A. Friedman

Lawrence Livermore National Laboratory, Livermore, California, United States

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Publications (236)148.68 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: The ion accelerator NDCX-II is undergoing commissioning at Lawrence Berkeley National Laboratory (LBNL). Its principal mission is to explore ion-driven High Energy Density Physics (HEDP) relevant to Inertial Fusion Energy (IFE) especially in the Warm Dense Matter (WDM) regime. We have carried out hydrodynamic simulations of beam-heated targets for parameters expected for the initial configuration of NDCX-II. For metal foils of order one micron thick (thin targets), the beam is predicted to heat the target in a timescale comparable to the hydrodynamic expansion time for experiments that infer material properties from measurements of the resulting rarefaction wave. We have also carried out hydrodynamic simulations of beam heating of metallic foam targets several tens of microns thick (thick targets) in which the ion range is shorter than the areal density of the material. In this case shock waves will form and we derive simple scaling laws for the efficiency of conversion of ion energy into kinetic energy of fluid flow. Geometries with a tamping layer may also be used to study the merging of a tamper shock with the end-of-range shock. This process can occur in tamped, direct drive IFE targets.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/2014; · 1.14 Impact Factor
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    ABSTRACT: A barium titanate ferroelectric cylindrical plasma source has been developed, tested and delivered for the Neutralized Drift Compression Experiment NDCX-II at Lawrence Berkeley National Laboratory (LBNL). The plasma source design is based on the successful design of the NDCX-I plasma source. A 7 kV pulse applied across the 3.8 mm-thick ceramic cylinder wall produces a large polarization surface charge density that leads to breakdown and plasma formation. The plasma that fills the NDCX-II drift section upstream of the final-focusing solenoid has a plasma number density exceeding 1010 cm-3 and an electron temperature of several eV. The operating principle of the ferroelectric plasma source are reviewed and a detailed description of the installation plans is presented. The criteria for plasma sources with larger number density will be given, and concepts will be presented for plasma sources for driver applications. Plasma sources for drivers will need to be highly reliable, and operate at several Hz for millions of shots.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/2014; · 1.14 Impact Factor
  • D. P. Grote, A. Friedman, W. M. Sharp
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    ABSTRACT: NDCX-II, the second neutralized drift compression experiment, is a moderate energy, high current accelerator designed to drive targets for warm dense matter and IFE-relevant energy coupling studies, and to serve as a testbed for high current accelerator physics. As part of the design process, studies were carried out to assess the sensitivities of the accelerator to errors, and to further optimize the design in concert with the evolving pulsed power engineering. The Warp code was used to carry out detailed simulations in both axisymmetric and full 3-D geometry. Ensembles of simulations were carried out to characterize the effects of errors, such as timing jitter and noise on the accelerator waveforms, noise on the source waveform, and solenoid and source offsets. In some cases, the ensemble studies resulted in better designs, revealing operating points with improved performance and showing possible means for further improvement. These studies also revealed a new non-paraxial effect of the final focus solenoid on the beam, which must be taken into account in designing an optimal final focusing system.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/2014; · 1.14 Impact Factor
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    ABSTRACT: Induction accelerators are appealing for heavy-ion driven inertial fusion energy (HIF) because of their high efficiency and their demonstrated capability to accelerate high beam current (≥10 kA in some applications). For the HIF application, accomplishments and challenges are summarized. HIF research and development has demonstrated the production of single ion beams with the required emittance, current, and energy suitable for injection into an induction linear accelerator. Driver scale beams have been transported in quadrupole channels of the order of 10% of the number of quadrupoles of a driver. We review the design and operation of induction accelerators and the relevant aspects of their use as drivers for HIF. We describe intermediate research steps that would provide the basis for a heavy-ion research facility capable of heating matter to fusion relevant temperatures and densities, and also to test and demonstrate an accelerator architecture that scales well to a fusion power plant.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/2014; · 1.14 Impact Factor
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    ABSTRACT: The Neutralized Drift Compression Experiment (NDCX-II) is a user facility located at Lawrence Berkeley National Laboratory which is uniquely designed for ion-beam-driven high energy density laboratory physics and heavy ion fusion research. Construction was completed in March 2012 and the facility is now in the commissioning phase. A significant amount of engineering was carried out in order to meet the performance parameters required for a wide range of target heating experiments while making the most cost-effective use of high-value hardware available from a decommissioned high current electron induction accelerator. The technical challenges and design of this new ion induction accelerator facility are described.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/2014; · 1.14 Impact Factor
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    ABSTRACT: This is the working summary of the Accelerator Science working group of the Computing Frontier of the Snowmass meeting 2013. It summarizes the computing requirements to support accelerator technology in both Energy and Intensity Frontiers.
    10/2013;
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    ABSTRACT: Toward the goal of maximizing the impact of computer modeling on the design of future particle accelerators and the development of new accelerator techniques & technologies, this white paper presents the rationale for: (a) strengthening and expanding programmatic activities in accelerator modeling science within the Department of Energy (DOE) Office of High Energy Physics (HEP) and (b) increasing the community-wide coordination and integration of code development.
    09/2013;
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    ABSTRACT: We describe near-term heavy ion fusion (HIF) research objectives associated with developing an inertial fusion energy demonstration power plant. The goal of this near-term research is to lay the essential groundwork for an intermediate research experiment (IRE), designed to demonstrate all the key driver beam manipulations at a meaningful scale, and to enable HIF relevant target physics experiments. This is a very large step in size and complexity compared to HIF experiments to date, and if successful, it would justify proceeding to a demonstration fusion power plant. With an emphasis on accelerator research, this paper is focused on the most important near-term research objectives to justify and to reduce the risks associated with the IRE. The chosen time scale for this research is 5–10 years, to answer key questions associated with the HIF accelerator drivers, in turn enabling a key decision on whether to pursue a much more ambitious and focused inertial fusion energy research and development program. This is consistent with the National Academies of Sciences Review of Inertial Fusion Energy Systems Interim Report, which concludes that ''it would be premature at the present time to choose a particular driver approach. . .'' and encouraged the continued development of community consensus on critical issues, and to develop ''options for a community-based roadmap for the development of inertial fusion as a practical energy source.''
    Physical Review Special Topics - Accelerators and Beams 02/2013; 16:024701. · 1.57 Impact Factor
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    ABSTRACT: form only given. The Warp code (and its framework of associated tools) was initially developed for Particle-in-Cell simulations of space-charge-dominated ion beams in accelerators, for heavy-ion-driven inertial fusion energy and related experiments. It has found a broad range of applications, including non-neutral plasmas in traps, stray “electron-clouds” in accelerators, laser-based acceleration, and the capture and focusing of ion beams produced when short-pulse lasers irradiate foil targets. We present an overview of the novel methods that have been developed and implemented in Warp. These include a time-stepping formalism conducive to diagnosis and particle injection; an interactive Python/Fortran/C structure that enables scripted and interactive user “steering” of runs; a variety of geometries (3-D; 2-D r,z; 2-D x,y); electrostatic and electromagnetic field solvers using direct and iterative methods, including MPI parallelization; a Shortley-Weller cut-cell representation for internal boundaries (no restriction to “Lego bricks”); the use of “warped” coordinates for bent beam lines; Adaptive Mesh Refinement, including the capability of simulating time-dependent space-charge-limited flow from curved surfaces; models for accelerator “lattice elements” (magnetic or electrostatic quadrupole lenses, solenoids, accelerating gaps, etc.) at user-selectable levels of detail; models for particle interactions with gas and walls; moment/envelope models that support sophisticated particle loading; a “drift-Lorentz” mover for rapid tracking of species that traverse regions of strong and weak magnetic field; a Lorentz-boosted frame formulation with a Lorentz-invariant modification of the Boris mover; and an electromagnetic solver with tunable dispersion and stride-based digital filtering. Use of Warp, together with the fast 1-D code ASP, to design LBNL's new NDCX-II facili- y is also presented.
    Plasma Science (ICOPS), 2013 Abstracts IEEE International Conference on; 01/2013
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    J-L Vay, D P Grote, R H Cohen, A Friedman
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    ABSTRACT: The Particle-In-Cell (PIC) Code-Framework Warp is being developed by the Heavy Ion Fusion Science Virtual National Laboratory (HIFS-VNL) to guide the development of accelerators that can deliver beams suitable for high-energy density experiments and implosion of inertial fusion capsules. It is also applied in various areas outside the Heavy Ion Fusion program to the study and design of existing and next-generation high-energy accelerators, including the study of electron cloud effects and laser wakefield acceleration for example. This paper presents an overview of Warp's capabilities, summarizing recent original numerical methods that were developed by the HIFS-VNL (including PIC with adaptive mesh refinement, a large-timestep 'drift-Lorentz' mover for arbitrarily magnetized species, a relativistic Lorentz invariant leapfrog particle pusher, simulations in Lorentz-boosted frames, an electromagnetic solver with tunable numerical dispersion and efficient stride-based digital filtering), with special emphasis on the description of the mesh refinement capability. Selected examples of the applications of the methods to the abovementioned fields are given.
    Computational Science & Discovery 12/2012; 5(1):014019.
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    ABSTRACT: We introduce a deterministic discrete-particle simulation approach, the Linearly-Transformed Particle-In-Cell (LTPIC) method, that employs linear deformations of the particles to reduce the noise traditionally associated with particle schemes. Formally, transforming the particles is justified by local first order expansions of the characteristic flow in phase space. In practice the method amounts to using deformation matrices within the particle shape functions; these matrices are updated via local evaluations of the forward numerical flow. Because it is necessary to periodically remap the particles on a regular grid to avoid excessively deforming their shapes, the method can be seen as a development of Denavit's Forward Semi-Lagrangian (FSL) scheme [J. Denavit, J. Comp. Physics 9, 75 (1972)]. However, it has recently been established [M. Campos Pinto, "Smooth particle methods without smoothing", arXiv:1112.1859 (2012)] that the underlying Linearly-Transformed Particle scheme converges for abstract transport problems, with no need to remap the particles; deforming the particles can thus be seen as a way to significantly lower the remapping frequency needed in the FSL schemes, and hence the associated numerical diffusion. To couple the method with electrostatic field solvers, two specific charge deposition schemes are examined, and their performance compared with that of the standard deposition method. Finally, numerical 1d1v simulations involving benchmark test cases and halo formation in an initially mismatched thermal sheet beam demonstrate some advantages of our LTPIC scheme over the classical PIC and FSL methods. Benchmarked test cases also indicate that, for numerical choices involving similar computational effort, the LTPIC method is capable of accuracy comparable to or exceeding that of state-of-the-art, high-resolution Vlasov schemes.
    Journal of Computational Physics 11/2012; · 2.14 Impact Factor
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    D. P. Grote, A. Friedman, E. P. Lee
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    ABSTRACT: In a standard scenario for focusing an ion beam onto a target, for example with ion beam driven inertial fusion energy, the beam is compressed longitudinally by a velocity ramp to enhance the current and then directed through a transverse focusing system to produce a small, bright spot on the target. To reach the highest levels of compression, the space-charge of the beam is neutralized, typically by the presence of a plasma with a density greater than the beam density. The system is arranged so that the peak longitudinal compression is coincident with the minimum transverse spot size. In this scenario, it has been discovered that nonparaxial effects can lead to degradation in the amount of compression. The transverse focusing causes a radially dependent variation in the axial velocity of the ions, leading to a radially dependent time delay that degrades the peak compression. This effect, nonparaxial pulse broadening, can become significant for short pulses and large focusing fields—the time delay can be comparable to the final pulse length. This pulse broadening will be present in both solenoid and quadrupole focusing systems. This paper describes this effect in solenoids, with some examples. It is expected that the size of the effect will be comparable with quadrupole focusing.
    Physical Review Special Topics - Accelerators and Beams 10/2012; 15(10). · 1.57 Impact Factor
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    ABSTRACT: The Korteweg model is a relatively old but seldom-investigated model for numericallysurface tension. We present some advanced applications of this model:wave propagation and thin-film flow. The results will be benchmarked against their analytic solution. In addition, we will investigate the performance of the model in full-scale expanding flow that breaks into droplets as the material enters the two-phase. The conjunction of this method with ALE-AMR will also be presented. Work performed under the auspices of the U.S. Department of Energy un-contract DE-AC52-07NA27344 at LLNL, and University of CaliforniaDE-AC02-05CH11231 at LBNL.
    10/2012;
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    ABSTRACT: NDCX-II is a newly completed accelerator facility at LBNL, built to study ion-heated warm dense matter and aspects of ion-driven targets for inertial-fusion energy. The baseline design calls for using twelve induction cells to accelerate 40 nC of Li+ ions to 1.2 MeV. During commissioning, though, we plan to extend the source lifetime by extracting less total charge. For operational flexibility, the option of using a helium plasma source is also being investigated. Over time, we expect that NDCX-II will be upgraded to substantially higher energies, necessitating the use of heavier ions to keep a suitable deposition range in targets. Each of these options requires development of an alternate acceleration schedule and the associated transverse focusing. The schedules here are first worked out with a fast-running 1-D particle-in-cell code ASP, then 2-D and 3-D Warp simulations are used to verify the 1-D results and to design transverse focusing.
    10/2012;
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    ABSTRACT: The Neutralized Drift Compression Experiment-II (NDCX-II) will generate ion beam pulses for studies of Warm Dense Matter science and heavy-ion-driven Inertial Fusion Energy. The machine accelerates 20-50 nC of Li+ to 1.2-3 MeV energy, starting from a 10.9-cm alumino-silicate ion source. At the end of the accelerator the ions are focused to a sub-mm spot size onto a thin foil (planar) target. The pulse duration is compressed from ˜500 ns at the source to sub-ns at the target following beam transport in a neutralizing plasma. We report on the results of early commissioning studies that characterize beam quality and beam transport, acceleration waveform shaping and beam current evolution. We present measurements of time-resolved beam phase space density and variation in transverse beam centroid position. We present simulation results to benchmark against the experimental measurements, and to predict performance in subsequent sections of the accelerator.
    10/2012;
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    ABSTRACT: Neutralized drift compression offers an effective means for particle beam focusing and current amplification with applications to heavy ion fusion. In the Neutralized Drift Compression eXperiment-I (NDCX-I), a non-relativistic ion beam pulse is passed through an inductive bunching module that produces a longitudinal velocity modulation. Due to the applied velocity tilt, the beam pulse compresses during neutralized drift. The ion beam pulse can be compressed by a factor of more than 100; however, errors in the velocity modulation affect the compression ratio in complex ways. We have performed a study of how the longitudinal compression of a typical NDCX-I ion beam pulse is affected by the initial errors in the acquired velocity modulation. Without any voltage errors, an ideal compression is limited only by the initial energy spread of the ion beam, ΔΕb. In the presence of large voltage errors, δU⪢ΔEb, the maximum compression ratio is found to be inversely proportional to the geometric mean of the relative error in velocity modulation and the relative intrinsic energy spread of the beam ions. Although small parts of a beam pulse can achieve high local values of compression ratio, the acquired velocity errors cause these parts to compress at different times, limiting the overall compression of the ion beam pulse.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 06/2012; 678:39–47. · 1.14 Impact Factor
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    ABSTRACT: The Neutralized Drift Compression Experiment II (NDCX-II) is an induction accelerator currently under construction at LBNL, scheduled for completion by March, 2012. The baseline design for NDCX-II will accelerate ˜0.03 μC of singly charged Li ions to 1.2 MeV (with planned upgrades up to 3.1 MeV), delivered in sub-ns pulses with sub-mm rms beam radii. The beam is predicted to heat metal foils several microns thick in a timescale comparable to the hydrodynamic expansion timescale of the target for experiments that infer material properties from measurements of the rarefaction wave. Experiments using metallic foam targets several tens of microns thick will infer ion energy coupling into kinetic energy of fluid flow. Geometries with multiple layers may be used to adiabatically compress target materials. We have carried out detailed hydrodynamic simulations of targets for several configurations, exploring how optical intensity measurements (from IR to UV), laser doppler measurements (VISAR), and X-ray density measurements can be used to distinguish EOS, and measure beam energy coupling in ion driven shock experiments. *Work performed under the auspices of the U.S. DOE under contract DE-AC52-07NA27344 at LLNL, and UC contract DE-AC02-05CH11231 at LBNL.
    11/2011;
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    ABSTRACT: NDCX-II is an accelerator facility being built at LBNL to study ion-heated warm dense matter and aspects of ion-driven targets for inertial-fusion energy. The baseline design calls for using twelve induction cells to accelerate 40 nC of Li+ ions to 1.2 MeV. During commissioning, though, we plan to extend the source lifetime by extracting less total charge. For operational flexibility, the option of using a helium plasma source is also being investigated. Over time, we expect that NDCX-II will be upgraded to substantially higher energies, necessitating the use of heavier ions to keep a suitable deposition range in targets. Each of these options requires development of an alternate acceleration schedule and the associated transverse focusing. The schedules here are first worked out with a fast-running 1-D particle-in-cell code ASP, then 2-D and 3-D Warp simulations are used to verify the 1-D results and to design transverse focusing.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 11/2011; · 1.14 Impact Factor
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    ABSTRACT: In this paper we describe an implementation of a single-fluid diffuse interface model in the ALE-AMR hydrodynamics code to simulate surface tension effects. This model works for 2D and 3D. We show simulations and compare them to other surface tension models. We benchmark this code against analytic models that incorporate surface tension (showing agreement with Laplace's equation describing the pressure difference between the interior and exterior of a droplet, for example). We also show how this simulation can be used for modeling the NDCX-II ion beam heated target experiments planned to begin in 2012.
    11/2011;
  • David Grote, Alex Friedman, William Sharp
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    ABSTRACT: The Neutralized Drift Compression Experiment-II (NDCX-II) will generate ion beams for use in driving targets for warm dense matter experiments and heavy ion fusion target studies and to do high-current beam physics.ootnotetextsee A. Friedman, et al., this meeting It is designed to produce beams of Li^+ ions with energies of 1 to several MeV compressed to sub-nanosecond pulses with peak currents of 10 or more Amps. Here, we discuss characterization of the design with simulation, including optimization of the operating point, examination of error tolerances, and integrated source to target simulations for validation. There is some flexibility in the shaping and timing of the induction waveforms that provides a large operating space to optimize the performance of NDCX-II. Some examples will be discussed. Simulation has been used to characterize the tolerances for errors. The resulting requirements appear to be feasible. Full validation of the experiment requires self-consistent inclusion of the plasma dynamics. To this end, simulations that include a particle-in-cell plasma model have been carried out and will be discussed.
    11/2011;

Publication Stats

713 Citations
148.68 Total Impact Points

Institutions

  • 1982–2013
    • Lawrence Livermore National Laboratory
      • Physics Division
      Livermore, California, United States
  • 2005–2010
    • Lawrence Berkeley National Laboratory
      Berkeley, California, United States
    • University of Maryland, College Park
      • Institute for Research in Electronics and Applied Physics (IREAP)
      College Park, MD, United States
    • University of California, Berkeley
      Berkeley, California, United States
  • 2001–2005
    • Loyola University Maryland
      Baltimore, Maryland, United States
  • 1998–2005
    • CSU Mentor
      Long Beach, California, United States
  • 2000–2002
    • Cornell University
      Ithaca, New York, United States