M. H. Chen

Bio: M. H. Chen is an academic researcher from Lawrence Livermore National Laboratory. The author has contributed to research in topics: Ionization & Opacity. The author has an hindex of 21, co-authored 49 publications receiving 1281 citations.

Spectroscopic absorption measurements of an iron plasma.

Abstract: The first quantitative measurement of photoabsorption in the region determining the Rosseland and Planck mean opacities is obtained for a well-characterized, radiatively heated iron plasma using new techniques and instrumentation. The plasma density and temperature are simultaneously constrained with high accuracy, allowing unambiguous comparisons with opacity models used in modeling radiative transfer in equilibrium astrophysical and laboratory plasmas. The experimental Rosseland and Planck group means are constrained to an accuracy of 15%.

Absorption experiments on x-ray-heated mid-Z constrained samples.

Abstract: Results of a niobium absorption experiment are presented that represent a major step in the development of techniques necessary for the quantitative characterization of hot, dense matter. The general requirements for performing quantitative analyses of absorption spectra are discussed. Hydrodynamic simulations are used to illustrate the behavior of tamped x-ray-heated matter and to indicate potential two-dimensional problems inherent in the technique. The absorption spectrum of a low-Z material, in this case aluminum, mixed with niobium provides a temperature diagnostic, which together with radiography as a density diagnostic fully characterizes the sample. A discussion is presented of opacity calculations and a comparison to the measurements is given that illustrates the need for experiments to provide a critical test of theory. The experimental technique is placed in context with a review of previous measurements using absorption spectroscopy to probe hot, dense matter. It is shown that the overall experimental concepts, although understood, were not always achieved in previous experiments. \textcopyright{} 1996 The American Physical Society.

Structure and Lamb shift of 2s1/2-2p3/2 levels in lithiumlike U89+ through neonlike U82+

Abstract: The first Doppler-shift-free crystal-spectrometer measurement of stationary highly stripped uranium ions from a high-energy electron beam ion trap is presented. Thirteen 2${\mathit{s}}_{1/2\mathrm{\ensuremath{-}}}$2${\mathit{p}}_{3/2}$ transitions in eight ionization states bteween Li-like ${\mathrm{U}}^{89+}$ and Ne-like ${\mathrm{U}}^{82+}$ are identified and measured with an accuracy as high as 37 ppm, providing benchmarks for testing relativistic correlation and quantum electrodynamic effects in highly charged multielectron ions. A value of 47.39\ifmmode\pm\else\textpm\fi{}0.35 eV is found for the 2${\mathit{s}}_{1/2}$ Lamb shift in Li-like ${\mathrm{U}}^{89+}$, in excellent agreement with theory.

Dielectronic recombination of heliumlike ions.

Abstract: We have measured \ensuremath{\Delta}n\ensuremath{\ge}1 dielectronic-recombination cross sections for the heliumlike ions ${\mathrm{Ni}}^{26+}$, ${\mathrm{Mo}}^{40+}$, and ${\mathrm{Ba}}^{54+}$ We observed the x rays emitted during dielectronic recombination by ions in an electron-beam ion trap and obtained cross sections from a calibration based upon radiative recombination The results generally agree well with theoretical predictions

Observation of interference between dielectronic recombination and radiative recombination in highly charged uranium ions.

Abstract: We have performed high-resolution measurements of photon excitation functions for radiative recombination and dielectronic recombination in highly charged uranium ions. The data show evidence for quantum interference between the two processes in the vicinity of the [ital KLL] resonances.

Search for New Physics with Atoms and Molecules

Abstract: Advances in atomic physics, such as cooling and trapping of atoms and molecules and developments in frequency metrology, have added orders of magnitude to the precision of atom-based clocks and sensors. Applications extend beyond atomic physics and this article reviews using these new techniques to address important challenges in physics and to look for variations in the fundamental constants, search for interactions beyond the standard model of particle physics, and test the principles of general relativity.

Experimental astrophysics with high power lasers and Z pinches

Abstract: With the advent of high-energy-density (HED) experimental facilities, such as high-energy lasers and fast Z-pinch, pulsed-power facilities, millimeter-scale quantities of matter can be placed in extreme states of density, temperature, and/or velocity. This has enabled the emergence of a new class of experimental science, HED laboratory astrophysics, wherein the properties of matter and the processes that occur under extreme astrophysical conditions can be examined in the laboratory. Areas particularly suitable to this class of experimental astrophysics include the study of opacities relevant to stellar interiors, equations of state relevant to planetary interiors, strong shock-driven nonlinear hydrodynamics and radiative dynamics relevant to supernova explosions and subsequent evolution, protostellar jets and high Mach number flows, radiatively driven molecular clouds and nonlinear photoevaporation front dynamics, and photoionized plasmas relevant to accretion disks around compact objects such as black holes and neutron stars.

Applications of B-splines in atomic and molecular physics

Abstract: One of the most significant developments in computational atomic and molecular physics in recent years has been the introduction of B-spline basis sets in calculations of atomic and molecular structure and dynamics. B-splines were introduced in applied mathematics more than 50 years ago, but it has been in the 1990s, with the advent of powerful computers, that the number of applications has grown exponentially. In this review we present the main properties of B-splines and discuss why they are useful to solve different problems in atomic and molecular physics. We provide an extensive reference list of theoretical works that have made use of B-spline basis sets up to 2000. Among these, we have focused on those applications that have led to the discovery of new interesting phenomena and pointed out the reasons behind the success of the approach.