Bulletin of the American Physical Society
2005 47th Annual Meeting of the Division of Plasma Physics
Monday–Friday, October 24–28, 2005; Denver, Colorado
Session FO1: Plasma Technology: ICF Targets, Plasma Probe, Shield and Thruster |
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Chair: Abbas Nikroo, General Atomics Room: Adam's Mark Hotel Governor's Square 10 |
Tuesday, October 25, 2005 9:30AM - 9:42AM |
FO1.00001: Overview of Target Fabrication in Support of Sandia National Laboratories Diana Schroen, Eric Breden, Joseph Florio, Joshua Gregory, Suzi Grine-Jones, Randy Holt, Wojtek Krych, Katherine Nelson, Nicole Petta, Chris Russell, Johann Seamen, Gary Smith, Justin Stolp, Jonathan Streit Sandia National Laboratories has succeeded in making its pulsed power driver, the Z machine, a valuable testbed for a great variety of experiments. These experiments include ICF, weapon physics, Equation of State and astrophysics. There are four main target types: Dynamic Hohlraum, Double Pinch Hohlraum, Fast Igniter and Equation of State. The target sizes are comparable to projected full power NIF sizes. For example capsules up to 5 mm have been fielded. This talk will give an overview of the work with the focus on the many advances in target assembly, foam target types and characterization of components and assemblies. For example, the 14 mg/cc foam with an embedded capsule (used in Dynamic Hohlraum experiments) can now be shaped or doped and its radiographic characterization has been improved for both resolution and speed of analysis. This work was funded under the auspices of the Department of Energy, Contract No. DE-AC03-01SF22260. [Preview Abstract] |
Tuesday, October 25, 2005 9:42AM - 9:54AM |
FO1.00002: Fabrication of Graded Germanium-doped CH Shells K.-C. Chen, H. Huang, A. Nikroo, S. Letts, R. Cook One of the capsule designs for achieving ignition on the National Ignition Facility (NIF) is a 2~mm diameter graded germanium-doped plastic (CH) shell with a 160~$\mu$m thick wall. The graded Ge-doped design allows a somewhat relaxed outer surface finish requirement than the original uniformly Ge-doped CH design. We produced Ge-doped shells that met nearly all the NIF design specifications using plasma-assisted polymer deposition with (CH$_3$)$_4$Ge as the doping source. The Ge concentration, layer thickness and surface smoothness were determined by quantitative contact radiography, x-ray fluorescence analysis, and atomic force microscopy. The shell has an inner 10~$\mu$m undoped CH layer, followed by 481~$\mu$m of 0.83~atom \% Ge-doped CH, 10~$\mu$m of 0.38~atom \% Ge-doped CH and then 90~$\mu$m of undoped CH, with an outer surface rms roughness of $\sim$24~nm (modes 10-1000). A few isolated surface domes about 1~$\mu$m high and 20~$\mu$m in diameter were present. [Preview Abstract] |
Tuesday, October 25, 2005 9:54AM - 10:06AM |
FO1.00003: Laser Welding Micro-Holes in Beryllium Capsules N.B. Alexander, R. Gallix, D.T. Frey, S.E. Grant In order to produce gas filled beryllium capsules for inertial confinement fusion (ICF) experiments, we are developing laser welding as a tool to seal micro-holes drilled through the capsule wall. Micro-holes of diameter 5 to 10~$\mu$m drilled through 100~micron thick cold rolled beryllium foils have been welded closed. Welds were tested to be leak tight with a helium leak detector. A windowed pressure chamber has been built to allow capsules to be welded while under a pressure of up to 30~atm. Cryocondensing fill gas into the capsules will potentially allow higher fill pressures. The current formulation of sputter-deposited beryllium used to produce capsules appears to be more susceptible to cracking than the cold-rolled beryllium foil. The progress on welding closed micro-holes in beryllium capsules made by sputter deposition will be presented. [Preview Abstract] |
Tuesday, October 25, 2005 10:06AM - 10:18AM |
FO1.00004: Measuring Dopant Concentration in Graded NIF Targets through Quantitative Contact \hbox{X-Radiography} H. Huang, R.B. Stephens, J. Gunther Doping level must be known to 0.05 atomic percent and its radial distribution to one micron for graded targets used in NIF experiments. We have developed a quantitative contact x-radiography system (x-radiograph, film digitizer, and analysis software) that can meet those conditions. Traditional x-radiograph systems (either film- or scintillator-based) contain 1)~spatial distortion errors and 2)~opacity uncertainties that are unacceptable for this case. For the first, we designed a high precision digitization system with 0.5~$\mu$m optical resolution and added a customized algorithm to remove the lens pincushion distortion and the CCD pixel size effect. For the second, we have developed a detailed film model to convert gray scale information into \hbox{x-ray} absorption strength under polychromatic radiation conditions. The model is calibrated on polypropylene flats and can measure the \hbox{x-ray} absorption (and thereby dopant level) to $\sim$10\% in each sublayers. Our measurement results on Cu-doped Be shells and Ge-doped GDP shells agrees with those from destructive techniques. [Preview Abstract] |
Tuesday, October 25, 2005 10:18AM - 10:30AM |
FO1.00005: Phase contrast radiography for dynamic plasma experiments Brian Spears, D.H. Munro, K. Twelker, M.M. Marinak, M.J. Edwards Common x-ray imaging relies on differential attenuation of x-rays by the object to produce intensity contrast in the image. Such contrast is known as absorption contrast. However, intensity contrast may be enhanced due to interference resulting from phase shifts introduced by wave propagation through the object. This is known as phase contrast. We examine the utility and feasibility of phase contrast imaging for diagnosing dynamic laser plasma experiments in support of the National Ignition Campaign. We do this using numerical simulations of phase contrast radiographs produced with PHAT, a modification of the ray trace code DRAT. PHAT takes as input data from the radiation hydrodynamics code HYDRA, and accounts for both absorption and phase effects. As specific examples, we consider plasma jets produced by indirectly driving planar beryllium foils. We also look at imploding National Ignition Facility ignition capsules. We finally discuss the influence of constraints, such as source size, target chamber geometry, and noise, on expected experimental phase contrast results. [Preview Abstract] |
Tuesday, October 25, 2005 10:30AM - 10:42AM |
FO1.00006: Phase-contrast imaging and femtosecond stroboscopy with an ultrafast laser-based hard x-ray source J.C. Kieffer, R. Toth, A. Krol, S. Fourmaux, J.L. Bourgade We investigated performance of ultrafast laser-based x-ray source for phase contrast imaging in 2D projection imaging and in enhanced micro-CT imaging. Good quality images were obtained in the single energy and multiple energy, \textit{in line} phase-contrast enhancing geometry using x-ray line energy matching object thickness and density. Phase information has been inferred from images obtained at the same x-ray energy but at different object-to-detector distances and also from images obtained at the same object-to-detector distance but with different K-alpha line energies. We demonstrated that ultrafast laser-based, compact, x-ray source is a promising technique for micro-CT system, allowing practical implementation of dual-energy and phase-contrast imaging micro-CT that is not possible with conventional micro-CT. In addition, by carefully controlling the excitation conditions and the target design, it is possible to generate K-alpha radiation pulses with a few hundreds of femtosecond in duration. Thus it becomes possible to combine phase contrast imaging and femtosecond time scale with a femtosecond phase-contrast stroboscopy technique based on ultrafast laser produced K-alpha radiation flash. This laser-based technique could open new opportunity for ICF diagnostics (target control, femtosecond and picosecond imaging of hydro-instability dynamics, shock wave propagation etc..). [Preview Abstract] |
Tuesday, October 25, 2005 10:42AM - 10:54AM |
FO1.00007: Calibration of the Cryogenic Target Optical Shadowgraphic Characterization System at LLE D.H. Edgell, R.S. Craxton, L.M. Elasky, D.R. Harding, L.S. Iwan, R.L. Keck, L.D. Lund, S.J. Verbridge, M.D. Wittman, W. Seka Reflection and refraction of light by a cryogenic target produce rings on a shadowgraph image that characterize the ice surface position. Many different views give a 3-D ice-layer representation and the global ice-layer roughness. Calibration of the image resolution and accuracy is needed to measure the 1-\textit{$\mu $}m rms ice layers required for ignition. The position of the outer edge and bright ring can be resolved to $\sim $0.1-pixel rms (just over 0.1 \textit{$\mu $}m) in LLE shadowgraphs. Pincushion distortion because of lens aberration can add a several tenths of a micron $n$ = 2 artifact to the measurements. Using precision patterns to align the system minimizes the optical distortion and characterizes it for image correction. Comparison between shadowgraphic and high-precision atomic force microscopy 3-D characterizations of a sapphire sphere shows the accuracy of the 3-D analysis. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC52-92SF19460. [Preview Abstract] |
Tuesday, October 25, 2005 10:54AM - 11:06AM |
FO1.00008: Neutron Time-of-Flight Detectors Based on Vacuum Photodiodes for the NIF and LMJ V.Yu. Glebov, T.C. Sangster, C. Stoeckl, S. Roberts, M.J. Moran, B. Davis A traditional neutron time-of-flight (nTOF) detector uses a scintillator coupled with a fast photomultiplier tube with gains from 10$^{3}$ to 10$^{6}$. The high neutron yields that will be produced at the NIF and LMJ make the use of vacuum photodiodes with a gain of 1 in the nTOF detectors possible. The advantages of vacuum photodiodes are that they are insensitive to hard x-ray and gamma-ray backgrounds and that they a have a very large dynamic range. The sensitivities and time responses of PDD-99 and PD040 vacuum photodiodes were measured in DT and DD implosions on the 60-beam OMEGA Laser System. The sensitivities of the detectors to hard x rays, gammas, and EMP noise were studied. The implementation of the nTOF detectors based on vacuum photodiodes on the NIF will be discussed. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC52-92SF19460. [Preview Abstract] |
Tuesday, October 25, 2005 11:06AM - 11:18AM |
FO1.00009: Radially-Resolved Measurements of the Effect of Boundary Walls in Radiation Transport Experiments C.A. Back, O.A. Hurricane, J.H. Hammer, J.I. Castor, S.A. Maclaren, O.L. Landen, M.D. Rosen We have performed high-powered laser experiment to investigate the effect of the boundary wall of finite mm-sized samples on the propagation of a Marshak wave. We present radially-resolved emission measurements of a Ta$_2$O$_5$ aerogel heated from the opposite side by x-ray drive created by a halfraum. The experiments are performed on the Omega laser and data are obtained by a 1D streaked spectrometer which records photon energies of 550~eV. It complements work presented previously in which we measured the propagation of a diffusive supersonic Marshak wave in different length samples [1]. Here we give details of the measurements and the effects of boundary conditions of finite samples. Data will be compared from a high-Z Au boundary versus a low-Z Be cylindrical and discussed with respect to an analytic model that takes into account the albedo of the boundary wall. [Preview Abstract] |
Tuesday, October 25, 2005 11:18AM - 11:30AM |
FO1.00010: Evaluation of liquid Sn as a plasma-facing component: Sputtering yield measurements Matthew Coventry, David Ruzic Flowing liquid metal surfaces are being considered for divertor or first wall use as PFC's in reactor-level magnetic fusion machines primarily to obviate the need for periodic PFC replacement due to erosion. The use of Sn allows a high operating temperature due to its low vapor pressure and a liquid Sn divertor or first-wall looks promising from an erosion/redeposition standpoint if its self-sputtering yields do not strongly increase with temperature. Sn has exhibited temperature enhancement sputtering under low energy light ion beam bombardment, but not with heavy ions for the same energies and up to 380$^{o}$C. The Ion-surface InterAction eXperiment (IIAX) has recently been upgraded for high target temperature ($>$ 1000$^{o}$C) operation and has been used to measure the sputtering yield of liquid Sn under low energy ion beams at 45$^{o}$ incidence. The sputtering yields are measured using a monoenergetic ion beam to bombard the target and dual quartz-crystal microbalances (QCM's) to directly monitor the amount of sputtered material. The yields and effect on the overall operating temperature limit are discussed. [Preview Abstract] |
Tuesday, October 25, 2005 11:30AM - 11:42AM |
FO1.00011: Development of an energetic plasma source for simulating edge localized mode plasma interactions with first wall and diverter materials David Ruzic, Travis Gray, Benjamin Masters Edge Localized Modes (ELMs) pose a significant problem to current and future fusion reactors. One concern in a device such as ITER is that ELMs may be the limiting factor for successful operation. ITER ELMs are predicted to impart between 1 -- 10 MJ/m$^{2}$ onto the divertor surface and first wall of the reactor. This may lead to significant erosion of the divertors and possible melting. The ELM Simulating Plasma gun (ESP-gun) in operation at UIUC is intended to produce plasmas similar to those found in TOKAMAK ELM events. ESP-gun operates with several small pulse forming networks (PFN) that are sequentially triggered to produce a ringing, under-damped current waveform with peak currents in excess of 50 kA. Each PFN is connected to the conical theta pinch to produce high T$_{e}$, high n$_{e}$ plasmas similar to ELM events. A Triple Langmuir Probe (TLP) diagnoses and measures the quality of the plasmas produced by the ESP-gun. To date, an n$_{e}$ of 1(10)$^{19}$/m$^{3}$ and greater with a T$_{e}$ greater than 50 eV in the target area have been measured. From these measurements, plasma energies can be calculated. Axial magnetic field measurements during the theta pinch at the location of the coil and at a downstream target are accomplished. [Preview Abstract] |
Tuesday, October 25, 2005 11:42AM - 11:54AM |
FO1.00012: Using Laser Deflection Diagnostics to Profile Densities of Accelerated SCTs on CTIX Samuel Brockington, David Hwang, Robert Horton, Russell Evans, Stephen Howard Having demonstrated laser deflection as a valid technique for obtaining plasma density profiles of Spheromak-like Compact Toroids (SCTs) [1], we have made modifications to increase the reliability and repeatability of the deflection diagnostic so larger data sets can be obtained to produce good statistics. Primarily, improvements to the photodiode preamplifier design were made to make laser photon statistics the limiting source of noise. A deflection assembly was used to measure plasma density profiles of SCTs of different peak densities created by CTIX. By assuming a density profile for a SCT, plasma peak densities proportional to laser deflection angles were calculated and compared to heterodyne interferometer measurements at the same location. Values from interferometry and deflectometry for different density SCTs will be compared, as a well as peak densities from both axial and radial deflection. By measuring both the radial and axial defection, the assumed SCT density profile can be checked. \newline [1] Brockington, S. et al, ``Plasma Density Gradient Measurement Using Laser Deflection,'' Review of Scientific Instruments 76, 1 (2005) [Preview Abstract] |
Tuesday, October 25, 2005 11:54AM - 12:06PM |
FO1.00013: Plasma Shield Ady Hershcovitch The Plasma Shield is a vortex-stabilized arc that is employed to shield beams and workpiece area of interaction from atmospheric or liquid environment. A vortex-stabilized arc is established between a beam generating device (laser, ion or electron gun) and the target object. The arc, which is composed of a pure noble gas (chemically inert), engulfs the interaction region and generates an outward flow, thus, shielding it from any surrounding liquids (water) or atmospheric gases. The vortex is composed of a sacrificial gas or liquid that swirls around and stabilizes the arc. In current art, many industrial processes that involve ion and electron beams like, dry etching, micro-fabrication, machining, welding and melting are performed exclusively in vacuum, since guns, and accelerators must be kept at a reasonably high vacuum, and since chemical interactions with atmospheric gases adversely affect various processes. Various processes involving electron ion and laser beams can, with the Plasma Shield be performed in practically any environment (under water). It should allow for in situ repair of ship and nuclear reactor components, as well as in-air ion implantation of semiconductors. The plasma shield results in both thermal (since the plasma is hotter than the environment) and chemical shielding. The latter feature brings about in-vacuum process purity out of vacuum, and the thermal shielding aspect results in higher production rates. Experimental results will be presented. *Plasma Shield/Work supported by Acceleron, Inc., Connecticut Light \& Power Co., US DOE funding under a NICE3 grant DE-FG41-01R110925, and Connecticut DEP. [Preview Abstract] |
Tuesday, October 25, 2005 12:06PM - 12:18PM |
FO1.00014: Double layer and thrust Amnon Fruchtman It is shown that the net momentum delivered by the possibly large electric fields inside a double layer is zero. The total particle momentum is the same while the momentum partitioning between the various species is different on both sides of the layer. The momentum balance is demonstrated schematically for the double layer at the boundary of the ionosphere and the aurora. Implications for plasma accelerators are discussed, in particular for the recently observed acceleration to supersonic velocities by a double layer at the exit of a helicon source $^{1}$. It is shown that a double layer can be formed by both area expansion $^{2}$ and neutral density decay$^{3}$. The plasma acceleration is shown to be a result of an efficient conversion of plasma pressure to thrust. \begin{enumerate} \item C. Charles and R. Boswell, Appl. Phys. Lett. \textbf{82}, 1356 (2003); S. A. Cohen \textit{et al.}, Phys. Plasmas \textbf{10}, 2593 (2003). \item W. M. Manheimer, IEEE Trans. Plasma Sci. \textbf{29}. 75 (2001). \item A. Meige \textit{et al.}, Phys. Plasma \textbf{12}, 052317 (2005). \end{enumerate} [Preview Abstract] |
Tuesday, October 25, 2005 12:18PM - 12:30PM |
FO1.00015: History of improvements in single-pass ICRH ion acceleration in the VASIMR engine Edgar Bering, Leonard Cassady, Michael Brukardt, Franklin Chang-Diaz, Jared Squire, Timothy Glover, Alfonso Tarditi, Verlin Jacobson, Greg McCaskill, Roger D. Bengtson The Variable Specific Impulse Magnetoplasma Rocket (VASIMR) is a high power magnetoplasma rocket, capable of Isp/thrust modulation at constant power. The plasma is produced by helicon discharge. The bulk of the energy is added by ion cyclotron resonance heating (ICRH.) Axial momentum is obtained by adiabatic expansion of the plasma in a magnetic nozzle. Thrust/specific impulse ratio control in the VASIMR is primarily achieved by the partitioning of the RF power to the helicon and ICRH systems, with the proper adjustment of the propellant flow. Ion dynamics in the exhaust were studied using probes, gridded energy analyzers (RPA's), microwave interferometry and optical techniques. This paper will review 3 years of single-pass ICRH ion acceleration data. During this interval, the available power to the helicon ionization stage has increased from 3 to 20 kW. The increased plasma density has produced increased plasma loading of the ICRH antenna and isignificant improvements in antenna coupling efficiency and in ion heating efficiency. [Preview Abstract] |
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