Search

Abstract: We report observations of strongly anisotropic flows of electron events originating from Jupiter that were observed during Ulysses distant Jupiter flyby. A scan of the period January 1, 2003 through February 8, 2005 (extending roughly 13 months before and after the closest approach of 0.8AU in early 2004) identified a total of 15 events with significant and short-lived (hours) intensity increases accompanied by strongly anisotropic flows away from Jupiter. We describe the properties of these events, most of which were observed within 1.4AU of Jupiter. We also discuss their implications for large-scale direct magnetic connections across the mean magnetic field and suggest that they may provide evidence for a previously unconsidered way of enhancing propagation of energetic charged particles across the average Parker spiral heliospheric magnetic field, thus increasing the apparent rate of latitudinal and radial cross-field diffusion. [Copyright &y& Elsevier]

Abstract: We describe a phoswich-based detector concept for studies of low energy (∼1–10MeV) solar neutrons in the innermost heliosphere (R <∼0.5AU). The detector has applications both as a very low mass (<∼1kg), low power (∼1–2W) stand-alone instrument, and as a component to enhance the capabilities of more sophisticated instruments, for example, the fast neutron imaging telescope instrument described by Moser et al. [Moser, M.R., Flückiger, E.O., Ryan, J.M., et al. A fast neutron imaging telescope for inner heliosphere missions. Adv. Space Res., in press, this issue, doi:10.1016/j.asr.2005.03.037]. In its most basic form, the detector consists of a small volume (∼1 cm3) of fast organic scintillator completely surrounded by a slow inorganic scintillator. The dimensions of the organic scintillator are chosen to minimize multiple n–p scatterings while retaining adequate sensitivity. The inorganic scintillator provides anti-coincidence protection against energetic charged particles. A single PM tube views light from both scintillators. Pulse shape analysis identifies as potential neutrons those events where only the organic scintillator contributes to the signal. The signal size corresponds to the energy of the recoil proton from an n–p elastic scatter, on average half the energy of the incident neutron. An instrument based on this concept would provide measurements of the neutron flux and, through statistical analysis of recoil proton energies, basic information about the neutron spectrum. [Copyright &y& Elsevier]

Abstract: For about the last 40 years, we have been trying to understand the propagation of cosmic rays and other energetic charged particles through the interplanetary medium. Identification of the basic processes affecting the propagation, namely diffusion, convection by the solar wind, adiabatic deceleration, and gradient and curvature drifts, was attained early on, but reaching detailed physical understanding, particularly of the roles of diffusion and gradient and curvature drifts, continues as an active topic of research to this day. Particularly unclear is the nature of the cross-field propagation. Many observations seem to require more efficient cross-field propagation than theoretical propagation models can easily produce. At the same time, there are other observations that seem to show strong guidance of the particles by the interplanetary magnetic field. With current measurements from spacecraft near Earth and from the Ulysses spacecraft, which samples nearly the complete range of heliographic latitudes in the inner heliosphere, critical tests of the ways in which cosmic rays and other energetic charged particles propagate through the interplanetary medium are possible. I briefly review the status of observations that are relevant to the characterization of diffusive propagation in the inner heliosphere and will present evidence for a possibly previously overlooked contribution from transport along magnetic flux tubes that deviate dramatically from the average interplanetary spiral configuration. [Copyright &y& Elsevier]

Abstract: The measurement of cosmic rays and Solar energetic particles in space is basic to our understanding of the Galaxy, the Sun, phenomena in the Heliosphere and what has come to be known broadly as “space weather”. For these reasons, cosmic ray instruments are common on both scientific spacecraft and operational spacecraft such as weather satellites. The resource constraints on spacecraft generally mean that instruments that measure cosmic rays and Solar energetic particles must have low mass (a few kg) and low power (a few W), be robust and reliable yet still highly capable. Such instruments must identify ionic species (at least by element, preferably by isotope) from protons through the iron group. The charge and mass resolution of heavy ion instruments in space depends upon determining ions’ angles of incidence. The Angle Detecting Inclined Sensor (ADIS) system is a highly innovative and uniquely simple detector configuration used to determine the angle of incidence of heavy ions in space instruments. ADIS replaces complex position sensing detectors (PSDs) with a system of simple, reliable and robust Si detectors inclined at an angle to the instrument axis. In August 2004, we tested ADIS prototypes with a 48Ca beam at the National Superconducting Cyclotron Laboratory''s (NSCL) Coupled Cyclotron Facility (CCF). Among the analyses performed on the data taken at the NSCL, we demonstrate that our prototype design with an ADIS system has a charge resolution of less than 0.25e. We also present a more generalized analytic derivation of instrument response and report on the corresponding analysis of Monte-Carlo modeling data. [Copyright &y& Elsevier]

Abstract: In this paper, we present the final report of the data obtained from the Space Dust (SPADUS) instrument on the Earth-orbiting Advanced Research and Global Observation Satellite (ARGOS). The University of Chicago''s SPADUS instrument on the US Air Force''s Advanced Research and Global Observation Satellite has been operating in a nearly polar orbit, at an altitude of approximately 850km, since soon after its launch on day 54, 1999 (23 February) until termination of the SPADUS operations on day 248, 2001 (5 September). The instrument consists of a polyvinylidene fluoride (PVDF) dust trajectory system, which includes two planar arrays of PVDF sensors (a total of 16 sensors per array) separated by 20.25cm to provide time of flight (TOF) measurements. The trajectory system measures dust particle flux, mass distribution, velocity and trajectory. The instrument also includes the SPADUS Ancillary Diagnostic Sensor (ADS) subsystem, which measured energetic charged particles (electrons, protons, etc). The PVDF dust trajectory system detected a total of 368 dust impacts over the SPADUS live-time interval of 739 days, yielding an average particle flux of 0.50 impacts/day. Of these 368 impacts, 35 were D1–D2 type events—where particles impacted and penetrated a D1 sensor, then impacted a D2 rear array sensor—allowing for time-of-flight measurements. Of the 35 D1–D2 impacts on SPADUS, we identified 19 D1–D2 impacts yielding TOF values. Of these 19 events, 14 were ambiguous (either bound or interplanetary) and 5 were unambiguous interplanetary impacts. Examples of particle orbits for debris particles as well as D1–D2 impacts are detailed. We also describe transient particle streams detected by the SPADUS trajectory system, resulting from the passage of ARGOS through streams of debris particles in Earth orbit. One of the streams was shown to result from detection by SPADUS of the debris generated by the explosion of a Chinese booster rocket. The SPADUS flight data accumulated over the 30-month mission shows that PVDF-based dust instruments utilizing two planar arrays of PVDF dust sensors in a TOF arrangement—can provide useful measurements of particle velocity, mass distribution, flux, trajectory and particle orbital elements. [Copyright &y& Elsevier]

Abstract: Since the 1970''s interplanetary electrons in the MeV energy range, of Jovian origin, have been extensively studied from close to the Sun to beyond the Kronian orbit, near the ecliptic. The Ulysses trajectory allowed to study the propagation of these particles, in a wide range of heliographic latitudes. The location of Jupiter with respect to the structure of the heliospheric magnetic field is precisely determined and non-central. This makes Jovian electrons an ideal opportunity for studying the particle propagation parallel and perpendicular to the heliospheric magnetic field. 12 years after its first encounter in February 1992, the Ulysses mission encountered Jupiter for a second time in February 2004 at a distance of 1684 Jovian radii. The first flyby took place at a distance of closest approach of 6 Jupiter radii () and changed the inclination of the Ulysses trajectory so that it would pass above the Sun''s polar regions. During the 2004 encounter, in contrast to 1992, Ulysses did not enter the Jovian magnetosphere but remained upstream of it. In mid 2002, the MeV electron flux started increasing and displaying large short term variations. These features lasted throughout the encounter, making the electron intensities less obviously correlated with the proximity to Jupiter compared with the first Jovian encounter. In previous studies it has been shown that the diffusion coefficient perpendicular to the heliospheric magnetic field in polar direction increased in 1998 during the transition from solar minimum to solar maximum close to the ecliptic plane. Although the distant Ulysses encounter took place during the declining phase of the solar cycle the absence of an intensity variation with latitude indicate an unexpected further increase of . Thus the diffusion coefficients, and in particular perpendicular diffusion in the polar direction, are highly time-dependent. In this paper, we present the corresponding data and discuss the implication for particle propagation in the three-dimensional heliospheric magnetic field. [Copyright &y& Elsevier]

A design for a low-mass (10 kg) Large-Area Dust Detection Array (LADDA) that can directly detect interstellar dust particles in the size range of 1 to 10 μm is described. Because of the low fluxes of interstellar dust, a large-area detector is needed. Two parallel layers of position-sensitive PVDF films, with a total sensitive area of ∼ 10m2, are utilized to allow the direction of motion of the impacting dust grain to be determined to better than 1 degree. The time flight between the PVDF layers allows the determination of the particle velocity with an accuracy of ∼ 0.2 km/s. This will allow interstellar dust to be unambiguously distinguished from interplanetary dust and man-made debris. During the operational lifetime of the mission (2 years), it is anticipated that over 1000 interstellar grains will be detected. These will be characterized by their size distribution, upstream direction, and velocity relative to the Solar System. [Copyright &y& Elsevier]