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At least 433 records · Page 24

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NASA NTRS1976

Evaluation of clad scintillating light pipes

Arrays of fibers made of scintillating material were used as position-sensitive detectors or hodoscopes for beam-finding at ion accelerators. Experiments were made with alpha's from an Am241 source incident upon one end of the fiber, the other end being viewed with a photomultiplier tube. The scintillation light was not detected in any of the fibers tested beyond about 5 cm. The effective useful lengths for detection of relativistic heavy ions were given.

Source record↗

NASA NTRS2011

Plasma IMS Composition Measurements for Europa, Ganymede, and the Jovian System

NASA and ESA are now planning a reduced version of the joint Europa Jupiter System Mission (EJSM), potentially including a radically descoped Jupiter Europa Orbiter (JEO) but still with magnetometer and plasma instruments. Similar field and plasma instrumentation would also reside on ESA's Jupiter Ganymede Orbiter (JGO), which conceivably could carry out multiple flybys of Europa before entering orbit at Ganymede. We are developing the 3D Ion Mass Spectrometer (IMS) designed to measure both major and minor ion species within the high radiation environment of Jupiter's magnetosphere and the icy Galilean moons. The IMS covers the energy range from 10 eV to 30 keY, wide field-of-view (FOV) capability and 10-60 sec time resolution for major ions. This instrument has two main goals: 1) measure the plasma interaction between Europa and Jupiter's magnetosphere and 2) infer the global surface composition to trace elemental and significant isotopic levels; these goals are also applicable for in-situ measurements at Ganymede and Callisto, and remotely everywhere via the iogenic plasma for 10. The first goal supports the magnetometer (MAG) measurements, primarily directed at detection of Europa's sub-surface ocean, while the second goal gives information about transfer of material between the Galilean moons, e.g. mainly from 10 to the other moons, and further allows detection of oceanic materials emergent to the moon surfaces from subsurface layers putatively including salt water oceans. Outgassed exospheric materials are probed by the IMS by measuring pickup ions accelerated up to spacecraft altitudes of approximately 100-200 km in electric fields extending through the local magnetospheric environment and moon exosphere to the surface. Our 3D hybrid kinetic model of the moon-magnetosphere interaction is used to construct a global model of electric and magnetic fields for tracing of pickup ion trajectories back to the sources at approximate surface resolution of 100 km. We show that Europa's exospheric ionosphere is dominated by pickup ions with energies of 100-1000 eV. We also expect field aligned polar ion outflows driven by ionospheric electrons via the polarization electric field at Europa; the IMS will observe such outflows and thus sample the ionosphere below spacecraft orbit altitude approximately 100 km. Based on previous Ganymede studies, we also comment on IMS applications to a Ganymede orbiter. The IMS and the Europa interaction model are respectively being developed with support from NASA's Astrobiology Instrument Development (ASTID) and Outer Planets Research (OPR) programs.

Sittler, E. C., Jr.↗

NASA NTRS2011

Plasma IMS Composition Measurements for Europa, Ganymede, and the Jovian Systems

NASA and ESA are now planning a reduced version of the joint Europa Jupiter System Mission (EJSM), potentially including a radically descoped Jupiter Europa Orbiter (JEO) but still with magnetometer and plasma instruments. Similar field and plasma instrumentation would also reside on ESA's Jupiter Ganymede Orbiter (JGO), which conceivably could carry out multiple flybys of Europa before entering orbit at Ganymede. We are developing the 3D Ion Mass Spectrometer (IMS) designed to measure both major and minor ion species within the high radiation environment of Jupiter s magnetosphere and the icy Galilean moons. The IMS covers the energy range from 10 eV to 30 keV, wide field-ofview (FOV) capability and 10-60 sec time resolution for major ions. This instrument has two main goals: 1) measure the plasma interaction between Europa and Jupiter s magnetosphere and 2) infer the global surface composition to trace elemental and significant isotopic levels; these goals are also applicable for in-situ measurements at Ganymede and Callisto, and remotely everywhere via the iogenic plasma for Io. The first goal supports the magnetometer (MAG) measurements, primarily directed at detection of Europa's sub-surface ocean, while the second goal gives information about transfer of material between the Galilean moons, e.g. mainly from Io to the other moons, and further allows detection of oceanic materials emergent to the moon surfaces from subsurface layers putatively including salt water oceans. Outgassed exospheric materials are probed by the IMS by measuring pickup ions accelerated up to spacecraft altitudes of approximately 100-200 km in electric fields extending through the local magnetospheric environment and moon exosphere to the surface. Our 3D hybrid kinetic model of the moon-magnetosphere interaction is used to construct a global model of electric and magnetic fields for tracing of pickup ion trajectories back to the sources at approximate surface resolution of 100 km. We show that Europa's exospheric ionosphere is dominated by pickup ions with energies of 100-1000 eV. We also expect field aligned polar ion outflows driven by ionospheric electrons via the polarization electric field at Europa; the IMS will observe such outflows and thus sample the ionosphere below spacecraft orbit altitude approximately 100 km. Based on previous Ganymede studies, we also comment on IMS applications to a Ganymede orbiter. The IMS and the Europa interaction model are respectively being developed with support from NASA's Astrobiology Instrument Development (ASTID) and Outer Planets Research (OPR) programs.

Sittler, E.↗

NASA NTRS2003

Polar, Cluster and SuperDARN Evidence for High-Latitude Merging during Southward IMF: Temporal/Spatial Evolution

Magnetic merging on the dayside magnetopause often occurs at high latitudes. Polar measured fluxes of accelerated ions and wave Poynting vectors while skimming the subsolar magnetopause. The measurements indicate that their source was located to the north of the spacecraft, well removed from expected component merging sites. This represents the first use of wave Poynting flux as a merging discriminator at the magnetopause. We argue that wave Poynting vectors, like accelerated particle fluxes and the Walen tests, are necessary, but not sufficient, conditions, for identifying merging events. The Polar data are complemented with nearly simultaneous measurements from Cluster in the northern cusp, with correlated observations from the SuperDARN radar, to show that the locations and rates of merging vary. Magnetohydrodynamic (MHD) simulations are used to place the measurements into a global context. The MHD simulations confirm the existence of a high-latitude merging site and suggest that Polar and SuperDARN observed effects are attributable to both exhaust regions of a temporally varying X-line. A survey of 13 merging events places the location at high latitudes whenever the interplanetary magnetic field (IMF) clock angle is less than approximately 150 degrees. While inferred high-latitude merging sites favor the antiparallel merging hypothesis, our data alone cannot exclude the possible existence of a guide field. Merging can even move away from equatorial latitudes when the IMF has a strong southward component. MHD simulations suggest that this happens when the dipole tilt angle increases or when IMF B(sub X) increases the effective dipole tilt.

Maynard, N. C.↗

NASA NTRS1980

Thermal iron ions in high speed solar wind streams Detection by the IMP 7/8 energetic particle experiments

The first measurements of the abundance of iron ions in high speed (greater than 600 km/s) solar wind streams have been made with the NOAA/JHU energetic particles experiments (EPE) on IMP 7/8. The identification of iron ions is quantitatively established using 4 years of observations and heavy ion accelerator calibrations of detectors similar to those flown on the spacecraft. Preliminary estimates of the Fe/H ratio are within a factor of 2 of the adopted coronal abundance (0.00005), and there is some evidence that Fe/H may remain approximately constant within a given stream. In the peaks of fast streams (700-800 km/s), about 50 iron ion counts are obtained every 20 s, offering the possibility of studying the Fe/H ratio with approximately 1 m time resolution in high speed streams throughout the decline of Solar Cycle 20 and the rise of Solar Cycle 21.

Mitchell, D. G.↗

NASA NTRS1977

Wave-particle interaction phenomena associated with shocks in the solar wind

Microscopic wave-particle interaction phenomena must generally affect the evolution of a traveling interplanetary discontinuity such as a collisionless shock, and solar wind plasma instabilities should also be associated with interplanetary acceleration, diffusion, and dissipation. Recent local measurements from diagnostics on widely separated spacecraft illustrate some examples of these interaction phenomena, and two bounding cases are considered in detail here. It is shown that the interplanetary shock of September 14, 1974 (detected on IMP-7, 8, Hawkeye-1, and Pioneer 11) was associated with intense local electrostatic noise and ion acceleration, while the shock of January 6, 1975 (detected on IMP-7 and Helios-1) had no detectable electrostatic turbulence.

Scarf, F. L.↗

NASA NTRS1979

Increased capabilities of the 30-cm diameter Hg ion thruster

A 30-cm-diam mercury ion thruster, using two or three grid ion accelerating systems, is operated at increased values of beam current. Comparisons with the SEP (Solar Electric Propulsion) and EPSEP (Extended Performance SEP) baseline thrusters are made with respect to performance and lifetime. It is found that when a third, or decelerator, grid is added to the conventional two-grid optics of a SEP-like thruster, the ion beam focusing properties are improved, as expected from theoretical considerations. The total thruster efficiency as a function of specific impulse, is increased for values of specific impulse in the range 1200-2800 sec. Lifetime test results predict a thruster lifetime, under space conditions, not less than that of the baseline SEP thruster.

Rawlin, V. K.↗

NASA NTRS2013

Development And Testing Of The Inertial Electrostatic Confinement Diffusion Thruster

The Inertial Electrostatic Confinement (IEC) diffusion thruster is an experiment in active development that takes advantage of physical phenomenon that occurs during operation of an IEC device. The IEC device has been proposed as a fusion reactor design that relies on traditional electrostatic ion acceleration and is typically arranged in a spherical geometry. The design incorporates two radially-symmetric spherical electrodes. Often the inner electrode utilizes a grid of wire shaped in a sphere with a radius 15 to 50 percent of the radius of the outer electrode. The inner electrode traditionally has 90 percent or more transparency to allow particles (ions) to pass to the center of the spheres and collide/recombine in the dense plasma core at r=0. When operating the IEC, an unsteady plasma leak is typically observed passing out one of the gaps in the lattice grid of the inner electrode. The IED diffusion thruster is based upon the idea that this plasma leak can be used for propulsive purposes. The IEC diffusion thruster utilizes the radial symmetry found in the IEC device. A cylindrical configuration is employed here as it will produce a dense core of plasma the length of the cylindrical grid while promoting the plasma leak to exhaust through an electromagnetic nozzle at one end of the apparatus. A proof-of-concept IEC diffusion thruster is operational and under testing using argon as propellant (Figure 1).

Becnel, Mark D.↗

NASA NTRS1989

Low-frequency electrostatic instabilities excited by injections of an electron beam in space

One-dimensional particle simulations have been carried out to study the low-frequency broadband electrostatic noise that propagates almost perpendicularly from the magnetic field line when a nonrelativistic electron beam is injected into space from a spacecraft. For T(e) = T(i) the electrostatic ion cyclotron waves appear as well as the waves near the lower hybrid frequency. When the magnetic field is reduced so that Omega(e) is much less than omega(pe) in a nonisothermal plasma, T(e) greater than T(i) oblique ion acoustic instabilities appear to propagate almost perpendicular to the magnetic field. In addition, a very low frequency mode at omega much less than Omega(i) is found to be generated by the electrons flowing into the conductor. Both the injected beam electrons as well as the ambient electrons flowing into the spacecraft are responsible for generating those instabilities, which accelerate ions perpendicular to the magnetic field.

Hwang, Y. S.↗

NASA NTRS1982

Particle acceleration at planetary bow shock waves

One property of the collisionless shocks that may be studied through a comparison of their behavior in a variety of plasma conditions at several different planets is the occurrence of MHD waves, associated with particle beams accelerated at these shocks and flowing backward to the sun. Mercury, Venus, earth and Jupiter observations of one of these wave classes show that (1) the empirical relationship between interplanetary field strength and wave frequency in the observer's rest frame is approximately true at all the planets considered, and (2) the observed frequencies are consistent with resonance with beams of ions of the same energy at each of the planets. This is, in turn, in keeping with the Sonnerup (1969) geometrical model of ion reflection at collisionless shocks. It is suggested that this ion acceleration mechanism may occur in astrophysical systems similar to the solar system, providing a source of acceleration for cosmic rays.

Hoppe, M. M.↗

DOE OSTI2021

Electric field reversals resulting from voltage waveform tailoring in Ar/O 2 capacitively coupled plasmas sustained in asymmetric systems

The etching of nanometer scale high-aspect-ratio (HAR) features into dielectric materials in low pressure radio frequency excited plasmas is often accompanied by charge accumulation inside the features which can slow etching rates and produce distortions such as twisting. The intra feature charging is at least partially produced by differences in electron and ion energy and angular distributions (EADs). Positive ions, accelerated to high energies having narrow angular spreads by the sheath electric field, can penetrate deeply into HAR features. Electrons typically arrive at the wafer with nearly thermal and isotropic distributions and do not penetrate deeply into HAR features. These disparities lead to differential charging of the inside of the feature, which can lead to reductions in etch rate and feature distortion due to ion deflection. With in-creasing aspect ratio of features, charging challenges are expected to continue for the foreseeable future. In this work, the use of tailored voltage waveforms in geometrically asymmetric capacitively coupled plasmas sustained in Ar/O 2 at 40 mTorr was computationally investigated with the goal of shaping the EAD of electrons incident onto the substrate to address differential charging. The tailored waveform consisted of a sinusoidal wave and its higher harmonics with a fundamental frequency of 1 MHz. Further, we found that electric field reversals in the sheath and presheath can occur during the anodic portion of the cycle. The electric field reversal increases the energy and decreases the angular spread of electrons incident onto the substrate. The magnitude of the electric field reversal can be controlled by the phase angle of the even harmonics and the gas composition. Due to its electronegative nature, increasing mole fractions of O 2 impedes electron transport to the surface which further increases the electric field reversal.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2025

Design workflow of a symmetric traveling wave antenna for fast ion production on DD tokamaks

Initial computational plasma physics scoping and a finite element method antenna modeling design workflow for a symmetric center-fed high-field side high harmonic fast wave traveling wave array (TWA) antenna are reported here. The TWA is designed to generate a test population of fast deuterium ions in an existing D–D tokamak by heating neutral beam deuterium ions, accelerating them from 80 keV to several hundred keV. The resulting fast particles are tailored to mimic key reactor energetic particle parameters with regards to exciting Alfven eigenmode instabilities, allowing for a D–D tokamak like DIII-D or ASDEX-U to replicate reactor-relevant conditions experimentally. Initial scenario scoping for high single-pass absorption as well as good preferential fast ion damping relative to electron damping was completed using the ray-tracing/Fokker–Planck codes GENRAY and CQL3D. Python RF network analysis packages were used to create a custom TWA optimization tool to inform a COMSOL flat antenna design, and Petra-M was used to study cold plasma effects. The TWA produced by this workflow has several novel features when compared to previous TWA studies, including symmetric center feeding, and passive end straps for image current cancellation for reduced impurity production. We show here that the antenna design workflow can readily produce TWA antennas optimized for reflection coefficient, image current cancellation, and launched power spectrum shape; and that a population of fast ions can be generated in the correct region of parameter space, warranting future more detailed studies.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

NASA NTRS2008

The Lunar Potential Determination Using Apollo-Era Data and Modern Measurements and Models

Since the Apollo era the electric potential of the Moon has been a subject of interest and debate. Deployed by three Apollo missions, Apollo 12, Apollo 14 and Apollo 15, the Suprathermal Ion Detector Experiment (SIDE) determined the sunlit lunar surface potential to be about +10 Volts using the energy spectra of lunar ionospheric thermal ions accelerated toward the Moon. More recently, the Lunar Prospector (LP) Electron Reflectometer used electron distributions to infer negative lunar surface potentials, primarily in shadow. We will present initial results from a study to combine lunar surface potential measurements from both SIDE and the LP/Electron Reflectometer to calibrate an advanced model of lunar surface charging which includes effects from the plasma environment, photoemission, secondaries ejected by ion impact onto the lunar surface, and the lunar wake created downstream by the solar wind-lunar interaction.

Collier, Michael R.↗

NASA NTRS1997

Characteristics of the Thermal Ion Bulk Parameters in the Cleft

Bulk parameters for the thermal ions (0.3 to 25 eV) have been derived using data from the Scanning Thermal Ion Composition Spectrometer (STICS) on the Sounding of the Cleft Ion Fountain Energization Region (SCIFER) experiment. The SCIFER rocket was launched into the ionospheric cleft region at 1000 MLT with a maximum altitude of 1450 km. The heated cleft plasma was observed to be H(+) dominated, in sharp contrast with observations of the same region near solar maximum. Regions of particular interest include the sharp, heated equatorward wall of the cleft and highly structured patches of transversely-accelerated ions (TAI). Densities, temperatures and velocities are used to characterize and distinguish these regions and to compare to predicted bulk parameters from candidate heating mechanisms.

Coffey, V. N.↗

NASA NTRS2015

The Role of the Hall Effect in Global Structure and Dynamics of Planetary Magnetospheres: Ganymede as a Case Study

We present high-resolution Hall MHD simulations of Ganymede's magnetosphere demonstrating that Hall electric fields in ion-scale magnetic reconnection layers have significant global effects not captured in resistive MHD simulations. Consistent with local kinetic simulations of magnetic reconnection, our global simulations show the development of intense field-aligned currents along the magnetic separatrices. These currents extend all the way down to the moon's surface, where they may contribute to Ganymede's aurora. Within the magnetopause and magnetotail current sheets, Hall J x B forces accelerate ions to the local Alfven speed in the out-of-plane direction, producing a global system of ion drift belts that circulates Jovian magnetospheric plasma throughout Ganymede's magnetosphere. We discuss some observable consequences of these Hall-induced currents and ion drifts: the appearance of a sub-Jovian 'double magnetopause' structure, an Alfvenic ion jet extending across the upstream magnetopause, and an asymmetric pattern of magnetopause Kelvin-Helmholtz waves.

Magnetic Reconnection↗

DOE OSTI2023

Neutron generation using pyroelectric crystals

A method for producing a neutrons includes producing a voltage of negative polarity of at least −100 keV on a surface of a deuterated or tritiated target in response to a temperature change of a pyroelectric crystal of less than about 40° C., the pyroelectric crystal having the deuterated or tritiated target coupled thereto, pulsing a deuterium ion source to produce a deuterium ion beam, accelerating the deuterium ion beam to the deuterated or tritiated target, and directing the ion beam onto the deuterated or tritiated target to make neutrons using at least one element of the following: a voltage of the pyroelectric crystal and a high gradient insulator (HGI) surrounding the pyroelectric crystal. The accelerating of the deuterium ion beam is achieved by using an ion accelerating mechanism comprising a pyroelectric stack accelerator having a first thermal altering mechanism for changing a temperature of the pyroelectric stack accelerator.

Tang, Vincent↗

DOE OSTI2022

Experimental verification of TNSA protons and deuterons in the multi-picosecond moderate intensity regime

Ion acceleration from high intensity short pulse laser interactions is of great interest due to a number of applications, and there has been significant work carried out with laser energies up to a few 100 J with 10's of femtosecond to 1 ps pulse durations. Here, we report results from an experiment at the OMEGA EP laser, where laser energy and pulse length were varied from 100 to 1250 J and 0.7–30 ps, respectively, in the moderate (2 × 10 17 –2 × 10 18 W/cm 2 ) laser intensity regime. Ions and electrons were simultaneously measured from disk targets made of CH and CD by a Thomson parabola and a magnetic spectrometer, respectively. Measurements showed that the electron temperature, T e (MeV), has a dependence on the laser energy, E L (J), and pulse duration, τ L (ps), and its empirical scaling was found to be 0.015 × E L 0.90 τ L –0.48. The maximum proton and deuteron energies are linearly dependent on the electron temperature, (5.60 ± 0.26) × T e and (3.17 ± 0.18) × T e , respectively. A significant increase in proton numbers with the laser energy was also observed. Furthermore, the increase in the maximum proton energy and proton count with higher energy longer duration pulses presented in this article shows that such laser conditions have a great advantage for applications, such as the proton radiograph, in the moderate laser intensity regime.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2024

Proton rings from late-forming ballistic sheath fields

Many laser-driven ion experiments have seen ring-like patterns in the proton angular distribution across a wide array of laser and target parameters. These rings can impede measurement due to the small acceptance angle of detectors and often inhibit potential applications. A myriad of explanations for their formation have been proposed, yet most studies attribute them to some aspect of the laser–plasma interaction. Using 3D particle-in-cell simulations, we show that late-forming strong radial electric fields can arise due to charge separation while the beam is in flight, long after the laser–plasma interaction. These fields can accelerate ions to significant divergences (≈ 10°) as they propagate away from the target. We compare our results to a recent experiment where a high intensity, short pulse laser (I 0 ≈ 10 21 W/cm 2 , τ ≈ 30 fs) was incident upon thin (≈ 1 μm) liquid crystal targets. Our simulations capture all the main features of the experimental results—namely, robust ring formation and larger rings for higher energy protons. In addition, we show that rings do not form for sufficiently short preplasma scale lengths. Finally, we develop a phenomenological model to describe the spatiotemporal structure of the radial electric field and use this to explain the proton rings' energy and preplasma dependencies.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗