A. Friedman

Lawrence Livermore National Laboratory, Livermore, California, United States

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Publications (175)128.28 Total impact

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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; 733:75-79. DOI:10.1016/j.nima.2013.05.091 · 1.32 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; DOI:10.1016/j.nima.2013.05.083 · 1.32 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; DOI:10.1016/j.nima.2013.05.063 · 1.32 Impact Factor
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    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; DOI:10.1016/j.nima.2013.05.096 · 1.32 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.
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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. DOI:10.1088/1749-4699/5/1/014019
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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). DOI:10.1103/PhysRevSTAB.15.104001 · 1.52 Impact Factor
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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.
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    ABSTRACT: The Particle-In-Cell (PIC) Framework Warp is being developed by the Heavy Ion Fusion Science Virtual National Laboratory (HIFSVNL) 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 to the study and design of existing and next generation high-energy accelerators including the study of electron cloud effects, laser wakefield acceleration, coherent synchrotron radiation, etc. We will present a selection of original numerical methods that were developed by the HIFSVNL, including: PIC with adaptive mesh refinement (AMR), a large-timestep mover for particles of arbitrary magnetized species, a new relativistic leapfrog particle pusher, simulations in Lorentz boosted frames, an electromagnetic solver with tunable numerical dispersion and efficient stride-based digital filtering. Examples of applications of the methods to the abovementioned fields will also be given.
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    ABSTRACT: The Neutralized Drift Compression Experiment-II (NDCX-II) will generate ion beams for studies of Warm Dense Matter, target physics for heavy-ion-driven Inertial Fusion Energy, and intense-beam dynamics. NDCX-II will accelerate a 20-50 nC Li pulse to 1.2-3 MeV, compress it to sub-ns duration in a neutralizing plasma, and focus it onto a target. Construction of the induction accelerator and compression line at LBNL is approaching completion. We briefly describe the NDCX-II ``physics design'' [A. Friedman, et al., Phys. Plasmas 17, 056704 (2010)], the simulation studies that enabled it, variations (e.g., for other ions), plans for commissioning over the next year, and some possible experiments using the machine itself and extensions.
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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; DOI:10.1016/j.nima.2013.05.081 · 1.32 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.
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    ABSTRACT: An unneutralized ion beam is subject to a self-pinching force and electrostatic defocusing, and normally the latter wins. However, if the transverse electrostatic forces can be reduced sufficiently, a net pinching can occur. There has been interest recently in utilizing this concept for heavy-ion fusion applications. We consider several approaches to reducing electrostatic defocusing. Two that have particular promise are use of closely spaced conducting foils transverse to the beam propagation direction, and introduction of a counterstreaming relativistic electron beam in a guide magnetic field. We present electromagnetic particle simulations (with the WARP code) that demonstrate pinching with both approaches. The conducting foil approach yields cleaner focusing in an idealized simulation, but is subject to limitations from non-ideal effects including field-emission of electrons and knock-on electrons.
  • T.J. Fessenden, A. Friedman
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    ABSTRACT: The 1990 International Symposium on Heavy Ion Inertial Fusion (HIF) was the fifth in a series, following meetings in Darmstadt (1982), Tokyo (1984), Washington, DC (1986) and Darmstadt (1988). The meeting was sponsored by the American Physical Society and the United States Department of Energy (USDOE). It was hosted by the Lawrence Berkeley Laboratory (LBL). The Proceedings of the symposium will be published as a refereed special issue of Particle Accelerators, edited by D. Judd (LBL).
    Nuclear Fusion 01/2011; 31(8):1567. DOI:10.1088/0029-5515/31/8/019 · 3.24 Impact Factor
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    ABSTRACT: The Heavy Ion Fusion Science Virtual National Laboratory in the USA is constructing a new Neutralized Drift Compression eXperiment (NDCX-II) at LBNL. This facility is being developed for high energy density physics and inertial fusion energy research. The 12 m long induction linac in NDCX-II will produce a Li{sup +} beam pulse, at energies of 1.2-3 MeV, to heat target material to the warm dense matter regime ( 1 eV). By making use of special acceleration voltage waveforms, 2.5T solenoid focusing, and neutralized drift compression, 20 - 50 nC of beam charge from the ion source will be compressed longitudinally and radially to achieve a subnanosecond pulse length and mm-scale target spot size. The original Neutralized Drift Compression Experiment (NDCX-I) has successfully demonstrated simultaneous radial and longitudinal compression by imparting a velocity ramp to the ion beam, which then drifts in a neutralizing plasma to and through the final focussing solenoid and onto the target. At higher kinetic energy and current, NDCX-II will offer more than 100 times the peak energy fluence on target of NDCX-I. NDCX-II makes use of many parts from the decommissioned Advanced Test Accelerator (ATA) at LLNL. It includes 27 lattice periods between the injector and the neutralized drift compression section (Figure 1). There are 12 energized induction cells, 9 inactive cells which provide drift space, and 6 diagnostic cells which provide beam diagnostics and pumping. Custom pulsed power systems generate ramped waveforms for the first 7 induction cells, so as to quickly compress the beam from 600 ns at the injector down to 70 ns. After this compression, the high voltages of the ATA Blumleins are then used to rapidly add energy to the beam. The Blumleins were designed to match the ferrite core volt-seconds with pulses up to 250 kV and a fixed FWHM of 70 ns. The machine is limited to a pulse repetition rate of once every 20 seconds due to cooling requirements. The NDCX-II beam is highly space-charge dominated. The 1-D ASP code was used to synthesize high voltage waveform for acceleration, while the 3-D Warp particle-in-cell code was used for detailed design of the lattice. The Li{sup +} ion was chosen because its Bragg Peak energy (at 2 MeV) coincides with the NDCX-II beam energy. The 130 keV injector will have a 10.9 cm diameter ion source. Testing of small (0.64 cm diameter) lithium doped alumino-silicate ion sources has demonstrated the current density ( 1 mA/cm²) used in the design, with acceptable lifetime. A 7.6 cm diameter source has been successfully produced to verify that the coating method can be applied to such a large emitting area. The ion source will operate at 1275 C; thus a significant effort was made in the design to manage the 4 kW heating power and the associated cooling requirements. In modifying the ATA induction cells for NDCX-II, the low-field DC solenoids were replaced with 2.5 T pulsed solenoids. The beam pipe diameter was decreased in order to reduce the axial extent of the solenoid fringe fields and to make room for water cooling. In addition, an outer copper cylinder (water-cooled) was used to exclude the solenoid magnetic flux from the ferrite cores. Precise alignment is essential because the beam has a large energy spread due to the rapid pulse compression, such that misalignments lead to corkscrew deformation of the beam and reduced intensity at focus. A novel pulsed-wire measurement method is used to align the pulsed solenoid magnets. Alignment accuracy has been demonstrated to within 100 m of the induction cell axis. The neutralized drift compression region after the last induction cell is approximately 1.2 m long and includes ferroelectric plasma sources (FEPS) fabricated by PPPL similar to those successfully operating in NDCX-I. The 8-T final focus pulsed solenoid, filtered cathodic arc plasma sources (FCAPS), and target chamber from NDCX-I are to be relocated to NDCX-II. The NDCX-II project started in July 2009 and is expected to complete in fall of 2011. As future funds become available, additional induction cells and pulsed power systems will be added to increase the beam energy.
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    ABSTRACT: The Neutralized Drift Compression Experiment II (NDCX II) is an induction accelerator now being constructed at LBNL and scheduled for project completion in 2012. The design calls for a ˜2 - 3 MeV, ˜30 A Li^+ ion beam, delivered in a bunch with sub ns pulse duration, and transverse dimension less than ˜ 1 mm. The purpose of NDCX II is to carry out experimental studies of material in the warm dense matter regime and ion beam and hydrodynamic coupling experiments relevant to heavy ion fusion (HIF). In preparation for NDCX-II, we have carried out hydro simulations of ion-beam-heated, porous and solid, metallic and non-metallic, targets. We have shown the sensitivity of observables on equations of state. Pulse formats include single pulses of fixed ion energy, and and single or double pulses with variable energy to create shocks and investigate ion-coupling efficiency. Comparisons are made with simulations of ion driven direct drive HIF capsules.
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    ABSTRACT: The Virtual National Laboratory for Heavy-Ion Fusion Science is now constructing NDCX-II, an accelerator facility for studying ion-heated warm dense matter and aspects of ion-driven targets for inertial-fusion energy. Plans call for using twelve or more induction cells to accelerate 30-50 nC of Li^+ ions to 1.2-3 MeV. Plasma neutralization will enable compression of the beam to the sub-millimeter radius and sub-nanosecond duration needed for the desired target experiments. The initial NDXC-II physics design was developed using idealized analytic waveforms. Acceleration schedules were first worked out with a fast-running 1-D particle-in-cell code ASP (Acceleration Schedule Program), then 2-D and 3-D Warp simulations were used to verify the 1-D model, design transverse focusing, and establish tolerances for beam and lattice errors. As part of recent work to refine and validate this physics design, the idealized waveforms in the simulations have been replaced by experimentally measured ones. ASP and Warp results obtained with these realistic waveforms are compared with those from earlier simulations, and ongoing work to optimize the acceleration schedule is discussed.
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    ABSTRACT: Construction of the Neutralized Drift Compression Experiment-II (NDCX-II) is underway at LBNL; completion is due March, 2012. This ion induction accelerator will enable studies of Warm Dense Matter and basic target physics for heavy-ion-driven Inertial Fusion Energy. NDCX-II compresses and accelerates a 20-50 nC Li+ pulse to 1.2-3 MeV, then shortens it to sub-ns duration in a neutralizing plasma and focuses it onto a target. ootnotetextA. Friedman, et al., Phys. Plasmas 17, 056704 (2010). Extensive simulations optimized the design and adapted it to induction waveforms generated on a test stand; ensembles of runs established tolerances and expected performance. NDCX-II is extensible and reconfigurable; we describe the baseline design and variants, and the status of the project.
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    ABSTRACT: The Neutralized Drift Compression Experiment II (NDCX II) is an induction accelerator planned for initial commissioning in 2012. The final design calls for a ~3 MeV, ~30 A Li+ ion beam, delivered in a bunch with characteristic pulse duration of 1 ns, and transverse dimension of order 1 mm. The purpose of NDCX II is to carry out experimental studies of material in the warm dense matter regime, and ion beam/hydrodynamic coupling experiments relevant to heavy ion based inertial fusion energy. In preparation for this new machine, we have carried out hydrodynamic simulations of ion-beam-heated, metallic solid targets, connecting quantities related to observables, such as brightness temperature and expansion velocity at the critical frequency, with the simulated fluid density, temperature, and velocity. We examine how these quantities depend on two commonly used equations of state.
    Journal of Physics Conference Series 09/2010; 244(3):032027. DOI:10.1088/1742-6596/244/3/032027
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    ABSTRACT: The capture of laser-accelerated proton beams accompanied by co-moving electrons via a solenoid field has been studied with particle-in-cell simulations. The main advantages of the Warp simulation suite that we have used, relative to envelope or tracking codes, are the possibility of including all source parameters energy resolved, adding electrons as second species and considering the non-negligible space-charge forces and electrostatic self-fields. It was observed that the influence of the electrons is of vital importance. The magnetic effect on the electrons outbalances the space-charge force. Hence, the electrons are forced onto the beam axis and attract protons. Beside the energy dependent proton density increase on axis, the change in the particle spectrum is also important for future applications. Protons are accelerated/decelerated slightly, electrons highly. 2/3 of all electrons get lost directly at the source and 27% of all protons hit the inner wall of the solenoid.
    Journal of Physics Conference Series 09/2010; 244(2):022052. DOI:10.1088/1742-6596/244/2/022052