Bulletin of the American Physical Society
2014 Annual Meeting of the Far West Section of the APS
Volume 59, Number 14
Friday–Saturday, October 24–25, 2014; Reno, Nevada
Session C1: Plasma Physics |
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Chair: Alla Safronova, University of Nevada, Reno Room: JCSU 422 |
Friday, October 24, 2014 2:00PM - 2:12PM |
C1.00001: X-ray image and x-ray burst features of under-dense plasma produced in high-density gas jets on the Leopard Laser at UNR K.A. Schultz, V.L. Kantsyrev, A.S. Safronova, J.J. Moschella, P. Wiewior, V.V. Shlyaptseva, M.E. Weller, E.E. Petkov, I.K. Shrestha, A. Stafford, M.C. Cooper Results of Ar and Kr gas-puff experiments performed on the high-power Leopard laser at UNR are presented. The Leopard laser operated in two regimes: 350 fs, 40 TW pulse or 0.8 ns, 25 GW pulse with wavelength of 1.057 $\mu $m. A supersonic linear nozzle was compared with a cylindrical sub-sonic nozzle. Diagnostics included two sets of filtered Si-diodes, x-ray pinhole cameras, x-ray spectrometers, and PCDs. Specifically, x-ray images and structure of x-ray bursts are investigated and compared as a function of the linear or cylindrical gas jet, laser pulse duration, and target gas. Strong anisotropy with respect to laser beam polarization was observed in the x-ray output of the linear gas jet. Also, the addition of Kr to an Ar gas jet increased the intensity of the x-ray output compared to a pure Ar jet. The importance of analysis of x-ray burst features for better understanding the mechanisms of the laser energy to x-ray conversion efficiency and future research directions are discussed. [Preview Abstract] |
Friday, October 24, 2014 2:12PM - 2:24PM |
C1.00002: Positron Production Using a Laser-Wakefield Electron Source Jackson Williams, Felicie Albert, Hui Chen, Jaebum Park, Brad Pollock Positron generation using wakefield-accelerated electrons driven into a second mm-scale target was investigated using the Callisto Laser at the Jupiter Laser Facility at Lawrence Livermore National Laboratory. This technique [1] is in contrast to previous experiments that use direct laser-target interactions to create positron-electron pairs [2], and has the potential to make laser-produced positron sources widely available to smaller scale laboratories. Monte Carlo simulations show a collimated wakefield electron beam produces a positron beam with a significantly larger divergence angle ($>$100 mrad) due to multiple small angle coulomb scattering, resulting in an emitted pair density of $10^{13}$ particles/cm$^{3}$. At the Callisto Laser, we did not observe a signal consistent with positrons.. This could be due to a high noise environment and a large detection threshold. \\[4pt] [1] G. Sarri et al., Phys. Rev. Lett., 110:255002, Jun 2013.\\[0pt] [2] H. Chen et al., Phys. Rev. Lett., 105:015003, Jul 2010. [Preview Abstract] |
Friday, October 24, 2014 2:24PM - 2:36PM |
C1.00003: ??ray production and transport in ultra-fast heated high Z matter Rishi Pandit, Yasuhiko Sentoku Radiation transport code coupled with fully relativistic collisional Particle-in-Cell (PIC) code, PICLS, has been developed to study the transport of X-ray photons produced in laser-solid interaction. We have implemented the differential cross-section of emitted radiation with respect to frequency and emission angle of Bremsstrahlung and also the radiative damping to simulate high energy photons, ??ray, production and transport in ultra-intense laser - matter interactions. We discuss the laser energy dependence of the emission energy and the intensity dependence of the angular distribution of ??rays. By solving the transport of hard X-rays we find that high energy photons emitted by relativistic electrons are co-moving with the electrons and they are intensified continuously in the Bremsstrahlung process. As a result the ??rays have the signature of the fast electrons' temporal and spatial distribution. We also calculate the number of pairs by solving the Bethe-Heitler cross-section in the radiation transport simulation. Comparing the details of ??rays via Bremsstrahlung and radiative damping with varying laser intensities, we will discuss the laser parameters and the target conditions (material) to increase the ??ray yields. [Preview Abstract] |
Friday, October 24, 2014 2:36PM - 2:48PM |
C1.00004: Study of Hard X-rays and Electron Beams on 1.7 MA Z-pinch and Laser Plasma Experiments I. Shrestha, V.L. Kantsyrev, A.S. Safronova, V.V. Shlyaptseva, K.A. Schultz, M.E. Weller, A. Stafford, E.E. Petkov, M.C. Cooper, P. Wiewior The studies of Hard X-ray (HXR) emission and electron beam generation in Z-pinch and laser plasmas are very important for development of sources of K-shell and L-shell radiation and Inertial Confinement Fusion (ICF) research. The configuration as well as elemental composition of Z-pinch loads (planar and cylindrical wire arrays) or laser targets (gas-puff) is an important feature for both total hard x-ray radiation (HXR) and electron beam generation. There is variation of HXR and electron beam generations when testing different wire loads on Z-pinch generator and in the interaction of laser with different gases (Ar, Kr and mixture of Ar/Kr). Also for laser plasma experiments, the HXR yield and electron beam depends on anisotropy with respect to laser beam polarization. The comparative study of HXR yield and electron beam generation in both experiments will be discussed. [Preview Abstract] |
Friday, October 24, 2014 2:48PM - 3:00PM |
C1.00005: Formation of Plasma from Thick Metal Pulsed with Multi-Megagauss Magnetic Field B.S. Bauer, K.C. Yates, S. Fuelling, V.V. Ivanov, I.R. Lindemuth, R.E. Siemon, A.A. Anderson, T. Hutchinson, J. Mei, T.J. Awe, R.S. Bauer Understanding the evolution of ohmically heated conductors is exceptionally important for basic physics and applications (e.g., fusion energy). The thermal ionization of the surface of metal rods with radii larger than the magnetic skin depth is being investigated with well-characterized experiments and detailed numerical modeling. Metal rods of initial diameter 0.50-2.00 mm are pulsed to 1.0 MA peak current in 100 ns. The rod material (Al-6061, Al-1100, Cu-101, Cu-145, Ni-200, or Ti-Grade-II) and surface finish (finely or coarsely machined, electropolished or not) are varied. Time-resolved imaging, radiometry, spectroscopy, and laser shadowgraphy track the evolution of the rod surface. Plasma forms when the surface magnetic field reaches a critical value (e.g., 2.2 MG for Al-6061). At the threshold, the optical emission from the surface is non-uniform, initially showing discrete bright points. Then plasma filaments form, mainly in the direction of the current, until the surface emission is quite uniform. Radiation-MHD simulations with the numerical code MHRDR can reproduce macroscopic features of the data on aluminum by using certain choices of models for resistivity, equation of state, other transport coefficients, and radiation opacities. [Preview Abstract] |
Friday, October 24, 2014 3:00PM - 3:12PM |
C1.00006: Improvements to a novel photoionized plasma experiment and calculations at the Z facility T.E. Lockard, D.C. Mayes, T. Durmaz, R.C. Mancini, G. Loisel, J.E. Bailey, G.A. Rochau, D.A. Liedahl, R.F. Heeter A large scale effort has been made to understand and explain photoionized plasmas in astrophysical observations made by X-ray orbiting telescopes like Chandra and XMM-Newton. The atomic kinetics and radiation transfer of these plasmas are driven by a large flux of high energy photons required by the photoionization process. While these sources of high flux drivers are more abundantly found in celestial mediums, the difficulty comes into play when trying to create such a source in a controlled laboratory environment. This has been part of the crux and hindrance of the progress in studying this fundamental aspect of nature. Luckily, with recent developments and utilization of pulsed power technologies the Z machine at Sandia National Laboratory helps alleviate this obstruction. To understand the complex environment where a collapsing wire array is used to create the intense source of X-rays required to produce a photoionized plasma, a large array of geometric, radiation-hydrodynamic and atomic kinetic codes help to give insight into the X-ray environment and plasma hydrodynamics of the system. These calculations complement experimental data attained to give a more complete understanding and deepen our knowledge of the competing processes in laboratory photoionized plasmas. [Preview Abstract] |
Friday, October 24, 2014 3:12PM - 3:24PM |
C1.00007: Renovated Compact Z-pinch Facility ``Sparky'' and Development and Tests of Focusing Crystal X-ray Spectrometers M.C. Cooper, V.L. Kantsyrev, A.S. Safronova, I.K. Shrestha, K.A. Schultz, V.V. Shlyaptseva, M.E. Weller, A. Stafford, E.E. Petkov, M.T. Schmidt-Petersen, M.Y. Lorance, W. Cline, C. Davidson The compact x-ray/EUV facility ``Sparky'' at the UNR Physics Department's Plasma Physics and Diagnostics Laboratory (PPDL) was renovated to obtain high density and temperature plasmas with gas-puff z-pinch experiments. The renovated facility will be used for plasma dynamics and radiation studies, x-ray spectroscopic research, benchmarking of theoretical codes, calibration of x-ray and diagnostic instrumentation, and education and training of UNR physics students. The SCREAMER code was used to model the device's circuit and predicted a 200-230 kA current pulse with a rise time of 600 ns. To develop new diagnostics, a vertical focusing Hamos type spectrometer with a cylindrically bent mica crystal and a horizontal focusing Johann type spectrometer with a cylindrically bent Si crystal were designed for x-ray spectroscopy of the gas jets. Both spectrometers were tested with the NTF Leopard fs laser and captured x-ray spectra from laser interactions with Ar and Kr gas-puff jets from a supersonic nozzle. [Preview Abstract] |
Friday, October 24, 2014 3:24PM - 3:36PM |
C1.00008: Plasma Formation and Evolution on the Surface of Aluminum, Copper, Titanium and Nickel Driven by a Mega-Ampere Current Kevin Yates, Bruno Bauer, Stephan Fuelling, Vladimir Ivanov, Austin Anderson, Jeffrey Mei, Trevor Hutchinson, Thomas Awe, Rebecca Bauer An important question for both fundamental science as well as applications is what state of matter is produced when a metal conductor is pulsed by an intense current. Aluminum, copper, titanium and nickel mm-diameter rods have been driven by a 1-MA, 100-ns current pulse. The intense current produces megagauss surface magnetic fields that diffuse into the load, ohmically heating the metal to temperatures that cause multiple phase changes. Because the radius is much thicker than the skin depth, the magnetic field reaches a much higher value than around a thin-wire load. With the novel ``barbell'' load design, plasma formation in the region of interest due to contact arcing or electron avalanche is avoided, allowing for the study of ohmically heated loads. Work presented here will show first evidence of a magnetic field threshold for plasma formation in titanium, copper alloys 145 and 101, nickel alloy 200, and compare with previous work done with aluminum. Copper alloys 101 and 145, aluminum 6061, titanium grade II, and nickel alloy 200 form plasma when the surface magnetic field reaches 3.9, 3.2, 2.2, 2.2, and 2.5 megagauss, respectively. [Preview Abstract] |
Friday, October 24, 2014 3:36PM - 3:48PM |
C1.00009: Comparison of Radiative Properties of Wire Arrays and X-Pinches on the 1.7 MA Zebra Generator A. Stafford, A.S. Safronova, V.L. Kantsyrev, M.E. Weller, I. Shrestha, V.V. Shlyaptseva, A.S. Chuvatin The Zebra generator, a pulse power device, of 1 MA and 100 ns rise time was upgraded with a Load Current Multiplier (LCM) to implode wire loads at higher current of 1.7 MA. Radiative properties of two different wire load configurations, Cylindrical Wire Arrays (CWA) and X-Pinches, are considered and compared. The CWA is 6 Ni-60 wires, mostly Cu, arranged in a cylindrical pattern. The CWA has a total radiation yield of 16 kJ from a column like source including a precursor plasma column prior to the implosion of the wires. The X-pinch was composed of a Ti alloy (6{\%} Al, 4{\%} V). The total radiation yield was 19 kJ and was primarily a point like source with a higher density than the CWAs. Additionally K-shell Al radiated unexpectedly strong in X-pinches for its low percentage of the material. Plasma properties will be described using pinhole images to display the structure and spectra to estimate electron temperatures and densities. [Preview Abstract] |
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