[en] The SAMPEX LEICA instrument is designed to measure ∼0.5--5 MeV/nucleon solar and magnetospheric ions over the range form He--Ni. The instrument is a time-of-flight mass spectrometer which measures particle time-of-flight over a ∼0.5 m path, and the residual energy deposited in an array of Si solid state detectors. Large area microchannel plates are used, resulting in a large geometrical factor for the instrument (0.6 cm² sr) which is essential for accurate compositional measurements in small solar flares, and in studies of precipitating magnetospheric heavy ions

[en] We have addressed the problem of the discrepancy between observations of solar cosmic rays, often showing sharp-gradients, and observations of galactic and anomalous cosmic rays which are consistent with the diffusive-transport description. We have carried out numerical simulations of the propagation of energetic charged particles in a turbulent magnetic field similar to that observed in the solar wind. If the particles are released impulsively near the sun, in a region small compared with the field coherence scale (a solar flare, for example), they exhibit characteristic fluctuations in intensity at 1 AU (dropouts), associated with very-steep localized gradients. The field coherence scale near the sun is the size of a supergranulation cell, and is about 0.01 AU at the orbit of Earth. These numerical simulations are quantitatively very similar to recent observations by the ACE spacecraft. These fluctuations occur naturally as part of the particle transport in the same field which results in large-scale cross-field diffusion and which has previously been used to study the propagation of CIR-associated particles to high heliographic latitudes

[en] Theoretical studies of particle acceleration by shocks have successfully modeled many observed features of the particle energy spectra and temporal variations; however, spectral slopes do not agree with in situ observations, and intensities show huge variations not explained by the models. Recent observations have shown that trace ions in the solar wind, such as 3He and He+, are present in the accelerated particles with enhanced abundances. The average heavy ion composition is also found to differ significantly from the solar wind. It is observed that these features correlate significantly with ambient suprathermal material abundances, giving evidence that the suprathermals are the seed population that is actually energized. This raises important new questions such as why the suprathermals are favored over the much more abundant solar wind. Since the suprathermal ion population has many more contributors, and much larger variability than the solar wind, this population needs much more detailed study to allow a closure of theory and observations in interplanetary space

[en] Recent theoretical work has posited that proton-generated Alfven waves scatter ions according to their rigidity during propagation from the acceleration region to the observed position. In particular, predictions have been made for the initial behavior of the high energy (> 2 MeV/nucleon) He/H and Fe/O ratios during large solar energetic particle (SEP) events based on this theory. In this paper, we have examined the temporal variations of low energy (∼0.3 MeV/nucleon) hydrogen, helium and iron ions throughout thirty large SEP events using the ULEIS instrument on the ACE spacecraft. These events originated from different solar longitudes; hence we compare events that have similar magnetic connection to minimize the transport effect. All events exhibited an eventual decrease in the He/H ratio as is suggested by the wave-particle model, but the degree of variation of He/H varies from event to event. However, the time variation of the Fe/O ratio does not correlate at all with that of the He/H in most of the events that we studied

[en] Using instrumentation on board the ACE spacecraft we describe short-time scale (∼3 hour) variations observed in the arrival profiles of ∼20 keV nucleon-1 to ∼2 MeV nucleon-1 ions from impulsive solar flares. These variations occurred simultaneously across all energies and were generally not in coincidence with any local magnetic field or plasma signature. These features appear to be caused by the convection of magnetic flux tubes past the observer that are alternately filled and devoid of flare ions even though they had a common flare source at the Sun. In these particle events we therefore have a means to observe and measure the mixing of the interplanetary magnetic field due to random walk. In a survey of 25 impulsive flares observed at ACE between 1997 November and 1999 July these features had an average time scale of 3.2 hours, corresponding to a length of ∼0.03 AU. The changing magnetic connection to the flare site sometimes lead to an incomplete observation of a flare at 1 AU; thus the field-line mixing is an important effect in studies of impulsive flare energy spectra

[en] The five large solar particle events during October-November 2003 presented an opportunity to test shock acceleration models with in-situ observations. We use solar particle spectra of H to Fe ions, measured by instruments on ACE, SAMPEX, and GOES-11, to investigate the Q/M-dependence of spectral breaks in the 28 October 2003 event. We find that the break energies scale as (Q/M)b with b ≤ 1.56 to 1.75, somewhat less than predicted. We also conclude that SEP spectra >100 MeV/nucleon are best fit by a double power-law shape

[en] Using data from the SIS and ULEIS instruments on the Advanced Composition Explorer (ACE) we have identified periods during which energetic 3He is present in near-Earth interplanetary space between November 1997 and May 2002. The data, which cover the energy intervals 0.2-1 MeV/nuc (ULEIS) and 4.5-16.3 MeV/nuc (SIS), show that 3He is present a significant fraction of the time, as would be required if these suprathermal particles were the major source of the 3He being accelerated by shocks in the interplanetary medium. Specifically, we find that energetic 3He is present at least ∼ 60% of the time, and perhaps significantly more often