled launch in 2010. The Integrated Science Instrument Module (ISIM), shares these challenges. The major challenge addressed in this paper is the data network used to collect, process, compresses and store Infrared data. A total of 114 Mbps of raw information must be collected from 19 sources and delivered to the two redundant data processing units across a twenty meter deployed thermally restricted interface. Further data must be transferred to the solid-state recorder and the spacecraft. The JWST detectors are kept at cryogenic temperatures to obtain the sensitivity necessary to measure faint energy sources. The Focal Plane Electronics (FPE) that sample the detector, generate packets from the samples, and transmit these packets to the processing electronics must dissipate little power in order to help keep the detectors at these cold temperatures. Separating the low powered front-end electronics from the higher-powered processing electronics, and using a simple high-speed protocol to transmit the detector data minimize the power dissipation near the detectors. Low Voltage Differential Signaling (LVDS) drivers were considered an obvious choice for physical layer because of their high speed and low power. The mechanical restriction on the number cables across the thermal interface force the Image packets to be concentrated upon two high-speed links. These links connect the many image packet sources, Focal Plane Electronics (FPE), located near the cryogenic detectors to the processing electronics on the spacecraft structure. From 12 to 10,000 seconds of raw data are processed to make up an image, various algorithms integrate the pixel data Loss of commands to configure the detectors as well as the loss of science data itself may cause inefficiency in the use of the telescope that are unacceptable given the high cost of the observatory. This combination of requirements necessitates a redundant, fault tolerant, high- speed, low mass, low power network with a low Bit error Rate(1E-9- 1E-12). The ISIM systems team performed many studies of the various network architectures that meeting these requirements. The architecture selected uses the Spacewire protocol, with the addition of a new transport and network layer added to implement end-to-end reliable transport. The network and reliable transport mechanism must be implemented in hardware because of the high average information rate and the restriction on the ability of the detectors to buffer data due to power and size restrictions. This network and transport mechanism was designed to be compatible with existing Spacewire links and routers so that existing equipment and designs may be leveraged upon. The transport layer specification is being coordinated with European Space Agency (ESA), Spacewire Working Group and the Consultative Committee for Space Data System (CCSDS) PlK Standard Onboard Interface (SOIF) panel, with the intent of developing a standard for reliable transport for Spacewire. Changes to the protocol presented are likely since negotiations are ongoing with these groups. A block of RTL VHDL that implements a multi-port Spacewire router with an external user interface will be developed and integrated with an existing Spacewire Link design. The external user interface will be the local interface that sources and sinks packets onto and off of the network (Figure 3). The external user interface implements the network and transport layer and handles acknowledgements and re-tries of packets for reliable transport over the network. Because the design is written in RTL, it may be ported to any technology but will initially be targeted to the new Actel Accelerator series (AX) part. Each link will run at 160 Mbps and the power will be about 0.165 Watt per link worst case in the Actel AX.
Efficient prediction of attosecond two-colour pulses from an X-ray free-electron laser with machine learning
Abstract X-ray free-electron lasers are sources of coherent, high-intensity X-rays with numerous applications in ultra-fast measurements and dynamic structural imaging. Due to the stochastic nature of the self-amplified spontaneous emission process and the difficulty in controlling injection of electrons, output pulses exhibit significant noise and limited temporal coherence. Standard measurement techniques used for characterizing two-coloured X-ray pulses are challenging, as they are either invasive or diagnostically expensive. In this work, we employ machine learning methods such as neural networks and decision trees to predict the central photon energies of pairs of attosecond fundamental and second harmonic pulses using parameters that are easily recorded at the high-repetition rate of a single shot. Using real experimental data, we apply a detailed feature analysis on the input parameters while optimizing the training time of the machine learning methods. Our predictive models are able to make predictions of central photon energy for one of the pulses without measuring the other pulse, thereby leveraging the use of the spectrometer without having to extend its detection window. We anticipate applications in X-ray spectroscopy using XFELs, such as in time-resolved X-ray absorption and photoemission spectroscopy, where improved measurement of input spectra will lead to better experimental outcomes.
High frequency plasma generators for ion thruster applications
Two concepts for high frequency discharge ion thrusters are described. Both sources are designed for use with 30 cm grid sets and argon propellant and utilize multi-cusp permanent magnet geometries for plasma confinement. The RF induction source is a conventional design representing a synthesis of the RIT and multi-cusp concepts. The preliminary data (without system optimization) indicate a discharge efficiency comparable to that obtained in 30 cm hollow cathode multi-cusp argon thrusters. The electron cyclotron heating source is electrodeless and exhibits plasma characteristics which should lead to greatly reduced discharge chamber and screen sputter rates with the optimization of the magnetic fields, microwave frequency, and feed configuration.
Possible source mechanism for low-energy galactic electrons.
Low energy galactic electrons attributed to knock- on collisions of primary nuclear beam with interstellar gas
A study of electron density profiles in relation to ionization sources and ground-based radio wave absorption measurements, part 1
An extensive set of ground-based measurements of the diurnal variation of medium frequency radio wave adsorption and virtual height is analyzed in terms of current understanding of the D- and lower E-region ion production and loss process. When this is done a gross discrepancy arises, the source of which is not known.
A study of electron density profiles in relation to ionization sources and ground-based radio wave absorption measurements, part 2
The D-region ion production functions are used to calculate the relationship between radio wave absorption and the flux level of X-rays in the 1-8A wavelength band. In order to bring this calculation into agreement with the empirically established relationship, it was found necessary to reduce by, a factor of about 5, the Meira nitric oxide densities below 90 km.
A Co-Investigator Proposal for the Cornell University CAPER Rocket: Cleft Accelerated Plasma Experiment Rocket
The objectives are: 1) To support the Cornell wave instruments in a study of dayside ion outflow. 2) In conjunction with the U. of Alaska ground optical data, a prime objective was to measure the topside Cusp ion spectra responsible for dayside proton aurora. If such a correlative measurement could be made, then monitoring of this cusp precipitation from the ground could be routinely achieved. The nature of Cusp ions has and will continue to provide information about dayside magnetic reconnection. 3) A third objective was to study the dayside microburst electron precipitation from the BPS/CPS population. The Scifer rocket flight showed a bursty electron population at 1000 km altitude correlated closely with pulsation ground aurora on closed field lines. The frequency of this pulsating aurora is about 1 Hz. Ground pulsation measurements have recorded dayside bursts of Pc1 waves which could very well be the source of the electrons responsible for the pulsating aurora. In support of the Caper flight, UNH provided ground induction antennas to measure the equatorial Pc1 waves that might be dumping trapped electrons from the Central Plasma Sheet population. The Caper flight was launched on the last day of the window and all the Cornell and UNH instrumentation worked perfectly. Unfortunately the rocket trajectory flew very far to the west of the ground site at Longyearbyen missing conjugacy by several hundred kilometers. This meant the intended aurora was not crossed and all the ground experiments were far from being near the foot print of the rocket ruling out correlative science. The "miss" was primarily due to a decision during the countdown by the Andoya Rocket Range to move the azimuth of the rocket to the west to avoid Norwegian fishing boats at the splash point of the first two stages, and to make matters worse, the dispersion of the fourth stage of the rocket added entirely in this direction. Although no publications have resulted from the UNH data up to this point, a joint publication with the U. of Alaska group using both the Scifer and Caper data is in preparation. The data will continue to be worked on. There is interest in the Caper data as evidence by two recent papers presented at the "Low Latitude Boundary Layer Chapman Conference" held in New Orleans, Louisiana in April 2001.
Simultaneous event‐specific estimates of transport, loss, and source rates for relativistic outer radiation belt electrons
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Free Electron Lasers: The Biggest and Brightest Light Sources
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BLAZED REFLECTION GRATINGS PATTERNED VIA ELECTRON-BEAM LITHOGRAPHY FOR X-RAY SOURCES
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