Bulletin of the American Physical Society
2011 Annual Meeting of the California-Nevada Section of the APS
Volume 56, Number 14
Friday–Saturday, November 11–12, 2011; Menlo Park, California
Session B1: AMO & Plasma Physics |
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Chair: Peter Beiersdorfer, Lawrence Livermore National Laboratory Room: Bldg 48 - ROB Redwood A/B |
Friday, November 11, 2011 1:30PM - 1:42PM |
B1.00001: Spectroscopic Measurements of Photo Pumped Highly Charged Ions A. Graf, P. Beiersdorfer, G.V. Brown, J.R. Crespo Lopez Urrutia We report on recent x-ray laser spectroscopic measurements of line emission from photo-excited highly charged ions. The ion cloud of the HI-LIGHT portable electron beam ion trap (EBIT) was used as a target for the Linac Coherent Light Source (LCLS) free electron laser in the Soft X-Ray (SXR) end station. The SXR monochromator allowed a precision investigation of transition energies and oscillator strength ratios of emission lines from Na-like Fe$^{15+}$ and Ne-like Fe$^{16+}$ important for astrophysical diagnostics. We have demonstrated a technique for calibration of the SXR monochromator photon energy scale using photo-excited resonant fluorescence spectra of very well known lines from H-like and He-like F and O. Numerous instruments were used to diagnose the fluorescent and autoionizing decay channels of the trapped plasma including an Iglet-X broadband germanium detector, a variable line spacing reflection grating soft x-ray/VUV spectrometer and a Wien filter based ion extraction system. An overview of the experiment as well as preliminary results will be presented. [Preview Abstract] |
Friday, November 11, 2011 1:42PM - 1:54PM |
B1.00002: Size dependent ionization dynamics of argon clusters in intense x-ray pulses Sebastian Schorb, M. Swiggers, D. Rupp, R. Coffee, M. Messerschmidt, S. M\"{o}ller, G. Williams, J. Bozek, T. Osipov, S. Wada, O. Kornilov, T. M\"{o}ller, C. Bostedt Free Electron Lasers open the door for novel experiments in many science areas ranging from ultrafast chemical dynamics to single shot imaging of molecules. For the success of virtually all experiments with free electron lasers a detailed understanding of the light - matter interaction in the x-ray regime is pivotal. The Linac Coherent Light Source (LCLS) free electron laser in Stanford allows for the first time to study inner shell ionization dynamics of intense x-ray pulses on a femtosecond time scale. We performed experiments on the ionization dynamics of Argon clusters at different pulse length using the slotted spoiler foil in the second LCLS bunch compressor [1]. The Auger rate of argon clusters is predicted to be size dependent and lower than in atoms due to delocalization of the valence electrons [2]. We observe a dependence of the ionization dynamics on pulse length and cluster size. The results are discussed and also compared to recent atomic and molecular data from LCLS.\\[4pt] [1] P. Emma et al. PRL 92, 074801 (2004)\\[0pt] [2] U. Saalmann, JM Rost, PRL 89, 14 (2002) [Preview Abstract] |
Friday, November 11, 2011 1:54PM - 2:06PM |
B1.00003: High-Energy Neutron Source For Fusion Material Property Studies Using Short Pulse Lasers D.P. Higginson, J.M. McNaney, D.C. Swift, D. Bleuel, A.J. Mackinnon, P.K. Patel, G.M. Petrov, J. Davis, V. Yu Glebov, C. Stoeckl, J. Cobble, J.A. Frenje, R. Kodama, H. Nakamura, K.L. Lancaster, L.C. Jarrott, G. Tynan, F.N. Beg High-energy ($>$10 MeV) neutron generation is of interest to applications including fusion energy, material damage studies and nondestructive material detection. A novel technique to create high-energy neutrons was demonstrated using short pulse (10 ps), high-energy (350-1000 J) lasers at the Titan and Omega EP laser systems. In this method, the laser accelerates deuterons from a CD foil, which produce neutrons as they pass through a LiF block via the reaction $^7$Li(d,xn), $Q$=15 MeV. The spectrum is forward peaked in both energy and number. The presence of proton contaminants on the CD foil dramatically inhibits the acceleration of deuterons, which reduces the neutron generation. Activation diagnostics and CR39 detectors recorded single shot neutron fluences of up to 3$\times10^9$ n sr$^{-1}$. Neutron time-of-flight spectrometer detectors indicate the production of neutrons with energies up to 18 MeV in the forward direction. Methods to improve neutron yield and directionality will be presented. [Preview Abstract] |
Friday, November 11, 2011 2:06PM - 2:18PM |
B1.00004: Visible Spectroscopy on the Plasma Liner Experiment (PLX) Jacob Schwartz, Tom Awe, Scott Hsu, Elizabeth Merritt, Alan Lynn, Mark Gilmore, Stephan Fuelling The Plasma Liner Experiment (PLX) will study the merging of thirty high Mach number jets of argon plasma in a spherically convergent configuration. Initial experiments will study single jet propagation, where it is important to measure the jet density, velocity, and temperature to evaluate jet evolution during its transit from the chamber wall toward the center. We have constructed a broad band visible light survey spectrometer to observe light emitted from the plasma jet in order to identify the best specific argon emission lines on which to perform Doppler and Stark broadening analysis. Special attention has been paid to maximize throughput because of low expected light levels. Light is collected by a lens coupled to a hexagonal bundle of seven 1 mm core diameter fibers. The fibers fan out to couple to the slit of a 14 cm focal length spectrometer which is observed by an intensified CCD camera. We discuss the design and assembly of this spectrometer system and (time permitting) initial data from single jet experiments. This work will inform the design of a high resolution spectroscopy system for future PLX experiments. [Preview Abstract] |
Friday, November 11, 2011 2:18PM - 2:30PM |
B1.00005: FTIR Spectroscopy and Density Functional Theory of the 1474 cm$^{-1}$ Absorption in C$_{n}$ Carbon Cluster Spectra Mekena McGrew, Christina Le, W.R.M Graham The identification of the infrared frequencies of carbon clusters is significant for astrophysical and material science research. By using FTIR spectroscopy, density functional theory, and argon matrix trapping numerous C$_{n}$ carbon clusters have been observed in the Nd:YAG laser ablation products trapped in solid argon. An unidentified absorption at 1474 cm$^{-1}$ has been observed in our experiments, and $^{13}$C isotopic shift measurements and DFT calculations have been performed to test potential C$_{n}$ candidates for the carrier of the band. The number and relative intensities of the isotopic shifts suggest a molecule consisting of 4 or 6 atoms. Simulated $^{13}$C shift spectra have been calculated for a variety of 4- and 6-member C$_{n}$ structure$_{ }$using the B3LYP functional and ccPVDZ basis set. Potential sources of the 1473 cm$^{-1}$ band will be discussed. [Preview Abstract] |
Friday, November 11, 2011 2:30PM - 2:42PM |
B1.00006: Quantum Transport through Fullerenes Shambhu Das, Peter Winkler Quantum transport of electron pathways has recently attracted increased interest in the field of nano-technology. The study of transport through mesoscopic system can explain a wide range of interesting experimental features such as rectification, switching mechanism and transistor actions. The present study is aimed at the possible use of transmission spectra to distinguish between various isomers of certain fullerene molecules. While the famous $C_{60}$ is found as a single isomer, other fullerenes come in different isomeric structures, for example, there are forty distinct isomers known for $C_{40}$. [Preview Abstract] |
Friday, November 11, 2011 2:42PM - 2:54PM |
B1.00007: Direct Frequency Comb Spectroscopy of Alkali Atoms Trinity Pradhananga, Christopher Palm, Khoa Nguyen, Srikanth Guttikonda, Derek Jackson Kimball We are using direct frequency comb spectroscopy to study transition frequencies and excited state hyperfine structure in potassium and rubidium using 2-photon transitions excited directly with the frequency-doubled output of a erbium fiber optical frequency comb. The frequency comb output is directed in two counterpropagating directions through a vapor cell containing the atomic vapor of interest. A pair of optical filters is used to select teeth of the comb in order to identify the transition wavelengths. A photomultiplier tube (PMT) measures fluorescence from a decay channel wavelength selected with another optical filter. Using different combinations of filters enables a wide range of transitions to be investigated. By scanning the repetition rate, a Doppler-free spectrum can be obtained enabling kHz-resolution spectral measurements. The thermal motion of the atoms in the vapor cell actually eliminates the need to fine-tune the offset frequency and repetition rate, alleviating a somewhat challenging requirement for spectroscopy of cold atoms. Our investigations are laying the groundwork for a long-term research program to use direct frequency comb spectroscopy to understand the complex spectra of rare-earth atoms. [Preview Abstract] |
Friday, November 11, 2011 2:54PM - 3:06PM |
B1.00008: A test of the (circular) Unruh effect using atoms Douglas Singleton We propose a test for the (circular) Unruh effect using certain atoms -- fluorine and oxygen. For these atoms the centripetal acceleration of the outer shell electrons implies an effective Unruh temperature in the range $1000 - 2000$ K. This range of Unruh temperatures is large enough to excite a significant fraction of the outer electrons into low lying energy levels above the ground state. Examining these atoms at low ambient temperatures and finding a larger than expected number of electrons in low lying excited states beyond what is expected via background thermal excitation would provide experimental evidence for the Unruh effect. [Preview Abstract] |
Friday, November 11, 2011 3:06PM - 3:18PM |
B1.00009: Progress toward a search for spin-mass couplings of the proton Jerlyn Swiatlowski, Julian Valdez, Ian Lacey, Caitlin Montcrieffe, Derek Jackson Kimball We report progress in our development of a dual-isotope rubidium magnetometer to be used to search for a long-range coupling between proton spins and the mass of the Earth. The valence electron dominates magnetic interactions and serves as a precise co-magnetometer for the nuclei in a simultaneous measurement of Rb-85 and Rb-87 spin precession frequencies, enabling accurate subtraction of magnetic perturbations. Both Rb nuclei have valence protons, but in Rb-87 the proton spin is parallel to the nuclear spin and magnetic moment while for Rb-85 the proton spin is anti-parallel to the nuclear spin and magnetic moment. Thus anomalous interactions of the proton spin produce a differential shift between the Rb spin-precession frequencies, whereas many sources of systematic error produce common-mode shifts of the spin-precession frequencies which can be controlled through auxiliary measurements. We discuss our optimization of the magnetometer sensitivity and methods to control systematic effects due to light shifts, collisions, and the gyro-compass effect. [Preview Abstract] |
Friday, November 11, 2011 3:18PM - 3:30PM |
B1.00010: Physics in Screening Environments Ondrej Certik, Peter Winkler The calculation of electronic states of atoms in screening environments, e.g. plasmas, is often performed using Debye's approach which replaces the frequency independent part of screening by a simple, distance dependent function. Only later has this approach been extended to include also screened electron-electron interactions. This generalization faces the difficulty that for the Debye interaction an expansion as simple as the one for the Coulomb interaction, the $r^{k}/r^{k+1}$ - rule, has not been known. In the present work a method has been developed that allows for the analytic calculation of the screened electron-electron interaction matrix elements. This method has been applied to small atoms and quantum dots. For larger systems such as clusters, numerical methods of calculation are preferable and being developed. Of particular interest are the scattering resonances of atoms and ions in screening systems because they give direct experimental evidence of the degree of screening. [Preview Abstract] |
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