Bulletin of the American Physical Society
50th Annual Meeting of the Division of Plasma Physics
Volume 53, Number 14
Monday–Friday, November 17–21, 2008; Dallas, Texas
Session TO3: Electron and Ion Beams |
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Chair: Gennady Shvets, University of Texas Room: Reunion A |
Thursday, November 20, 2008 9:30AM - 9:42AM |
TO3.00001: Scientific objectives and key features of a sequence of heavy-ion-beam-driven facilities for high energy density physics and fusion B. Grant Logan (On behalf of Heavy Ion Fusion Virtual National Laboratory-LBNL, LLNL, PPPL). Successful longitudinal and radial compression of intense neutralized heavy ion beams in the Neutralized Drift Compression Experiment (NDCX-I), together with novel acceleration and compression waveforms using existing induction accelerator modules will lead to an upgraded facility (NDCX-II) capable of driving warm dense matter targets to 1 Mbar, and planar direct drive targets to study hydro-coupling efficiency with beams ramping up in velocity and range. Two further significant enhancements in the heavy ion program, construction of IB-HEDPX with more existing accelerator modules, and commencement of design and R{\&}D for a Heavy Ion Driven Target Implosion Experiment (HIDDIX), could occur after successful experiments in NDCX-II, and after successful ignition in NIF, respectively. Fruition of these research opportunities for heavy-ion-driven high energy density physics (HEDP) and fusion over the next twenty years could establish the HEDP target physics knowledge base needed for a heavy ion fusion test facility, as well as for fundamental HEDP in warm dense matter important to many scientific applications as well as to fusion. [Preview Abstract] |
Thursday, November 20, 2008 9:42AM - 9:54AM |
TO3.00002: Toward a physics design for NDCX-II, a next-step platform for ion beam-driven physics studies A. Friedman, D.P. Grote, W.M. Sharp, E. Henestroza, M. Leitner, B.G. Logan, W.L. Waldron The Heavy Ion Fusion Science Virtual National Laboratory, a collaboration of LBNL, LLNL, and PPPL, is studying Warm Dense Matter physics driven by ion beams, and basic target physics for heavy ion-driven Inertial Fusion Energy. A low-cost path toward the next-step facility for this research, NDCX-II, has been enabled by the recent donation of induction cells and associated hardware from the decommissioned Advanced Test Accelerator (ATA) facility at LLNL. We are using a combination of analysis, an interactive one-dimensional kinetic simulation model, and multidimensional Warp-code simulations to develop a physics design concept for the NDCX-II accelerator section. A 30-nC pulse of singly charged Li ions is accelerated to $\sim $3 MeV, compressed from $\sim $500 ns to $\sim $1 ns, and focused to a sub-mm spot. We present the novel strategy underlying the acceleration schedule and illustrate the space-charge-dominated beam dynamics graphically. [Preview Abstract] |
Thursday, November 20, 2008 9:54AM - 10:06AM |
TO3.00003: A thin column of dense plasma for space-charge neutralization of intense ion beams P.K. Roy, P.A. Seidl, A. Anders, J.J. Barnard, F.M. Bieniosek, A. Friedman, E.P. Gilson, W. Greenway, A.B. Sefkow, J.Y. Jung, M. Leitner, S.M. Lidia, B.G. Logan, W.L. Waldron, D.R. Welch Typical ion driven warm dense matter experiment requires a plasma density of 10$^{14}$/cm$^{3}$ to meet the challenge of n$_{p}>$n$_{b}$, where n$_{p}$, and n$_{b}$ are the number densities of plasma and beam, respectively. Plasma electrons neutralize the space charge of an ion beam to allow a small spot of about 1-mm radius. In order to provide n$_{p}>$n$_{b}$ for initial warm, dense matter experiments, four cathodic arc plasma sources have been fabricated, and the aluminum plasma is focused in a focusing solenoid (8T field). A plasma probe with 37 collectors was developed to measure the radial plasma profile inside the solenoid. Results show that the plasma forms a thin column of diameter $\sim $7mm along the solenoid axis. The magnetic mirror effect, plasma condensation, and the deformation of the magnetic field due to eddy currents are under investigation. Data on plasma parameters and ion beam neutralization will be presented. [Preview Abstract] |
Thursday, November 20, 2008 10:06AM - 10:18AM |
TO3.00004: Multiplication of field enhancement factors on field-emission cathodes Ryan Miller, Y.Y. Lau, John Booske Of great interest to high power microwave, millimeter wave to terahertz sources, x-ray tubes, electrons guns, etc., is the field enhancement obtained from emitting structures fabricated by laser ablation or various microfabrication methods [1]. Here we extend our conformal mapping theory [2] to a quadrilateral-cross-section double ridge, and show that the net field enhancement factor of the double ridge with a micro-protrusion on top of a macro-protrusion is equal to the product of the individual protrusions' field enhancements [3] over a very wide range of dimensional aspect ratios. Significant deviation from this product rule, conjectured by Schottky [3], occurred almost exclusively when the width of the macro-protrusion is less than the height of the micro-protrusion. This work was supported by an AFOSR Cathodes and Breakdown MURI04, AFRL, L-3, and Northrop-Grumman. [1] J. H. Booske, Phys. Plasmas \textbf{15}, 055502 (2008). [2] R. Miller, Y. Y. Lau, J. H. Booske, Appl. Phys. Lett. \textbf{91, }074105 (2007). [3] W. Schottky, Z. Physik \textbf{14}, 63 (1923). [Preview Abstract] |
Thursday, November 20, 2008 10:18AM - 10:30AM |
TO3.00005: Surface and Bulk Characteristics of Cesium Iodide (CsI) coated Carbon (C) Fibers for High Power Microwave (HPM) Field Emission Cathodes Vasilios Vlahos, Dane Morgan, John H. Booske, Don Shiffler CsI coated C fibers [1] are promising field emission cathodes for HPM applications. \textit{Ab initio} computational modeling has shown that atomically-thin CsI coatings reduce the work function of C substrates by a surface dipole mechanism [2]. Characterization measurements of the composition and morphology of the CsI-coated C fibers are underway for determining the properties and characteristics of the following important regions of the fiber: (i) the surface on the tip of the fiber where the majority of electron emission is believed to occur, (ii) the surface covering the body of the fiber and its role on the emission properties of the system, and (iii) the interior volume of the fiber and its effects on the CsI surface re-supply process and rate. The results will be interpreted in terms of surface electronic properties and theoretical electron emission models. [1]D. Shiffler, et al., Phys. Plasmas 11 (2004) 1680. [2]V.Vlahos et al., Appl. Phys. Lett. 91 (2007) 144102. [Preview Abstract] |
Thursday, November 20, 2008 10:30AM - 10:42AM |
TO3.00006: Nonequilibrium model of ultrafast laser induced electron emission from a dc-biased metallic surface Lin Wu, Lay Kee Ang, Wee Shing Koh The production of very short electron bunches is critical for X-ray free electron lasers. Recently, many experiments have been conducted in using picosecond-laser or ultrafast laser to induce photo-field emission from a metallic sharp tip and the electron pulse is from 16 picoseconds down to 6 femtoseconds [1]. In this paper, we will present a nonequilibrium model to describe the low-power ultrafast laser excited electron emission from a metallic surface with a dc voltage. Using a microscopic kinetic approach, we determine the nonequilibrium electron distribution after the laser excitation, and calculate the time-dependence of the emitted electron charges and current density. It is found that the classical two temperature model valid of picosecond time scale is no longer valid when the pulse duration is less than 100 femtoseconds. Comparison with the experiments [1] and the transition to the ultrafast space charge limited current [2] will be demonstrated. \textbf{References} [1] R. Canter \textit{et al}., Phys. Rev. Lett. \textbf{100}, 064801 (2008); C. Ropers \textit{et al}., Phys. Rev. Lett. \textbf{98}, 043907 (2007); B. Barwick \textit{et al}., New J. Phys. \textbf{9}, 142 (2007); P. Hommelhoff \textit{et al}., Phys. Rev. Lett. \textbf{97}, 247402 (2006). [2] L. K. Ang and P. Zhang, Phys. Rev. Lett. \textbf{98} 164802 (2007). [Preview Abstract] |
Thursday, November 20, 2008 10:42AM - 10:54AM |
TO3.00007: Halo simulations and particle tracking in intense charged particle beams Christos Papadopoulos, Irving Haber, Rami Kishek, Patrick O'Shea, Martin Reiser, Diktys Stratakis One of the major factors limiting the reliable transport of high intensity charged particle beams is the creation of halos of particles around the beam core. In this study, we use the WARP particle-in-cell code to numerically investigate halo creation due to beam core oscillations, for a parameter regime corresponding to the University of Maryland Electron Ring (UMER). Using particle tracking techniques in the simulations, we are able to identify the halo particles, track their orbits and study their phase space properties. The phase space distribution of the halo particles points to particle-core resonances as the underlying mechanism for halo creation, as described in the literature. In addition, we discuss the implications of using stationary and non-stationary initial particle distributions. [Preview Abstract] |
Thursday, November 20, 2008 10:54AM - 11:06AM |
TO3.00008: ABSTRACT WITHDRAWN |
Thursday, November 20, 2008 11:06AM - 11:18AM |
TO3.00009: Simulating Space-Charge Physics of High-Current Beams with a Green's Function Approach Mark Hess, Chong Shik Park High-current (100's A-10 kA) bunched electron beams are featured in a wide variety of high-power microwave sources, such as klystrons, backward wave oscillators, magnetrons, and ubitrons, for producing microwave power in the range of 100's MW-1 GW. For these beams, space-charge fields are extremely important, and the combination of beam bunching and the presence of nearby conductor surfaces imply that a fully electromagnetic approach is needed to calculate the fields. We demonstrate how a time-dependent Green's function approach can be utilized for computing space-charge fields. Since a Green's function is generated from a delta function source, it can be readily used for modeling arbitrarily small beam bunches making this method attractive for high-current bunched beam simulations. [Preview Abstract] |
Thursday, November 20, 2008 11:18AM - 11:30AM |
TO3.00010: Start currents in gyro-backward-wave oscillators of the THz frequency range Gregory Nusinovich, Samir Chainani, Victor Granatstein Gyro-backward-wave oscillators (gyro-BWOs) are unique frequency-tunable sources of high-power, high-frequency electromagnetic radiation. Our group is planning to start experiments in the THz frequency range with gyro-BWOs having highly selective confocal waveguides. At such high frequencies, the wave attenuation in the circuit walls can be significant. In the present paper, analysis of the start currents of such gyro-BWOs is carried out. It is shown how to use known results of the linear theory of conventional backward-wave oscillators for analyzing the starting conditions in the gyro-BWO with finite attenuation. When a thin annular electron beam is injected in a confocal waveguide, different beamlets interact with the electromagnetic field of a different intensity. The effect of this transverse nonuniformity on the start current and the efficiency is also analyzed. [Preview Abstract] |
Thursday, November 20, 2008 11:30AM - 11:42AM |
TO3.00011: Gyrotron amplifiers for plasma heating Adrian Cross, Colin Whyte, Wenlong He, Alan Young, Craig Robertson, Kevin Ronald, Alan Phelps In the non-neutral, relativistic plasma Cyclotron Resonance Maser (CRM) instability, electrons gyrating in a uniform magnetic field interact with electromagnetic radiation. The action of the electric field of the radiation is to accelerate some electrons and decelerate others, depending on their location in the orbital phase. The accelerated electrons increase in momentum, gyro-radius and relativistic mass, and therefore drop in frequency and retard in phase. The opposite is true for decelerating electrons resulting in the formation of a phase bunch. If the gyrofrequency of the beam is slightly less than the wave frequency then the bunches move naturally into decelerating phase and reinforce the wave. This type of interaction has hitherto been successfully exploited in gyrotron oscillators. The research to be presented has built upon the fundamental breakthrough that occurred in gyro-amplifiers where the gain mechanism of the successful gyrotron oscillator has been exploited effectively in a Gyrotron Travelling Wave amplifier, Gyro-TWA. The design, construction and operation of a Gyro-TWA experiment will be presented. The amplifier achieved a peak power of 1.3MW, a saturated gain of 35dB in the frequency range of 8.4GHz to 10.2GHz with an efficiency of 30{\%}. [Preview Abstract] |
Thursday, November 20, 2008 11:42AM - 11:54AM |
TO3.00012: Peltier Refrigerators for Molecular Ion Sources Ady Hershcovitch Molecular ion sources have been considered for various applications. In particular, there is considerable effort to develop decaborane and octadecaborane ion sources for the semiconductor industry. Since the invention of the transistor, the trend has been to miniaturize semiconductor devices. As semiconductors become smaller (and get miniaturized), ion energy needed for implantation decreases, since shallow implantation is desired. But, due to space charge (intra-ion repulsion) effects, forming and transporting ion beams becomes a rather difficult task. These problems associated with lower energy ion beams limit implanter ion currents, thus leading to low production rates. One way to tackle the space charge problem is to use singly charged molecular ions. A crucial aspect in generating large molecular ion beam currents is ion source temperature control. Peltier coolers, which have in the past successfully utilized in BaF$_{2}$ and CSI gamma ray detectors, may be ideal for this application. Clogging prevention of molecular ion sources is also a hurdle, which was overcome with special slots. Both topics are to be presented. [Preview Abstract] |
Thursday, November 20, 2008 11:54AM - 12:06PM |
TO3.00013: Self-consistent non-stationary model for the analysis of multipactor phenomenon in dielectric-loaded accelerating structures Oleksandr Sinitsyn, Gregory Nusinovich, Thomas Antonsen, Rami Kishek Multipactor (MP) may occur in many situations: one- and two-surface MP, resonant and poly-phase-MP, on the surface of metals and dielectrics etc. We consider this phenomenon in dielectric loaded accelerating (DLA) structures. The starting point for our work is experimental and theoretical studies of such structures jointly done by Argonne National Lab and Naval Research Lab (J. G. Power et al., PRL, 92, 164801, 2004). In the theoretical model developed during those studies, the space charge field due to the accumulated charged particles is taken into account as a parameter. We offer a non-stationary model where the DC field is taken into account self-consistently. In this work, some improvements have been made to our earlier (see materials of High-Gradient Collaboration Workshop, University of Maryland, Jan. 23-24, 2008, web: http://www.ireap.umd.edu/High-Gradient-Workshop-2008/Itinerary.htm) model, in particular the effect of cylindricity has been taken into account. Some results of our recent simulations will be presented and discussed. [Preview Abstract] |
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