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NASA NTRS2014

Integrated Science Investigation of the Sun (ISIS): Design of the Energetic Particle Investigation

The Integrated Science Investigation of the Sun (ISIS) is a complete science investigation on the Solar Probe Plus (SPP) mission, which flies to within nine solar radii of the Sun's surface. ISIS comprises a two-instrument suite to measure energetic particles over a very broad energy range, as well as coordinated management, science operations, data processing, and scientific analysis. Together, ISIS observations allow us to explore the mechanisms of energetic particles dynamics, including their: (1) Origins-defining the seed populations and physical conditions necessary for energetic particle acceleration; (2) Acceleration-determining the roles of shocks, reconnection, waves, and turbulence in accelerating energetic particles; and (3) Transport-revealing how energetic particles propagate from the corona out into the heliosphere. The two ISIS Energetic Particle Instruments measure lower (EPI-Lo) and higher (EPI-Hi) energy particles. EPI-Lo measures ions and ion composition from approx. 20 keV/nucleon-15 MeV total energy and electrons from approx.25-1000 keV. EPI-Hi measures ions from approx. 1-200 MeV/nucleon and electrons from approx. 0.5-6 MeV. EPI-Lo comprises 80 tiny apertures with fields-of-view (FOVs) that sample over nearly a complete hemisphere, while EPI-Hi combines three telescopes that together provide five large-FOV apertures. ISIS observes continuously inside of 0.25 AU with a high data collection rate and burst data (EPI-Lo) coordinated with the rest of the SPP payload; outside of 0.25 AU, ISIS runs in low-rate science mode whenever feasible to capture as complete a record as possible of the solar energetic particle environment and provide calibration and continuity for measurements closer in to the Sun. The ISIS Science Operations Center plans and executes commanding, receives and analyzes all ISIS data, and coordinates science observations and analyses with the rest of the SPP science investigations. Together, ISIS' unique observations on SPP will enable the discovery, untangling, and understanding of the important physical processes that govern energetic particles in the innermost regions of our heliosphere, for the first time. This paper summarizes the ISIS investigation at the time of the SPP mission Preliminary Design Review in January 2014.

Coronal Mass Ejections↗
NASA NTRS1999

CUSP Energetic Particles: Confinement, Acceleration and Implications

The cusp energetic particle (CEP) event is a new magnetospheric phenomenon. The events were detected in the dayside cusp for hours, in which the measured helium ions had energies up to 8 MeV. All of these events were associated with a dramatic decrease and large fluctuations in the local magnetic field strength. During January 1999 - December 1999 covered by this report, I have studied the CEP events by analyzing the POLAR, GEOTAIL, and WIND particle and magnetic field data measured during the geomagnetic quiet periods in 1996 and one geomagnetic storm period in 1998. The simultaneous observations indicated that the ion fluxes in the CEP events were higher than that in both the upstream and the downstream from the bow shock. The pitch angle distribution of the helium ions in the CEP events was found to peak around 90 deg. It was found that the mirror parameter, defined as the ratio of the square root of the integration of the parallel turbulent power spectral component over the ultra-low frequency (ULF) ranges to the mean field in the cusp, is correlated with the intensity of the cusp MeV helium flux, which is a measure of the influence of mirroring interactions and an indication of local effect. It was also found that the turbulent power of the local magnetic field in the ultra-low frequency (ULF) ranges is correlated with the intensity of the cusp energetic helium ions. Such ULF ranges correspond to periods of about 0.33-500 seconds that cover the gyroperiods, the bounce periods, and the drift periods of the tens keV to MeV charged particles when they are temporarily confined in the high-altitude dayside cusp. These observations represent a discovery that the high-altitude dayside cusp is a new acceleration and dynamic trapping region of the magnetosphere. The cusp geometry is connected via gradient and curvature drift of these energized ions to the equatorial plasma sheet as close as the geostationary orbit at local midnight. It implies that the dayside cusp is potentially an important source of magnetospheric particles. The discovery of the CEP events has been recognized as one of the most significant results from POLAR. I was invited to give a talk at 1999 IUGG meeting to interpret the CEP events. This discovery has also been written into the web-based Space Physics Text Book (http://www.oulu.fi/- spaceweb/textbook/cusp.html).

Chen, Jiasheng↗
NASA NTRS1982

Shock acceleration of energetic particles in the heliosphere

The apparent distinction between 'V x B' and 'Fermi' mechanisms is clarified in a discussion of the theory of the shock acceleration of energetic particles which restricts attention to those cases where the energetic particles do not themselves influence the given shock structure. The theory is applied to the acceleration of energetic particles in corotating interaction regions (CIR) in the solar wind, where particles are accelerated at either the forward and reverse shocks which bound the CIR by being compressed between the shock fronts and magnetic irregularities upstream of the shocks, or by being compressed between upstream irregularities and those downstream from the shocks. The model is shown to account for the observed exponential spectra at the earth, observed spectra behavior with radial distance and radial intensity gradients, and differences in spectra intensity at the forward and reverse shocks. Energy spectra are also calculated for the shock acceleration of energetic particles in large solar flare events.

Lee, M. A.↗
NASA NTRS1980

Shock acceleration of energetic particles in corotating interaction regions in the solar wind

A simple shock model for the acceleration of energetic particles in corotating interaction regions (CIRs) in the solar wind is presented. Particles are accelerated at the forward and reverse shocks which bound the CIR by being compressed between the shock fronts and magnetic irregularities upstream from the shocks, or by being compressed between upstream irregularities and those downstream from the shocks. Particles also suffer adiabatic deceleration in the expanding solar wind, an effect not included in previous shock models for acceleration in CIRs. The model is able to account for the observed exponential spectra at earth, the observed behavior of the spectra with radial distance, the observed radial gradients in the intensity, and the observed differences in the intensity and spectra at the forward and reverse shocks.

Fisk, L. A.↗
NASA NTRS1986

Acceleration of energetic particles at solar wind shocks

A review of the acceleration of energetic ions at interplanetary shocks is presented with an emphasis on the theory of diffusive shock acceleration and interplanetary traveling shocks. The basic theory is discussed briefly, including wave excitation. Ten predictions of the theory as outlined by Kennel et al. (1985) are presented and found to compare favorably with the observations of the 11, 12 November 1978 event. Some problems are presented which should be addressed by future theoretical/experimental work. A simple illustrative application of diffusive acceleration theory is made to the acceleration of ions at shocks in the distant heliosphere and compared qualitatively with the intensity profiles observed by Pioneer 10. Finally, Some brief thoughts on shock acceleration at high solar latitudes are presented.

Lee, M. A.↗
NASA NTRS1990

Acceleration of energetic particles by shock waves from large solar flares

Time-intensity profiles for solar proton events are analyzed with respect to the acceleration of energetic particles from the ambient solar wind by an interplanetary shock. The time-intensity profiles are derived from the Helio 1 particle data base for 1974 to 1984. It is found that many of the large proton events display a prolonged plateau. The Fe/O abundances in the large proton events are studied. It is observed that initially the Fe/O ratio is high (about 1.0), but after proton intensities increase to about 100 protons/sq cm sr sec MeV the Fe/O ratio decreases to a value near 0.1.

Reames, Donald V.↗
NASA NTRS1994

Sources and acceleration of energetic particles in planetary magnetospheres

Energetic particles in the magnetospheres of the solar system originate from various different sources, such as the solar wind, the planetary ionospheres as well as the moons and rings of the planetary systems. Important acceleration sites are the auroral regions, the magnetotail, and the equatorial regions of the magnetospheres where electric fields, wave-particle interactions, and magnetic pumping are among the major acceleration mechanisms proposed. Over the last decade mass- and charge-sensitive particle spectrometers on satellites and space probes have collected a wealth of information about the relative contribution of the various particle sources and the major acceleration processes to the energetic particle populations. Emphasis will be put on recent studies of the source populations and the acceleration processes in the Earth's auroral zones and magnetotail. Furthermore, the Jovian system with the largest magnetosphere and its unique mixture of particle sources with strong contributions from moons will be highlighted in some results from Ulysses.

Moebius, Eberhard↗
NASA NTRS1990

The EPACT experiment for the WIND spacecraft

The Energetic Particle: Acceleration, Composition and Transport (EPACT) experiment for the WIND spacecraft to be launched in late 1992 is presented. This experiment is designed to study the acceleration, composition and transport of a wide variety of energetic particle populations, including particles accelerated in interplanetary shocks, particles from solar flares, the anomalous component, and the Galactic cosmic rays.

Von Rosenvinge, T. T.↗
NASA NTRS1994

Acceleration of energetic particles which accompany coronal mass ejections

The causal association of major solar particle events seen at earth with coronal mass ejections (CME's), and not with solar flares, is discussed. Evidence that led to the demise of the flare dominated paradigm for major solar energetic particle events are described. The possibility of distinguishing particles from impulsive and gradual events using only observations is described. Particle acceleration at the CME level is discussed. Multi-spacecraft observations of CME events are described. Concerning the interplanetary CME, bidirectional proton events are discussed. Conclusions from progress in understanding the characteristics of solar energetic particles and their relation to the physical mechanisms of acceleration are given.

Reames, Donald V.↗
NASA NTRS1985

Shock and statistical acceleration of energetic particles in the interplanetary medium

Definite evidence for particle acceleration in the solar wind came around a decade ago. Two likely sources are known to exist: particles may be accelerated by the turbulence resulting from the superposition of Alfven and Magnetosonic waves (Statistical Acceleration) or they may be accelerated directly at shock fronts formed by the interaction of fast and slow solar wind (CIR's) or by traveling shocks due to sporadic coronal mass ejections. Naurally both mechanisms may be operative. In this work the acceleration problem was tackled numerically using Helios 1 and 2 data to create a realistic representation of the Heliospheric plasma. Two 24 hour samples were used: one where there are only wave like fluctuations of the field (Day 90 Helios 1) and another with a shock present in it (Day 92 of Helios 2) both in 1976 during the STIP 2 interval. Transport coefficients in energy space have been calculated for particles injected in each sample and the effect of the shock studied in detail.

Valdes-Galicia, J. F.↗
NASA NTRS1986

Rapid acceleration of energetic particles in the 1982 February 8 solar flare

Hard X-ray and gamma-ray measurements of the February 8, 1982 (1250 UT) solar flare made with spectrometers aboard the ISEE 3 and SMM spacecraft show that bursts of photons from 40 keV to 40 MeV are coincident within + or - 1 s. This indicates that the acceleration of particles to relativistic velocities can occur promptly (within 1 s). As far as the energetic particles interacting at the sun are concerned, the 'two-phase' process, which requires several minutes for particle acceleration to relativistic velocities, cannot account for the present gamma-ray observations. Even the 'two-step' acceleration process, which is assumed to occur in a small magnetic loop, is severely constrained by the present observations.

Kane, S. R.↗
NASA NTRS1976

On the acceleration of energetic particles in the interplanetary medium

Fermi scattering and transit time damping are two possible mechanisms for accelerating low energy protons (approximately 1 Mev) in co-rotating particle streams. Solutions to the equations which govern particle behavior in such streams are presented. It was found that acceleration by Fermi scattering requires a scattering mean-free path more than an order of magnitude smaller than the nominal value for low energy particles of 0.1 AU. Transit time damping of only the observed low level of magnitude fluctuations in the interplanetary magnetic field appears to yield the required acceleration rate. Measurements of the direction of the anisotropy in the particle streams could help in deciding which mechanism is operative. In the case of Fermi scattering the anisotropy must be in the heliocentric radial direction, whereas for transit time damping a significant azimuthal anisotropy could be present.

Fisk, L. A.↗
NASA NTRS1979

Implications of gamma ray observations for particle acceleration Experimental prospects

The relationship of gamma ray observations to the energetic particle acceleration phenomena is discussed. In particular the requirements for production of gamma rays by energetic particles are reviewed. The present state of observations of gamma rays is also reviewed and where there is a clear connection, the implications for particle acceleration theory is pointed out. In conclusion, a brief summary is given for instrument capabilities for the next major USA satellite experiments to be conducted in the 1980s.

Chupp, E. L.↗
NASA NTRS1976

The acceleration of energetic particles in the interplanetary medium by transit-time damping

Transit time damping is examined as a possible means for accelerating low energy particles in co-rotating streams and interstellar ions. Data show that: the protons in co-rotating streams may be accelerated by transient-time damping the small-scale variations in the field magnitude that are observed at a low level in the inner solar system. The interstellar ions may be accelerated by transit time damping large-scale field variations in the outer solar system.

Fisk, L. A.↗
NASA NTRS2007

Turbulence Evolution and Shock Acceleration of Solar Energetic Particles

We model the effects of self-excitation/damping and shock transmission of Alfven waves on solar-energetic-particle (SEP) acceleration at a coronal-mass-ejection (CME) driven parallel shock. SEP-excited outward upstream waves speedily bootstrap acceleration. Shock transmission further raises the SEP-excited wave intensities at high wavenumbers but lowers them at low wavenumbers through wavenumber shift. Downstream, SEP excitation of inward waves and damping of outward waves tend to slow acceleration. Nevertheless, > 2000 km/s parallel shocks at approx. 3.5 solar radii can accelerate SEPs to 100 MeV in < 5 minutes.

Chee, Ng K.↗
NASA NTRS2019

Energetic Particles of Cosmic Accelerators II: Active Galactic Nuclei and Gamma-ray Bursts

The high-energy universe has revealed that energetic particles are ubiquitous in the cosmos and play a vital role in the cultivation of cosmic environments on all scales. Our pursuit of more than a century to uncover the origins and fate of these cosmic energetic particles has given rise to some of the most interesting and challenging questions in astrophysics. Within our own galaxy, we have seen that energetic particles engage in a complex interplay with the galactic environment and even drive many of its key characteristics (for more information, see the first white paper in this series). On cosmological scales, the energetic particles supplied by the jets of active galactic nuclei (AGN) are an important source of energy for the intracluster and intergalactic media, providing a mechanism for regulating star formation and black hole growth and cultivating galaxy evolution (AGN feedback). Gamma-ray burst (GRB) afterglows encode information about their circumburst environment, which has implications for massive stellar winds during previous epochs over the stellar lifecycle. As such, GRB afterglows provide a means for studying very high-redshift galaxies since GRBs can be detected even if their host galaxy cannot. It has even been suggest that GRB could be used to measure cosmological distance scales if they could be shown to be standard candles. Though they play a key role in cultivating the cosmological environment and/or enabling our studies of it, there is still much we do not know about AGNs and GRBs, particularly the avenue in which and through which they supply radiation and energetic particles, namely their jets. Despite the enormous progress in particle-in-cell and magnetohydrodynamic simulations, we have yet to pinpoint the processes involved in jet formation and collimation and the conditions under which they can occur. For that matter, we have yet to identify the mechanism(s) through which the jet accelerates energetic particles – is it the commonly invoked diffusive shock acceleration process or is another mechanism, such as magnetic reconnection, required? Do AGNs and GRBs accelerate hadrons, and if so, do they accelerate them to ultra-high energies and are there high-energy neutrinos associated with them? MeV gamma-ray astronomy, enabled by technological advances that will be realized in the coming decade, will provide a unique and indispensable perspective on the persistent mysteries of the energetic universe. This White Paper is the second of a two-part series highlighting the most well-known high-energy cosmic accelerators and contributions that MeV gamma-ray astronomy will bring to understanding their energetic particle phenomena. Specifically, MeV astronomy will: 1. Determine whether AGNs accelerate CRs to ultra-high energies; 2. Provide the missing pieces for the physics of the GRB prompt emission; 3. Measure magnetization in cosmic accelerators and search for acceleration via reconnection.

Venters, Tonia M.↗
NASA NTRS1992

Particle acceleration in the heliosphere

This review presents an overview of the various populations of energetic particles accelerated in the heliosphere: energetic storm particles. corotating ion events, upstream ions at Earth's bow shock, the cosmic ray anomalous component, and interstellar and cometary pickup ions. In each case the review presents or describes original and/or key observations, the current understanding of its origin, and its particular impact on theoretical progress.

Lee, Martin A.↗