SH54B-01 INVITED
Ionic Charge States of Energetic Nuclei In Large Solar Particle Events
Data from SAMPEX and ACE acquired over solar cycle 23 have shown that in many large solar energetic particle (SEP) events associated with fast coronal mass ejections (typically referred to as gradual events), the mean ionic charge states of energetic nuclei from O to Fe increase with increasing kinetic energy. For example, in the November 6, 1997 event the mean charge state of Fe increased from +10 at 0.1 MeV/nucleon to +20 at energies >25 MeV/nucleon. The presence of highly ionized charge states appears to be correlated with the Fe/O ratio of the event. Several possibilities have been suggested for explaining the presence of highly ionized charge states, including: 1) the seed particle population includes remnant material from previous impulsive SEP events; 2) mixtures of flare and shock-accelerated ions from the same SEP event; and 3) electron stripping during the shock-acceleration process and subsequent transport to 1 AU. This talk will review the experimental data on ionic charge states in large SEP events and compare it with the predictions of these models.
SH54B-02 INVITED
An Overview of Solar Energetic Particle Ionic Charge States in Flare-Related Events
The ionic charge state of solar energetic particles may be determined by both the source temperature and collisional effects during acceleration. Early observations by Luhn et al., 1987, revealed a tendency for ions in impulsive events to have a higher charge state than those in gradual events. More recent observations from the ACE/SEPICA instrument show that ions with energy dependent charge states occur in a variety of cases, including impulsive, flare-related events. The energy dependence in flare-related events may be established by the source temperature, collisional effects and propagational effects. An overview of ionic charge state observations for impulsive events will be shown, emphasizing energy-dependent aspects.
SH54B-03 INVITED
Ionic Charge States of Low Energy Ions in Solar Energetic Particle Events: an Overview
Measurements with advanced instrumentation on the SAMPEX, SOHO and ACE spacecraft over an extended energy range show a large variability of the energy dependence of the ionic charge of heavy ions, in particular for Fe. In this review we present an overview of ionic charge observations obtained in the energy range ~0.01- 0.50 MeV/nuc with instruments onboard the SAMPEX, SOHO, and ACE spacecraft during the time period 1992 - 2000. We compare ionic charge states as obtained in interplanetary shock related events with solar wind charge states and with charge states in 3He- and Fe-rich events. Most of the interplanetary shock related events show for iron in the energy range 0.01 - 0.25 MeV/nuc mean ionic charge states QFe ~ 9 -- 11, similar to solar wind charge states, with a significant increase of QFe with energy by 1-2 charge units between 0.01 and 0.5 MeV/nuc only in a few cases. In 3He-rich and Fe-rich events, on the other hand, all events show a significant increase of the mean ionic charge in this energy range, for Fe by up to 6 charge units. The implications of the energy dependence of the ionic charge states for possible sources contributing to the accelerated population, e.g. solar wind, suprathermal particles, and contributions from Fe-rich impulsive events, will be discussed.
SH54B-04
Searching For Charge Interchange Cross-Sections Of Energetic Ions In Finite Temperature Matter
- On basis to our knowledge in atomic physics of charge interchange cross sections of high energy ions (electron capture and electron loss) it is pretended to create cross sections for energetic ions in finite temperature matter – Temperature, T, is introduced by means of a relative velocity between ion projectiles and thermal targets – It is established criteria for charge interchange when ions are undergoing an acceleration process: these allow to determine whether ions undergo both electron loss and capture , or only one of the process, or even no one of them - on this basis, it is created an analytical expression describing the evolution of ion charge (namely effective charge qeff) when ions are being accelerated from local thermal energies up to energies where qeff reaches the atomic number Z – the expression for qeff is calibrated by fitting data of energy dependence of charge state of solar energetic ions, obtaining a quite reasonable fit; consequently, a 1st inference is that the created cross sections are not so distant from those prevailing in solar atmospheric matter – a 2nd calibration is carried out with the well known semi-empirical expression in laboratory experiments, by introducing collisional deceleration in the theoretical qeff expression instead of an acceleration process, so that beginning a high energies where the charge is Z there is a trend toward qeff ---> 0 as particles are being decelerated, in such a way that by taking T = 0 in our theoretical formalism it is expected to approach to the semi- empirical curve – the degree of deviation of such a fitting process gives an indication of how much the created cross sections are over/under estimated, such that by correcting them to reproduce the semi-empirical expression, we should obtain a calibration factor that when introduced in out T-dependent theoretical expression, should allows us to obtain still a better fitting of charge evolution of solar ions.
SH54B-05 INVITED
Formation of charge states of heavy ions in SEP events
One can divide the formation of charge states of heavy ions in SEP events into two stages - formation of charge states during ion acceleration and their transformation due to coronal and interplanetary propagation. At the first stage the charge states of ions are formed as a result of competition of ionization and recombination processes, with possible charge-dependent acceleration. If ions were moving with a constant speed through a plasma for infinitely long time, the ionic charge of energetic ions would asymptotically reach an upper limit, the equilibrium mean charge, so that the mean charge of accelerated ions is between its thermal and equilibrium value. Coronal and interplanetary propagation can modify the charge spectra; coronal propagation by additional stripping after acceleration in a sufficiently dense environment, interplanetary propagation due to adiabatic deceleration in the expanding solar wind by shifting the charge spectra towards lower energies. The absolute value of this shift depends on the mean free path of energetic ions in interplanetary space that can be derived from the observed intensity-time profiles and anisotropies. In this paper we review recent achievements in the modeling of the charge-consistent acceleration and transport of solar ions as applied to the ionic charge states of iron.