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At least 235 records · Page 13

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DOE OSTI2025

Investigation of new superconducting materials for the next generation high-performance RF superconducting cavities for particle accelerators

In this DOE-funded project DE-SC0010081-020 Old Dominion University (ODU) in collaboration with University of Wisconsin (UW) and Jefferson Laboratory have investigated both experimentally and theoretically electromagnetic response and losses in multilayered superconducting structures made of new SRF materials which can push the field and Q performance limits of accelerating cavities.

43 PARTICLE ACCELERATORS↗

NASA NTRS1978

Potential drops above pulsar polar caps - Ultrarelativistic particle acceleration along the curved magnetic field

The paper calculates the acceleration of a nonneutral stream of charged particles from the surface of an isolated rotating magnetized neutron star in the case where the particle stream flows along the open field lines of a curved poloidal magnetic field. It is shown that very large electrostatic potential drops can occur in steady unidirectional space-charge-limited flow along the curved open field lines. The explicit incorporation of magnetic field line curvature is the essential element leading to this new result, assuming that all the charges are supplied by emission from the surface. It is emphasized that the current flow and charge density are unique if all of the assumptions are met, with the result that the accelerating electric field near the stellar surface is quite small compared to the vacuum field.

Scharlemann, E. T.↗

NASA NTRS1986

Space experiments with particle accelerators: SEPAC

The SEPAC instruments consist of an electron accelerator, a plasma accelerator, a neutral gas (N2) release device, particle and field diagnostic instruments, and a low light level television system. These instruments are used to accomplish multiple experiments: to study beam-particle interactions and other plasma processes; as probes to investigate magnetospheric processes; and as perturbation devices to study energy coupling mechanisms in the magnetosphere, ionosphere, and upper atmosphere.

Roberts, B.↗

DOE OSTI2024

Low-energy H- beam injectors for particle accelerators: upgrade requirements, challenges and future plans [Slides]

High brightness, negative hydrogen ion sources are used extensively in large, accelerator-based, user facilities operating worldwide. Negative hydrogen beams have become the preferred means of filling circular accelerators and storage rings as well as enabling efficient extraction from cyclotrons. Much larger beams of H- ions are also utilized for neutral beams injection into fusion machines and will be discussed in a separate companion presentation. Some of the accelerator facilities include the US Spallation Neutron Source (SNS), Japan Proton Accelerator Research Complex (J-PARC), Rutherford Appleton Laboratory (RAL-ISIS), Los Alamos Neutron Science Center (LANSCE), Fermi National Accelerator Laboratory (FNAL), Brookhaven National Laboratory (BNL), the CERN LHC injector, the Chinese Spallation Neutron Source (CSNS) as well as numerous installations of D-Pace (licenced by TRIUMF) ion sources used mainly with cyclotrons. Many facilities are currently working on various improvement / upgrade projects, both in the near and long term, which are driving further development of their ion source and LEBT (Low Energy Beam Transport) and, in some cases, their overall front end injector system. This report will first provide a simple description of each facilities existing ion source and LEBT and summarize the operational parameters which are currently being routinely injected into their accelerators. Next, the parametric goals of each of the facilities upgrade projects are specified as well as development efforts currently underway to meet these requirement and improvement goals. It is hoped that that this work will not only capture the current state-of-the-art of worldwide H- beam injectors and clarify the research goals and efforts of the community in general but will also encourage further inter laboratory collaborations.

43 PARTICLE ACCELERATORS↗

NASA NTRS1981

Observations of the ionization states of energetic particles accelerated in solar flares

Results of a survey of ten solar flare particle events, in which the ionization states and spectra of 0.3 to 2.4 MeV/nuc He, C, O and Fe were measured, are reported. He+ was present in all events (He+/He++ approximately 0.1 to 0.25), and the mean ionization states of C, O and Fe are high. The distribution functions of He+, He++ and heavier elements are well represented by simple exponentials of the particle speed times its rigidity to a power n, where n is between O and 1, and equal e-folding values. Results are consistent with a model whereby ions are accelerated in the corona by multi-dimensional shocks out of a population taken from both hot and cold coronal regions.

Gloeckler, G.↗

NASA NTRS1974

Physical conditions for conducting radiobiological experiments in beams of accelerated particles with high linear energy transfer

The design and construction of an accelerator to conduct radiobiological experiments is reported that uses aluminum filters to control the accelerated ion beam while preserving its stability, and a vacuum chamber to conduct the ion beam with the help of a collector through a lavsan exit port to the target. Depth distribution of the absorbed dose from a monodirectional ion beam is practically completely represented by the change in the energy spectrum of the biological object.

Kudryashov, Y. I.↗

NASA NTRS1973

Magnetic field reconnection and particle acceleration

After a brief review of steady state reconnection models, the processes are discussed which place an upper limit on the reconnection rate. In many applications the requirement that the width of the diffusion region exceed the ion gyroradius leads to a severe restriction on this limit. Unless the conductivity is much less than the value given by Spitzer's formula, solar flare times may result which are too long by a factor of 1000 or more. Turbulent and gyro effects which may lead to a reduced conductivity are shown to be operative, but only for sufficiently small ratios of plasma to magnetic pressure in the inflow. Particle energization processes associated with magnetic field reconnection and particle reflection by fast shocks are considered. These processes are effective as a first stage in the acceleration of charged particles, but additional multistep processes are needed to reach proton energies above a few MeV.

Sonnerup, B. U. O.↗

NASA NTRS1990

Particle acceleration in step function shear flows - A microscopic analysis

The transport of energetic particles in a moving, scattering fluid, which has a large shear in its velocity over a distance small compared with the scattering mean free path is discussed. The analysis is complementary to an earlier paper by Earl, Jokipii, and Morfill (1988), which considered effects of more-gradual shear in the diffusion approximation. The case in which the scattering fluid undergoes a step function change in velocity, in the direction normal to the flow is considered. An analytical, approximate calculation and a Monte Carlo analysis of particle motion are presented. It is found that particles gain energy at a rate proportional to the square of the magnitude of the velocity change.

Jokipii, J. R.↗

NASA NTRS2023

A Data-driven, Physics-based Transport Model of Solar Energetic Particles Accelerated by Coronal Mass Ejection Shocks Propagating through the Solar Coronal and Heliospheric Magnetic Fields

In an effort to develop computational tools for predicting radiation hazards from solar energetic particles (SEPs), we have created a data-driven physics-based particle transport model to calculate the injection, acceleration, and propagation of SEPs from coronal mass ejection (CME) shocks traversing through the solar corona and interplanetary magnetic fields. The model runs on an input of corona and heliospheric plasma and magnetic field configuration from a magnetohydrodynamic model driven by solar photospheric magnetic field measurements superposed with observed CME shocks determined from coronagraph images. SEP source particles are injected at the shock using the result of diffusive shock acceleration formulation from a characteristic obliquity-dependent injection from a heated solar wind thermal tail population. With several advanced computation techniques involving stochastic simulation and integration, the model obtains the particle intensity at any location in interplanetary space through the rigorous solution to the time-dependent 5D focus transport equation in the phase space that includes perpendicular diffusion. We apply the model to the 2011 November 3 CME event. The calculation results reproduce multispacecraft SEP observations at Earth and STEREO-B reasonably well without normalization of particle flux. The observations at STEREO-A can be reproduced by rescaling particle energy or modified energy dependence of particle diffusion coefficients. This circumsolar SEP event seen by spacecraft at Earth, STEREO-A, and STEREO-B at widely separated longitudes can be explained by diffusive shock acceleration by a single CME shock with a moderate speed.

Solar energetic particles↗

NASA NTRS1996

The role of impulsive particle acceleration in magnetotail circulation

Recent results from investigations carried out using the active magnetospheric particle tracer explorer/ion release module (AMPTE/IRM) satellite and International Sun-Earth Explorer (ISEE) show that bursty, near-neutral sheet fast flows are an important part of the transport in the near-earth tail. The results related to such flows are reviewed, and information is presented on their relation to the average plasma sheet characteristics and substorms. The average ion density, temperature and flow variability in the quiet inner plasma sheet exhibit a spatial dependence which suggests a dependence on Bursty Bulk Flows (BBFs). The energy and flux transport in the tail is discussed and it is stated that BBFs are responsible for such transport. The tailward progression of activity is considered.

Angelopoulos, V.↗

NASA NTRS1985

Particle acceleration in Saturn's outer magnetosphere - In memoriam Alois Schardt

Fluctuations in field strength and particle flux observed during the outbound pass of Voyager 2 through the Saturnian magnetosphere are discussed. The observations of injections of energetic electrons and ions, associated plasma wave activity, and magnetic field perturbations are described. These data imply the existence of an acceleration or heating site some distance from the Voyager 2. A correlation between impulsive injections of 0.35-2 MeV electrons, increase in the hot ion flux of 28-215 KeV, a dip in magnetic field magnitude, and a signal from the plasma wave instrument in the 562 Hz channel was detected. An explanation of these observations is provided.

Schardt, A. W.↗

NASA NTRS1994

Particle acceleration and transport in the tail and at the front side of the magnetosphere, task 1 and 2

The work under this grant involved studies of: (1) the acceleration and heating of ions in the course of magnetospheric substorms and the spatial distributions of the ion populations in the magnetotail; and (2) the comparison in in-situ acceleration at the bow shock and the leakage of energetic particles from the magnetosphere as source of energetic ions upstream of the Earth's bow shock.

Kistler, Lynn M.↗

NASA NTRS2019

MeV Emission from Pulsar Wind Nebulae: Understanding Extreme Particle Acceleration in Highly Relativistic Outflows

The Earth is constantly bombarded from outer space by energetic particles. Where and how these "cosmic rays" are produced is poorly understood, with various particle types and energies likely originating from different sources. Particularly mysterious is the source of high-energy e+/- produced in our Galaxy, especially those responsible for both the high fraction of e+ in the GeV cosmic ray lepton spectrum and the e+/- and observed excess of microwaves and gamma-rays detected towards the Galactic center and bulge. While these particles could be evidence for exotic forms of dark matter, they might also be produced by "normal" astrophysical sources such as pulsars the strongly magnetized, rapidly rotating neutron stars whose rotational energy powers an ultra-relativistic outflow (commonly referred to as a "pulsar wind") whose interaction with the surrounding medium creates a pulsar wind nebula .While the detection of TeV emission from numerous PWNe strongly suggest they contain e+/- with PeV or higher energies, how and to what energies these particles are produced is unknown, let alone their dependence on the properties of the pulsar, pulsar wind, and surrounding medium. A major reason for this uncertainty is the lack of information concerning their MeV properties, since the synchrotron emission from the highest energy e+/- peaks in this waveband. Only by combining the MeV spectrum of PWNe measured by proposed missions with that obtained at lower (primarily radio and X-ray) and higher (TeV) photon energies by current and hopefully future facilities is it possible to measure the full spectrum of e+/- in these sources. The resultant insights into the underlying acceleration mechanism would significantly impact many areas of astrophysics from indirect searches for dark matter to the origin of cosmic rays to the physics of relativistic outflows observed from active galactic nuclei, gamma-ray bursts, and some gravitational wave events.

Gelfand, Joseph D.↗

NASA NTRS1979

Particle acceleration in solar flares by cyclotron damping of cascading turbulence

It is pointed out that cyclotron damping of cascading turbulence can be a very efficient acceleration process because the turbulence is generally damped by the suprathermal tail of the particle distribution. Using a simplified approach to the transfer of wave energy down the spectrum, analytic time-dependent solutions are derived which describe the growth of the tail and its effect back on the turbulence. They suggest that with this mechanism, a sizable fraction of all the available energy ends up in a very small minority of the particles at the flare site, in accord with observations. Preferential acceleration of heavy elements is generally expected. The enhancement mechanism is very sensitive; and if He-3 is preaccelerated by even a modest amount, it could be enhanced by many orders of magnitude, as observed in some flares.

Eichler, D.↗

NASA NTRS1990

Shock-drift particle acceleration in superluminal shocks - A model for hot spots in extragalactic radio sources

Shock-drift acceleration at relativistic shock fronts is investigated using a fully relativistic treatment of both the microphysics of the shock-drift acceleration and the macrophysics of the shock front. By explicitly tracing particle trajectories across shocks, it is shown how the adiabatic invariance of a particle's magnetic moment breaks down as the upstream shock speed becomes relativistic, and is recovered at subrelativistic velocities. These calculations enable the mean increase in energy of a particle which encounters the shock with a given pitch angle to be calculated. The results are used to construct the downstream electron distribution function in terms of the incident distribution function and the bulk properties of the shock. The synchrotron emissivity of the transmitted distribution is calculated, and it is demonstrated that amplification factors are easily obtained which are more than adequate to explain the observed constrasts in surface brightness between jets and hot spots.

Begelman, Mitchell C.↗

NASA NTRS1978

The location of the particle acceleration region in the 1 September 1971 solar cosmic ray event

A numerical model of interplanetary propagation is used to reconstruct the shape of particle spectra near the sun shortly after release, from the proton and electron fluxes observed at 1 AU after the solar cosmic-ray event of September 1, 1971. A calculation of the spectral changes that would be produced by collisional energy losses is employed to estimate the amount of matter through which the particles passed, the height at which they were accelerated, and, for the proton, the temperature of the plasma. A temperature of about 2.4 million K in the proton acceleration region is obtained, along with a column density of material traversed equal to about 140 micrograms/sq cm for the protons and a column density of less than 4 micrograms/sq cm for the electrons. These results are shown to imply proton acceleration near the base of the corona and electron acceleration at a height greater than about 1 solar radius.

Mcguire, R. E.↗

NASA NTRS1994

Monte Carlo simulations of particle acceleration at oblique shocks

The Fermi shock acceleration mechanism may be responsible for the production of high-energy cosmic rays in a wide variety of environments. Modeling of this phenomenon has largely focused on plane-parallel shocks, and one of the most promising techniques for its study is the Monte Carlo simulation of particle transport in shocked fluid flows. One of the principal problems in shock acceleration theory is the mechanism and efficiency of injection of particles from the thermal gas into the accelerated population. The Monte Carlo technique is ideally suited to addressing the injection problem directly, and previous applications of it to the quasi-parallel Earth bow shock led to very successful modeling of proton and heavy ion spectra, as well as other observed quantities. Recently this technique has been extended to oblique shock geometries, in which the upstream magnetic field makes a significant angle Theta(sub B1) to the shock normal. Spectral resutls from test particle Monte Carlo simulations of cosmic-ray acceleration at oblique, nonrelativistic shocks are presented. The results show that low Mach number shocks have injection efficiencies that are relatively insensitive to (though not independent of) the shock obliquity, but that there is a dramatic drop in efficiency for shocks of Mach number 30 or more as the obliquity increases above 15 deg. Cosmic-ray distributions just upstream of the shock reveal prominent bumps at energies below the thermal peak; these disappear far upstream but might be observable features close to astrophysical shocks.

Baring, Matthew G.↗

NASA NTRS1986

Particle acceleration by the sun

A review is given of the analysis of new observations of energetic particles and energetic secondary emissions obtained over the solar maxium (approx. 1980) by the Solar Maximum mission, Hinotori, the international Sun-Earth Explorer, Helios, Explorer satellites, and Voyager spacecraft. Solar energetic particle events observed in space, He(3)- rich events, solar gamma rays and neutrons, and solar neutrinos are discussed.

Lin, R. P.↗