B. R. Beck

Development of a pure cryogenic positron plasma using a LINAC positron source

The development of a high density cryogenic pure positron plasma trap at the LLNL positron beam facility opens new possibilities for antihydrogen research. We discuss a planned measurement of the three-body collisional recombination rate in magnetized plasmas, a possible antihydrogen atomic beam experiment, and other applications of pure positron plasmas.

FUDGE: A Program for Performing Nuclear Data Testing and Sensitivity Studies

We have developed a program called FUDGE that allows one to modify data from LLNL’s nuclear database. After modifying data, FUDGE can then be instructed to process the data into the formats used by LLNL’s deterministic (ndf) and the Monte Carlo (MCAPM) transport codes. This capability allows users to perform nuclear data sensitivity studies without modification of the transport modeling codes. FUDGE is designed to be user friendly (object‐oriented) and fast (the modification and processing typically takes about a minute). It uses Python as a front‐end, making it flexible and scriptable. Comparing, plotting, and printing of the data are also supported. An overview of FUDGE will be presented as well as examples.

RETRAP: An ion trap for laser spectroscopy of highly-charged ions

The possibility of highly-charged ions, captured and stored in an ion trap, and cooled by elastic collisions with confined Be ions, has been achieved in RETRAP; a cryogenic Penning trap system coupled to the Electron Beam Ion Trap (EBIT), which was used as a source of highly-charged ions. Be+ cooling in RETRAP has been carried out with a combination of resistive damping of the axial motion of the ions by a tuned circuit, and laser cooling. Spectroscopic goals of the research include metastable level lifetime measurements and precision laser spectroscopy on magnetic dipole transitions of selected highly-charged ions. Potential measurements of the hyperfine structure splitting, level lifetime, and bound state g-factor of a high-Z hydrogen-like ion 165Ho66+ already studied by emission spectroscopy in Super-EBIT, are discussed with relation to current progress.

Collisions and spectroscopy of cold, highly charged high-Z ions in RETRAP

Abstract Recent experimental results from the RETRAP apparatus, including electron capture measurements on highly charged high-Z ions and laser cooling of a mixed cloud of Be+ and Be2+ ions, are briefly described. These results are used as a basis for discussion of planned spectroscopy measurements on hydrogen-like and beryllium-like high-Z highly charged ions. Experimental parameters for potential measurements of the ground state hyperfine structure of a hydrogen-like high-Z ion, and the g-factor of the electron bound in that ion, are emphasized.

Observation of sequential electron capture to individual highly-charged Th ions

Electron transfer from H2 to Th79+ was studied in a cryogenic Penning trap by non-destructively observing the sequential development with time of the charge state of one or a few stored particles. The ratio of the true double capture cross section to the total capture cross section was found to be 0.21 ± 0.11 at a mean center-of-mass energy near 6 eV.

NADS — Nuclear and Atomic Data System

We have developed NADS (Nuclear and Atomic Data System), a web‐based graphical interface for viewing pointwise and grouped cross sections and distributions. Our implementation is a client / server model. The client is a Java applet that displays the graphical interface, which has interactive 2‐D, 3‐D, and 4‐D plots and tables. The server, which can serve and perform computations of the data, has been implemented in Python using the FUDGE package developed by Bret Beck at LLNL. Computational capabilities include algebraic manipulation of nuclear evaluated data in databases such as LLNL’s ENDL‐99, ENDF/B‐V, and ENDF/B‐VI, as well as user data. Processed data used in LLNL’s transport codes are accessible as well. NADS is available from http://nuclear.llnl.gov/.

Molecular Dynamics Simulations of Collisional Cooling and Ordering of Multiply Charged Ions in a Penning Trap

Molecular dynamics simulations are used to help design new experiments by modeling the cooling of small numbers of trapped multiply charged ions by Coulomb interactions with laser-cooled Be{sup +} ions. A Verlet algorithm is used to integrate the equations of motion of two species of point ions interacting in an ideal Penning trap. We use a time step short enough to follow the cyclotron motion of the ions. Axial and radial temperatures for each species are saved periodically. Direct heating and cooling of each species in the simulation can be performed by periodically rescaling velocities. Of interest are Fe{sup 11+} due to a EUV-optical double resonance for imaging and manipulating the ions, and Ca{sup 14+} since a ground state fine structure transition has a convenient wavelength in the tunable laser range.

Highly charged ion Coulomb crystallization in mixed strongly coupled plasmas

The investigation of highly charged ion Coulomb crystallization in mixed strongly coupled plasmas is of interest in many areas: white dwarf astrophysical plasmas are believed to have very similar thermodynamic properties, cold highly charged ions can be used as an object for high precision laser spectroscopy of fine and hyperfine transitions in the visible due to the absence of Doppler broadening and, an entirely new area of research is the potential application to highly charged ion based quantum computing schemes.We report the formation of such plasmas in a cryogenic Penning trap. These plasmas consisting of many species including Be+ and Xe44+ or Be+ and Xe15+ ions, are formed at a temperature of less than 4 K. The temperatures were obtained by applying a laser based sympathetic cooling scheme. The determination of the temperature and density from the laser resonance width and the fluorescence imaging of the Be+ clouds, respectively, yields a Coulomb coupling constant for the centrifugally separated Xe plasma high enough for crystallization.A molecular dynamics code, developed just for this purpose, was run to clarify the understanding of these plasmas and it was possible to show consistency between experiment and simulation.

Highly charged ion trapping and cooling

In the past few years a cryogenic Penning trap (RETRAP) has been operational at the Electron Beam Ion Trap (EBIT) facility at Lawrence Livermore National Laboratory. The combination of RETRAP and EBIT provides a unique possibility of producing and re-trapping highly charged ions and cooling them to very low temperatures. Due to the high Coulomb potentials in such an ensemble of cold highly charged ions the Coulomb coupling parameter (the ratio of Coulomb potential to the thermal energy) can easily reach values of 172 and more. To study such systems is not only of interest in astrophysics to simulate White Dwarf star interiors but opens up new possibilities in a variety of areas (e.g. laser spectroscopy, cold highly charged ion beams).

Collisions and spectroscopy of low-energy highly-charged ions using an ion trap

Electron transfer from H2 to highly-charged Xeq+ (q=35, 43–46) and Thq+ (q=73–80) ions at center-of-mass energies near 6 eV has been studied using the RETRAP system at Lawrence Livermore National Laboratory. The ions were produced in the Electron Beam Ion Trap and retrapped in the Penning ion trap. Initial cross section data are in reasonable accord with the predictions of the absorbing sphere model, and true double capture is found to be about 25% of the total. The development with time of the charge of a single ion undergoing collisions has been observed non-destructively. Certain spectroscopic measurements are planned, following cooling of the stored ions to cryogenic temperatures.