Bulletin of the American Physical Society
51st Annual Meeting of the APS Division of Plasma Physics
Volume 54, Number 15
Monday–Friday, November 2–6, 2009; Atlanta, Georgia
Session NP8: Poster Session V: Electron and Ion Beams and Radiation Generation; Low Temperature Plasmas; Pinches, Equations of State, and Simulations; Edge |
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Room: Grand Hall East |
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NP8.00001: ELECTRON AND ION BEAMS AND RADIATION GENERATION |
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NP8.00002: Results of the upgraded Neutralized Drift Compression Experiment Steven M. Lidia, F.M. Bieniosek, E.P. Gilson, P.K. Roy, P. Ni, P.A. Seidl, K. van den Bogert, W.L. Waldron Recent changes to the NDCX beamline offer the promise of higher current compressed bunches, with correspondingly greater fluence delivered to the target plane for ion-beam driven warm dense matter experiments. We report modeling and commissioning results of the upgraded NDCX beamline that includes a new induction bunching module with approximately twice the volt-seconds and greater tuning flexibility, combined with a longer neutralized drift compression channel. [Preview Abstract] |
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NP8.00003: Simultaneous induction acceleration and bunching in the Neutralized Drift Compression Experiment Peter Seidl, G. Bazouin, S.M. Lidia, P.K. Roy, W.L. Waldron The Neutralized Drift Compression Experiment uses a ramped, bipolar induction module waveform to compress the beam to nanosecond bunches for the study of warm dense matter (WDM). We have recently explored beam dynamics and possible beamline modifications required to simultaneously compress and accelerate the beam using a unipolar waveform. This has the advantage of a higher energy deposition in the target, and mimics beam manipulations in next-generation ion accelerators for WDM experiments. We report modeling and experimental results of this beam manipulation on the NDCX beamline with the new induction bunching module with approximately twice the volt-seconds. [Preview Abstract] |
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NP8.00004: Design Studies for the induction cells for NDCX-II J.W. Kwan, A. Faltens, J.Y. Jung, E.P. Lee, M. Leitner, B.G. Logan, W.L. Waldron, A. Friedman The Heavy Ion Fusion Science Virtual National Lab is funded to build NDCX-II, at LBNL for high energy density (warm dense matter) and IFE target physics research. The goal is to produce Li+ ion beam with pulse length $\sim $1 ns, energy $\sim $3 MeV, beam charge per pulse $\sim $20 nC, and rep rate $\sim $0.02 Hz. The linac will reuse induction cells and Blumleins from the decommissioned Advanced Test Accelerator (ATA) at Lawrence Livermore National Laboratory. Among other changes, the original dc solenoid magnets will be replaced with new 2-3 T pulsed solenoids. The machine will have about 30 cells, a neutralized drift compression section, and a final focusing solenoid (8 T) followed by a target chamber. The total length of the machine will be about 15 m. One critical need is to avoid premature saturation of the induction cores due to the stray field generated by the pulsed solenoids. Another issue is beam steering due to misalignment of the magnetic axis. Testing of a prototype cell will be done to characterize the pulsed power and magnetic performance. These results will be presented in the meeting. [Preview Abstract] |
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NP8.00005: Multi-Meter-Long Plasma Source for Heavy Ion Beam Charge Neutralization P.C. Efthimion, E.P. Gilson, R.C. Davidson, B.G. Logan, P.A. Seidl, W. Waldron Plasmas are a source of unbound electrons for neutralizing heavy ion beams to focus their radial and compress their axial dimensions to achieve high intensity beams for warm dense matter experiments. Long metal plasma columns are produced by the ferroelectric ceramic, BaTiO$_{3}$. The drift tube inner surface of the Neutralized Drift Compression Experiment (NDCX) is covered with ceramic material. High voltage ($\sim $ 8 kV) is applied across the ceramics. A BaTiO$_{3}$ source comprised of five 20-cm-long sources produced uniform plasma in the 5x10$^{10}$ cm$^{-3}$ density range and was used to achieve high beam compression ratios on NDCX. The source was extended to 2 meters and resulted in the heavy ion beam density increasing from 2x10$^{8}$ to 7x10$^{11}$ cm$^{-3}$ and reducing the spot size to 1.5 mm. Present research is developing higher density sources by examining smaller diameter ferroelectric sources and flashboard circuits. A ferroelectric source of 2.9 cm ID achieved densities of 6x10$^{11}$ cm$^{-3}$. Flashboards have the potential to achieve densities approaching 10$^{13}$ cm$^{-3}$. [Preview Abstract] |
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NP8.00006: Collective Instabilities and Beam-Plasma Interactions for an Intense Ion Beam Propagating Through Background Plasma Ronald Davidson, Mikhail Dorf, Igor Kaganovich, Hong Qin, Edward Startsev This paper presents a survey of the present theoretical understanding based on advanced analytical and numerical studies of collective interactions and instabilities for intense one-component ion beams, and for intense ion beams propagating through background plasma. The topics include: discussion of the condition for quiescent beam propagation over long distances; the electrostatic Harris instability and the transverse electromagnetic Weibel instability in highly anisotropic, one-component ion beams; and the dipole-mode, electron-ion two-stream instability (electron cloud instability) driven by an unwanted component of background electrons. For an intense ion beam propagating through a charge-neutralizing background plasma, the topics include: the electrostatic electron-ion two-stream instability; the multispecies electromagnetic Weibel instability; and the effects of a velocity tilt on reducing two-stream instability growth rates. Operating regimes are identified where the possible deleterious effects of collective processes on beam quality are minimized. [Preview Abstract] |
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NP8.00007: Collective Focusing of a Plasma-Neutralized Intense Ion Beam Propagating Along a Weak Solenoidal Magnetic Field Mikhail A. Dorf, Igor D. Kaganovich, Edward A. Startsev, Ronald C. Davidson Two schemes are considered for focusing intense ion beams utilizing the collective dynamics of plasma electrons. In the first approach, an ion beam propagates through a neutralizing background plasma along a uniform magnetic field. In the second approach, an ion beam passes through a finite size plasma, extracts neutralizing electrons from the plasma, and then enters a magnetic lens. In the both cases, a strong radial electric field is produced due to the collective electron dynamics. This self-electric field provides the enhanced transverse focusing of the ion beam. Detailed analytical and advanced numerical studies using particle-in-cell simulations are performed for both approaches. The radial focusing force acting on beam ions is calculated for an arbitrary ratio between the electron cyclotron and plasma frequencies. Collective focusing effects are shown to be important for the design of heavy ion drivers for high energy density and warm dense matter physics applications. [Preview Abstract] |
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NP8.00008: Approximate matched solution of an intense charged particle beam propagating through periodic quadrupole focusing lattice E. Startsev, R. Davidson, M. Dorf The transverse dynamics of an intense charged particle beam propagating through a periodic quadrupole focusing lattice is described by the nonlinear Vlasov-Maxwell system of equations, where the propagating distance plays the role of time. To find matched-beam quasi-equilibrium distribution functions one needs to determine a dynamical invariant for the beam particles moving in the combined applied and self-generated fields. In this paper, we present a perturbative Hamiltonian transformation method which is an expansion in the particle's vacuum phase advance $\epsilon=\sigma_v/2\pi$, treated as a small parameter, which is used to transform away the fast particle oscillations and obtain the average Hamiltonian accurate to order $\epsilon^3$. The average Hamiltonian is an approximate invariant of the original system, and can be used to determine self-consistent beam equilibria that are matched to the focusing channel. In the third-order, the average self-field acquires a octupole component which results in the average motion of some beam particles being non-integrable and their trajectories chaotic. This chaotic behavior of the beam particles may significantly change the nature of the Landau damping (or growth) of collective excitations supported by the beam. [Preview Abstract] |
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NP8.00009: Generalized Courant-Snyder theory and Kapchinskij-Vladimirskij distribution for high intensity beams in coupled transverse focusing lattices Hong Qin, Ronald Davidson, Moses Chung Courant-Snyder (CS) theory for uncoupled transverse dynamics of charged particles is generalized to the case of coupled transverse dynamics with two degree of freedom. The generalized theory has the same structure as the original CS theory for one degree of freedom. The four basic components of the original CS theory, i.e., the envelope equation, phase advance, transfer matrix, and the CS invariant, all have their counterparts, with remarkably similarity, in the generalized theory. The envelope function is generalized into an envelope matrix, and the envelope equation becomes a matrix envelope equation with matrix operations that are non-commutative The generalized theory gives a new parameterization of the 4D symplectic transfer matrix that has the same structure as the parameterization of the 2D symplectic transfer matrix in the original CS theory. For high intensity beams, the generalized Courant-Snyder theory is applied to discover a generalized Kapchinskij-Vladimirskij distribution for high-intensity beams in coupled focusing lattices. This self-consistent distribution, which solves the nonlinear Vlasov-Maxwell equations, is 4D ellipsoid in the phase space. A set of envelope equations are derived to describe the dynamics of the phase space ellipsoid. [Preview Abstract] |
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NP8.00010: Relativistic Electron Beam Propagation in the Presence of Plasma Electron-Ion Collisions Carl Siemon, Vladimir Khudik, Gennady Shvets The physics of relativistic electron beam propagation through a collisional background plasma and electromagnetic Weibel Instability is described. A reduced hybrid approach treats the beam electrons as macro-particles, plasma electrons as a fluid, and assumes stationary plasma ions. This treatment, along with the assumption of quasi-neutrality, provides a simplified, computationally efficient framework for solving this system. Collisional simulation results are presented, which sharply contrast collisionless dynamics in several areas. One striking feature of these simulations is the enhancement of beam stopping. The most obvious mechanism for this effect is a persistent stopping electric force along the propagation direction. During the merging of filaments, the coupling of Weibel Instability with collisions leads to beam deflection in addition to electric stopping, slowing the beam down further. This coupling occurs because of increased magnetic field strength due to enhanced current imbalance from collisions. The increased field strength decreases filament merging time, thus augmenting transverse thermalization, which occurs when filaments merge. Transverse thermalization results in a loss of beam momentum in the propagation direction. Other interesting phenomena present in collisional simulations include the reversal of the return current direction in selected regions. [Preview Abstract] |
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NP8.00011: Halo characterization of mismatched beams using the theory of violent relaxation Renato Pakter, Yan Levin, Tarcisio N. Teles Relaxation to a final stationary state of particles interacting through long-range forces, such as Coulomb, is intrinsically different than that of systems with short-range interactions. While in the latter case it is known that the interparticle collisions drive the system to an equilibrium Maxwell-Boltzmann distribution, in the former case, the collision duration time diverges and the state of thermodynamic equilibrium is never reached. In this paper, we extend previous results on the relaxation of initially rms mismatched beams,\footnote{Y. Levin, R. Pakter, T.N. Teles, Phys. Rev. Lett., {\bf 100}, 040604 (2008).} by taking into consideration more general initial beam distributions. We also present results on the beam relaxation and halo formation based on an approximation of the theory that allows simpler analytic expressions for the final stationary state [Preview Abstract] |
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NP8.00012: The controlling role of envelope mismatches in intense inhomogeneous charged beams Felipe Rizzato, Everton Souza, Antonio Endler, Renato Pakter, Roger Nunes Inhomogeneous cold beams undergo wave breaking as they move along the axis of a magnetically focusing system. All the remaining control parameters fixed, the earliest wave breaking is a sensitive function of the inhomogeneity parameter: the largest the inhomogeneity, the soonest the breaking The present work analyzes the role of the envelope size mismatches in the wave breaking process. The analysis reveals that the wave breaking time is also very susceptible to the mismatch. As mismatched and matched beams are compared, one finds out that judiciously chosen mismatches can largely extend the beam lifetimes. The work is extended to include some recently discussed issues: the presences of fast and slow regimes of wave breaking regimes are identified, and the role of thermal velocity distributions in space-charge dominated beams. In all instances, the theory is shown to be accurate against simulations. [Preview Abstract] |
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NP8.00013: Vlasov analysis of relaxation of intense inhomogeneous charged beams Antonio Endler, Everton Souza, Roger Nunes, Renato Pakter, Felipe Rizzato This work analyzes the dynamics of inhomogeneous, magnetically focused high intensity beams of charged particles. Initial inhomogeneities lead to density waves propagating transversely in the beam core, and the presence of transverse waves eventually results in particle scattering. Particle scattering off waves in the beam core ultimately generates a halo of particles with concomitant emittance growth. Emittance growth indicates a beam relaxing to its final stationary state, and the purpose of the present paper is to describe halo and emittance in terms of the Vlasov equation. [Preview Abstract] |
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NP8.00014: Effect of Accelerator Impedance on Electron Cloud Instability Brian Allen, Patric Muggli, Wolfram Fischer, Michael Blaskiewicz, Thomas Katsouleas Interaction between a beam and electron clouds (e-cloud) present in circular accelerators is known to limit accelerator performances through instabilities, beam loss, beam-blowup, and the resulting reduced luminosity. The RHIC beam is most susceptible to instabilities as it crosses energy transition ($\gamma _{t}$=22.9) and it is posited that ring impedance could play a role in the development of instabilities during this transition. We use the quasi-static particle in cell code QuickPIC to describe the interaction between the RHIC Au beam and the electron cloud. In QuickPIC the electron cloud density is uniform around the ring and the beam has a constant beta function given by the accelerator circumference and the beam tune. We incorporate in the current QuickPIC version the ring impedance for a circular accelerator and we take a first look at the effect this impedance has on the beam and e-cloud interaction for typical RHIC parameters. [Preview Abstract] |
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NP8.00015: Dispersion characteristics of space-charge waves on elliptic electron beams Kathleen Geyer, Andrew Brainerd, Chiping Chen A small-signal theory of space-charge waves on a relativistic elliptic electron beam has been developed recently [A. E. Brainerd, C. Chen and J. Zhou, J. Appl. Phys., in press (2009)]. This paper discusses results of a comprehensive parametric study of dispersion characteristics of space-charge waves on such beams over a wide range of the parameter space, using the MIT Elliptic Beam Small Signal (EBSS) code. Applications of the theory in elliptic-beam klystrons are discussed. Implications of the space-charge wave theory are discussed in the research and development of elliptic- or sheet-beam klystrons. [Preview Abstract] |
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NP8.00016: Charged-Particle Dynamics in an Adiabatic Thermal Beam Equilibrium Haofei Wei, Chiping Chen The dynamics of charged particles in a recently-discovered adiabatic thermal beam equilibrium [J. Zhou, K.R. Samokhvalova and C. Chen, Phys. Plasmas \textbf{15, }023102 (2008)] are studied. In particular, test particle motion is analyzed numerically, assuming the beam equilibrium fields in a periodic solenoidal focusing channel. Poincare surface-of-section maps are generated to examine the behavior of the test particles in phase space such as nonlinear resonances and chaotic regions. Comparisons are made between the adiabatic thermal and rigid-rotor Vlasov beam equilibria [C. Chen, R. Pakter and R. C. Davidson, Phys. Rev. Lett. \textbf{79}, 225 (1997)]. [Preview Abstract] |
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NP8.00017: Piezoelectric Transformer Accelerator Systems for Neutron Interrogation Emily Baxter, Scott Kovaleski, Andrew Benwell, Tongtawee Wacharasindhu, Jae Kwon The detection of nuclear materials such as highly enriched uranium has become increasingly important. The University of Missouri is developing a compact accelerator system for active neutron interrogation using a piezoelectric transformer with an ion diode for neutron production. The piezoelectric high voltage generator is composed of a rotated y-cut bar of lithium niobate and will ultimately be used to accelerate deuterium ions. When driven near resonance the device is capable of yielding very high voltages. The ion source will be attached to an electrode on a piezoelectric transformer for subsequent ion acceleration. A number of ion sources are being studied, and relative merits of each will be presented, along with piezoelectric transformer performance results. [Preview Abstract] |
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NP8.00018: Electron Beam Coupling to Electrical Metamaterial Structures Don Shiffler, John Luginsland, Jack Watrous, David French, Y.Y. Lau Many authors over many decades have considered the coupling of electron beams to various microwave structures. These structures range from slow wave structures, such as traveling wave tubes, to dielectrics, such as the dielectric Cherenkov maser. In this presentation, we consider the coupling of relativistic electron beams to electronic metamaterials. We consider cylindrical and planar geometries and treat the electron beam as a cold, non-neutral plasma confined by an infinite magnetic field, confining motion of the electrons to the axial direction. We treat the metamaterial, which loads the cylindrical waveguide along its outer wall, using effective medium theory, considering cases of double positive, single positive, and double negative dielectrics. The presentation begins with a review of the cold structure characteristics in the absence of an electron beam and then moves to consider the coupling of the electron beam to the metamaterial. In particular we study the dispersion and small signal growth rate of this system, the frequency range of applicability, and the power handling potential of such structures. . [Preview Abstract] |
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NP8.00019: RF power loss and electric and magnetic field enhancements due to surface roughness Peng Zhang, Yue Ying Lau, Ronald Gilgenbach Surface roughness plays an important role in a cavity or slow wave structure. It may cause enhanced RF power absorption. Excessive local electric field enhancement may trigger RF breakdown. In a superconducting cavity, local magnetic field enhancement due to surface roughness may lead to rapid loss of superconductivity. In this work, we analytically compute the power absorption due to a hemispherical protrusion with arbitrary values of $\varepsilon $, $\mu $ and $\sigma $ on a metallic surface. Scaling laws are derived [1]. The local field enhancement factors of both electric and magnetic field on the protrusion are also calculated analytically, and spot-checked against a Maxwell-3D code [1]. The protrusion may represent a foreign object, or is made of the same material as the conducting surface, since its $\varepsilon $, $\mu $ and $\sigma $ may take on arbitrary values. \\[4pt] [1] P. Zhang \textit{et al.}, J. Appl. Phys. \textbf{105}, 114908 (2009). [Preview Abstract] |
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NP8.00020: Experiments and Simulations on a Discrete Element Nonlinear Transmission Line David French, Don Shiffler, John Luginsland, Ronald Gilgenbach, Y.Y. Lau Nonlinear transmission lines have been demonstrated to be an effective technique for generating high power ultrawideband or mesoband radiation without the need for a vacuum system, electron beam, or magnet. Preliminary experiments have been performed at AFRL and UM on a discrete element nonlinear transmission line with nonlinear capacitance. Depending on the injected pulse, either pulse sharpening or RF generation could be observed. The differences between these two cases and the threshold for RF generation will be discussed. Time frequency analysis has been applied to analyze the generated RF spectrum. These effects were reproduced in circuit simulations. Results from these preliminary experiments and plans for future high power nonlinear transmission line experiments using LTD technology at UM will be presented. [Preview Abstract] |
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NP8.00021: Metal-Dielectric Washer Cathode for Relativistic Magnetron Plasma, Pulsed Power and Microwave Lab, University of Michigan, Ann Arbor, MI 48109-2104 Matthew Franzi, Ronald Gilgenbach, Brad Hoff, Y.Y. Lau, Ed Cruz The UM/L-3 relativistic magnetron operates at -300 kV, 2-10 kA, for durations of up to 1 microsecond and generates microwave pulses of 100's MW output power at 1 GHz for 100's ns. Recent research with the magnetron has focused on the exploitation of electrical triple points on the cathode to generate electron avalanching. This Metal-Dielectric Washer (MDW) cathode consists of alternating washers of OFHC-Cu and BN, which vary in radius for each tested triple point configuration. The MDW cathode exhibits high current and fast turn on times and does not degrade under magnetron operating conditions. Initial experimental results of the MDW cathode on the magnetron have shown electron emission currents up to 4 kA and microwave power between 100-200 MW. Experiments will be compared to simulation results. [1] N.M. Jordan, R.M. Gilgenbach, B.W. Hoff, and Y.Y. Lau, Rev. Sci. Inst. \underline {79,} 064705 (2008) [2] N. M. Jordan, Y. Y. Lau, D. M. French, R. M. Gilgenbach, and P. Pengvanich,, J. Appl. Phys. \underline {102}, 033301 (2007) [Preview Abstract] |
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NP8.00022: Buneman-Hartree Condition Re-Visited Y.Y. Lau, W. Tang, B. Hoff, R. Gilgenbach, J. Luginsland, K. Cartwright The Buneman-Hartree condition (BHC) is re-examined in a cylindrical, smooth-bore, relativistic magnetron using both the conventional, single particle model, and the Brillouin flow model. These two models yield the same result for the BHC only in the limit of a planar magnetron. When b/a = 1.3, where a is the cathode radius and b ($>$ a) is the anode radius, the difference in BHC for the two models is significant. When b/a = 4, this difference becomes unexpectedly large. Such a difference is always present, whether the gap voltage is relativistic or not. These results are quantified for b/a $>>$ 1 using Davidson's model [1], conveniently cast in terms of the normalized gap voltage and normalized magnetic flux imposed on the cylindrical magnetron. This work is supported by AFOSR, AFRL, L-3, and Northrop-Grumman. \\[4pt] [1] R. C. Davidson, Prco. SPIE 1061, p. 186 (1989). [Preview Abstract] |
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NP8.00023: Experimental Verification of Peer-to-Peer Magnetron Locking Edward Cruz, Ron Gilgenbach, Yue Lau, Brad Hoff, Phongphaeth Pengvanich Injection locking of conventional magnetrons, and other types of oscillators, employing a master-to-slave configuration has been studied theoretically and experimentally [1,2]. We have recently derived the condition for peer-to-peer locking of two conventional magnetrons [3]. This condition reduces to Adler's classical locking condition (master-to-slave) if the coupling is one way. Dependent on the coupling, the frequency of oscillation when locking occurs does not necessarily lie between the free running frequencies of the two isolated, stand-alone magnetrons. Likewise, when the locking condition is violated, the beat frequency is not necessarily equal to the difference between these free running frequencies. These features were revealed in our recent experiments on the peer-to-peer locking of two 1-kW magnetrons. The necessary condition under which the two magnetrons may be locked to a common frequency is also experimentally verified.\\[4pt] [1] P. Pengvanich et al., J. Appl. Phys. 98, 114903 (2005).\\[0pt] [2] V. B. Neculaes, Ph.D. Dissertation, U. Michigan, Ann Arbor, MI (2005).\\[0pt] [3] P. Pengvanich et al., Phys. Plasmas 15, 103104 (2008). [Preview Abstract] |
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NP8.00024: Effect of Cathode Alignment on Magnetron Operation Sarita Prasad, Marvin Roybal, C. Jerald Buchenauer, Kenneth Prestwich, Mikhail Fuks, Edl Schamiloglu Recently, relativistic magnetron experiments were conducted at the University of New Mexico (UNM) to demonstrate the effect of using a transparent cathode on magnetron operation. We fabricated an A6 magnetron at UNM and during the procedure the magnetron got distorted and the result is a slightly elliptical cross-section magnetron. Consequently, the anode-cathode (AK) gap is not uniform. Magnetron operation is known to be sensitive to RF field distribution in the interaction region, which in turn is sensitive to the AK gap. Despite the asymmetry the transparent cathode was still capable of showing overall improvement in magnetron operation, i.e. faster start of microwave oscillations, higher output powers and single mode operation over a wide range of magnetic field. Interestingly, the magnetron operated in the $\pi $-mode instead of the expected 2$\pi $-mode. The solid cathode on the other hand showed mode competition and produced very low output powers. The elliptical magnetron geometry was studied using the 3-dimensional particle-in-cell code MAGIC in order to explain the experimental results. [Preview Abstract] |
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NP8.00025: Study of a Simple Gyrotron System Meixuan Shi, Harold Weitzner This study surveys a typical coupled equations of the gyrotron system. A hypothetic non-constant media is proposed in order to study different parameter regions of the system. Instead of linearizing the equations, an asymptotic analysis is performed directly onto the Maxwell equation to get the asymptotic waveforms. Results of the linearized equations are recovered at faraway from the transition regions. In two transition regions, one for cut-off, one for resonance, connections forms are obtained. Conditions of getting high amplitude outgoing waves are achieved by substituting the asymptotic waveform back to the momentum distribution equation. [Preview Abstract] |
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NP8.00026: Testing of an Advanced Internal Mode Converter for a 1.5 MW, 110 GHz Gyrotron D.S. Tax, I. Mastovsky, J. Neilson, M.A. Shapiro, J.R. Sirigiri, R.J. Temkin, A.C. Torrezan Megawatt gyrotrons are under development for the electron cyclotron heating (ECH) of plasmas, including ITER. To optimize the efficiency of gyrotrons and of the transmission lines, the internal mode converter (IMC) should output a perfect Gaussian beam. The TE$_{22,6 }$110 GHz IMC we have implemented consists of a helically-cut launcher and three smooth curved mirrors. The theoretically predicted output beam has waist W$_{z}$ = W$_{x}$ = 2.9 cm at the gyrotron window. Cold test measurements using a VNA and a 3-axis scanner were in good agreement with theory with measured beam waists W$_{z}$ = 2.9 cm and W$_{x}$ = 2.7 cm. We also installed the IMC in a 110 GHz, 1.5 MW, 3 $\mu $s pulsed gyrotron and measured the field pattern with over 40 dB signal to noise accuracy using an rf diode on a 2-axis scanner. Measured beam waists W$_{z}$ = 4.8 cm and W$_{x}$ = 4.2 cm compared well with theoretical waists W$_{z}$ = W$_{x}$ = 4.7 cm at a plane 124 cm from the gyrotron window. [Preview Abstract] |
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NP8.00027: Precision 0.5 GW X-band rf system for advanced Compton scattering source T.S. Chu, G. Anderson, D. Gibson, F.V. Hartemann, C.P.J. Barty, A. Vlieks, S. Tantawi, E. Jongewaard, S.G. Anderson A Mono-Energetic Gamma-Ray (MEGa-Ray) Compton scattering light source is being developed at LLNL. The electron beam for the Compton scattering interaction will be generated by a X-band RF gun and a X-band LINAC at the frequency of 11.424 GHz. High power RF in excess of 500 MW is needed to accelerate the electrons to energy of 250 MeV or greater for the interaction. Two high power klystron amplifiers, each capable of generating 50 MW, 1.5 msec pulses, will be the main high power RF sources for the system. These klystrons will be powered by state of the art solid-state high voltage modulators. A RF pulse compressor, similar to the SLED II pulse compressor, will compress the klystron output pulse with a power gain factor of five. This will give us 500 MW (0.5 GW) at output of the compressor. The compressed pulse will then be distributed to the RF gun and to the LINAC with specific phase and amplitude control points to allow for parameter control during operation. This high power RF system is being designed and constructed. In this paper, we will present the design, layout, and status of this RF system. [Preview Abstract] |
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NP8.00028: Commissioning of a Compton-Scattering-Based Gamma Ray Source David Gibson, Felicie Albert, Scott Anderson, Fred Hartemann, Mike Messerly, Miro Shverdin, Dennis McNabb, Craig Siders, Chris Barty Recently a Compton-scattering based gamma-ray source, in which a high-intensity laser scatters off a high-brightness electron beam and emerges as a narrow-band gamma-ray beam, has been commissioned at Lawrence Livermore National Laboratory. Operating at energies from 0.1 to 0.9 MeV, the source produces fluxes upwards of $10^6$ photons/sec with a brightness of $10^ {15} $ photons/s/mm$^2$/mrad$^2$/0.1\% BW. Presented here is a discussion of the design and performance of the laser and electron subsystems that are used to drive the source, and an overview of the parameters of the generated gamma-ray beam. [Preview Abstract] |
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NP8.00029: 120-Hz Diode-Pumped Kilowatt Class Laser for Compton Scattering Sources Andy Bayramian, Glenn Beer, Rob Campbell, Barry Freitas, William Molander, Steve Sutton, Steve Telford, Chris Barty A Mono-Energetic Gamma-Ray (MEGa-ray) Compton scattering light source is currently based on a 120-Hz electron accelerator. A 120-Hz laser source can increase the current gamma ray production by more than an order of magnitude and further enhancements are possible. Diode pumped solid state lasers (DPSSLs) offer the potential to operate at these higher repetition rates where flash lamp pumped laser systems are currently limited by thermal and lamp lifetime issues. Utilizing LLNL expertise in high energy DPSSLs, a 10-J, 120-Hz diode-pumped Nd:YAG laser architecture has been developed. The laser design makes use of advances in diode packaging, power conditioning, and beam conditioning to provide over 100-kW peak power array. Sapphire heatsinks and longitudinal cooling of the amplifier yields low parasitic loss and low wavefront distortion. An image relayed architecture and adaptive optics will yield a diffraction limited beam ideal for Compton scattering. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. [Preview Abstract] |
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NP8.00030: Generating radiation in terahertz frequency range by means of two-stream instability Nikolai Yampolsky, Kip Bishofberger, Bruce Carlsten, Rickey Faehl, Tengiz Svimonishvili Generating radiation in the terahertz frequency range using methods developed in electronics is complicated. These methods imply the use of a slow-wave structure which is designed to match the dispersion curves of the electro-magnetic mode and the electron beam traveling slower than the speed of light. Such a slow-wave structure should have the scale on the order of the radiation wavelength, which is 100 $\mu$m for 3 THz radiation. Moreover, metal-based structures become ineffective in this frequency range due to high losses. Alternatively, two electron beams having close energies develop the two-stream instability resulting in the beam bunching. The resulting bunched beam can be utilized for generating radiation either by means of transition radiation or through the coupling of the output radiation with the second harmonic of the beam density modulations. The frequency of the output radiation can be easily controlled by adjusting the voltage, current, and spot size of the electron beams coupled by the two-stream instability. Therefore, the proposed scheme can be used for generating high-power radiation in a broad frequency range. [Preview Abstract] |
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NP8.00031: Harnessing the plasma magnetic mode for the generation of brilliant synchrotron radiation Luis Silva, Frederico Fiuza, Samuel Martins, Ricardo Fonseca, Chan Joshi The existence of a plasma magnetic mode (PMM), or picket-fence mode, excited in the collision of a light pulse with a relativistic ionization front, has been predicted theoretically, but a clear experimental evidence of this fundamental plasma mode is still missing. We study the possibility to generate ultrashort-wavelength, high-brilliance radiation by using the PMM as a short-wavelength plasma undulator. The synchrotron radiation, generated when a relativistic energy beam traverses this magnetic structure, allows for a clear signature of the PMM. In order to check the validity of our scheme, we have performed simulations both with OSIRIS 2.0, including tunneling ionization, and with GENESIS 1.3, for an equivalent magnetic field structure. Our results demonstrate the possibility for controlled generation of radiation in the PMM, with high brilliance, equivalent to a compact gamma-ray synchrotron source, providing a clear experimental evidence of this plasma mode and opening the way towards the use of short-wavelength magnetostatic structures in plasmas. [Preview Abstract] |
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NP8.00032: Harmonics Generation in the Reflection of a Linearly Polarized Laser Beam Normally Incident on an Overdense Plasma Magdi Shoucri, Bedros Afeyan We study the harmonics generation in the reflection of a high intensity linearly polarized laser wave normally incident on an overdense plasma. We use an Eulerian Vlasov code for the numerical solution of the one-dimensional relativistic Vlasov-Maxwell equations for both electrons and ions. The oscillation of the laser wave at the plasma edge creates an oscillating space-charge, giving rise to an oscillating electric field. If the intensity of the wave is sufficiently high to make the oscillation of the electrons relativistic, then the plasma edge oscillates nonlinearly in the field of the high intensity laser beam (similar to the relativistic oscillating mirror ROM), which results in an important distortion in the reflected wave associated with the generation of harmonics. The combined effects of the edge electric field with the incident ponderomotive pressure have also important consequences on the ion dynamics, with the ion density profile forming a solitary-like structure close to the plasma edge. We consider the case when the laser beam wavelength is much greater than the scale length of the jump in the plasma density at the edge. [Preview Abstract] |
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NP8.00033: Generation of Phase-Coherent Soft X-Ray Laser Beams by Seeding Plasma Amplifiers David Alessi, Mark Berrill, Yong Wang, Scott Domingue, Dale Martz, David Kemp, Brad Luther, Jorge Rocca Injection seeding of soft x-ray plasma amplifiers with high harmonic pulses offers important advances for applications including full spatial and temporal coherence, reduced divergence, shorter pulsewidth, and increased brightness. We report detailed measurements and simulations of the near-field and far-field beam patterns from a 13.9 nm Ni-like Ag seeded soft x-ray laser. A comparison of the ASE and seeded soft x-ray lasers beam characteristics gives insight into the underlying physics of the plasma amplifier, including the extent and duration of the gain. Model results are compared to 2D model simulations. Work supported by the NSF EUV ERC Award {\#}EEC-0310717. M.B. was supported by DOE CSGF Grant {\#}DE-FG02-97ER25308 References Y. Wang et al., Nature Photonics 2, 94-98 (2008) Y. Wang et al., Physical Review A, 79, 023810 (2009) [Preview Abstract] |
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NP8.00034: LOW TEMPERATURE PLASMAS |
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NP8.00035: CVD technologies assisted with millimeter waves Alexander Litvak, Anatoly Vikharev, Sergey Golubev, Alexey Gorbachev, Petr Sennikov Gas discharges supported by quasi-optical millimeter wave beams are considered. Application in the plasma enhanced chemical vapour deposition technologies of such discharges that are characterized by high electron density allow to increase essentially the rate of activation of the gas medium as compared with traditional microwave based reactors with frequencies 2.45 GHz and 0.915 GHz. The results of films deposition in the plasma reactors pumped by 30 GHz gyrotron are presented for two cases: high rate growth of diamond films and production of nanocrystalline silicon films enriched with Si-isotope. [Preview Abstract] |
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NP8.00036: Feature Profile Simulation Taking into Account the Finite Penetration Depth Paul Moroz Feature profile simulations so far were mainly done under an assumption that incoming gas species of all energies physically or chemically interact only with the surface monolayer of the material. In a more advanced studies, a constant-width mixing layer was considered to take into account energetic particles which could go deep inside the material. However, the penetration depth is not a constant and should be different for different particles, because it strongly depends on the particle energy, on the type of the particle, and on the type of the material. In our work, the penetration depth is derived from analytic theory, molecular dynamics simulations, and from stopping and range software. The resulting fitting curves for the finite penetration depth are then used in the FPS feature profile simulator. The proposed simulation is discussed and the results of simulation are presented. [Preview Abstract] |
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NP8.00037: Impact of low pressure plasma discharge on etch rate of SiO$_{2 }$wafer Dusan Popovic, Vladimir Milosavljevic, Andrijana Zekic, Niall Macgearailt, Stephen Daniels Low-k materials as SiO$_{2}$ play important role in semiconductor industry. In this work a treatment of SiO$_{2}$ single crystal by DC plasma discharge is studied in details. Our work is focused on interaction between ions and dielectric surface. The etch rates, surface morphology and chemical composition of modified surface layer obtained by DC plasma etching are reported. Influence of plasma chemistry (SF$_{6}$, O$_{2}$, N$_{2}$, Ar and He), discharge voltage (up to 1.2 kV), gas flow (up to 25 sccm, for each gas) and electrode-wafer geometry on etch rate of SiO$_{2 }$wafer have been studied. Offline metrology is conducted for SiO$_{2}$ wafer by SEM/EDAX technique and Raman scattering. Effects of plasma treatment conditions on integrated intensity of broad Raman peak at around 2800cm$^{-1 }$are reported in the paper. An analysis of this correlation\textbf{ }could be a framework for creating virtual etches rate sensors, which might be of importance in managing of plasma etching processes. [Preview Abstract] |
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NP8.00038: Use of a dielectric barrier discharge reactor for hydrogen production Angel Mario Figueroa-Hernandez, Martin Nieto-Perez, Gonzalo Ramos, Joel Pacheco-Sotelo A dielectric barrier discharge reactor is used to produce hydrogen from a methane feed mixed with water vapor. The dielectric barrier reactor uses an anodized electrode to generate a thin oxide layer that serves as a second dielectric barrier, as well as a support for catalytic sites. Diagnostics of the system include optical spectroscopy and gas analysis using a differentially-pumped quadrupole residual gas analyzer, capable of sampling feed, exit and recirculation streams of gas to determine the conversion efficiency and the selectivity towards hydrogen of the system. Results on the initial operation of the system are presented in this work. [Preview Abstract] |
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NP8.00039: Physical and biological aspects of cold plasma jet interaction with tissue Alexey Shashurin, M.N. Shneider, A. Dogariu, R.B. Miles, M.A. Stepp, M. Keidar Parameters of helium atmospheric plasma jet are measured by means of microwave scattering, fast photographing and measuring of jet currents. Streamer (``plasma bullet'') propagating along with gas flow is generated immediately after the breakdown of the interelectrode gap. It is observed that post-streamer afterglow plasma column remains on the way of streamer passing. Lifetime of this afterglow plasma column is longer (about 3-5 $\mu$s) than that for the streamer (about 1 $\mu$s). The effects induced in living cells due to treatment with cold atmospheric plasma jet are studied by means of time-lapse microscopy and flow cytometry. We show that treatment of cells with plasma jet affects the cells on sub-cellular level, namely decreases expression of cell surface integrins. This change in integrin expression might be the original cause for the effects observed on cellular level, such as reduced cell migration rate and cell detachment. The living tissue response on treatment with plasma jet may be probably caused by post-streamer plasma column and excited species (due to their longer lifetime) rather than by ``plasma bullets''. We would like to acknowledge the technical assistance of Dr. Y. Raitses, through the PPPL Offsite University Research Program supported by the Office of Fusion Energy Sciences. [Preview Abstract] |
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NP8.00040: A helicon hydrogen plasma source for PMI studies R. Goulding, G. Chen, S. Meitner, L. Owen, F.W. Baity, J.B.O. Caughman, M. Cole Linear plasma devices are important tools for studying phenomena occurring in the plasma material interface (PMI) regions of fusion experiments. An electrodeless rf helicon based plasma source is being designed and constructed at ORNL for possible use in a high power flux ($\sim$ 20 MW/m$^{2}$) linear PMI test device. The source will produce high density hydrogen and deuterium plasmas with density $>$10$^{19}$ m$^{-3}$, and total ion production $\geq$ 10$^{21}$s$^{-1}$. It consists of a 1.3 m long, 15 cm diameter vacuum chamber, with a helical antenna transmitting rf power at f= 10-26 MHz through a cylindrical aluminum nitride (AlN) vacuum window, and four circular coils creating an axial magnetic field with $|B| \leq$ 1T. Preliminary modeling using the EMS2D code indicates that antenna plasma loading $\geq$ 5 $\Omega$ should be acheivable, permitting coupled power $P >$ 50 kW. The device will operate for pulse lengths up to 3 s, with data obtained permitting the design of a later steady state version. The design will be reviewed, as well as well as power deposition and electric field profiles calculated using EMS2D and CST Microwave Studio. Thermal stress calculations for the AlN window will also be reported. [Preview Abstract] |
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NP8.00041: Enhanced Output from the High Power Helicon Resulting from Modification of the Downstream Magnetic Field with a Magnetic Nozzle Race Roberson, Robert Winglee, Tim Ziemba, James Prager The high power helicon plasma source developed at the University of Washington is capable of transferring tens of kilowatts of power into the plasma with source plasma densities near 2x10$^{20 }$m$^{-3}$. The helicon operates with a B$_{0}$ magnetic field of .2 to .6 kG on axis that diverges with axial distance from the source. The addition of a magnetic nozzle downstream of the source region increases the magnetic field along the source axis and limits the divergence of the magnetic field at the source exit. Optical emissions from the plasma show an intense axially peaked central plasma core, typical of a helicon discharge. Light emission occurs outside of the source region within one antenna length downstream, and with the addition of the nozzle the optical emission region extends more than one antenna length. Density along the source axis is increased downstream as expected and time of flight estimates show an increase in bulk plasma velocity downstream of the nozzle. Measurements of plasma density with Langmuir probes and ion energies with a retarding field energy analyzer will be presented. [Preview Abstract] |
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NP8.00042: ABSTRACT WITHDRAWN |
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NP8.00043: Study of OH radical generation in atmospheric pressure microwave plasma jets of Ar, N$_{2}$ and O$_{2}$ gases using pulsed cavity ringdown spectroscopy Chuji Wang, Nimisha Srivastava We employ UV-pulsed laser cavity ringdown spectroscopy, optical emission spectroscopy and visual imaging, to characterize OH radical generation in atmospheric pressure microwave plasma jets created, respectively, by argon, mixture of Ar and N$_{2}$, mixture of Ar and O$_{2}$, and mixture of Ar, N$_{2}$ and O$_{2}$. OH radicals were observed in far downstream for all of these plasma jets (Far downstream is referred to as the location where ratio of the distance from the jet orifice to the length of the jet column is $>$ 3).We also investigated the effect of variations in humidity on OH generation in the APJs. Absolute number densities were measured for OH (v'' = 0, J''= 3.5) along the plasma column axis. Effects on OH radical concentrations along the plasma column axis with variations of plasma powers, gas flow rates with different mixing ratios and humidity levels were also studied. The rotational T$_{rot}$, vibrational T$_{vib}$ and electronic excitation temperature T$_{elex}$ were provided by simulations of emission spectra of the plasmas. [Preview Abstract] |
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NP8.00044: Laser Assisted Plasma Coatings at Atmospheric Pressure (LAPCAP) Zihao Ouyang, Vijay Surla, KyongNam Kim, Martin Neumann, David Ruzic The Center for Plasma-Material Interactions (CPMI) has developed a new Laser Assisted Plasma Coatings at Atmospheric Pressure (LAPCAP) system that will allow high quality, non-porous and uniform coatings on variety of substrates. The basic principle of LAPCAP is to utilize a pulsed Nd:YAG laser (5-10 ns) with an intensity in the range of 10$^{10 }$-- 10$^{11}$ W/cm$^{2}$ to ablate target particles and feed them into the plasma torch for deposition. A large range of materials such as metals and ceramics can be ablated using the laser. A new atmospheric pressure plasma torch based on microwave frequency (2.45 GHz) is developed for this purpose, which is characterized using optical emission spectroscopy (OES). The velocity of the plasma jet is measured using a Pitot tube. In addition, the laser ablation of Yttria-stabilized zirconia (YSZ) target material is currently being investigated for different laser operating parameters to optimize the particle flux and distribution as suitable for the coating requirements. [Preview Abstract] |
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NP8.00045: Observing Pseudowaves in a Multi-Species Plasma using an Antenna/Receiver Setup J.P. Sheehan, Noah Hershkowitz Ion bursts known as pseduowaves are created and detected in a low temperature (T$_{e} \quad \approx $ 1eV, n$_{e} \quad \approx $ 10$^{8}$ cm$^{-3})$ plasma confined in a multi-dipole chamber. A negative-going square wave on a gridded antenna (14 cm diameter) is used to launch the pseudowaves in an argon/neon plasma. They are detected by a single-sided plate receiver (3.5 cm diameter) collecting ion saturation current. Results show the ability of this technique to create and observe pseudowaves in a multi-ion species plasma. Application in determining ion concentrations in a multi-ion species plasma is presented. [Preview Abstract] |
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NP8.00046: Non-Perturbative PlasmaTransducer Carlos Lobo High/low energy physics and Biomimmetics computer vision artifacts are used to simulate a femtosecond isomerization of 3D Rhodopsin-humor vitreous neuron subsystem that is triggered by real time 2D nanoplasma reflecting 90{\%} of the incident radiation with a wavefront similar to the initial solid surface. A complex plasma mirror map is created. It's outlined an holographic transducer that is embedded inside orbital channel superconducting nanorings plasma crystals clusters synchronized by tokamak-like simultaneous regulation controls of injection, electron/proton/neutron retranscript production rate, line density, edge pressure, vortex islands, radiated power fraction in the divertor region, small ``spontaneous'' discharges and others coherent oscillations. EPICS input/output controller is the injection program source Vorpal assemblies QCD-centric parameters to a special class of plasma accelerator in a cell (PIC). A Rhodopsin-based ``computer'' accelerator model that produce photoproduct data is presented. [Preview Abstract] |
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NP8.00047: Imaging with spherically bent crystals or reflectors M. Bitter, K.W. Hill, F. Jones, S. Scott, A. Ince-Cushman, M. Reinke, J.E. Rice, P. Beiersdorfer, M.-F. Gu, S.G. Lee, S. Morita, M. Goto This paper deals with the astigmatism of spherically bent crystals or reflectors and presents new imaging schemes, which can be applied to a wide spectrum of the electromagnetic radiation, including x-rays and EUV radiation. In Part I, we describe an x-ray imaging crystal spectrometer, where the astigmatism of a spherically bent crystal is being used with advantage to obtain radial profiles of the ion temperature and toroidal plasma rotation velocity in tokamaks and stellarators. In Part II, we present two new imaging schemes, where the astigmatism has been eliminated by matched pairs of spherical reflectors, enabling point to point imaging with almost arbitrary angles of incidence. Potential applications are the x-ray diagnosis of laser-produced plasmas, imaging of biological samples with monochromatic radiation from synchrotron light sources, and EUV lithography. - Work supported by US Department of Energy Contracts: DE-FC02-99ER54512 and DE-AC02-09CH11466. [Preview Abstract] |
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NP8.00048: Rotating Spoke in a Cylindrical Hall Thruster Jeffrey B. Parker, Yevgeny Raitses, Nathaniel J. Fisch In a cylindrical Hall thruster (CHT)\footnote{Y.~Raitses and N.~J.~Fisch, \emph{Phys.~Plasmas} 8, 2579 (2001)}, a spoke of increased visible light emission propagates azimuthally and has been imaged with the use of a high speed camera. The spoke frequency is about 15 kHz. The observation of the rotating spoke depends on the magnetic field configuration. When the CHT is configured to have a cusp magnetic field, the rotating spoke is visible, while when it is configured to have an enhanced mirror field, the rotating spoke is not visible. The rotating spoke is also suppressed due to enhancing the cathode electron emission above its self-sustained level. In the regimes where the rotating spoke is not visible, steady-state probe measurements have found the electron cross-field mobility to be reduced\footnote{A.~Smirnov, Y.~Raitses, and N.~J.~Fisch, \emph{Phys.~Plasmas} 14, 057106 (2007)}, indicating the spoke may contribute to anomalous electron transport. [Preview Abstract] |
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NP8.00049: Negative differential conductivity and discharge current oscillations in Hall thrusters Yevgeny Raitses, Jeffrey B. Parker, Nathaniel J. Fisch Large-amplitude, low-frequency, discharge current oscillations invariably occur in the Hall thrusters. The oscillations are thought to result from ionization instability [1]. Increase of the cathode electron emission was recently shown to suppress these oscillations [2]. This suppression correlates with a change in the local V-I characteristics of the discharge. In this regime, there are no plasma regions with negative differential conductivity, which are normally observed for the self-sustained thruster discharge. A similar effect can be achieved by using the thruster channel with low secondary electron emission (SEE) walls. The common feature between enhanced cathode electron emission and low SEE wall effects is that in both cases, the electron cross-field mobility is reduced inside the channel and therefore, the ion accelerating and ionization regions are located mainly in this region of a strong magnetic field. [1] S. Barral, E. Ahedo, Phys. Rev. E 79, 046401 (2009), [2] Y. Raitses, A. Smirnov, N. J. Fisch, Phys. Plasmas 16, 057106 (2009). [Preview Abstract] |
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NP8.00050: Surface Material Deposition on a Ferroelectric Plasma Thruster B.T. Hutsel, S.D. Kovaleski, T. Wacharasindhu, R. Almeida, J.W. Kwon The ferroelectric plasma thruster (FEPT) is being developed for micropropulsion. The FEPT produces thrust by the acceleration of ions from plasma formed at the surface of a ferroelectric disk. Ions are accelerated due to the electrostatic fields generated from an applied RF voltage. The generated surface plasma is composed of electrode material (silver or aluminum) deposited on the crystal. Experiments are being conducted to optimize the material deposition on the FEPT. Finite element simulation software is used to model the materials effect on the generated electrostatic fields. Measurements of total ion currents and plasma composition for various depositions are compared. [Preview Abstract] |
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NP8.00051: Effects of Secondary Electron Emission on the Two-Stream Instability in Hall Thrusters Anton Stepanov, N.J. Fisch In Hall thruster discharges, secondary electron emission (SEE) electrons produced at the chamber wall are accelerated radially into the channel by the sheath potential. The plasma inside the channel moves in the azimuthal direction due to E x B rotation. Next to the channel wall, this rotation could give the bulk plasma a greater azimuthal velocity compared to the SEE beam. The resulting nonmonotonic electron velocity distribution function (EVDF) might be two-stream unstable. In this work we consider the possibility of such a two-stream instability in the combined SEE beam/plasma EVDF in the azimuthal dimension. [Preview Abstract] |
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NP8.00052: Characterization of the Micro Pulsed Inductive Thruster James Prager, Timothy Ziemba, David Peters, Robert Winglee The micro pulsed inductive thruster (uPIT) is a low mass ($<$500 g) pulsed plasma thruster with an inductive drive section that was invented and developed at Eagle Harbor Technologies, Inc. and investigated at the University of Washington. This thruster is designed for primary propulsion of nanosatellites and satellite missions that require very fine impulse bit for precision pointing. Here we present data demonstrating increased performance with the use of the inductive drive section. Also presented is data to characterize the thruster including spectrometer data, exhaust speed data, preliminary thrust stand data, and long duration operation data. We demonstrate that uPIT is a viable option for a micropropulsion concept that fills an open niche in thruster concepts. [Preview Abstract] |
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NP8.00053: Wave-driven plasma centrifuge Abraham Fetterman, Nathaniel Fisch A method for driving rotation in a fully ionized plasma centrifuge is described. The rotation is produced by radiofrequency waves near the cyclotron resonance. The wave energy is transferred into potential energy in a manner similar to the $\alpha$ channeling effect. By driving the rotation using waves instead of electrodes, physical and engineering issues may be avoided. [Preview Abstract] |
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NP8.00054: Spatially-Resolved Spectroscopic Study of Arcjet Helium Plasmas Expanding through a Rectangular-Shaped Converging-Diverging Nozzle Shinichi Namba, Noriyasu Yashio, Kazuki Kozue, Keisuke Nakamura, Takuma Endo, Ken Takiyama, Kuninori Sato An arcjet discharge device with a rectangular-shaped converging and diverging nozzle has been developed, which allowed us to optically observe high density plasmas inside the anode nozzle. Spectroscopic observation along the plasma expansion axis was carried out to examine the characteristics of plasma parameters inside the nozzle. Analyzing the intense continuum and line emission spectra, we successfully obtained the spatial variations of electron temperature and density. Moreover, it was found that two dimensional optical measurement was of great use in visualizing the transition from the atmospheric thermal plasma to strong non-equilibrium recombining phase due to an adiabatic expansion. [Preview Abstract] |
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NP8.00055: A Zero Dimensional Model of High-Pressure Ablative Capillary Discharge Leonid Pekker, Oksana Pekker The presented model of high-pressure ablative capillary discharge includes: a heat-transfer radiation model based on radiation database constructed using PrismSPECT, a commercially available radiation software, to calculate the radiation heat flux output from a uniform plasma slab; a model of the transition boundary layer between the uniform plasma core and the ablative wall to calculate the thermal and radiation heat fluxes at the capillary wall; capillary wall thermal conduction and radiation absorption; and a RLC circuit. Thus, the model self-consistently calculates plasma parameters of the capillary discharge and distribution of wall temperature vs. time. We show that the radiation grey factor varies from 0.06 to 0.95 with time. This illustrates that the grey factor can change significantly with time in nonsteady operation regime and, therefore, assuming that it is constant can lead to false results. The model also shows that small extinction coefficients of the wall material lead to large energy losses from the capillary discharges (the heat is absorbed by the bulk of the capillary wall or just escapes the capillary) and to spikes in plasma temperature. If the extinction coefficient is too small, the discharge may become extinguished because the temperature of ablative surface does not increase fast enough to compensate the plasma exhaust from the open end of the capillary. [Preview Abstract] |
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NP8.00056: ePLAS modeling of laser induced lightning streamers W. Atchison, R.J. Mason, J. Zinn The ePLAS code is a derivative of ANTHEM\footnote{R. J. Mason, J. Comp. Phys. 71, 429 (1987)} originally developed to model long pulse laser interactions. The code has been enhanced to treat opening switch plasmas, plasma jets, and short pulse laser interactions with cones and wires.\footnote{R. J. Mason, et al., Bull. Am. Phys. Soc. 53, 152 (2008).} We address new features for application to lightning and guided arcs. ePLAS models collisional background plasma with cold electron and ion components. Self-consistent \textit{E- and B-}fields are determined implicitly for time steps well beyond the plasma period; hybridization permits spatial scales exceeding the Debye length. For lightning studies an initial start-up potential in a strongly ionized region has been added, plus ``air chemistry'' to create additional plasma in intense, propagating $E-$field regions at the leading edge of ``streamers.'' We discuss the motion of both positive and negative streamers in nitrogen on nanosecond time scales, showing streamer guidance in added plasma seeded by a laser. $B$-field inclusion permits the study of return strikes. [Preview Abstract] |
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NP8.00057: Formation and Radial Propagation of Filaments in a Plasma Ball Michael Campanell, S. Vasquez, C. Czarnocki, M. Burin, S.J. Zweben High speed photography was used to analyze the formation and propagation of the filaments in a commercial plasma ball. Videos made at up to 500,000 frames/sec show that the filaments propagate radially at about 10,000 m/s during each cycle at the 25 kHz driving frequency and follow the same path in consecutive cycles. Just after the initial switching on of the voltage, the filaments develop out of a diffuse glow and self-organize into their final form over about 1 msec. It is also found that the number of filaments varies with applied voltage frequency and the radial length of filaments varies with voltage amplitude. A custom plasma ball apparatus has been built to analyze the dependence of the filamentary behavior on gas composition, pressure, applied voltage waveform and electrode geometry. Initial results will be presented. [Preview Abstract] |
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NP8.00058: PINCHES, EQUATION OF STATE, AND SIMULATIONS |
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NP8.00059: The Affects of Ablation, Two-Dimensional Instability, and Current Losses on K-Shell Emission in Wire Array Z-Pinch Implosions. J.W. Thornhill, J.L. Giuliani, J.P. Apruzese, Y.K. Chong, J. Davis, A. Dasgupta, R.W. Clark, K.G. Whitney, B. Jones, C.A. Coverdale, D.J. Ampleford, C.A. Jennings, M.E. Cuneo We present the results of a 2D radiation MHD based theoretical investigation that examines how wire ablation, the level of two-dimensional instability, and current losses in the load region of the pinch affect K-shell radiation for copper and stainless steel wire array implosions on the refurbished Z machine. We find that the broad mass distribution produced by including ablation physics largely overcome the diminishing effects on K-shell yield of two-dimensional instability growth. On the other hand, results of calculations that model suspected current losses near the load region\footnote{C. A. Jennings, Invited talk ICOPS (2009).} show substantial reductions in K-shell yield. [Preview Abstract] |
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NP8.00060: Ablation studies of low number wire arrays on the GenASIS Linear Transformer Driver (LTD) at 200 kA Simon Bott, Farhat Beg, Gilbert Collins IV, Miles Abarr The ablation of wires in a wire array z-pinch remains one of the critical challenges in scaling these systems to drive currents required for Inertial Confinement Fusion (ICF) ignition. Whilst the dynamical evolution of wire arrays is well understood, and multi-dimensional Magneto-Hydrodynamic (MHD) modeling has demonstrated significant progress, a predictive capability has not been realized to date. In addition, recent experimental investigations have highlighted the need to more closely examine the ablation structure and its dependence on the initial parameters of the array. We present investigations on the ablation in wire arrays on a recently completed generator at UCSD. The radial and axial variation of the plasma density is examined quantitatively using laser interferometry, and temperature estimates are made from time integrated and time-gated emission images. Results are compared to analytical models of the ablation process which show that the effective ablation velocity varies continuously in the axial direction as a result of the ablation process at the wire. [Preview Abstract] |
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NP8.00061: An Investigation of the Radiation and Implosion Performance of Al/Mg Nested Wire Arrays on the Refurbished Z Simulator Y.K. Chong, W. Thornhill, J. Giuliani, R. Clark, D. Ampleford, C. Jennings, B. Jones, C. Coverdale A set of Al/Mg nested wire array Z-pinch load experiments has been recently performed on the refurbished Z accelerator. The initial 1D predictions display a K-shell yield increasing w/ mass load, but the exp. data showed the opposite trend. In this study, we present the results from the modeling of the exp. using a 1-D non-LTE radiation MHD code with a detailed atomic model and the prob.-of-escape radiation transport. Our focus will be on the characterization of the radiation emission, absorption {\&} transport, {\&} the energetics {\&} dynamics of the Z-pinch plasma as a function of the load mass {\&} wire array distribution. The effects of the current loss {\&} the e-i energy coupling physics on the radiation power {\&} yield and the implosion performance will be investigated. Finally, an examination of the role of multidimensional structures on the radiation {\&} implosion physics will be made using appropriate models w/ relevant improvements suitable for studying the Z-pinch loads in order to help bridge the gap between the exp. {\&} the previous 1-D predictions. [Preview Abstract] |
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NP8.00062: Analysis of implosion dynamics of nested cylindrical wire arrays of Mo and Al on the Zebra and Cobra generators M.E. Weller, M.F. Yilmaz, A.S. Safronova, V.L. Kantsyrev, A.A. Esaulov, K.M. Williamson, I. Shrestha, G.C. Osborne, N.D. Ouart, V. Shylaptseva Results of experiments with nested cylindrical wire arrays of Mo and Al that were performed on the 1.6 MA, 100 ns Zebra generator and the 1.0 MA, 100 ns Cobra generator are presented. Both the Zebra and Cobra experiments had loads with Al tracer wires with different concentrations in linear mass ($\sim $30{\%} Al for Zebra and $\sim $15{\%} Al for Cobra). The full set of diagnostics produced data that were compared and analyzed, which include PCD, XRD, and bolo signals, laser shadowgraphy and optical streak images, and time-gated/integrated pinhole and spectra images. Implosion dynamics is analyzed with a wire-ablation dynamics model. Non-LTE kinetic modeling was utilized to derive plasma parameters of electron temperature and density and to estimate opacity effects. The advantage of using Mo wires for future study of L-shell radiators from wire arrays is demonstrated. [Preview Abstract] |
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NP8.00063: Comprehensive Analysis of Implosions of Single Planar Tungsten Wire Arrays with Aluminum Center Wires Produced on a 1-MA generator G.C. Osborne, A.S. Safronova, V.L. Kantsyrev, A.A. Esaulov, M.F. Yilmaz, K.M. Williamson, M.E. Weller, I. Shrestha An analysis of five-wire W single planar wire array (SPWA) experiments with Al center wires is presented. Comparisons are drawn to previous work which focused on SPWAs with smaller inter-wire gaps of pure W loads and W loads with single Al wires on the edge of the array. Experiments were performed on the 1MA generator ``Zebra'' at UNR, with data taken on a pulse laser shadowgraphy apparatus, an x-ray time-gated pinhole camera, and both time-integrated spatially resolved and time-gated spatially integrated spectrometers. Utilizing this full suite of plasma diagnostics, comprehensive set of data with staggered timings has been compiled. Non-LTE kinetic modeling is used to describe temperature and density features of the spectral data, while the Wire Ablation Dynamics Model is utilized to better understand implosion dynamics. [Preview Abstract] |
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NP8.00064: Magneto-Rayleigh-Taylor Instability Experimental Progress on Thin Foils Driven by a 1-MA LTD* J.C. Zier, Y.Y. Lau, M.R. Gomez, W.W. Tang, M.A. Franzi, D.M. French, R.M. Gilgenbach, M.G. Mazarakis, M.E. Cuneo, M.R. Lopez, B.V. Oliver, T.A. Mehlhorn Foils may soon become necessary to achieve the required mass for higher current-driven x-ray sources. They may also offer useful options for x-ray pulse shaping and as imploding liners for magnetized target fusion. This paper reports our latest design and experimental progress on the dominant instability, the magneto-Rayleigh-Taylor instability (MRT). Planar Al foils as thin as 400 nm driven by the 1-MA linear transformer driver (LTD), MAIZE, at the U of Michigan, are used as the dynamic loads for this investigation. A higher inductance feed will be used to lengthen the current drive to achieve $>$10 e-foldings of MRT growth for observation with a laser backlighter. Inductance considerations, schlieren and interferometry diagnostics, and experimental progress will be presented along with MRT theory. *This work was supported by US DoE through Sandia National Labs award numbers 240985 and 76822 to the U of Michigan. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the US DoE's NNSA under Contract DE-AC04-94AL85000. JCZ was supported by a NPSC fellowship through Sandia National Labs. MRG was supported by a SSGF fellowship through NNSA. [Preview Abstract] |
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NP8.00065: Development of the Axial Instability in Low Wire Number Wire Array Z-Pinches Patrick Knapp, John Greenly, Pierre Gourdain, Cad Hoyt, Matthew Martin, Sergei Pikuz, Tania Shelkovenko, David Hammer, Bruce Kusse We investigate the growth of the axial instability in wire-array Z-pinches. In these experiments we image individual wires in aluminum wire arrays using laser shadowgraphy and XUV framing cameras at times ranging from 0 to 100 ns after the start of a 1 MA, 100 ns rise time current pulse. We document the radial growth of the coronal plasma around each wire and the development of the wavelength and amplitude of the instability from the time of plasma formation until the instability stops growing. The ratio of the dominant instability wavelength to the coronal plasma radius is $\sim $1 during this time. The magnetic field topology is also probed using small B-dot probes inside the array. The change in topology from local- to global- field dominated near an exploding wire correlates well in time with the moment that the instability stops growing. In addition, preliminary experiments show that perturbations seeded in the coronal plasma using twisted wires grow at the twist wavelength and evolve to much larger amplitude than in the unseeded case. This research was supported by the SSAA program of the National Nuclear Security Administration under DOE Cooperative agreement DE-FC03-02NA00057. [Preview Abstract] |
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NP8.00066: Coronal plasma development in wire-array z-pinches made of twisted-pairs C.L. Hoyt, J.B. Greenly, P.A. Gourdain, P.F. Knapp, S.A. Pikuz, T.A. Shelkovenko, D.A. Hammer, B.R. Kusse We have investigated coronal and core plasma development in wire array z-pinches in which single fine wires are replaced by twisted-pairs (``cable'') on the 1 MA, 100 ns rise time COBRA pulsed power generator. X-ray radiography, employed to investigate dense wire core expansion, showed periodic axial nonuniformity and evidence for shock waves developing where the individual wire plasmas collide. Laser shadowgraphy images indicated that the axial instability properties of the coronal plasma are substantially modified from ordinary wire arrays. Cable mass per unit length, material and the twist wavelength were varied in order to study their effects upon the instability wavelength. Implosion uniformity and bright-spot formation, as well as magnetic topology evolution, have also been investigated using self-emission imaging, x-ray diagnostics and small B-dot probes, respectively. Results from the cable-array z-pinches will be compared with results from ordinary wire-array z-pinches. This research was supported by the SSAA program of the National Nuclear Security Administration under DOE Cooperative agreement DE-FC03-02NA00057. [Preview Abstract] |
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NP8.00067: Embedding magnetic field lines in the plasma jet of an exploding radial foil on COBRA Peter Schrafel, Pierre Gourdain, John Greenly, Bruce Kusse Previous investigations of exploding radial foils have shown the formation of an axial plasma jet in the early stages of the foil explosion. In this case a thin load foil was pressed at an outer annulus held at ground, and contacted in the center by a small straight rod cathode driven by the 1MA COBRA accelerator. The present experiments look at the effects of inducing a transient magnetic field in the region containing the plasma jet. This induced magnetic field is created in one of two ways: twisting the rod cathode to have a helical coil segment near the foil, or putting an inductive current path in parallel to the straight rod cathode. Of great interest is whether this applied magnetic field can be embedded into the plasma jet and influence its development. The jet is diagnosed visually with laser shadowgraphy and observation of XUV emission. B-dot probes measure the magnetic field strength in the region near the jet. [Preview Abstract] |
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NP8.00068: Compression of an Applied Bz field by a z-pinch onto a Tamped DT Fiber for Inertial Confinement Fusion Tom Nash Simulations of a z-pinch compressing an applied 100 kG Bz field onto an on-axis DT fiber tamped with beryllium show the field reaching over 100 MG in the tamp, sufficient to confine DT alpha particles and to form a thermal barrier. The barrier allows the DT plasma to burn at a rho*r value as low as 0.045 g/cm$^2$, and at temperatures over 50 keV for a 63 MA drive current. Driving currents between 21 and 63 MA are considered with cryogenic DT fiber diameters between 600 $\mu $m and 1.6 mm. Pinch implosion times are 120 ns with a peak implosion velocity of 35 cm/$\mu $s. 1D simulations are of a foil pinch, but for improved stability we propose a nested wire-array. Simulated fusion yields with this system scale as the sixth power of the current, with burn fractions scaling as the fourth power of the current. At 63 MA the simulated yield is 521 MJ from 4.2 mg/cm of DT with a 37{\%} burn fraction at a rho*r of only 0.18 g/cm$^2$. [Preview Abstract] |
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NP8.00069: Neutron Production in Deuterium Gas-Puff Z-Pinch Implosions on Refurbished Z R.W. Clark, A.L. Velikovich, J. Davis, J.L. Giuliani, C.A. Coverdale, D. Flicker Earlier experiments with deuterium gas puff implosions on Z [Coverdale et al., Phys. Plasmas \textbf{14}, 022706 and 056309 (2007)] demonstrated reproducible production of high neutron yields, up to $\sim $3$\times $10$^{13}$, a large part of which might be of thermonuclear origin. We report a scoping study for such experiments on refurbished Z which can implode deuterium gas-puff loads at high-current, longer pulse ($\sim $250 ns) regime. Significantly higher thermal DD neutron yields are predicted for ZR. We discuss the relative roles of kinetic-to-thermal energy conversion and adiabatic compression in heating the central deuterium column to the fusion temperature. We quantify the effect on the thermal neutron yield produced by loading the outer shells of the multi-shell gas-puff with a heavier gas to improve matching of the implosion to the current pulse, by additional heating of the central jet area with a Z-Beamlet laser and by applying an axial magnetic field in order to stabilize the implosion from a large initial radius. [Preview Abstract] |
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NP8.00070: Parallel X pinches on the 1 MA COBRA pulser S.A. Pikuz, T.A. Shelkovenko, P.F. Knapp, C.L. Hoyt, J.B. Greenly, H. Wilhelm, D.A. Hammer Two standard and nested X pinches have been tested in parallel as the load on the 1MA, 100 ns risetime COBRA pulsed power generator at Cornell University. The spatial, temporal, and spectral parameters of the X pinches were studied using laser-based imaging, time gated XUV-sensitive cameras, a slit-step-wedge and pinhole cameras, X-ray spectroscopy and x-ray radiography. The latter includes testing a new method of point-projection quasi-monochromatic radiography. Electrical cross-talk of the X pinches was studied using very small B-dot probes placed in the space between X-pinches. The experiments show that the parallel nested x-pinches produce smaller, brighter and more stable x-ray source points than the standard configuration. [Preview Abstract] |
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NP8.00071: X pinch experiments on the table-top MINI-generator T.A. Shelkovenko, S.A. Pikuz, D.A. Hammer, I.N. Tilikin, A.R. Mingaleev, S.A. Chaikovsky The MINI-generator, a 340 kA peak current, 170 ns risetime, 40-50 kV, pulsed power generator with energy storage of 1 kJ, was designed and built at the High Current Electronic Institute (Tomsk, Russia). The generator is 45~cm diameter, 33~cm high and weights about 80 kg. The main goal was to design a table-top generator for use with X pinches to create a point source of soft x-ray radiation for radiography of plasma and biological objects. The first experiments with X-pinch loads performed in P.N. Lebedev Physical Institute (Moscow, Russia) showed that the MINI-generator has very high efficiency in transformation of a stored energy to radiated energy of an X-pinch hot spots in the range of 1 to 5 $\mu $m diameter, depending on the photon energy range. Results obtained in X-pinch experiments on MINI-generator and the XP--generator (0.5 MA, 45 ns risetime) at Cornell University will be compared. [Preview Abstract] |
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NP8.00072: Axial x-ray backlighting of wire array Z-pinches using X pinches I.C. Blesener, J.B. Greenly, S. Pikuz, T. Shelkovenko, S. Vishniakou, B.R. Kusse, D.A. Hammer A high resolution axial x-ray imaging system for wire-array Z-pinch experiments has been developed. Calibrated areal density measurements of the Z-pinch plasma; including wire cores, coronal plasma, streaming plasma, and precursor can be obtained. The system uses Mo X pinches in series and below the Z-pinch load to provide point sources of x-rays for point-projection radiography. Images have a 15 mm diameter field of view at the center height of the array and a magnification of about 7.5:1. Ti filters in front of the film transmit continuum radiation in the spectral range of 3-5 keV. A separate film of the same thickness Ti and placed the same distance away with an unobstructed path includes step wedges for calibration of the Z-pinch plasma. The step wedges have thicknesses of W ranging from 0.015 to 1.1 $\mu $m to obtain areal density measurements of the W plasma from the wire-array. Images have subnanosecond temporal resolution and about 10 $\mu $m spatial resolution. The diagnostic will also be used in the future for imaging thin foil cylinder Z-pinches. Recent calibrated images as well as a discussion of future foil experiments will be presented. [Preview Abstract] |
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NP8.00073: Dynamic measurement of plasma density in wire array z-pinches by using continuum interferometry A. Haboub, V.V. Ivanov, G.S. Sarkisov Measurement of the electron plasma density with regular laser interferometery encounters the zero-number fringe issue on the axis of the z-pinch. From the ablation stage on, the density of the inhomogeneous plasma increases quickly and produces a very complicated structure of fringes. We suggested a new continuous interferometry diagnostic that has been developed for the 1-MA Zebra generator. This diagnostic can record a continuous history of the interferograms and the individual evolution of the streaked fringes. It is based on a Nd:YAG laser with a long probing pulse of 300 ns at either the fundamental wavelength or the second harmonic, a Mach Zehnder interferometer, and an optical streak camera. By using this new diagnostic, the precursor z-pinch plasma density can be precisely measured during the ablation and the implosion phases in wire arrays. [Preview Abstract] |
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NP8.00074: Development of laser based diagnostics for wire array z-pinch experiments on the MAGPIE generator George Swadling, S.V. Lebedev, S.N. Bland, G.N. Hall, F. Suzuki-Vidal, N. Niasse, G. Burdiak, E. Khoory, L. Pickworth, C. Hutchison End on Interferometric imaging is a useful technique for diagnosing the electron density distribution in the interior of wire array z-pinches during their ablation phase. These measurements are limited as there is often no known density reference point in the image. By using a time resolved, CW line integrated interferometry system, we can measure the electron density for a single point on the image. This allows us to calculate the density distribution across the remainder of the image. Two new quadrature interferometry systems are discussed, the first free space and the second fiber based. Also discussed is a new fiber based multipoint Heterodyne Velocimetry (HET-V) system, for the time resolved measurement of large velocities and accelerations, and a new faraday rotation current probe system, to measure rapidly rising currents in new switched mode wire arrays. [Preview Abstract] |
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NP8.00075: Development of laser-based diagnostics for 1-MA z-pinch plasmas V.V. Ivanov, P. Hakel, R.C. Mancini, P. Wiewior, R. Presura, J.M. Kindel, A.P. Shevelko, O. Chalyy, A. Astanovitskiy, A. Haboub, S.D. Altemara, D. Papp, T. Durmaz The 50 TW Leopard laser coupled with the 1-MA Zebra generator was used for development of new diagnostics of z-pinch plasmas. Two plasma diagnostics are presented: an x-ray broadband backlighting for z-pinch absorption spectroscopy and parametric two-plasmon decay of the laser beam in dense z-pinch plasma. Implementation of new diagnostics on the Zebra generator and the first results are discussed. The absorption spectroscopy is based on backlighting of z-pinch plasma with a broadband x-ray radiation from a Sm laser plasma. Detailed analysis of the absorption spectra yields the electron temperature and density of z-pinch plasma at the non-radiative stage. The parametric two-plasmon decay of intensive laser radiation generates 3/2$\omega $ and 1/2$\omega $ harmonics. These harmonics can be used to derive a temperature of z-pinch plasma with the electron density near the quarter of critical plasma density. [Preview Abstract] |
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NP8.00076: Optical Spectroscopy Experiments on the 500 kA XP Pulsed Power Generator Kate Blesener, Tania Shelkovenko, Sergei Pikuz, Isaac Blesener, David Chalenski, Cad Hoyt, Patrick Knapp, John Greenly, David Hammer, Yitzhak Maron A new diagnostic technique using non-perturbing emission spectroscopy at visible wavelengths is being developed to determine the magnetic field in high energy density plasmas. This technique which makes use of the Zeeman Effect, has been demonstrated in experiments performed at the Weizmann Institute of Science in plasmas with lower energy densities [1]. Experiments on the 500 kA XP pulsed power generator at Cornell University are exploring the properties of optical spectra emitted by single exploding wires, wire-arrays, and X pinches. We are studying the time resolved visible spectra to identify appropriate spectral lines for measuring magnetic field strength. Preliminary results will be discussed. \\[4pt] [1] E. Stambulchik, K. Tsigutkin, and Y. Maron. Phys. Rev. Lett. 98, 225001 (2007). [Preview Abstract] |
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NP8.00077: Non-LTE modeling and simulations for spectroscopic analysis of stainless-steel Z-pinch plasma A. Dasgupta, J.L. Giuliani, J. Davis, J.W. Thornhill, R.W. Clark, C.A. Coverdale, B. Jones, D.J. Ampleford We have developed a collisional-radiative spectroscopic model that combines the accuracy of detailed accounting for all important excited states coupling with the completeness of a highly averaged Rydberg state model. The model was used to investigate the implosion dynamics of nested Stainless-Steel (SS) wire arrays and generate K- and L-shell spectra using a 1-D non-LTE radiation hydrodynamics model self-consistently coupled to a transmission line description of the device. We compare our SS spectra with experimental data of shot Z581 and Z1860 on the Z and the refurbished Z accelerators respectively, at Sandia National Laboratories. The simulations self-consistently include the effects of radiation transport and line broadening. We include level-specific dielectronic recombination data in order to investigate the \textit{Ly}$_{\_{\rm g}}$satellite lines that are useful for diagnosing line broadening in a Z-pinch plasma at stagnation. [Preview Abstract] |
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NP8.00078: Modeling of Ion Thermalization in a Ne Gas Pinch J. Giuliani, J. Thornhill, A. Dasgupta, A. Velikovich, J. Davis, R. Clark, E. Kroupp, D. Osin, Y. Maron, A. Starobintes, E. Stambulchik, V. Fisher, V. Bernshtam, A. Fisher, C. Deeney Understanding of the dynamics, population kinetics, and energy budget of a K-shell radiating Z pinch remains a challenging problem in high energy density plasma physics. Large ion kinetic energies have been reported for Ne pinches at $\sim $1 MA.\footnote{E. Kroupp, et al., PRL, 98, 115001 (2007), D. Osin, Ph.D. Thesis (2008).} The present work examines the dynamics of this pinch with a 1D radial magnetohydrodynamic simulation code including collisional-radiative ionization dynamics and radiation transport. Synthetic spectra from the simulations can match the measured H-like satellite line profiles if the ion-electron equilibration rate is reduced by a factor of $\sim $10. In anticipation of further experiments, radially resolved synthetic spectra of the satellite lines will also be presented to analyze the plasma structure at stagnation. [Preview Abstract] |
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NP8.00079: Experimental Post-Hole Convolute Plasma Studies on a 1-MA Linear Transformer Driver (LTD)* M.R. Gomez, R.M. Gilgenbach, D.M. French, J.C. Zier, Y.Y. Lau, M.E. Cuneo, M.R. Lopez, M.G. Mazarakis Post-hole convolutes are used to combine current from several parallel transmission lines, such that there is a low-inductance path to a single anode-cathode gap at the load. Experimental observations of the post-hole convolute are difficult to make on large systems, such as the Z-Machine at Sandia National Laboratories. A single post-hole convolute has been designed as the load for the 1 MA LTD at U. of Michigan. The geometry of the design allows diagnostic access to the post-hole region. The goal of these experiments is to monitor plasma formation in the convolute and to measure the current losses as a result of that plasma. Diagnostics under development for this experiment include B-dots for current measurement, optical spectroscopy for plasma composition, temperature and density measurements, and pinhole and laser diagnostics for imaging plasma dynamics. Experimental results will be compared to Particle-In-Cell simulations of this system using MAGIC PIC.* Research supported by Sandia National Labs subcontacts to UM. MRG sponsored by SSGF through NNSA and JZ sponsored by NPSC through DOE. Sandia is a multi-program laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the US DOE's NNSA under contract DE-AC04-94AL85000. [Preview Abstract] |
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NP8.00080: Higher Dimensional Theory of Contact Resistance and Experimental Validation W. Tang, M. Gomez, D. French, J. Zier, P. Zhang, Y.Y. Lau, R. Gilgenbach Electrical contact is an important issue to Z-pinches, pulsed power systems, field emitters, and wafer evaluation, etc. Because of the surface roughness on a microscopic scale, true contact between two pieces of metal occurs only on the asperities of the two contacting surfaces, resulting in contact resistance [1]. We recently developed a higher dimensional theory of contact resistance for an asperity of transverse dimension (a) and finite axial length (h) connecting two metal blocks [2]. For asperity of rectangular, cylindrical or funnel shape, the contact resistance is found to be of the form R[1+p(h/a)] where R is the corresponding h=0 ``a-spot'' theory limit of Holm and Timsit [1], p has a simple form which is geometry-dependent. This scaling law is verified against electrostatic code results [2]. It is also recently validated in a series of controlled experiments [3]. This work is supported by Sandia, AFOSR, AFRL, L-3, and Northrop-Grumman. \\[4pt] [1] R. Holm, \textit{Electric Contact} (Springer-Verlag, 1967); R. S. Timsit, \textit{IEEE Trans. Components Packaging Tech}. \textbf{22}, 85 (1999). \\[0pt] [2] Y. Y. Lau and W. Tang, \textit{J. Appl. Phys.} \textbf{105}, 124902 (2009). \\[0pt] [3] M. R. Gomez et al., \textit{Appl. Phys. Lett}. (submitted). [Preview Abstract] |
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NP8.00081: Current Switching and 0D-like Implosions Produced Using Inverse Wire Array Z-Pinches Adam Harvey-Thompson, Sergey Lebedev, Gareth Hall, Simon Bland, Guy Burdiak, Fransisco Suzuki-Vidal, George Swadling, Essa Khoori, Jeremy Chittenden, Louisa Pickworth Experiments using an inverse (exploding) wire array setup (where the wires hang down from a central current conductor, acting as a return current cage) to rapidly switch current into a cylindrical wire array have been fielded on the MAGPIE generator (1.5MA, 240ns). The setup has been found to rapidly switch current into the cylindrical array, delivering $\sim $1.5MA in 95ns. The implosion of the cylindrical array deviates substantially from the standard snowplough dynamics, suppressing the ablation phase and producing a 0D-like implosion. Data suggests that the change in dynamics is due to a $\sim $5kA pre-pulse driven over 10ns into the cylindrical array over 100ns before the current switch operates which preconditions the wires in the array. This paper will focus on the effectiveness of the current switch. [Preview Abstract] |
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NP8.00082: Experimental study of features on burn for direct-drive capsules G.R. Magelssen, J.A. Cobble, I.L. Tregillis, M.J. Schmitt, S.H. Batha, P.A. Bradley, K.A. DeFriend Obrey, H.W. Herrmann, M.D. Wilke The effect of small localized perturbations, such as fill tubes and mounting tents, on the NIF ignition capsule and the effect of hemi-joints on high gain double shell capsules are an important issue in achieving ignition on NIF. To begin the study of defects on yield, an exploding pusher has been designed. In this presentation experimental results and simulations will be presented. Exploding pushers with defect rings 15-17 microns wide and 2.2-2.7 microns deep were shot on the OMEGA laser. The capsules were CH shells 431-436 microns in radius and 8.1-8.5 microns thick. They were filled with a 50-50 ratio of 5 atm DT and were directly driven. These results were compared to thicker shell CH targets. These targets were 440-445 microns in radius and 15.1-15.2 microns thick. The defects were similar to those for the exploding pusher. Calculations with both Eularian AMR and Lagrangian codes were done and compared to the experimental results. For the exploding pushers, the codes predict and the experiments gave about a factor of 2 decrease in the neutron yield over the unperturbed results. The yield for the thicker targets showed at most a factor of 2 loss in yield much higher than predicted. [Preview Abstract] |
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NP8.00083: Multiple Scattering of Slow Ions in a Partially Degenerate Electron Fluid Romain Popoff, Gilles Maynard, Claude Deutsch We extend former investigations to a partially degenerate electron fluid at any temperature of multiple slow ion scattering at T=0. We implement an analytic and mean-field interpolation of the target electron dielectric function between T=0 (Lindhard) and T$\rightarrow$oo (Fried-Conte). A specific attention is given to multiple scattering of proton projectiles in the keV energy range stopped in a hot electron plasma at solid density. [Preview Abstract] |
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NP8.00084: The ionization balance of gold in the Livermore Electron Beam Ion Trap M. May, S. Hansen, H.-K. Chung, K. Reed, J. Scofield, M. Schneider, B. Wilson, K. Wong, P. Beiersdorfer Spectra have been recorded from gold that has been injected into the Lawrence Livermore Electron Beam Ion Trap (EBIT-II). Both monoenergetic and experimentally simulated Maxwell-Boltzmann (MB) non-local thermodynamic equilibrium (NLTE) plasmas were created for these measurements. The beam plasmas had energies of 2.75, 3.0, 3.6, 4.6, 5.5, 6.0 and 6.5 keV. The MB plasmas had electron temperatures of 2.0, 2.5 and 3.0 keV. M-band gold spectra (n = 4-3, 5-3, 6-3 and 7-3 transitions) were recorded between 1-8 keV from K-like to Kr-like ions in the X-ray. The emission of gold was recorded by crystal spectrometers and a micro-calorimeter from the Goddard Space Flight Center. The experimental charge state distribution was inferred by fitting the observed spectra with modelled spectra from the Hebrew University Lawrence Livermore Atomic Code and the Flexible Atomic Code (FAC). The charge state distribution has been modelled using the SCRAM collisional radiative model with FAC atomic data. Fairly good agreement between the experimental and the calculated charge state distributions for several of the beam plasmas has been achieved by including dielectric recombination from high n = 10 to 15 states. This work was done under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. [Preview Abstract] |
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NP8.00085: Experiment to determine electrical conductivity and equation of state data from Ohmically exploded tamped planar foils - preliminary diagnostic results and modeling E.L. Ruden, D.J. Amdahl, D.J. Brown, T.C. Grabowski, C.W. Gregg, M.R. Kostora, B.M. Martinez, J.V. Parker, J.F. Camacho, S.K. Coffey, P. Poulsen Diagnostic results from initial nondestructive (thick foil, low current) tests are presented for an experiment to simultaneously determine the electrical conductivity, pressure, density, specific energy, and temperature time histories of a planar metal foil tamped by a well characterized transparent material and exploded by a 36~$\mu $F, 50~kV rated capacitor bank discharge. Voltage differentials measure the foil's surface electric field, a B-dot probe measures surface current density, and a laser velocity interferometer (VISAR) measures dynamic foil thickness. From such and future filtered photodiode measurements, the desired properties will be inferred up to a few eV and within an order of magnitude of solid density. The purpose of the present phase of the experiment is to develop and validate diagnostic designs, data analysis techniques, and 2-D MHD simulations of the process using the MACH2 code. [Preview Abstract] |
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NP8.00086: Characteristics of warm dense matter produced by a relativistic electron beam Thomas Kwan, Mark Schmitt, Michael Berninger Accurate equation-of-state theory on warm dense matter is a big challenge to model and good experimental data is difficult to obtain. One of the difficulties is the creation of a warm dense matter (WDM) suitable for experiments to examine its equation of state. We have performed calculations using MCNP and LASNEX to examine the warm dense matter created by a highly energetic electron beam such as the DARHT beam at LANL in a cylindrical sample confined by a collar. Energy deposition by the electron beam in the target and collar of different materials were calculated with different beam profiles. The energy deposition was sourced into LASNEX calculations to examine the dynamic evolution of the target and the generation of radially outward propagating shock waves. Our calculations indicated warm dense matter with a temperature of a few electron volts is achievable and the speed of the shock wave can be determined using photonic Doppler velocimetry technique. We will present results from our calculations for various materials of the target and collar and in different geometries. [Preview Abstract] |
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NP8.00087: Effects of Coulomb and Fermi corrections on the equation of state of dense plasmas Igor Sokolov, Eric Myra, Alexander Potashev In this presentation, we derive corrections for two frequently neglected or poorly approximated components of the equation of state for dense plasmas: (i) the Coulomb correction, which accounts for electron-electron interactions and (ii) the Fermi correction, which accounts for (frequently important) quantum-mechanical behavior of electrons. We demonstrate a more accurate approach to these calculations and discuss their effects on thermodynamic properties, ionization, and emissivity of dense plasmas. [Preview Abstract] |
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NP8.00088: Improving predictive simulation of high-energy-density physics experiments: effects of Coulomb and Fermi corrections Eric Myra, Igor Sokolov, Alexander Potashev The work of Sokolov et al. (also in this poster session) discusses the important effects of Coulomb and Fermi corrections to the thermodynamic properties and emissivity of dense plasmas. In this presentation, we apply these equation-of-state corrections to a set of test problems to help gauge their importance in the predictive simulation of an HEDP experiment. The simulations are performed with the CRASH code, which is a radiation-hydrodynamic simulation code developed at the Center for Radiative Shock Hydrodynamics at the University of Michigan. [Preview Abstract] |
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NP8.00089: Platform development of x-ray absorption-based temperature measurements above 100-eV Paul Keiter, John Benage, Nick Lanier, Kunegunda Belle, Glenn Magelssen, Barbara Devolder, Andrew Comley, John Morton, Mark Taylor Experiments are being performed on the OMEGA laser system at the University of Rochester to develop experimental techniques for measuring the temperature of radiatively heated foams. The development of this technique in the temperature range of 100 -- 200 eV is required for future NIF experiments. We will present a current summary of the experimental data as well as direction for the future campaigns. This was performed by the Los Alamos National Laboratory under the auspices of the United States Department of Energy under contract no. DE-AC52-06NA25396. [Preview Abstract] |
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NP8.00090: X-ray emission measurements from implosion experiments with Fe doped glass capsules Fred Wysocki, John Benage, George Kyrala, Evan Dodd, Doug Wilson Recent results obtained for glass capsule implosions at the Omega laser indicate that when the gas contains a high z dopant gas, simulations do not match the compression and yield of the capsule, even when using a mix model. A critical time for when the experiments deviate from predictions occurs when the reflected shock hits the imploding shell. We have identified two possible issues that the codes may have incorrect, the density of the shell at this critical time and the density and temperature profile in the gas. To address these questions, we are attempting two new measurements in these experiments. These are x-ray radiography of the shell and temporally and spatially resolved temperature and density measurements in the gas. In this poster, we present our plan for the time and space resolved gas measurements utilizing a new multiframe monochromatic imager (MMI) diagnostic. This diagnostic will utilize emission from Fe ions that have been mixed into the gas from the shell. We will present data from some recent measurements that determine the K-shell Fe emission from the gas as a function of Fe dopant levels in the glass. We will also give results for the impact such mixing has on the performance of the capsules. The implications to obtaining the desired temperature and density profiles will be discussed. [Preview Abstract] |
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NP8.00091: Cone-guided Target Acceleration for Impact Ignition Hideo Nagatomo, Masakatsu Murakami, Tomoyuki Johzaki, Hiroshi Azechi Various ignition schemes have been proposed in laser fusion. One of the latest concepts is Impact ignition [1], which does not include uncertain physics, such as laser plasma interaction, or core heating by hot electrons. In the Impact ignition scheme, one of the most critical issues is how to achieve very high speed projectile made of fuel. If most of the kinetic energy of the impactor is converted into thermal energy, the impactor velocity needs to be 1100--1500 km/s to achieve the ignition temperature of Te=5-10keV. In addition, impactor is isolated from impactee, a main fuel part by guiding cone in similar way of Fast ignition. In this study, preliminary numerical simulations were performed for the target acceleration in guiding cone, where radiation transport, shock-wall interaction are included. \\[4pt] [1] M. Murakami and H. Nagatomo, Nucl. Instrum. Methods, Phys. Res., Sect. A 544, 67 (2005).\\[0pt] [2] H. Azechi, et al., Phys. Rev.Lett. 102, 235002 (2009). [Preview Abstract] |
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NP8.00092: Nuclear energy without radioactivity: Laser driven block ignition of hydrogen-lithium7 Heinrich Hora, George Miley Side-on block ignition of uncompressed solid fusion fuel by multi-petawatt-picosecond laser pulses following the Chu-Bobin scheme may be possible using a drastic anomaly of laser-plasma interaction. It is essential that the laser pulses are extremely clean (contrast ratio 10$^{8})$ to avoid relativistic self-focusing$^{1}$ as shown for DT with next available laser pulses after updating the Chu-Bobin scheme.$^{2}$ Using p$^{11}$B (HB11) turned out to be only about ten times more difficult for laser fusion by this side-on ignition in contrast to impossible ignition by the usual spherical laser compression. Results for p-7Li fusion are similar to HB11. Controlled laser fusion energy may be produced with less radioactivity per energy than burning coal. \\[4pt] $^{1}$H. Hora, J. Badziak et al. Phys. Plasmas, \textbf{14}, 072701 (2007);\\[0pt] $^{2}$H. Hora, B. Malekynia et al. Appl. Phys. Lett. \textbf{93}, 011101 (2008);\\[0pt] $^{3}$H. Hora, G.H. Miley et al. Laser {\&} Part. Beams \textbf{27}, (2009) doi:10.1017/8S026303460999022X. [Preview Abstract] |
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NP8.00093: Simulations of Targets for Warm Dense Matter and Inertial Fusion Energy Applications on NDCX II J.J. Barnard, J. Armijo, F.M. Bieniosek, A. Friedman, M. Hay, E. Henestroza, B.G. Logan, R.M. More, P.A. Ni, L.J. Perkins, S.F. Ng, S.A. Veitzer, J.S. Wurtele, S.S. Yu, A.B. Zylstra The Neutralized Drift Compression Experiment II (NDCX II) is an induction accelerator now being constructed at LBNL. The baseline design calls for a 3 MeV, 30 A Li+ ion beam, delivered in a bunch with pulse duration of $\sim $1 ns, and transverse dimension $\sim $ 1 mm. The purpose of NDCX II is to experimentally study material in the warm dense matter regime and ion beam/hydrodynamic coupling, relevant to heavy ion fusion. In preparation for NDCX II, we have performed hydrodynamic simulations of ion-beam-heated, metallic targets, connecting observable quantities with the simulated density, temperature, and velocity, exploring the sensitivity of EOS on observables. Simulated target geometries include spherical and cylindrical bubbles (to create regions of higher pressure), and planar solid and foam targets. Pulse formats include single pulses of fixed ion energy $E$, and single and double pulses with variable $E$ to study ion-coupling efficiency. Comparisons are made with simulations of ion driven direct drive capsules that show high coupling efficiencies. [Preview Abstract] |
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NP8.00094: Optimized Ion Energy Profiles for Heavy Ion Direct Drive Targets Michael J. Hay, John J. Barnard, L. John Perkins, B. Grant Logan Recent 1-D implosion calculations [1] have characterized pure-DT targets delivering gains of 50-90 with less than 0.5 MJ of heavy ion direct drive. With a payload fraction of 1/3, these low-aspect ratio targets operate near the peak of rocket efficiency and achieve $\sim $10{\%} overall coupling efficiencies (vs. the 15-20{\%} efficiencies analytically predicted for less stable, higher-aspect ratio targets). In Ref. 1, the ion energy is ramped directly from a 50 MeV foot pulse to a 500 MeV main pulse. In this paper, we instead tune the ion energy throughout the drive to closely match the beam deposition with the inward progress of the ablation front. We will present the ion energy and intensity time histories that maximize drive efficiency and gain for a single target at constant integrated drive energy. [1] L. J. Perkins, B. G. Logan, J. J. Barnard, and M. J. Hay. ``High Efficiency High Gain Heavy Ion Direct Drive Targets,'' \textit{Bulletin of the American Physical Society}, vol. 54: DPP, Nov. 2009. [Preview Abstract] |
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NP8.00095: Warm Dense Matter Experiments Driven by Ion Beams F.M. Bieniosek, E. Henestroza, J.Y. Jung, M.A. Leitner, S. Lidia, B.G. Logan, R.M. More, P.A. Ni, P.K. Roy, P.A. Seidl, W.L. Waldron, J.J. Barnard, A. Friedman Intense beams of heavy ions are capable of heating volumetric samples of matter to high energy density. We present results from warm dense matter (WDM) experiments at NDCX-I. The 0.3 MeV, 30-mA K$^{+}$ beam from the NDCX-I accelerator heats foil targets by combined longitudinal and transverse neutralized drift compression of the ion beam to a spot size $\sim $ 1 mm, and compressed pulse length $\sim $ 2 ns. The uncompressed beam flux is $\ge $500 kW/cm$^{2}$, and the compressed pulse flux is $>$ 5 MW/cm$^{2}$. Both the compressed and uncompressed parts of the NDCX-I beam heat targets. Future plans include construction of the NDCX-II accelerator, which is designed to heat targets at the Bragg peak using a 3-4 MeV lithium ion beam. We have developed a target chamber and target diagnostics including a fast multi-channel optical pyrometer, optical streak camera, and high-speed gated cameras. We compare measurements of temperature, droplet formation and other target parameters with model predictions. Continued improvements in beam tuning, bunch compression, and other upgrades are expected to yield higher flux on target. [Preview Abstract] |
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NP8.00096: Thermal simulations of the NDCX-I target experiments E. Henestroza, F.M. Bienioske, P.A. Ni, R.M. More, J.J. Barnard Experiments on ion-beam target heating use a 0.3 MeV K+ beam from the Neutralized Drift Compression Experiment (NDCX-I) accelerator at LBNL. The NDCX-I delivers a long pulse beam (several microseconds) with a power density of 500 kW/cm$^2$ over a sampled spot size on the target of several hundred micrometers. With the addition of an imposed velocity tilt from an induction core, the NDCX-I can compress a portion of the long pulse to reach a power density of 25 MW/cm$^2$ over 2 nanoseconds. Under these conditions, the free-standing thin foil targets used in the experiments go through the melting and vaporization phases to reach temperatures up to 4000 K. Since the targets are thin foils of fractions of a micron in thickness we can model the target thermal dynamics using the equation of heat conduction for the temperature T(x,t) as function of time and the spatial dimension along the beam direction; we also include cooling processes from energy flux from the surface of the foil due to evaporation, radiation, and thermionic (Richardson) emission. [Preview Abstract] |
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NP8.00097: Numerical studies on plasma jets and minirailguns at HyperV Linchun Wu, F. Douglas Witherspoon, Dale R. Welch, Michael W. Phillips Computational study of plasma jets using contoured gap coax and parallel plate minirailguns are underway using helium, argon and xenon plasmas with injection speeds of up to 10-20 km/s and plasma density of 10$^{15}$ - 10$^{17}$ cm$^{-3}$. The study is performed using the recently improved Lsp code, which now implements a new sheath model and direct implicit algorithms enabling more accurate and faster simulations. The new radiation transport model in Lsp, with atomic data from Prism, is used in these 2D simulations. Results are shown and compared between these high-Z plasma species. Blow-by instability and restrike are observed in these simulations and will be discussed. The effects of ion stripping on high-Z plasma acceleration in the railguns will be studied as well using available atomic data. Work supported by the U.S. DOE Office of Fusion Energy Sciences. [Preview Abstract] |
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NP8.00098: 3D Kinetic Simulation of Plasma Jet Penetration in Magnetic Field Sergei A. Galkin, I.N. Bogatu, J.S. Kim A high velocity plasmoid penetration through a magnetic barrier is a problem of a great experimental and theoretical interest. Our LSP PIC code 3D fully kinetic numerical simulations of high density (10$^{16}$ cm$^{-3})$ high velocity (30-140 km/sec) plasma jet/bullet, penetrating through the transversal magnetic field, demonstrate three different regimes: reflection by field, penetration by magnetic field expulsion and penetration by magnetic self-polarization. The behavior depends on plasma jet parameters and its composition: hydrogen, carbon (A=12) and C$_{60}$-fullerene (A=720) plasmas were investigated. The 3D simulation of two plasmoid head-on injections along uniform magnetic field lines is analyzed. Mini rail plasma gun (accelerator) modeling is also presented and discussed. [Preview Abstract] |
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NP8.00099: IMC Photonics in HYDRA NIF Simulations G.D. Kerbel, M.M. Marinak, N. Gentile One option in the radiation hydrodynamics code HYDRA for computing radiation transport is IMC (Implicit Monte Carlo) direct simulation. Well-converged simulations run with IMC spend most of their time doing radiation transport. We desire the run time to be as short as possible for the (NIF) experimental campaign and thus we have focussed efforts on ways to speed the IMC computation. Techniques were implemented to accomplish variance reduction through angular biasing, reducing the amount of computation required for given accuracy. We have improved load balance through multi-level parallelism and dynamic domain data distribution across processes. In addition we have added domain data replication to attain strong scaling with process count as more computing resources become available. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. [Preview Abstract] |
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NP8.00100: New capabilities in HYDRA for simulations of Inertial Confinement Fusion targets M.M. Marinak, G.D. Kerbel, J.M. Koning, M.V. Patel, S.M. Sepke, P.N. Brown, B. Chang, R. Procassini, D. Larson A variety of new capabilities have been installed in the HYDRA 2D/3D multiphysics ICF simulation code. We discuss how these enhance its ability to simulate various aspects of inertial confinement fusion targets. A novel polar S$_{N}$ multigroup radiation transport package now operates on 2D meshes. It converges with second order accuracy without significant ray effects. Simulations of targets illuminated with short pulse lasers are now possible by running HYDRA in conjunction with an explicit relativistic particle in cell code. Data is exchanged between the two codes automatically, enabling the plasma heating and magnetic fields generated by the short pulse laser to be included consistently in the full target simulation. A Monte Carlo burn package has also been incorporated and is being applied to model diagnostic signatures of neutrons, gamma rays and charged particles produced in NIF capsule implosions. [Preview Abstract] |
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NP8.00101: The Hydra Magnetohydrodynamics Package J.M. Koning, G.D. Kerbel, M.M. Marinak The Magnetohydrodynamics package of the ALE radiation-hydrodynamics code Hydra is being extended to model the magnetic field and its effect on temperature for ICF targets. The current package capabilities include a fully three-dimensional resistive MHD package in the small Hall limit. An operator split method is used to couple the MHD to the hydrodynamics and is fully implicit in time and second order accurate in space. A three-dimensional vector finite element method is utilized to define a set of spaces and differential operators that maintain the zero divergence of the magnetic field exactly. The Hydra MHD package has been improved by the addition of an exact circuit solution method that enables the potential for multiple circuits. A significant enhancement of Hydra is the addition of a Python interpreter embedded in the code. The Python interpreter allows users to make full use of Python's features in parallel with full access to the parameters and variables in the simulation. Examples of the Python interpreter used with MHD package and Hydra in general will be presented. [Preview Abstract] |
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NP8.00102: Simulating NIF Neutron Diagnostics with HYDRA Mehul V. Patel, Scott Sepke, Michael M. Marinak, Michael S. McKinley, Matthew O'Brien, Richard Procassini, Doug Wilson LLNL's 3D radiation hydrodynamics code, HYDRA, is routinely used for modeling laser inertial confinement fusion (ICF) targets (both direct drive and indirect drive). Since neutron and gamma diagnostics will play a critical role in assessing the performance of capsule implosions at the National Ignition Facility (NIF), we have installed a particle Monte Carlo (PMC) package into HYDRA to model the transport of light nuclei (Z=1,2), gammas, and neutrons. The PMC package uses both domain decomposition (using HYDRA's existing computational domains) and dynamic replication of domains to maximize utilization of available computational resources. Recent results from simulations of NIF capsules will be presented to demonstrate our ability to produce realistic simulated neutron images and spectra. [Preview Abstract] |
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NP8.00103: Modeling ICF Spherical Implosion Instabilities in 3D with Exact Energy Conservation Milad Fatenejad, Gregory Moses We will present the results of 3D instability simulations performed on spherically convergent geometries with a new 3D Lagrangian hydrodynamics code, cooper. The code uses a compatible discretization of the conservation equations to ensure that energy is conserved to within machine round off error [Caramana \textsl{JCP} 146, 227 (1998)]. Modifications are made to the discrete equations to ensure that spherically symmetric implosions can be performed on non-orthogonal Cartesian grids [Caramana \textsl{JCP} 157, 89 (2000)]. Subzonal restoring forces counteract anomalous grid distortions [Carmana \textsl{JCP} 142, 521 (1998)] and an edge-centered viscosity is used to capture shocks [Caramana \textsl{JCP} 215, 385 (2006)]. Cooper is parallelized using domain decomposition. This is necessary due to the large processor and memory requirements associated with simulations in three dimensions. Advanced computational libraries are used to reduce the complexity of the code without sacrificing features. One example is the MOAB library [Tautges \textsl{Engr. Comput.} 20, 286 (2004)] which manages the mesh and is responsible for communicating information between processes. [Preview Abstract] |
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NP8.00104: Simulation of the Radiative Emission from Plasmas Based on LSP Particle-In-Cell Simulations Joseph MacFarlane, Igor Golovkin, Pamela Woodruff, Dale Welch, Carston Thoma, Douglas Witherspoon Particle-in-cell (PIC) simulation codes are valuable tools in simulating the physical properties of plasmas in a wide variety of high energy density laboratory plasma experiments. Two examples of this are short-pulse laser experiments, which are used to study the fast ignition concept for inertial fusion, and plasma jet experiments, which are of interest to magnetic fusion and mageto-inertial fusion studies. The LSP code is a widely-used PIC simulation code that computes the detailed characteristics of electron and ion particle distributions in such experiments. To compute the radiative emission characteristics of plasmas based on PIC simulation predictions, we use the SPECT3D multi-dimensional collisional-radiative package to generate high-resolution spectra and images which can be compared with experimental measurements. SPECT3D includes the effects of energetic particles (including relativistic electrons) in computing non-LTE atomic level populations, emergent spectra, and images for the target plasma. We will present results for the radiative characteristics of plasmas created in short-pulse laser and plasma jet experiments. [Preview Abstract] |
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NP8.00105: Simulation of non LTE opacity with incoming radiation Marcel Klapisch, Michel Busquet Simulation of radiative properties of hot plasmas is important for ICF, other laboratory plasmas, and astrophysics. When mid-Z or high-Z elements are involved, the spectra are so complex that one commonly uses LTE approximation. This was recently done in interpreting a carefully calibrated experiment on Fe at 160 eV [1]. However some disagreement remains concerning the ion charge distribution. The newest version of HULLAC [2] has the capability to take into account an incoming radiation field in solving the rate equations of the coronal radiative model (CRM). We will show results with different representation of the radiation field.\\[4pt] [1] J.E. Bailey, G.A. Rochau, C.A. Iglesias, et al., Phys. Rev. Lett. 99, (2007) 265002-4.\\[0pt] [2] M. Klapisch and M. Busquet, High Ener. Dens. Phys. 5, (2009) 105-9. [Preview Abstract] |
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NP8.00106: Particle-in-Cell Simulations of the High Frequency Hybrid Instability and Two Plasmon Decay Frank Tsung, W.B. Mori, B.B. Afeyan A comprehensive set of PIC simulations of laser-plasma interactions at or near the quarter critical density of laser-produced plasmas has been conducted. In order to isolate physical effects, we conduct fixed, mobile ion simulations, and simulations with rapid and adiabatic rise times. In the fixed ion simulations near threshold the instability is dominated by absolute modes with growth rates and ranges of transverse wave numbers in agreement with the theoretical results Afeyan and Williams (1995 {\&} 1997)[1,2]. These include the high frequency hybrid modes (HFHI). Further above threshold, modes with larger transverse wave numbers occur at lower densities and these were identified as convective modes. There can be a strong interaction between the modes at low density and the absolute modes at higher densities on the hot electron spectrum. The role of the adiabatic rise time on the instability will be discussed. Finally, we will also investigate the role of mobile ions on the excitation of the 2wp/HFHI modes, and the subsequent absorption of speckles in regimes relevant to direct ICF and fundamental HEDLP studies. [1] B. B. Afeyan, E. A. Williams, \textit{Phys. Rev. Lett.,}\textbf{ 75} 4218 (1995). [2] B. B. Afeyan, E. A. Williams, \textit{Phys. Plas., }\textbf{4}, 3827 (1997). [Preview Abstract] |
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NP8.00107: Condensed Matter Deuterium Cluster Target for Study of Pycnonuclear Reactions Xiaoling Yang, Miley George Fusion reactions have two main classes: thermonuclear and the pycnonuclear. Thermonuclear fusion occurs in low density high temperature plasmas, and is very sensitive to the ion temperature due to Columbic repulsion effects. As the density increases, the Columbic potential barrier is depressed by increased electron screening, allowing fusion at lower temperatures. This type of nuclear reaction is termed a pycnonuclear fusion and is the basis for astrophysical fusion. Ichimarua [1] proposed a laboratory study of this process using explosive mechanical compression of H/D to metallic densities, which would be extremely difficult to implement. Instead, our recent research suggests that metallic-like H/D ``clusters'' can be formed in dislocation loops of thin Palladium foils through electrochemical processes. [2] If this technique is used as a laser compression target, the compressed cluster density would allow study of pycnonuclear reactions. This provides a means of studying astrophysical fusion process, and could also lead to an important non-cryogenic ICF target. [2] \\[4pt] [1] S. Ichimaru, H. Kitamura. Phys. Plasmas, 6, 2649 (1999) \\[0pt] [2] G. Miley and X. Yang, Deuterium Cluster Target for Ultra-High Density, 18TH TOFE, San Francisco, CA Sep. 28 -- Oct. 2, 2008 [Preview Abstract] |
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NP8.00108: New features in OSIRIS 2.0 R.A. Fonseca, S.F. Martins, P. Abreu, J. Martins, F. Fi\'uza, J. Vieira, L.O. Silva, V. Decyk, F. Tsung, J. Tonge, W.B. Mori OSIRIS 2.0 [1] is a state of the art, fully relativistic massively parallel particle in cell code, that is widely used in kinetic plasma modeling for many astrophysical and laboratory scenarios. We report on the new developments done in the code, focusing on the new high performance vector SIMD code (Altivec/SSE3) for single precision calculations, detailing performance and floating point efficiency, and also parallel I/O for diagnostics, allowing for higher performance and scalability on HPC systems. We will also describe the new numerical precision features in the code, and we will also present the new algorithms incorporated into the code, in terms of field solver (4$^{th}$ order Yee solver, etc.), new filtering techniques, perfectly matched layers (PML) boundary conditions, and boosted frame simulations. Finally, we also report on a new diagnostic tool to calculate the radiation produced with wavelengths below the simulation grid resolution. \\[4pt] [1] R. A. Fonseca et al., LNCS 2331, 342, (2002) [Preview Abstract] |
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NP8.00109: Progress report in developing a 3D parallel object-oriented Vlasov-Fokker-Planck code Michail Tzoufras, Anthony Bell, Raoul Trines, Peter Norreys, Frank Tsung We utilize the expansion of the electron distribution function to spherical harmonics to design an object-oriented VFP code [1]. Using this approach we significantly reduce the size of the computational grid, compared to what is required by standard VFP codes, thereby making it possible to model the entire distribution function in three dimensions. The object-oriented design allows for parallelism and interchangeability of numerical operators. The performance of the most up-to-date version of the code in terms of speed, accuracy and stability is discussed for standard plasma physics problems.\\[4pt] [1] A. R. Bell et al., Plasma Phys. Control. Fusion 48 (2006) R37-R57. [Preview Abstract] |
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NP8.00110: Simulating the NDCX-II Physics Design W.M. Sharp, A. Friedman, D.P. Grote, R.H. Cohen, S.M. Lund, M. Leitner, J.-L. Vay, W.L. Waldron The Virtual National Laboratory for Heavy-Ion Fusion is developing a physics design for NDCX-II, an experiment to study warm dense matter heated by ions near the Bragg-peak energy. Present plans call for using thirty-four induction cells to accelerate 30 nC of Li$^{+}$ ions to more than 3 MeV. Neutralized drift-compression is then used to compress the beam to the sub-millimeter radius and 1-ns duration needed to attain useful target temperatures. A 1-D particle-in-cell simulation ASP has been used for developing the NDCX-II acceleration schedule, and centroid equations have recently been added to study the effects of transverse-focusing errors. Multidimensional simulations with Warp have validated the ASP model and have been used both to design transverse focusing and to compensate for injection non-uniformities and 3-D effects. Results from this work are presented, and ongoing work to replace the analytic waveforms with output from circuit models is discussed. [Preview Abstract] |
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NP8.00111: EDGE |
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NP8.00112: Flush-mounted probes smaller than the ion gyroradius Ilon Joseph, Ron Cohen, Dmitri Ryutov When an electrically conducting probe with a cross-section that is smaller than an ion gyro-radius but larger than an electron gyro-radius is placed within a magnetized plasma, the electrostatic perturbation that is produced develops an extremely long length scale parallel to field lines. For such small-scale disturbances, collisions play an important role in determining the response of the lowest-order distribution function. In the fluid picture, the ion viscous force dominates and the ions effectively become demagnetized. Kinetically, the dominant non-adiabatic response is generated by electron-ion friction rather than parallel streaming, because the parallel length scale is typically much longer than the mean free path. This study also has direct application to the linear dispersion relation of modes that are dominated by electron-scale physics. For example, divertor leg instabilities can be terminated near an X-point due to the development of fine scales through the action of magnetic shear. The non-adiabatic correction to the dispersion relation of these modes is determined. [Preview Abstract] |
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NP8.00113: Peeling-Ballooning Mode Analysis in Shifted-Circle Tokamak Equilibria B. Burke, S.E. Kruger, C.C. Hegna, P.B. Snyder, C.R. Sovinec, P. Zhu Progress in understanding edge localized modes (ELMs) has been made by investigating the stability properties of edge localized peeling-ballooning modes. We focus on the evolution of ideal MHD modes over a large spectrum in two shifted-circle tokamak equilibria, using the extended-MHD code NIMROD. The TOQ-generated equilibria model a H-mode plasma with a pedestal pressure profile and parallel edge currents. ~A vacuum region is prescribed by a resistivity profile that transitions from a small to very large value at a specified location. The vacuum model is benchmarked against the linear ideal MHD codes ELITE {\&} GATO. We demonstrate vacuum effects on the stability by adjusting the vacuum location relative to the pedestal pressure region. Ballooning-like instabilities dominate distant vacuum cases, whereas peeling mode physics is expected to dominate as the vacuum approaches the pedestal. Numerical simulations of the early nonlinear stages of edge localized MHD instabilities are presented. Comparisons between equilibria that have ``ballooning'' dominated instabilities relative to equilibria that are ``peeling'' dominated are made. [Preview Abstract] |
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NP8.00114: Numerical Simulation of Giant Sawteeth in Tokamaks Using the NIMROD Code D.D. Schnack, S.E. Kruger, C.C. Kim, A.D. Turnbull A minority population of energetic particles can stabilized the n=1 sawtooth mode in tokamaks. This allows for giant sawteeth with long period and large amplitude. The crash can lead to degradation of confinement, NTM and ELMs, and a significant loss of stored energy. This could have important implications for the design and operation of ITER. In order to evaluate the efficacy of the Porcelli model, extensive linear studies have been performed recently to analyze the sawtooth activity in DIII-D discharge \#96043 through a sequence of equilibria reconstructed from experimantal data[1]. The results were consistent with the observed sawtooth crash. Here we begin a computational study of the non-linear consequences of the crash of a giant sawtooth using the NIMROD Extended MHD code[2]. We use the series of equilibrium reconstructions considered in Ref. 2. Initial linear results for both MHD and extended MHD, including energetic particle effects, are presented.\\[4pt] [1] M. Choi, A. D. Turnbull, V. S. Chan, et al., Phys. Plasmas 14, 112517 (2007).\\[0pt] [2] C. R. Sovinec, et al., J. Phys. Conf. Ser. 16, 25 (2005). [Preview Abstract] |
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NP8.00115: Modeling anomalous radial transport in kinetic transport codes K. Bodi, S.I. Krasheninnikov, R.H. Cohen, T.D. Rognlien Anomalous transport is typically the dominant component of the radial transport in magnetically confined plasmas, where the physical origin of this transport is believed to be plasma turbulence. A model is presented for anomalous transport that can be used in continuum kinetic edge codes like TEMPEST, NEO and the next-generation code being developed by the Edge Simulation Laboratory. The model can also be adapted to particle-based codes. It is demonstrated that the model with a velocity-dependent diffusion and convection terms can match a diagonal gradient-driven transport matrix as found in contemporary fluid codes, but can also include off-diagonal effects. The anomalous transport model is also combined with particle drifts and a particle/energy-conserving Krook collision operator to study possible synergistic effects with neoclassical transport. For the latter study, a velocity-independent anomalous diffusion coefficient is used to mimic the effect of long-wavelength ExB turbulence. [Preview Abstract] |
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NP8.00116: Comparison of cross-magnetic-field drift algorithms in UEDGE. S.K. Nam, T.D. Rognlien Inclusion of ExB, gradient-B, and curvature drift terms in 2D edge plasma transport codes typically results in substantially slower convergence or lack of convergence for obtaining steady-state profiles. Those cases where convergence is obtained show that drifts can have a strong effect of the scrape-off layer plasma profiles and flows, and thus improvement of the efficiency and robustness of edge transport codes with drifts is a high priority, especially as these codes become components within integrated whole-device models. Rozhansky \textit{et al.} [Nucl. Fusion 49 (2009) 025007] have proposed a new numerical formulation of the drift terms, and it is shown to improve the SOLPS code performance and accuracy, though an artificial stabilizing diffusive term is still required beyond the physical turbulent diffusive term. While the fully implicit algorithm in UEDGE requires no separate stabilizing term, it often does exhibit convergence difficulties for steep-gradient cases. Results from UEDGE implementation of the Rozhansky algorithm are presented and compared to the original algorithm for performance and accuracy. [Preview Abstract] |
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NP8.00117: Coupled turbulence and transport simulations for edge plasmas. T.D. Rognlien, M.V. Umansky, R.H. Cohen, X.Q. Xu Coupling between edge turbulence and transport has been demonstrated in the past using a type of Relaxed-Iteration Coupling (RIC) scheme [Shestakov et al., JCP 185 (2003) 399] where time-averaged turbulent fluxes (BOUT) are coupled to a transport code (UEDGE) in a series of time-lagged iteration to find a steady-state solution [Rognlien et al., JNM 337-339 (2005) 327]. A key issue for such a method applied to edge turbulence relates to the fact that here the transport events can be large, intermittent, and have spatial scales comparable to equilibrium gradients. Thus, the long-time averages of the resulting transport fluxes coupled to the transport code may not faithfully represent the actual transport/profile-modifications from large events. This issue is quantified by comparing BOUT/UEDGE simulations using the RIC algorithm to more time-consuming direct simulations where BOUT evolves the edge plasma profiles at each step of the turbulence simulation during the course of a long transport timescale simulation. [Preview Abstract] |
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NP8.00118: Tests of and plans for the ESL Code R.H. Cohen, M. Dorr, T.D. Rognlien, X.Q. Xu, P. Colella, D. Martin The Edge Simulation Laboratory (ESL) is a multi-institutional collaboration to develop kinetic edge codes using continuum techniques. A new code, based on fourth-order conservative finite-volume discretization of gyrokinetic equations, has recently become operational. Initially the code is electrostatic, 4D (axisymmetric), with a Miller (core, shaped) geometry, but with the optional addition of a toroidal limiter to provide a scrape-off-layer region. A number of test simulations have been or are being carried out, including advection and magnetic mirroring of phase space blobs, evolution of steep radial density and temperature profiles, collisional loss to a limiter with a model collision operator, and geodesic acoustic modes in periodic and bounded domains. Results of this test campaign will be reported. In addition we report on progress/plans for adding capability to the code, in particular extending the code to full divertor geometry, 5D, and, ultimately, electromagnetic physics. [Preview Abstract] |
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NP8.00119: Drift-orbit loss at the null-point in a snowflake divertor configuration M.V. Umansky, D.D. Ryutov The prompt loss of ion drift orbits at the null point may be an important effect in divertor tokamak edge plasmas [1]. In the snowflake divertor configuration [2], the prompt loss may be quite different from that in the standard X-point configuration, due to a quadratic dependence of the poloidal magnetic field on the distance from the null point. As a result, the zone affected by the prompt loss in snowflake geometry is significantly larger than that in the standard X-point configuration [3]. Continuing the analytic study in [3], here we consider more complicated cases using numerical calculation of drift orbits, including the effects of electric field and collisions. As a special case we include the case of heavy impurity ions in low charge states, where the effect of the vertical drift is the strongest. Results will be presented for realistic snowflake-like configurations based on parameters of existing tokamaks.\\[4pt] [1] C.S. Chang, S. Kue, and H. Weitzner, Phys. Plasmas, 9, 3854 (2002).\\[0pt] [2] D.D. Ryutov, Phys. Plasmas, 14, 064502, June 2007.\\[0pt] [3] D.D. Ryutov and M.V. Umansky, presentation at TTF 2009. [Preview Abstract] |
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NP8.00120: Instabilities and coherent structures in long-legged divertors D.D. Ryutov, R.H. Cohen, I. Joseph, T.D. Rognlien, M.V. Umansky In some versions of tokamak divertor designs the distance between the strike point and the X-point is large, approaching and even exceeding the tokamak minor radius (e.g., R.W. Conn et al, Nucl. Fusion Suppl., v. 3, p. 203, 1977; P.M. Valanju et al, Phys. Plasmas, 16, 056110, 2009). In such a situation, the plasma propagates from the vicinity of the X-point to the divertor plate along a narrow channel (``divertor leg''). The presence of a large geometrical factor, the length-to-thickness ratio, enhances the role of particle drifts and leads to the appearance of significant parallel currents, thereby enhancing the role of the divertor-plate boundary conditions. The divertor modes associated with the finite-beta effects (R.H. Cohen, D.D Ryutov. PPCF, 47, 1187, 2005) become more virulent and may lead to formation of a specific type of finite-beta blobs. The characteristics of these blobs are evaluated and possible damage to the vacuum chamber in the divertor legs is discussed. Prepared by LLNL under Contract DE-AC52-07NA27344. [Preview Abstract] |
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NP8.00121: Edge gyro-kinetic transport simulations with a kinetic neutral model X.Q. Xu We report on the derivation of a kinetic neutral model for gyro- kinetic continuum codes. The dominant interactions for hydrogen atoms are charge-exchange with proton, ionization by electron impact and three-body-recombination of ion-electron pairs back to neutrals. Since a neutral dynamics is intrinsic 3D in velocity space, while gyro-kinetic ion dynamics are 2D after gyro-averaging. A proper formulation will be presented to ensure that the essential physics is kept and conservation properties are preserved. An efficient numerical mapping between ion velocity coordinates and neutral velocity coordinates will have to be developed. Assuming the charge-exchange with proton to be dominant process, a simplified neutral diffusion model can be derived. In this case, both neutrals and ions could use the same velocity coordinates and therefore no coordinate mapping is needed. The preliminary simulations with the neutral model will be reported for plasma transport and flow dynamics in single- null tokamak geometry, including the pedestal region that can extend across the separatrix into the scrape-off layer (SOL) and private flux region. [Preview Abstract] |
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NP8.00122: Self-consistent edge-wall simulations with WALLPSI in FACETS A. Pigarov, S. Krasheninnikov, J. Cary, A. Hakim, S. Kruger, M. Miah, A. Pletzer, S. Shasharina, R. Cohen, T. Rognlien, T. Epperly The Framework Architecture for Core-Edge Transport Simulations (FACETS) is a SciDAC project for self-consistent simulations of core-edge-wall transport in tokamaks using leadership class computers [1]. For analysis of transient peak power load handling, PFC erosion/deposition and lifetime, plasma impurity contamination, and hydrogen retention issues in FACETS, we developed the 1D continuum code WALLPSI [2]. WALLPSI simulates highly non-linear transport, release and trapping of hydrogen species in wall, and calculates the wall temperature and emerging impurity fluxes. We present progress on the development of an interface to allow WALLPSI to be invoked from within the multiple-component FACETS infrastructure. Each wall segment is modeled by WALLPSI instance which are all run concurrently on separate CPUs. FACETS provides the mechanism for coupling the wall to plasma transport code UEDGE. The results are presented showing non-linear variation of hydrogen species wall inventory in response to incident plasma fluxes and abrupt changes in edge plasma parameters caused by wall switching from net pumping regimes to net outgassing ones using an initial slab edge plasma setup. [1] J.Cary et al J.Physics CS 125(2008)012040 [2] A.Pigarov et al JNM 390(2009)192 [Preview Abstract] |
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NP8.00123: Kinetic simulation of the plasma edge on high performance computers David Tskhakaya, Ralf Schneider, Siegbert Kuhn In the present contribution we describe results of to our knowledge first fully kinetic simulations of the plasma edge on High Performance Computers (HPC) with more than 500 processors. We demonstrate that these new type of modeling allow to simulate large (few meter size) systems with finest resolution up to Debye length and electron Larmor radius. The developed parallel BIT1 code incorporates new physics-based parallel 1D solver and adaptive processor loading scheme allowig highly scalable parallel runs for strongly nonuniform plasma edge. As an example, we consider kinetic simulations of the 1D plasma, 2D neutral and impurity transport in the tokamak Scrape-of Layer. The developed model includes nonlinear interaction between all particle species and linear plasma recycling and impurity sputtering models. [Preview Abstract] |
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NP8.00124: Initial Results from a Coupled Kinetic Plasma - Neutral Transport Code D.P. Stotler, C.S. Chang, G. Park To provide a kinetic neutral simulation capability for the Center for Plasma Edge Simulation, a subroutine interface to the DEGAS~2 Monte Carlo neutral transport code has been implemented and coupled into the XGC neoclassical particle transport code. The neutral transport routine simulates the collision of kinetic neutrals with a fluid plasma background provided by XGC; a complementary collision routine in XGC handles plasma particle collisions with a fluid neutral background. While mass conservation between the plasma and neutral species is ensured, the rates at which momentum and energy are exchanged will not be the same in the two calculations to the degree that the kinetic distributions are non-Maxwellian. We assess non-conservation of the instantaneous and time integrated momentum and energy exchanges in a physically relevant simulation. We will also compare the resulting neutral penetration and pedestal buildup obtained with that computed by the rudimentary Monte Carlo neutral transport routine used in the original XGC code. Extensions, such as the inclusion of molecules and time dependence, will be discussed. [Preview Abstract] |
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NP8.00125: Baseline neoclassical scaling law on H-mode pedestal width from XGC0 kinetic simulation Gunyoung Park, C.S. Chang, S. Ku In the H-mode pedestal before the ELM onset, nonlocal neoclassical self-organization is an important physical effect, to set the baseline pedestal width scaling law. Deviation from the neoclassical scaling will define the anomalous scaling. The neoclassical self-organization includes effects from the self-consistent radial electric field shear, strong magnetic field shear, ion-orbit loss across the last closed magnetic surface, finite ion banana width, particle source from neutral ionization, heat flux from the core plasma, and collisional transport. XGC0 code is used to perform an inter-machine study of the neoclassical pedestal scaling law between two representative devices DIII-D (low-B, low collisionality) and C- Mod (high-B, high collisionality). Anomalous scaling component in the experimental pedestal width data will be separated out from the neoclassical component. Prediction for ITER pedestal will be attempted based upon the combined neoclassical (theoretical) and anomalous (empirical) scaling laws obtained in this study. This ion-electron study indicates that the neoclassical pedestal width is broader than the previous ion only study results, closer to experimental pedestal width. [Preview Abstract] |
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NP8.00126: Nonlocal theory for the excitation of GAMs in the edge region of tokamak plasmas R.G. Kleva, P.N. Guzdar, N. Chakrabarti, J.J. Rasmussen, V. Naulin, P.K. Kaw, R. Singh A nonlocal theory of the excitation of geodesic acoustic modes by drift waves in an inhomogeneous plasma typical of the edge region of tokamaks, has been developed. The continuum GAM modes with coupling to the drift waves can give rise to discrete ``global'' unstable eigenmodes localized in the edge ``pedestal'' region of the plasma. These global eigenmodes have a two-space scale character. Inclusion of finite beta effects of the drift waves shows that the excitation of GAMs by the three-wave parametric coupling is stabilized by the Maxwell-Stress component of the nonlinear coupling. We will present comparison of our theoretical/numerical model with observations of GAMs spatial structure observed in various tokamak devices. [Preview Abstract] |
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NP8.00127: Modeling on Pellet Injection in Tokamak Plasmas Ki Min Kim, Hyunsun Han, Yong-Su Na, Sang Hee Hong, P.T. Lang, B. Alper, A. Boboc Modeling on pellet injection in tokamak plasmas is conducted with a 1.5D core transport code. The calculated electron density evolution after the sequential pellet injections appear to be in good agreements with the JET measurements. Some discrepancies are observed on the particle transport in the higher density enhanced in each pellet fueling phase. The modeling reproduces the measured data more closely by increasing the plasma transports when approaching the higher density. Based on this simulation, the pellet fueling in KSTAR is predicted to provide the design parameters of a pellet launching system. ELM triggering by pellet is studied with the transport code as well, which discusses that the enhancements of surface-averaged pressures and locally-perturbed pressure gradients by pellets might be responsible for driving the ideal ballooning mode to trigger ELMs. Density-enhanced ELMs in the post pellet phase are presented as additional ELMs induced by pellet injection. [Preview Abstract] |
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NP8.00128: On dust grain interactions with fusion plasmas Sergei Krasheninnikov, Roman Smirnov Recently different aspects of dust physics in fusion devices brought additional attention from both theoreticians and experimentalists, which, in part, was motivated by the work on the ITER project. To predict the role of dust in core plasma contamination and material migration we need to use some models describing the processes of the interactions of dust grains with fusion plasmas (including charging, forces and energy deposition). So far the models based on the interactions of collisionless plasma with the grain immersed in the self-consistent ambipolar electric field, which were developed for the study of so-called ``dusty plasmas'' are utilized. However, rather hot and dense edge plasma environment in fusion devices results in a strong heating of dust grain and subsequent grain sublimation and evaporation. When the vapor density and/or the amount of ionized impurity atoms become large enough they can alter the grain-plasma interactions. Somewhat similar processes occur during pellet injection in fusion plasma and the interactions of comets with sun radiation and Earth atmosphere. In this presentation we discuss: i) dust and plasma parameter range where the role of dust grain evaporation/sublimation and the processes associated with it do not have a significant impact on grain-plasma interactions, and ii) statistical issues of the description of dust-pasma interactions. This work was supported the US DoE under Grant DEFG02-04ER54852. [Preview Abstract] |
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NP8.00129: Li Experiments at the Tokamak T-11M Toward PFC Concept of Steady State Tokamak-Reactor S.V. Mirnov As practical method of using a liquid lithium as a renewable plasma-facing component (PCF) for steady state tokamak-reactor the concept of lithium emitter-collector is considered [1]. It is based on lithium filled capillary porous system proposed by V.A. Evtikhin et al. (1996). The lithium circulation process consists of four steps: (1) Li emission from the PFC emitter into the plasma; (2) plasma boundary cooling by non-coronal Li radiation; (3) Li ion capture by the collector (before they are lost to the tokamak chamber wall); (4) Li return from the collector to the emitter. T-11M tokamak experiments have used three local rail limiters made from lithium, molybdenum and graphite as lithium collectors. The lithium behavior was studied by analysis of the witness samples, and by a mobile graphite probe. The key findings are: (1) lithium collection on the ion side of the lithium limiter is 2-3 times larger than on the electron side; (2) total efficiency of Li collection integrated over all three rail limiters can reach 50-70{\%} of the lithium emission during the discharge pulse, while the theoretical limit is about 90{\%}. [1] S.V. Mirnov, J. Nucl. Mat., \textbf{390-391}, 876 (2009). [Preview Abstract] |
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NP8.00130: Sputtering and Evaporation Studies of Lithiated Graphite Vijay Surla, Kenzo Ibano, Martin Neumann, David Ruzic To understand the complex system of lithiated ATJ graphite, studies of sputtering and evaporation of lithium and lithiated ATJ graphite are conducted in the Ion InterAction eXperimental (IIAX) facility. The sputtering yields are measured using QCM for both graphite and lithiated graphite targets when bombarded by Li ions with energies ranging from 700 eV-2000 eV. Typical flux of Li ion beam obtained is $\sim $ 4 x 10$^{13}$ ions/ (cm$^{2}$- s). Results indicate suppressed amounts of sputtered yields after Li treatment. Deuterium saturation for target samples is also performed to simulate actual divertor conditions; however, no distinct difference in sputter yields is seen after D treatment. The percentage fraction of sputtered Li ions to neutrals is also determined. The thermal evaporation flux studies of Li on stainless steel (SS) and lithiated graphite show that there is an order of magnitude less evaporation from lithiated graphite compared to Li on SS, thereby enhancing the temperature limit on plasma facing components. [Preview Abstract] |
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NP8.00131: Thermoelectric magnetohydrodynamic (TEMHD) stirring of liquid lithium M.A. Jaworski, Wenyu Xu, Jason Kim, Matt Lee, Martin Neumann, Vijay Surla, David Ruzic The Solid/Liquid Lithium Divertor Experiment (SLiDE) was constructed to examine passive flows in liquid lithium under an applied heat load and external magnetic field. The offered explanation for the results of the CDX-U experiment, where liquid lithium was capable of transporting $>50$[MW/m$^2$] of incident heat flux without rapid evaporation, was thermocapillary (Marangonic) driven flows. The SLiDE apparatus utilizes a line-stripe heat source and external magnetic fields to mimic a divertor scenario to test the thermocapillary hypothesis. Instead of thermocapillary induced flows, TEMHD flows are observed on the order of 10 [cm/s]. The thermoelectric effect was confirmed through a series of qualitative experiments in the apparatus which will be described. A quantitative scaling matching the measured target temperatures and heat fluxes is compared to the measured velocities. A novel plasma facing component based on porous material TEMHD is also presented. [Preview Abstract] |
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