Solar Wind Ion Composition Measurements: Direct Measurements of Properties of the Corona

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1 Solar Wind Ion Composition Measurements: Direct Measurements of Properties of the Corona White Paper Submitted to the Decadal Survey Panel on Solar and Heliospheric Physics November 12, 2010 Stefano A. Livi, Antoinette Galvin, University of New Hampshire Lynn Kistler, University of New Hampshire Susan Lepri, University of Michigan Mark Popeki, University of New Hampshire Michael Collier, Goddard Space Flight Center Thomas Broiles, University of Texas in San Antonio

2 Summary The chemical composition and charge state distribution of heavy ion elements in the solar wind will establish the physical links between the outward transport of solar energy and the solar wind, will provide direct measurements of solar eruption products in coronal mass ejections, and will discover the fundamental processes by which interplanetary shocks accelerate suprathermal ions and produce hazardous particle radiation events. Introduction The Sun s million-degree corona generates the solar wind, which supersonically expands into the solar system and permeates the whole heliosphere. This flow of coronal particles defines the space weather that impacts and controls Earth s space environment, the plasma environments of all the planets, and the protective boundaries that surround our solar system. Despite remote observations of the rapidly changing magnetic structure of the corona from missions such as Hinode, STEREO, SOHO, RHESSI, and TRACE, advances in understanding of the 3D solar wind structure provided by Ulysses, and the discovery of the solar wind s control over the geospace environment provided by ACE, Wind, and IMAGE, the heliophysics community is not yet able to definitively connect the morphology and dynamics of the solar atmosphere with the global structure of the solar wind, the dangerous shocks that propagate therein, and the sources and acceleration mechanisms of solar energetic particle radiation Characterizing the heavy ion environment of the solar wind is a unique tool to determine how the Sun influences our environment: The measurement of the solar wind composition, in particular the heavy ion component is essential in tracing the sampled solar wind to its coronal source (Geiss et al, 1995): o Heavy ion composition (Figure 1), and bulk plasma parameters are correlated with solar source structures (loops, the legs or tips of the helmet streamer, spicules, polar plumes, and other solar magnetic morphologies), and are needed to unambiguously identify the source. o Statistical syntheses of these datasets over the mission lifetime will yield the sources and distributions Figure 1: example of mass vs. mass-per-charge distributions from ACE-SWICS of open-flux over various parts of the solar cycle, leading to a deep understanding of the physical processes leading to solar wind, coronal hole and streamer associated solar wind.

3 o Heavy ion composition identifies and characterizes overall CME morphology, particularly the different structures within a CME that relate to different parts of the solar feature from which the CME originated (Li et al, 2005). Ion composition measurements relate in situ plasma to coronal conditions near the source regions; o The ionic charge states will be interpreted together with the remote observations of the coronal plasma. Elemental and compositional signatures will be related to ultraviolet diagnostics of the solar source regions. o Furthermore, the kinetic properties of the heavy ions promise important clues about the non-thermal processes heating the solar corona and accelerating the solar wind and particle acceleration processes. o The measurement of suprathermal particles from 0.5 to 100 kev/q address the fundamental properties of particle acceleration throughout the heliosphere. o By comparing observed suprathermal ions with Figure 2: The composition of suprathermal tails varies with energy due to the different properties of suprathermal sources. The evolution and properties of shocks control the injection energy, acceleration rate, and, in turn, the composition of the SEPs energized from suprathermal ions [adapted from Mewaldt et al., 2006; shown here are oxygen fluences from ACE measured over a 3- year period]. energetic particles measurements (Figure 2), we expect to determine the mechanisms of particle injection and acceleration as functions of shock properties (Fisk and Gloeckler, 2007), and also stochastic sources. Primary Scientific Goals Elucidating the relationship between evolving global solar wind structures and the ever changing solar morphologies of coronal holes, loop populations, helmet streamers, plumes, and other solar structures. Determining the global structure of evolving shocks, the spatial variability of the suprathermal ion populations, and how these properties affect particle injection and acceleration mechanisms. Characterizing the global topology and evolution of CMEs and determining their roles in constraining and distinguishing between CME models.

4 Instrument Concept Solar wind ion composition instruments are of two basic types. The first type (i.e., Wind- MASS, SOHO-MTOF) is designed for isotopic and high resolution elemental composition measurements. The second type (i.e., ACE-SWICS, STEREO-PLASTIC) is designed to provide independent measurements of charge (q) and mass (m) for individual ions. Solar Wind characterization to link coronal properties to in-situ measured quantities demand a composition instrument with modest mass resolution obtained by the second type. Stateof-the art instruments designed to this purpose (for an example, see Figure 3) comprise two major components: (1) an Electrostatic Analyzer (EA) with Ion Steering (IS) that is designed to cover the required FOV, and (2) a Time-Of- Flight (TOF) telescope with solid- state detectors (SSD) for total ion energy (Etot) measurements, and microchannelplates (MCP) for detection of the timing signals generated by electrons coming from either the entrance foil or the face of the SSD. Such a sensor measures five key properties for all ions: mass (m), charge (q), speed Figure 3: 3D-view of a heritage-based design to measure the 3D velocity distribution, charge state, and composition of solar wind heavy ions (v) and direction of incidence (a,f). EA with IS provides E/q and elevation (f). TOF provides the azimuth (a) through the imaging of secondary electrons generated as the ion penetrates the entrance thin carbon foil. To enhance secondary electron emission and push the solar wind ions above the SSD energy threshold, the TOF/SSD telescope floats at an appropriate potential, typically of the order of kv. This potential accelerates the incoming solar wind ions so that their detection efficiencies are almost independent of the initial speed. Secondary electrons emitted from the front face of the SSDs are detected to complete the TOF measurement (t), and the SSD measures the total energy of the accelerated ions (Etot). This completes the five independent measurements required for unique ion identification and characterization. Heritage All subsystems of this design are based on heritage designs. The top-hat electrostatic analyzers/deflectors have heritage from STEREO-SWEA, Cluster-HIA, Mars and Venus EXPRESS-ASPERA; the 20 kv power supplies have heritage from ACE-SWICS, Ulysses-SWICS, STEREO-PLASTIC; the TOF-SSD subsystems have heritage from ACE-SWICS, Ulysses-SWICS, STEREO-PLASTIC; and the TOF subsystem is currently flying on MESSENGER FIPS.

5 Instrument Requirements To answer the scientific question posed above, the instrument must comply with following minimum requirements. These requirements are derived from the existing body of observations of solar wind composition existing to-date. Parameter Range/Resolution HIS Sensors 1xEA, 1 TOF-SSD Sensitivity Geometric factor 10-4 cm 2 s sr Mass Resolution (m/ m) 4 Charge He +1, +2 state C +1, (+4 : +6) O +1, (+5 : +8) Ne (+6 : +9) Mg (+6 : +12) Si (+6 : +12) Fe (+6 : +20) Energy Range kev/q Resolution (E/q)/ 6% (E/q) Angle Azimuth range -30 : +66 Elevation range -17 : +17 Temporal Resolution 30 sec References Fisk, L. A., & G. Gloeckler, Acceleration and Composition of Solar Wind Suprathermal Tails, Space Science Reviews, Volume 130, Issue 1-4, pp , Geiss, J., G. Gloeckler, R. von Steiger, H. Balsiger, L. A. Fisk, A. B. Galvin, F. M. Ipavich, S. Livi, J. F. McKenie, K. W. Ogilvie, and B. Wilken, The Southern High-Speed Stream Results from the SWICS Instrument on ULYSSES, Science, 268, 1033, 1995 Li, G., G. P. Zank, and W. K. M. Rice, Acceleration and transport of heavy ions at coronal mass ejection-driven shocks, Journal of Geophysical Research, Volume 110, Issue A6, CiteID A06104, 2005 Mewaldt, R. A., C. S. Cohen, and G. M. Mason, The source material for large solar energetic particle events in Washington, DC, American Geophysical Union Monograph 165: Solar Eruptions and Energetic Particles, p , 2006