HELIOS-CR is a user-oriented 1-D radiation-magnetohydrodynamics code to simulate the dynamic evolution of laser-produced plasmas and z-pinch plasmas. It includes an in-line collisionalradiative (CR) model for computing non-LTE atomic level populations at each time step of the hydrodynamics simulation. HELIOS-CR has been designed for ease of use, and is well-suited for experimentalists, as well as graduate and undergraduate student researchers. The energy equations employed include models for laser energy deposition, radiation from external sources, and high-current discharges. Radiative transport can be calculated using either a multi-frequency flux-limited diffusion model, or a multi-frequency, multi-angle short characteristics model. HELIOS-CR supports the use of SESAME equation of state (EOS) tables, PROPACEOS EOS/multi-group opacity data tables, and non-LTE plasma properties computed using the inline CR modeling. Time-, space-, and frequency-dependent results from HELIOS-CR calculations are readily displayed with the HydroPLOT graphics tool. In addition, the results of HELIOS simulations can be post-processed using the SPECT3D Imaging and Spectral Analysis Suite to generate images and spectra that can be directly compared with experimental measurements. The HELIOS-CR package runs on Windows, Linux, and Mac OSX platforms, and includes online documentation. We will discuss the major features of HELIOS-CR, and present example results from simulations.

Lake size and depth mediate the strength of interaction between fish and zooplankton. We test whether this variation in zooplanktivory indirectly affects the phytoplankton by comparing 19 lakes that represent two food webs resulting from the absence of piscivores in small, partial-winterkill lakes. Lakes with piscivorous fish are further distinguished by thermal stratification, which provides a refuge for zooplankton to avoid fish predation. We contrasted phytoplankton abundance in these three categories of lakes over six years, using both direct measures of concentration and a growth bioassay that measures phytoplankton from the perspective of a standard grazer (Daphnia). Contrary to expectations, phytoplankton abundance was largely unaffected by trophic structure or the presence of a deep-water refuge. However, grazer growth differed dramatically among the three categories of lakes. Consistent with trophic cascade, increased fish planktivory resulted in more phytoplankton food as measured from the grazer's perspective. This effect was independent of lake productivity or total abundance and size of phytoplankton. Instead, variation in food quality for grazers was associated with compositional differences in phytoplankton. These results indicate that persistent trophic cascades are more dramatic in the plankton than previously realized but primarily influence composition, rather than biomass. Although cryptic, such top-down effects create functional variation in grazer-resource coupling.

SPECT3D is a multi-dimensional collisional-radiative code used to post-process the output from radiation-hydrodynamics (RH) and particle-in-cell (PIC) codes to generate diagnostic signatures (e.g., images, spectra) that can be compared directly with experimental measurements. This ability to postprocess simulation code output plays a pivotal role in assessing the reliability of RH and PIC simulation codes and their physics models. SPECT3D has the capability to operate on plasmas in 1-D, 2-D, and 3-D geometries. It computes a variety of diagnostic signatures that can be compared with experimental measurements, including: time-resolved and time-integrated spectra, space-resolved spectra and streaked spectra; filtered and monochromatic images; and x-ray diode signals. Simulated images and spectra can include the effects of backlighters, as well as the effects of instrumental broadening and time-gating. SPECT3D also includes a drilldown capability that shows where frequency-dependent radiation is emitted and absorbed as it propagates through the plasma towards the detector, thereby providing insights on where the radiation seen by a detector originates within the plasma. SPECT3D has the capability to model a variety of complex atomic and radiative processes that affect the radiation seen by imaging and spectral detectors in high energy density physics (HEDP) experiments. LTE (local thermodynamic equilibrium) or non-LTE atomic level populations can be computed for plasmas. Photoabsorption rates can be computed using either escape probability models or, for selected 1-D and 2-D geometries, multi-angle radiative transfer models. The effects of non-thermal (i.e., non-Maxwellian) electron distributions can also be included. To study the influence of energetic particles on spectra and images recorded in intense short-pulse laser experiments, the effects of both relativistic electrons and energetic proton beams can be simulated.SPECT3D is a user-friendly software package that runs on Windows, Linux, and Mac platforms.A parallel version of SPECT3D is supported for Linux clusters for large-scale calculations. We will discuss the major features of SPECT3D, and present example results from simulations and comparisons with experimental data.

We have measured the partial cross sections for ionizing neutral helium to He+ in the 2s and 2p levels from threshold to 130 eV. Near threshold the data favor the closecoupling calculations of Jacobs and Burke rather than the many-body calculations of Chang, in contrast to the total N =2 cross section. We have also made a detailed study of the autoionizing resonances leading to the N =3, N =4, and N =5 thresholds. We present resonance parameters for the N =3 series. The energies of the resonances agree well with calculated and experimental values, but the widths show substantial disagreement with calculations.

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