Line Survey and Density Sensitivity Studies in Support of Hinode, MUSE, and Solar-C

OBJECTIVES: We will measure key atomic data used to analyze solar EUV spectra. Our work builds on expertise developed under our previous two H-TIDeS grants. Fe X traces 1 MK coronal gas. It has been observed by SERTS and EIS/Hinode and will be studied by EUVST/Solar-C. In addition to standard spectroscopic diagnostics, it offers a unique magnetic field diagnostic at 257.26 A. Our experiments have found significant errors in the Fe X line identifications. These hinder accurate interpretation of Fe X spectra and limit the utility of the magnetic field diagnostic. We will carry out a high-resolution Fe X line survey in the ~170-290 A bandpass to resolve these issue by unambiguously identifying Fe X lines in the EIS and EUVST bandpasses. Ca XV offers useful density diagnostics for high temperature emission from active regions and solar flares. Accurate densities are required for constraining steady-state vs. impulsive heating models. These diagnostics use the emission lines at 181.90, 182.86, and 200.97 A, which are observed by EIS and will be observed by EUVST. However, solar flare observations find that these lines do not agree as to the inferred density, likely due to errors in the underlying atomic data. We will experimentally calibrate these Ca XV density diagnostic line ratios. MUSE is a 35-slit spectrometer with bandpasses centered on three bright EUV lines: Fe XIX at 108 A, Fe IX at 171 A, and Fe XV at 284 A. The multiple slits will result in overlapping spectra. To disambiguate these data, a complex model will be used that accounts for all blending lines; but many of these blends are unidentified and significant contributions are expected from several charge states of O, Ne, Al, Si, S, Mg, Fe, and Ni. We have already carried out extensive line surveys for the 171 A bandpass for AIA/SDO. We will perform detailed line surveys for each of these elements in the 108 and 284 A bandpasses to precisely determine wavelengths, identify blends or unrecognized lines, and enable reliable use of the MUSE spectra. METHODS: We will use the Lawrence Livermore National Laboratory electron beam ion trap (EBIT-I) to resolve the above issues. EBIT-I has successfully been used for benchmarking solar-physics-relevant atomic data and offers a high spectral resolution that exceeds the requirements for solar data analysis. EBIT-I is a cylindrical device with an electron beam running down the axis of the trap. Elements are introduced into the trap and ionized by collisions with the electron beam. The ions are trapped by axial electrodes, an axial magnetic field, and by the radial electric potential of the beam. Their emission is measured by spectrometers. Line surveys are performed by varying the electron beam energy. As the beam energy is increased, the ions become more highly ionized. By measuring the spectrum while varying the beam energy, all the emission lines can be unambiguously associated with their charge state. Density diagnostic calibrations are obtained by varying the electron beam current, which changes the electron density in the trap. We measure the spectrum for different densities and thereby obtain an empirical calibration for the line intensity ratio vs. density. Experimentally, we work with the effective density, which depends on the overlap between the electron beam and ion cloud. We have developed methods to measure the ion cloud and accurately determine the effective density. We can achieve densities that are directly relevant to the solar corona. RELEVANCE: This work addresses the NASA Heliophysics Science Goal "Explore the physical processes in the space environment from the Sun to the Earth and throughout the solar system". Our unambiguous line surveys and accurate empirical density diagnostic calibrations will enable precise analysis of solar spectroscopic EUV data leading to advances in understanding the physical processes occurring in the solar atmosphere.

Support NASA's Heliophysics strategic science objectives to understand the Sun and its interactions with Earth and the solar system, including space weather. This will be achieved by developing/demonstrating instrumentation technology necessary to address the following science goals: Explore the physical processes in the space environment from the Sun to the Earth and throughout the solar system; Advance our understanding of the connections that link the Sun, the Earth, planetary space environments, and the outer reaches of our solar system; Develop the knowledge and capability to detect and predict extreme conditions in space to protect life and society and to safeguard human and robotic explorers beyond Earth.

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