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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 1,315 records · Page 73
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Effects of a lightning discharge detected by the DE 2 satellite over Hurricane Debbie

The satellite observation of a large, about 40-mV/m, transient electric field disturbance over Hurricane Debbie in September 1982 is reported. The electric field event is viewed as a spheric disturbance from a lightning discharge in the active weather system located beneath the satellite. To elucidate this observation of upward moving electrons in the ionosphere associated with a lightning event, several mechanisms for electron acceleration by electric field with components, E(parallel), along the magnetic field are compared. 'Runaway' electrons were accelerated in about 1 ms by a downward directed E(parallel) pulse of about 1 V/m magnitude. Such fields can result from rapidly exposed, negative space charges near the tops of clouds during positive cloud-to-ground discharges. HF frequency Fourier components of the E(parallel) pulse must propagate through the low-conducting nighttime atmosphere to the ionosphere with little dissipation.

Burke, William J.↗
NASA NTRS2012

Pulsar Polar Cap and Slot Gap Models: Confronting Fermi Data

Rotation-powered pulsars are excellent laboratories for studying particle acceleration as well as fundamental physics of strong gravity, strong magnetic fields and relativity. I will review acceleration and gamma-ray emission from the pulsar polar cap and slot gap. Predictions of these models can be tested with the data set on pulsars collected by the Large Area Telescope on the Fermi Gamma-Ray Telescope over the last four years, using both detailed light curve fitting and population synthesis.

Harding, Alice K.↗
DOE OSTI2014

Particle acceleration at corotating interaction regions in the heliosphere

Hybrid simulations are performed to investigate the dynamics of both solar wind protons and interplanetary pickup ions (PUIs) around the corotating interaction region (CIR). The one-dimensional system is applied in order to focus on processes in the direction of CIR propagation. The CIR is bounded by forward and reverse shocks, which are responsible for particle acceleration. The effective acceleration of solar wind protons takes place when the reverse shock (fast wind side) favors a quasi-parallel regime. The diffusive process accounts for this acceleration, and particles can gain energy in a suprathermal range (on the order of 10 keV). In contrast, the PUI acceleration around the shock differs from the conventional model in which the motional electric field along the shock surface accelerates particles. Owing to their large gyroradius, PUIs can gyrate between the upstream and downstream, several proton inertial lengths away from the shock. This 'cross-shock' gyration results in a net velocity increase in the field-aligned component, indicating that the magnetic mirror force is responsible for acceleration. The PUIs that remain in the vicinity of the shock for a long duration (tens of gyroperiods) gain much energy and are reflected back toward the upstream. These reflected energetic PUIs move back and forth along the magnetic field between a pair of CIRs that are magnetically connected. The PUIs are repeatedly accelerated in each reflection, leading to a maximum energy gain close to 100 keV. This mechanism can be evaluated in terms of 'preacceleration' for the generation of anomalous cosmic rays.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Implementation of Maxwell's equations in the reconstruction of the magnetic field in the g -2 storage ring

We present a method for implementing the constraints that are implied by Maxwell's equations in fits to measurements of the magnetic field in the muon storage ring of the $g - 2$ experiment. The method that we use makes use of toroidal-harmonic solutions of Laplace's equation. We point out that the fitting problem can be approximated well as a linear-algebra problem. We have devised an efficient algorithm for the linear-algebra problem that makes it possible to find a solution for 10 5 data points and 10 4 harmonics in less than an hour on a present-day desktop computer. We illustrate our method by applying it to some preliminary measurements of the magnetic field in the $g - 2$ storage ring.

43 PARTICLE ACCELERATORS↗
DOE OSTI2020

A First-principle Model for Polarization Swings during Reconnection-powered Flares

We show that magnetic reconnection in a magnetically dominated fast-cooling plasma can naturally produce bright flares accompanied by rotations in the synchrotron polarization vector. With particle-in-cell simulations of reconnection, we find that flares are powered by efficient particle acceleration at the interface of merging magnetic flux ropes, or “plasmoids.” The accelerated particles stream through the post-merger plasmoid toward the observer, thus progressively illuminating regions with varying plane-of-sky field direction, and so leading to a rotation in the observed polarization vector. Our results provide evidence for magnetic reconnection as the physical cause of highenergy flares from the relativistic jets of blazars (which recent observations have shown to be frequently associated with polarization rotations), and provide a first-principle physical mechanism for such flares.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

A MODEL OF THE HELIOSPHERE WITH JETS

An analytic model of the heliosheath (HS) between the termination shock (TS) and the heliopause (HP) is developed in the limit in which the interstellar flow and magnetic field are neglected. The heliosphere in this limit is axisymmetric and the overall structure of the HS and HP is controlled by the solar magnetic field even in the limit in which the ratio of the plasma to magnetic field pressure, β = 8πP/B{sup 2}, in the HS is large. The tension of the solar magnetic field produces a drop in the total pressure between the TS and the HP. This same pressure drop accelerates the plasma flow downstream of the TS into the north and south directions to form two collimated jets. The radii of these jets are controlled by the flow through the TS and the acceleration of this flow by the magnetic field—a stronger solar magnetic field boosts the velocity of the jets and reduces the radii of the jets and the HP. MHD simulations of the global heliosphere embedded in a stationary interstellar medium match well with the analytic model. The results suggest that mechanisms that reduce the HS plasma pressure downstream of the TS can enhance the jet outflow velocity and reduce the HP radius to values more consistent with the Voyager 1 observations than in current global models.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2006

A Magnetohydrodynamic Boost for Relativistic Jets

We have performed relativistic magnetohydrodynamic simulations of the hydrodynamic boosting mechanism for relativistic jets explored by Aloy & Rezzolla (2006) using the RAISHIN code. Simulation results show that the presence of a magnetic field may change the properties of the shock interface between the tenuous, overpressured jet (V(sub j) (sup z)) flowing tangentially to a dense external medium. Magnetic fields can lead to more efficient acceleration of the jet, in comparison to the pure-hydrodynamic case. A poloidal magnetic field (B(sup z)), tangent to the interface and parallel to the jet flow, produces both a stronger outward moving shock and inward moving rarefaction wave. This leads to a large velocity component normal to the interface in addition to acceleration tangent to the interface, and the jet is thus accelerated to a larger Lorentz factors than those obtained in the pure-hydrodynamic case. In contrast, a strong toroidal magnetic field (B(sup y)), tangent to the interface but perpendicular to the jet flow, also leads to stronger acceleration tangent to the shock interface relative to the pure-hydrodynamic case, but to a lesser extent than found for the poloidal case due to the fact that the velocity component normal to the shock interface is now much smaller. Overall, the acceleration efficiency in the toroidal case is less than that of the poloidal case but both geometries still result in higher Lorentz factors than the pure-hydrodynamic case. Thus, the presence and relative orientation of a magnetic field in relativistic jets can have a significant influence on the hydrodynamic boost mechanism studied by Aloy & Rezzolla (2006).

Mizuno, Yosuke↗
DOE OSTI2018

Contribution of the backstreaming ions to the self-magnetic pinch (SMP) diode current

The results presented here were obtained with a self-magnetic pinch (SMP) diode mounted at the front high voltage end of the RITS accelerator. RITS is a Self-Magnetically Insulated Transmission Line (MITL) voltage adder that adds the voltage pulse of six 1.3 MV inductively insulated cavities. The RITS driver together with the SMP diode has produced x-ray spots of the order of 1 mm in diameter and doses adequate for the radiographic imaging of high area density objects. Although, through the years, a number of different types of radiographic electron diodes have been utilized with SABER, HERMES III and RITS accelerators, the SMP diode appears to be the most successful and simplest diode for the radiographic investigation of various objects. Our experiments had two objectives: first to measure the contribution of the back-streaming ion currents emitted from the anode target and second to try to evaluate the energy of those ions and hence the Anode-Cathode (A-K) gap actual voltage. In any very high voltage inductive voltage adder utilizing MITLs to transmit the power to the diode load, the precise knowledge of the accelerating voltage applied on the A-K gap is problematic. This is even more difficult in an SMP diode where the A-K gap is very small (~1 cm) and the diode region very hostile. The accelerating voltage quoted in the literature is from estimates based on the measurements of the anode and cathode currents of the MITL far upstream from the diode and utilizing the para-potential flow theories and inductive corrections. Thus, it would be interesting to have another independent measurement to evaluate the A-K voltage. The diode's anode is made of a number of high-Z metals in order to produce copious and energetic flash x-rays. It was established experimentally that the back-streaming ion currents are a strong function of the anode materials and their stage of cleanness. We have measured the back-streaming ion currents emitted from the anode and propagating through a hollow cathode tip for various diode configurations and different techniques of target cleaning treatment: namely, heating at very high temperatures with DC and pulsed current, with RF plasma cleaning, and with both plasma cleaning and heating. In conclusion, we have also evaluated the A-K gap voltage by energy filtering technique. Experimental results in comparison with LSP simulations are presented.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Magnetic Field Mapper

The scientific program at the Integrable Optics Test Accelerator (IOTA) ring depends on a wide variety of specialized magnets, and validation of their field quality is important for ensuring proper performance. A number of these magnetic elements have both high field quality and a small physical aperture, and adequate field-mapping solutions have not been readily available in house or with external vendors. To solve this problem, a new magnetic-field mapping device needs to be developed. This new system features a high-precision tesla-meter, with a low-profile three-axis Hall probe, and stepper motors to allow for high-speed, accurate positioning of the probe. This new Magnetic Field Mapper (MFM), shown in Figure 1, will be capable of quickly mapping a wide variety of magnets to high precision, thus eliminating the need to send magnets off-site for expensive and time-consuming mapping.

43 PARTICLE ACCELERATORS↗
DOE OSTI2024

Technological developments and accelerator improvements for the FRIB beam power ramp-up

The Facility for Rare Isotope Beams (FRIB) began operation with 1 kW beam power for scientific users in May 2022 upon completion of 8 years of project construction. The ramp-up to the ultimate beam power of 400 kW, planned over a 6-year period, will enable the facility to reach its full potential for scientific discovery in isotope science and applications. In December 2023, a record-high beam power of 10.4 kW uranium was delivered to the target. Technological developments and accelerator improvements are being made over the entire facility and are key to completion of the power ramp-up. Major technological developments entail the phased deployment of high-power beam-intercepting systems, including the charge strippers, the charge selection systems, the production target, and the beam dump, along with support systems, including non-conventional utilities (NCU) and remote handling facilities. Major accelerator improvements include renovations to aging legacy systems associated with experimental beam lines and system automation for improved operational efficiency and better machine availability. Experience must be gained to safely handle the increased radiological impacts associated with high beam power; extensive machine studies and advanced beam tuning procedures are needed to minimize uncontrolled beam losses for the desired operating conditions. This paper discusses the technological developments and accelerator improvements with emphasis on major R&D efforts.

43 PARTICLE ACCELERATORS↗
DOE OSTI2014

Does one need a 4.5 K screen in cryostats of superconducting accelerator devices operating in superfluid helium? lessons from the LHL

Superfluid helium is increasingly used as a coolant for superconducting devices in particle accelerators: the lower temperature enhances the performance of superconductors in high-field magnets and reduces BCS losses in RF acceleration cavities, while the excellent transport properties of superfluid helium can be put to work in efficient distributed cooling systems. The thermodynamic penalty of operating at lower temperature however requires careful management of the heat loads, achieved inter alia through proper design and construction of the cryostats. A recurrent question appears to be that of the need and practical feasibility of an additional screen cooled by normal helium at around 4.5 K surrounding the cold mass at about 2 K, in such cryostats equipped with a standard 80 K screen. We introduce the issue in terms of first principles applied to the configuration of the cryostats, discuss technical constraints and economical limitations, and illustrate the argumentation with examples taken from large projects confronted with this issue, i.e. CEBAF, SPL, ESS, LHC, TESLA, European X-FEL, ILC.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Heating and acceleration of solar wind ions by turbulent wave spectrum in inhomogeneous expanding plasma

Near the Sun (< 10R{sub s}) the acceleration, heating, and propagation of the solar wind are likely affected by the background inhomogeneities of the magnetized plasma. The heating and the acceleration of the solar wind ions by turbulent wave spectrum in inhomogeneous plasma is studied using a 2.5D hybrid model. The hybrid model describes the kinetics of the ions, while the electrons are modeled as massless neutralizing fluid in an expanding box approach. Turbulent magnetic fluctuations dominated by power-law frequency spectra, which are evident from in-situ as well as remote sensing measurements, are used in our models. The effects of background density inhomogeneity across the magnetic field on the resonant ion heating are studied. The effect of super-Alfvénic ion drift on the ion heating is investigated. It is found that the turbulent wave spectrum of initially parallel propagating waves cascades to oblique modes, and leads to enhanced resonant ion heating due to the inhomogeneity. The acceleration of the solar wind ions is achieved by the parametric instability of large amplitude waves in the spectrum, and is also affected by the inhomogeneity. The results of the study provide the ion temperature anisotropy and drift velocity temporal evolution due to relaxation of the instability. The non-Maxwellian velocity distribution functions (VDFs) of the ions are modeled in the inhomogeneous solar wind plasma in the acceleration region close to the Sun.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRSDate not supplied

Flare Ribbon Signatures of Plasmoids

Solar flares are explosive space weather events that rapidly convert stored magnetic energy into bulk motion, plasma heating, and particle acceleration. Understanding the structure and dynamics of the magnetic reconnection that powers flares is critical for predicting the energy release. In particular, the amount of energy transferred to energetic particles is thought to be highly dependent on whether the reconnection is primarily turbulent (e.g., plasmoid dominated) or instead laminar. We present new high-resolution MHD simulations of three-dimensional reconnection in an eruptive flare and compare the results to recent data. Although flare reconnection is challenging to observe directly in the corona, highly detailed constraints on its dynamics can be obtained from observations of flare ribbons that track the chromospheric footpoints of newly reconnected field lines. The analogues of flare ribbons in our simulations are identified by tracking discontinuous changes in field-line magnetic connectivity due to the reconnection. In our highest-resolution calculations, we find that these ribbon analogues are highly structured and exhibit many ‘whorl’ patterns that are linked to turbulent plasmoids in the reconnecting current sheet. Such flare ribbon fine structure therefore reveals crucial information about the fundamental turbulent vs. laminar nature of the reconnection. Plasmoid-driven particle acceleration models would therefore predict co-location of energetic particle signatures with plasmoid-associated ribbon fine structure.

J T Dahlin↗
DOE OSTI2011

Magnetic Cusp Configuration of the SPL Plasma Generator

The Superconducting Proton Linac (SPL) is a novel linear accelerator concept currently studied at CERN. As part of this study, a new Cs-free, RF-driven external antenna H{sup -} plasma generator has been developed to withstand an average thermal load of 6 kW. The magnetic configuration of the new plasma generator includes a dodecapole cusp field and a filter field separating the plasma heating and H{sup -} production regions. Ferrites surrounding the RF antenna serve in enhancing the coupling of the RF to the plasma. Due to the space requirements of the plasma chamber cooling circuit, the cusp magnets are pushed outwards compared to Linac4 and the cusp field strength in the plasma region is reduced by 40% when N-S magnetized magnets are used. The cusp field strength and plasma confinement can be improved by replacing the N-S magnets with offset Halbach elements of which each consists of three magnetic sub-elements with different magnetization direction. A design challenge is the dissipation of RF power induced by eddy currents in the cusp and filter magnets which may lead to overheating and demagnetization. In view of this, a copper magnet cage has been developed that shields the cusp magnets from the radiation of the RF antenna.

43 PARTICLE ACCELERATORS↗
NASA NTRS2004

High Power Light Gas Helicon Plasma Source For VASMIR

The VASIMR space propulsion development effort relies on a high power (greater than 10kW) helicon source to produce a dense flowing plasma (H, D and He) target for ion cyclotron resonance (ICR) acceleration of the ions. Subsequent expansion in an expanding magnetic field (magnetic nozzle) converts ion lunetic energy to directed momentum. This plasma source must have critical features to enable an effective propulsion device. First, it must ionize most of the input neutral flux of gas, thus producing a plasma stream with a high degree of ionization for application of ICR power. This avoids propellant waste and potential power losses due to charge exchange. Next, the plasma stream must flow into a region of high magnetic field (approximately 0.5 T) for efficient ICR acceleration. Third, the ratio of input power to plasma flux must be low, providing an energy per ion-electron pair approaching 100 eV. Lastly, the source must be robust and capable of very long life-times (years). In our helicon experiment (VX-10) we have measured a ratio of input gas to plasma flux near 100%. The plasma flows from the helicon region (B approximately 0.1 T) into a region with a peak magnetic field of 0.8 T. The energy input per ion-electron pair has been measured at 300 plus or minus 100 eV. Recent results at Oak Ridge National Laboratory (ORNL) show an enhanced efficiency mode of operation with a high power density, over 5 kW in a 5 cm diameter tube. Our helicon is presently 9 cm in diameter and operates up to 3.5 kW of input power. An upgrade to a power level of 10 kW is underway. Much of our recent work has been with a Boswell double-saddle antenna design. We are also converting the antenna design to a helical type. With these modifications, we anticipate an improvement in the ionization efficiency. This paper presents the results from scaling the helicon in the VX-10 device from 3.5 to 10 kW. We also compare the operation with a double-saddle to a helical antenna design. Finally, we discuss modeling of these configurations using ORNL's EMIR code.

Squire, J. P.↗
DOE OSTI2015

Retuning the DARHT Axis-II Linear Induction Accelerator

The Dual-Axis Radiographic Hydrodynamic Test (DARHT) facility uses bremsstrahlung radiation source spots produced by the focused electron beams from two linear induction accelerators (LIAs) to radiograph large hydrodynamic experiments driven by high explosives. The Axis-II 1.7-kA, 1600-ns beam pulse is transported through the LIA by the magnetic field from 91 solenoids as it is accelerated to ~16.5 MeV. The magnetic field produced by the solenoids and 80 steering dipole pairs for a given set of magnet currents is known as the “tune” of the accelerator [1]. From June, 2013 through September, 2014 a single tune was used. This tune was based on measurements of LIA element positions made over several years [2], and models of solenoidal fields derived from actual field measurements [3] [4]. Based on the focus scan technique, changing the tune of the accelerator and downstream transport had no effect on the beam emittance, to within the uncertainties of the measurement. Beam sizes appear to have been overestimated in all prior measurements because of the low magnification of the imaging system. This has resulted in overestimates of emittance by ~50%. The high magnification imaging should be repeated with the old tune for direct comparison with the new tune. High magnification imaging with the new accelerator tune should be repeated after retuning the downstream to produce a much more symmetric beam to reduce the uncertainty of this measurement. Thus, these results should be considered preliminary until we can effect a new tune to produce symmetric spots at our imaging station, for high magnification images.

43 PARTICLE ACCELERATORS↗
NASA NTRS1992

Particle simulations of driven collisionless magnetic reconnection at the dayside magnetopause

Particle simulations (including both ions and electrons) of the driven collisionless magnetic reconnection process at the earth's dayside magnetopause were carried out using a specially developed two-and-one-half-dimensional electromagnetic particle code with a driven inflow boundary and an open outflow boundary. The simulations were used to examine many features associated with the dayside magnetic reconnection process, including the acceleration and heating of particles and the generation of energetic particles and particle heat flux. In addition, the fluctuating electromagnetic field associated with a driven collisionless magnetic reconnection was examined and compared with the satellite observations of flux transfer events at the day-side magnetopause.

Ding, D. Q.↗
DOE OSTI2015

High energy micro electron beam generation using chirped laser pulse in the presence of an axial magnetic field

In this paper, the generation of high-quality and high-energy micro electron beam in vacuum by a chirped Gaussian laser pulse in the presence of an axial magnetic field is numerically investigated. The features of energy and angular spectra, emittances, and position distribution of electron beam are compared in two cases, i.e., in the presence and absence of an external magnetic field. The electron beam is accelerated with higher energy and qualified in spatial distribution in the presence of the magnetic field. The presence of an axial magnetic field improves electron beam spatial quality as well as its gained energy through keeping the electron motion parallel to the direction of propagation for longer distances. It has been found that a 64 μm electron bunch with about MeV initial energy becomes a 20 μm electron beam with high energy of the order of GeV, after interacting with a laser pulse in the presence of an external magnetic field.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗