A5051043788- Magnetic confinement fusion research
- Stellar, planetary, and galactic studies
- Astrophysics and Star Formation Studies
- Astronomy and Astrophysical Research
- Ionosphere and magnetosphere dynamics
- Laser-Plasma Interactions and Diagnostics
- Atomic and Subatomic Physics Research
- Astro and Planetary Science
- Fusion materials and technologies
- Plasma Diagnostics and Applications
- Superconducting Materials and Applications
- Solar and Space Plasma Dynamics
- Radiation Detection and Scintillator Technologies
- Gamma-ray bursts and supernovae
- Particle accelerators and beam dynamics
- Spectroscopy and Laser Applications
- Molecular Spectroscopy and Structure
- Astronomical Observations and Instrumentation
- Atmospheric Ozone and Climate
- Scientific Research and Discoveries
- Space Exploration and Technology
- Planetary Science and Exploration
- Nuclear reactor physics and engineering
- High voltage insulation and dielectric phenomena
- Geomagnetism and Paleomagnetism Studies
University of Wisconsin–Madison
1998-2022
Vanderbilt University
2017-2021
Fisk University
2017-2019
University of Florida
2014-2015
Princeton Plasma Physics Laboratory
1984-1989
Princeton University
1984-1989
Los Alamos National Laboratory
1988
United States Department of Commerce
1986
We describe the design, manufacture, and performance of bare-fiber integral field units (IFUs) for SDSS-IV survey MaNGA (Mapping Nearby Galaxies at APO) on Sloan 2.5 m telescope Apache Point Observatory (APO). is a luminosity-selected integral-field spectroscopic 10,000 local galaxies covering 360-1030 nm R ~ 2200. The IFUs have hexagonal dense packing fibers with regularity 3 um (RMS), throughput 96+/-0.5% from 350 to 1 in lab. Their sizes range 19 127 (3-7 layers) using Polymicro FBP...
We present an analysis of spectrosopic and astrometric data from APOGEE-2 Gaia DR2 to identify structures towards the Orion Complex. By applying a hierarchical clustering algorithm 6-dimensional stellar data, we spatially and/or kinematically distinct groups young objects with ages ranging 1 12 Myr. also investigate star forming history within Complex, peculiar sub-clusters. With this method reconstruct older populations in regions that are presently largely devoid molecular gas, such as C...
Multiplicity is a fundamental property that set early during stellar lifetimes, and it stringent probe of the physics star formation. The distribution close companions around young stars still poorly constrained by observations. We present an analysis multiplicity derived from APOGEE-2 spectra obtained in targeted observations nearby star-forming regions. This largest homogeneously observed sample high-resolution stars. developed autonomous method to identify double lined spectroscopic...
The spatial morphology and dynamical status of a young, still-forming stellar cluster provide valuable clues on the conditions during star formation event processes that regulated it. We analyze Orion Nebula Cluster (ONC), utilizing latest censuses its content membership estimates over large wavelength range. determine center mass ONC, study radial dependence angular substructure. core appears rounder smoother than outskirts, consistent with higher degree processing. At larger distances...
Central ion temperatures up to 30 keV and rotation speeds 8\ifmmode\times\else\texttimes\fi{}${10}^{5}$ m/sec have been confirmed with new diagnostic measurements in the TFTR hot-ion enhanced-confinement regime, thermal diffusivity is found be non-neoclassical comparable anomalous electron diffusivity. The dominant effect of strong down-shifting neutral beam energies plasma frame, which results reduced heating on axis, presence off-axis from viscous damping rotation.
Abstract Open clusters are groups of stars that form at the same time, making them an ideal laboratory to test theories star formation, stellar evolution, and dynamics in Milky Way disk. However, utility open cluster can be limited by accuracy completeness its known members. Here, we employ a “top-down” technique, Extreme Deconvolution Gaussian Mixture Models (XDGMMs), extract evaluate from Gaia DR2 fitting distribution parallax proper motion along line sight. deconvolution techniques...
A beam emission spectroscopy system is being developed and deployed on the HL-2A tokamak to measure local low wavenumber (k⊥ρi < 1) density fluctuations by measuring Doppler-shifted from a 50 kV deuterium heating neutral beam. High spatial resolution (Δr ≤ 1 cm, Δz 1.5 cm) measurements are achieved with customized in-vacuum optics. frequency, high-gain preamplifiers sample light intensity at Nyquist frequency of MHz achieve high S/N ratio via optical throughput, low-noise preamplifiers,...
We study the degree of angular substructure in stellar position distribution young members Galactic star-forming regions, looking for correlations with distance from cluster center, surface number density stars, and local dynamical age. To this end we adopt catalog 18 (∼1–3 Myr) clusters Massive Young Star-Forming Complex Study Infrared X-ray Survey statistical analysis dispersion parameter, δADP, N. find statistically significant correlation between N physical projected center clusters,...
A new beam emission spectroscopy (BES) diagnostic is under development. Photon-noise limited measurements of neutral emissions are achieved using photoconductive photodiodes with a novel frequency-compensated broadband preamplifier. The BES system includes next-generation preamplifier and upgraded optical coupling system. Notable features the design surface-mount components, minimized stray capacitance, wide angular acceptance photodiode, differential output line driver, reduced input...
Bean-shaped configurations have been successfully formed in the PBX tokamak and $\ensuremath{\beta}$ values of over 5% obtained. These discharges still lie first stability regime for ballooning modes, magnetohydrodynamics analysis implicates external kink as responsible present limit.
Abstract We study the occurrence of spectroscopic binaries in young star-forming regions using INfrared Spectroscopy Young Nebulous Clusters (IN-SYNC) survey, carried out SDSS-III with APOGEE spectrograph. Multi-epoch observations thousands low-mass stars Orion A, NGC 2264, 1333, IC 348, and Pleiades have been out, yielding H -band spectra a nominal resolution R = 22,500 for sources < 12 mag. Radial velocity precisions ∼0.3 <?CDATA $\mathrm{km}\ {{\rm{s}}}^{-1}$?> were achieved, which we...
Abstract Radius inflation continues to be explored as a peculiar occurrence among magnetically active, low-mass stars. Recently, Somers & Stassun showed that radius stars in the young open cluster M45 (Pleiades Cluster) is correlated rotation rate: faster rotators are more inflated. Here we extend work sample of 68 older Hyades Cluster. We derive stars’ spectral energy distributions measure their bolometric fluxes. With spectroscopically defined T eff and Gaia distances calculate stellar...
Ion temperature profiles with a time resolution of 2–5 ms have been measured on the Princeton Beta Experiment tokamak (PBX) by charge-exchange recombination spectroscopy (CXRS) and neutral particle analyzer (NPA). The sightlines both diagnostics crossed trajectory near-perpendicular heating beam, which enhanced local density (∝ signal strength) provided spatial resolution. these two independent techniques is sufficient to see sawtooth oscillations other magneto- hydrodynamic activity....
A new high radial resolution 2D multichannel Charge eXchange Imaging (CXI) diagnostic is under development for deployment at DIII-D. The system will measure low-to-intermediate wavenumber carbon density fluctuations by observing the n = 8 - 7 (λ 529.06 nm) C-VI emission line, resulting from charge exchange collisions between heating neutral beam atoms and intrinsic ion density. CXI provide measurements with ΔR ∼ 0.4 cm to access higher kr instabilities (kr < cm-1) predicted arise in...
Abstract A beam emission spectroscopy (BES) diagnostic is designed for studying two-dimensional turbulent dynamics by measuring the Doppler-shifted Balmer-Alpha ( n = 3 → 2) from neutral heating beams on Wendelstein 7-X (W7-X) stellarator. The BES viewing geometry has been determined in conceptual design previously. However, small Doppler shifts and optical throughput compared to a typical demand dedicated efforts assemblies detector module system. We present detailed opto-mechanical...
A conceptual design for a 2D beam emission spectroscopy diagnostic system to measure ion gyro-scale plasma turbulence at Wendeslstein 7-X is described. The identifies field-aligned viewing geometries and ports cross-field measurements in the neutral volume. sightline grid covers outer region, configuration provides sufficient k-space coverage radial poloidal directions temperature gradient trapped-electron mode measurements. Emission intensity estimates, optical transmission losses, detector...
Two newly developed, eight-channel, integrated Beam Emission Spectroscopy (BES) detectors have been installed at Huan-Liuqi-2A tokamak, which extends the existing 16 single-channel modular BES system with additional spatial channels. The collects Doppler-shifted Balmer Dα emission a resolution of 1 cm (radial) × 1.5 (poloidal) and temporal 0.5 µs to measure long-wavelength (k⊥ρi < 1) density fluctuations. Compared BES, dark noise is reduced by 50%-60% on average. signal-to-noise ratio...
An upgraded detector and several optimizations have significantly improved the Ultra-Fast Charge Exchange Recombination Spectroscopy (UF-CHERS) diagnostic sensitivity to ion temperature parallel velocity fluctuations at turbulence relevant spatio-temporal scales. Normalized broadband down x̃x∼1% (x = Ti, v∥) up ∼450 kHz been measured in a variety of plasmas. The multi-field nature CHERS technique also allows measurements cross-phase angles fluctuating fields. UF-CHERS is optimized observe...
An ICRF heating experiment was perfomed on TFTR. A comparison of the antenna loading with a 1‐D theory reproduces much observed behavior. Good agreement between and regarding details ion distributions has also been obtained. (AIP)
The plasma torus of Jupiter is a diffuse, faintly emitting ionized gas surrounding in the vicinity Io's orbit. We have observed this region [SII] lines at 6716 Å and 6731 [SIII] line 9531 with an imaging spectrometer consisting narrow band tunable Fabry-Perot interferometer coupled to CCD camera. Because extreme faintness emissions requirement short exposure times imposed by motion torus, which co-rotates Jupiter, prebinning mode operation was developed. This partially overcomes...