A5014439787- Solar and Space Plasma Dynamics
- Atomic and Molecular Physics
- Ionosphere and magnetosphere dynamics
- Magnetic confinement fusion research
- Mass Spectrometry Techniques and Applications
- Astro and Planetary Science
- Stellar, planetary, and galactic studies
- X-ray Spectroscopy and Fluorescence Analysis
- Laser-induced spectroscopy and plasma
- Advanced Chemical Physics Studies
- Electron and X-Ray Spectroscopy Techniques
- Particle accelerators and beam dynamics
- Plasma Diagnostics and Applications
- Geophysics and Gravity Measurements
- Geomagnetism and Paleomagnetism Studies
- Ion-surface interactions and analysis
- Solar Radiation and Photovoltaics
- Medieval Literature and History
- Diamond and Carbon-based Materials Research
- Molecular Spectroscopy and Structure
- Radiation Therapy and Dosimetry
- Advanced Frequency and Time Standards
- Medieval Philosophy and Theology
- Advanced Data Storage Technologies
- Laser-Plasma Interactions and Diagnostics
Columbia University
2015-2024
University of California, Los Angeles
1986-2023
University of St Andrews
2018-2019
Justus-Liebig-Universität Gießen
2011
Los Alamos National Laboratory
2009
Kyoto Institute of Technology
2009
Applied Mathematics (United States)
2007
Carnegie Mellon University
2003-2005
Universität Ulm
2003
University of Pennsylvania
1992-1995
The Daniel K. Inouye Solar Telescope (DKIST) will revolutionize our ability to measure, understand and model the basic physical processes that control structure dynamics of Sun its atmosphere. first-light DKIST images, released publicly on 29 January 2020, only hint at extraordinary capabilities which accompany full commissioning five facility instruments. With this Critical Science Plan (CSP) we attempt anticipate some what those enable, providing a snapshot scientific pursuits hopes engage...
We have measured the widths of spectral lines from a polar coronal hole using Extreme Ultraviolet Imaging Spectrometer onboard Hinode. Polar holes are regions open magnetic field and source fast solar wind. find that line decrease at relatively low heights. Previous observations attributed such decreases to systematic effects, but we effects too small explain our results. conclude narrowing is real. The non-thermal believed be proportional amplitude Alfven waves propagating along these...
Dielectronic recombination (DR) of xenonlike ${\mathrm{W}}^{20+}$ forming ${\mathrm{W}}^{19+}$ has been studied experimentally at a heavy-ion storage ring. A merged-beams method employed for obtaining absolute rate coefficients electron-ion in the collision-energy range 0--140 eV. The measured coefficient is dominated by strong DR resonances even lowest experimental energies. At plasma temperatures where fractional abundance expected to peak fusion plasma, derived over factor 4 larger than...
We present a measurement of the energy carried and dissipated by Alfvén waves in polar coronal hole. have been proposed as source that heats corona drives solar wind. Previous work has shown line widths decrease with height holes, which is signature wave damping, but unable to quantify lost waves. This because depend on both non-thermal velocity vnt ion temperature Ti. implemented means separate Ti contributions using observation at low heights are undamped temperatures do not change height....
Abstract We have studied the propagation of inertial Alfvén waves through parallel gradients in speed using Large Plasma Device at University California, Los Angeles. The reflection and transmission inhomogeneities background plasma are important for understanding wave propagation, turbulence, heating space, laboratory, astrophysical plasmas. Here we present under conditions relevant to solar flares corona. find that is reduced as sharpness gradient increased. Any reflected were below...
Abstract The origin of the slow solar wind is not well understood, unlike fast that originates from coronal holes. In situ elemental abundances suggest it initially closed field lines become open. Coronal hole boundary regions are a potential source wind, as open there interact with loops through interchange reconnection. Our primary aim to quantify role reconnection at boundaries To this end, we have measured relative different elements these boundaries. Reconnection expected modulate first...
The hyperfine-induced $2s\phantom{\rule{0.16em}{0ex}}2p\phantom{\rule{0.28em}{0ex}}{}^{3}\phantom{\rule{-0.16em}{0ex}}{P}_{0}\ensuremath{\rightarrow}2{s}^{2}\phantom{\rule{0.28em}{0ex}}{}^{1}\phantom{\rule{-0.16em}{0ex}}{S}_{0}$ transition rate in Be-like sulfur was measured by monitoring the decay of isotopically pure beams ${}^{32}$S${}^{12+}$ and ${}^{33}$S${}^{12+}$ ions a heavy-ion storage ring. Within 4$%$ experimental uncertainty value $0.096(4)$ s${}^{\ensuremath{-}1}$ agrees with...
We present experimentally measured and theoretically calculated rate coefficients for the electron-ion recombination of ${\mathrm{W}}^{18+}\phantom{\rule{0.16em}{0ex}}([\mathrm{Kr}]\phantom{\rule{0.16em}{0ex}}4{d}^{10}\phantom{\rule{0.16em}{0ex}}4{f}^{10})$ forming ${\mathrm{W}}^{17+}$. At low collision energies, merged-beam coefficient is dominated by strong, mutually overlapping resonances. In temperature range where fractional abundance ${\mathrm{W}}^{18+}$ expected to peak in a fusion...
Large benzene clusters ionize with anomalously high efficiency when excited by ultraviolet radiation. The enhancement of the ionization and multiple-ionization cross sections over molecular values is quantitatively explained ultrafast fusion pairs excitations within a cluster.
We report ionization cross section measurements for electron impact single (EISI) of Fe^11+$ forming Fe^12+ and double (EIDI) Fe^11+ Fe^13+. The cover the center-of-mass energy range from approximately 230 eV to 2300 eV. experiment was performed using heavy ion storage ring TSR located at Max-Planck-Institut fur Kernphysik in Heidelberg, Germany. approach allows nearly all metastable levels relax ground state before data collection begins. find that is 30% smaller than previously measured a...
We have measured the energy and dissipation of Alfvénic waves in quiet Sun. A magnetic field model was used to infer location orientation lines along which are expected travel. The were using spectral wave amplitude. cause a non-thermal broadening lines, can be expressed as velocity vnt. By combining spectroscopic measurements with this model, we able trace variation vnt field. At each footpoint quiet-Sun loops, find that inject an flux range 1.3–5.5 × 105 erg cm−2 s−1. minimum range,...
We demonstrate that a nonthermal distribution of particles described by kappa can be accurately approximated weighted sum Maxwell–Boltzmann distributions. apply this method to modeling collision processes in kappa-distribution plasmas, with particular focus on atomic important for solar physics. The relevant process rate coefficients are generated summing appropriately Maxwellian coefficients. This reproduces the an estimated accuracy better than 3%. is equal or using "reverse-engineering"...
We report electron impact ionization cross section measurements for single of Fe12 + forming Fe13 and double Fe14 +. These are the first data any Si-like ion uncontaminated by an unknown metastable fraction. Recent distorted wave calculations agree with our results to within ∼15%. Double is dominated inner shell a 2l resulting in autoionization second as hole filled.
Abstract We compiled a set of electron-impact multiple-ionization (EIMI) cross section for astrophysically relevant ions. EIMIs can have significant effect on the ionization balance non-equilibrium plasmas. For example, it be important if there is rapid change in electron temperature or non-thermal energy distribution, such as kappa distribution. Cross EIMI are needed order to account these processes plasma modeling and spectroscopic interpretation. Here, we describe our comparison proposed...
Abstract We present a study of spectral line width measurements from the Extreme-ultraviolet Imaging Spectrometer on Hinode. used profiles Fe xvi 262.984 Å, xiv 264.787 270.519 274.203 and xv 284.160 studied 11 active regions. Previous studies widths have shown that in hot loops cores regions, observed nonthermal velocities are smaller than predicted models reconnection jets corona or shock heating associated with Alfvén waves. The also inconsistent chromospheric evaporation due to coronal...
Abstract We report the first experimental detection of a reflected Alfvén wave from an Alfvén-speed gradient under conditions similar to those in coronal holes. The experiments were conducted Large Plasma Device at University California, Los Angeles. present experimentally measured dependence coefficient reflection versus inhomogeneity parameter, i.e., ratio wavelength incident length scale gradient. Two-fluid simulations using Gkeyll code qualitatively agree with and support findings. Our...
We have performed a differential emission measure (DEM) analysis for polar coronal hole observed during solar minimum in 2007. Five observations are analyzed spanning the from central meridian to boundary with quiet-Sun corona. The heights ranged 1.05 1.20 R☉. shows that plasma is not strictly isothermal anywhere, but rather has high-temperature component extends up log T(K) = 6.2–6.3. size and importance of this depend on location, its evolving magnitude height marks between quiet corona,...
We have measured electron–ion recombination for C-like Mg6 + forming Mg5 +, and B-like Mg7 +. These studies were performed using a merged beam arrangement at the TSR heavy ion storage ring located in Heidelberg, Germany. Both primary ions metastable levels with significant lifetimes. Using simple cascade model we estimate population fractions these levels. For results, find that majority of stored are level, while fraction is insignificant. present beams rate coefficient DR via N = 2 → N'...
Experimentally measured and theoretically calculated rate coefficients for the recombination of ${\mathrm{W}}^{19+}([\mathrm{Kr}]\phantom{\rule{0.16em}{0ex}}4{d}^{10}\phantom{\rule{0.16em}{0ex}}4{f}^{9}$) ions with free electrons (forming ${\mathrm{W}}^{18+}$) are presented. At low electron-ion collision energies, merged-beam coefficient is dominated by strong, mutually overlapping, resonances as already found previously neighboring charge-state ${\mathrm{W}}^{18+}$ ${\mathrm{W}}^{20+}$. In...
The relaxation dynamics of a magnetized plasma system is subject fundamental importance in magnetohydrodynamics—with applications ranging from laboratory devices such as the toroidal-field pinch and spheromaks to astrophysical plasmas, stellar flaring activity, coronal heating. Taylor 1974 proposed that magnetic field plasma, certain constraints, relaxes minimum energy state final configuration constant α (linear) force-free field—where quantity describing twist lines. While Taylor's theory...
Efficient multiple ionization of large benzene clusters has been observed following irradiation a supersonic cluster beam by ArF-laser pulses at low fluences. The mechanism is shown to be distinct from that believed predominate in electron impact or synchrotron experiments. fluence dependence instead interpreted considering independent molecules within the cluster. efficiency over range laser can predicted quantitatively using recently proposed exciton annihilation model, and explains 106...
We have measured the root-mean-square (RMS) amplitude of intensity fluctuations, $\Delta I$, in plume and interplume regions a polar coronal hole. These fluctuations correspond to density fluctuations. Using data from \rev{Sun Watcher using Active Pixel System detector Image Processing} (SWAP) on \textit{Project for Onboard Autonomy (Proba2)}, our results extend up height about 1.35~$R_{\sun}$. One advantage RMS analysis is that it does not rely detailed evaluation power spectrum, which...