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Publications (105)23.14 Total impact

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    ABSTRACT: Magneto-inertial fusion (MIF) approaches take advantage of an embedded magnetic field to improve plasma energy confinement by reducing thermal conduction relative to conventional inertial confinement fusion (ICF). MIF reduces required precision in the implosion and the convergence ratio. Since 2008 (Wurden et al 2008 IAEA 2008 Fusion Energy Conf. (Geneva, Switzerland, 13–18 October) IC/P4-13 LA-UR-08-0796) and since our prior refereed publication on this topic (Degnan et al 2008 IEEE Trans. Plasma Sci. 36 80), AFRL and LANL have developed further one version of MIF. We have (1) reliably formed, translated, and captured field reversed configurations (FRCs) in magnetic mirrors inside metal shells or liners in preparation for subsequent compression by liner implosion; (2) imploded a liner with interior magnetic mirror field, obtaining evidence for compression of a 1.36 T field to 540 T; (3) performed a full system experiment of FRC formation, translation, capture, and imploding liner compression operation; (4) identified by comparison of 2D-MHD simulation and experiments factors limiting the closed-field lifetime of FRCs to about half that required for good liner compression of FRCs to multi-keV, 1019 ion cm−3, high energy density plasma (HEDP) conditions; and (5) designed and prepared hardware to increase that closed-field FRC lifetime to the required amount. Those lifetime experiments are now underway, with the goal of at least doubling closed-field FRC lifetimes and performing FRC implosions to HEDP conditions this year. These experiments have obtained imaging evidence of FRC rotation, and of initial rotation control measures slowing and stopping such rotation. Important improvements in fidelity of simulation to experiment have been achieved, enabling improved guidance and understanding of experiment design and performance.
    Nuclear Fusion 08/2013; 53(9):093003. · 2.73 Impact Factor
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    ABSTRACT: Detailed calculations of the formation, guide, and mirror applied magnetic fields in the FRC compression-heating experiment (FRCHX) were conducted using a commercially available generalized finite element solver, COMSOL Multiphysics(®). In FRCHX, an applied magnetic field forms, translates, and finally captures the FRC in the liner region sufficiently long to enable compression. Large single turn coils generate the fast magnetic fields necessary for FRC formation. Solenoidal coils produce the magnetic field for translation and capture of the FRC prior to liner implosion. Due to the limited FRC lifetime, liner implosion is initiated before the FRC is injected, and the magnetic flux that diffuses into the liner is compressed. Two-dimensional axisymmetric magnetohydrodynamic simulations using MACH2 were used to specify optimal magnetic field characteristics, and this paper describes the simulations conducted to design magnetic field coils and compression hardware for FRCHX. This paper presents the vacuum solution for the magnetic field.
    The Review of scientific instruments 04/2013; 84(4):043507. · 1.52 Impact Factor
  • S.D. Frese, M.H. Frese
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    ABSTRACT: form only given. The U.S. Air Force Research Laboratory Directed Energy Directorate and Los Alamos National Laboratory are forming, translating, capturing, and compressing magnetic field-reversed configuration plasmas (FRCs) in stationary and imploding aluminum cylinders, with the goal of creating a high-energy-density magnetized plasma configuration. We have previously described 1 2-d axisymmetric magnetohydrodynamic (MHD) simulations of these experiments with the geometric configuration of the actual device driven by the time-dependent currents of its pulsed power systems. Our simulations begin with the theta-pinch preionization phase based on the experimentally determined breakdown/ionization time to produce the correct flux trapped in the FRC and thus improve agreement with the experimental magnetic probe data. They have become the theoretical workhorse for delivering understanding of those experiments and assessing the potential impact of design variations upon them. FRC experiments have shown evidence of plasma rotation, a process which can lead to amplification of asymmetry and subsequent collision of plasma with the wall. In cylindrical symmetry, the magnetic force from either poloidal field or toroidal field alone has no toroidal component, but when all three components of the field are present, toroidal force and hence rotational acceleration are possible. Furthermore, in the presence of toroidal current, the Hall Effect can shear radial field into the toroidal direction, converting some poloidal field into toroidal field. Hence, extended MHD (XMHD) is necessary in order to model the generation of rotation in axisymmetric simulations of plasma motions induced by toroidal coils only.
    Plasma Science (ICOPS), 2013 Abstracts IEEE International Conference on; 01/2013
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    ABSTRACT: form only given. The objective of the Field-Reversed Configuration Heating Experiment (FRCHX) is to obtain a better understanding of the fundamental scientific issues associated with high energy density plasmas (HEDPs) in strong, closed-field-line magnetic fields. These issues have relevance to such topics as magneto-inertial fusion (MIF), laboratory astrophysical research, and intense radiation sources, among others. To create the HEDP, a field-reversed configuration (FRC) plasma of moderate density is first formed via reversed-field theta pinch. It is then translated into a cylindrical aluminum shell (solid liner), where it is trapped between two magnetic mirrors and then compressed by the magnetically-driven implosion of the shell. A requirement is that once the FRC is stopped within the shell, the trapped flux inside the FRC must persist while the compression process is completed. With the present shell dimensions and drive bank parameters, the total time required for implosion is ~25 microseconds. Lifetime measurements of recent FRCHX FRCs indicate trapped lifetimes now approaching ~14 microseconds, and with recent experimental modifications the liner compression can be initiated considerably earlier before formation is completed in order to close that gap further. A discussion of FRC lifetime-limiting mechanisms will be presented along with a description of FRCHX and recent changes that have been made to it. Results from recent experiments aimed at lengthening FRC lifetime will also be presented.
    Plasma Science (ICOPS), 2013 Abstracts IEEE International Conference on; 01/2013
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    ABSTRACT: form only given. The Field-Reversed Configuration Heating Experiment (FRCHX) is a collaborative experiment between the Air Force Research Laboratory (AFRL) and Los Alamos National Laboratory (LANL) to study high energy density laboratory plasma (HEDLP) phenomena, which encompass such topics as magneto-inertial fusion (MIF). In this experiment, field-reversed configuration (FRC) plasmas are formed via a reversed-field theta pinch and then translated into a cylindrical aluminum shell (solid liner), where they are compressed by the magnetically-driven implosion of the shell. Representative parameters for the initial FRC plasmas are density 5 × 1016 ions/cm3, temperature ∼200 eV, poloidal magnetic field ∼1 T, length 15∼20 cm, and field exclusion radius ∼2 cm. To date, however, the trapped-flux lifetime of the FRC has been too short to allow it to undergo useful compression. New experimental hardware has been designed and fabricated to increase that lifetime, following four approaches: 1) improved plasma pre-ionization via RF and other pulsed axial electric field breakdown assistance, 2) use of an array of axial plasma guns to externally produce the initial plasma, 3) implementation of axial bias rings above the liner, used in conjunction with gas puff prefill, to control end shorting of the open magnetic field lines surrounding the FRC and thereby control its rotation, and 4) optimized bank timing and trapping fields. Results from recent tests focusing on extending FRC lifetime will be summarized, and an analysis of the new systems' effectiveness will be presented.
    Plasma Science (ICOPS), 2012 Abstracts IEEE International Conference on; 01/2012
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    ABSTRACT: form only given. The Field-Reversed Configuration Heating Experiment (FRCHX) is a collaborative experiment between the Air Force Research Laboratory (AFRL) and Los Alamos National Laboratory (LANL) to explore the physics of magneto-inertial fusion (MIF) and other high energy density laboratory plasma (HEDLP) phenomena. In the experiment, a plasma in a field-reversed configuration (FRC), with density 5 × 1016 ions/cm3, total temperature ~200 eV, poloidal magnetic field ~1 T, length 15 ~ 20 cm, and field exclusion radius ~2 cm is formed via a reversed-field theta discharge and then translated a short distance (~1 m) into a magnetic mirror that has been established within a 30 cm long, 10 cm diameter, 0.11 cm thick aluminum solid liner. The high energy density state (1019 ions/cm3, multi-keV, MegaGauss fields) will be achieved when a 12 MA axial current, provided by the AFRL Shiva Star capacitor bank, implodes the liner and compresses the FRC within. Conventional FRC formation techniques trap only a small fraction of the initial axial bias field. Guided by extended 2D-MHD simulations, several factors limiting the closed field lifetime of the FRCs to about half that required for good liner compression have been identified, and new experimental hardware has been designed and prepared to increase that lifetime. Results from recent setup experiments will be presented, including a full-scale engineering test shot, along with a description of FRCHX's pulsed power systems and plasma diagnostics.
    Plasma Science (ICOPS), 2012 Abstracts IEEE International Conference on; 01/2012
  • Michael H. Frese, Sherry D. Frese
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    ABSTRACT: form only given. Field Reversed Configurations (FRCs) are formed by first trapping an initial bias field in an ionized plasma and then applying a large field opposite to the bias field. This reversal wraps the field lines around the ionized plasma forming a toroidal configuration that is then compressed by further increase of the reversed field.
    Plasma Science (ICOPS), 2012 Abstracts IEEE International Conference on; 01/2012
  • Sherry D. Frese, Michael H. Frese
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    ABSTRACT: form only given. NumerEx has developed, implemented, and applied two-dimensional (2-d) magnetohydrodynamic (MHD) simulations model of liner compression of field reversed configurations (FRCs) based on MACH2. These simulations concentrated on FRC formation, translation, capture, and liner compression. We also performed 2-d simulations to assess Rayleigh-Taylor instabilities in the r-theta plane during preionization.
    Plasma Science (ICOPS), 2012 Abstracts IEEE International Conference on; 01/2012
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    ABSTRACT: The goal of the Field-Reversed Configuration Heating Experiment (FRCHX) is to demonstrate magnetized plasma compression. A requirement is that the trapped flux inside the FRC must persist long enough for the compression process to be completed, which is approximately 20 microseconds. Lifetime measurements of the FRCs formed for FRCHX show lifetimes of only 7 ˜ 9 microseconds once the FRC has entered the capture region. Results from recent FRCHX experiments will be presented, and possible reasons for the lifetime limitations will be discussed along with several approaches for overcoming these limitations. This work is supported by DOE-OFES.
    IEEE International Conference on Plasma Science 01/2011;
  • V. Makhin, M.H. Frese
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    ABSTRACT: form only given. Pulsed power sources such as fast capacitor banks and flux compression generators can deliver tens of mega-amperes of current but require from a few to few tens of microseconds to reach that level of output. Plasma loads designed to achieve velocities of tens of centimeters per microseconds need current pulses of that magnitude but function in a few hundred nanoseconds. Using the former to drive the latter requires a transfer switch that can conduct those currents for the longer time scale with low losses and switch the current to the load in the shorter time scale. The plasma flow switch is just such a device. It consists of an annular plasma armature that is accelerated over the long time scale of the power source along a coaxial plasma gun toward an abrupt reduction in radius of the inner electrode. When the armature passes that end, an arc of low density plasma sweeps inward at very high velocity, quickly transferring the current to the load on its short time scale. It is important that the plasma armature move slowly, so that it does not extract too much inductive or kinetic energy from the source, and that the switching arc move quickly, so that as much current as possible is transferred while the load can make full use of it. Plasma armatures, whether formed from wire arrays, foils, or gas puffs, need to be symmetric, since they are subject to a variety of instabiliies during acceleration, a requirement is further complicated by the 1/r2 variation in the magnetic driving force. Excessive armature asymmetry will allow the low density plasma behind the armature and its embedded field to break through the higher density part of the switch resulting in early opening before the desired current is reached. For over two decades, we have simulated plasma opening switch behavior using 2-d MHD in the R-Z plane. Those simulations have predicted experiments well even though they could not capture current filamentation. Our recent pert- rbed 3-d simulations show us that armatures can indeed filament along the direction of the current; however, that filamentation is Rayleigh-Taylor, not thermal. Thus, these filaments collect both mass and current density, so the force goes up with the mass, and on the whole, the filaments move like the unfilamented armature.
    Plasma Science (ICOPS), 2011 Abstracts IEEE International Conference on; 01/2011
  • S.D. Frese, M.H. Frese
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    ABSTRACT: form only given. It is well known that it is desirable to increase trapped flux in Field Reversed Configurations (FRCs) to increase both temperature and lifetime. It is thus important to understand the mechanism that determines the amount of trapped flux during formation. FRCs are formed by first trapping an initial bias field in an ionized plasma and then applying a large field opposite to the bias field. This reversal wraps the field lines around the ionized plasma forming a toroidal configuration that is then compressed by further increase of the reversed field. The most common method for ionizing the plasma and trapping the flux in it is to embed a magnetic field in a cold gas, and then lower and raise that field abruptly by pulsing the azimuthal coil generating it. The induced electric field breaks down the gas and traps the flux in it. The observed breakdown occurs in the experiment only after the initial bias coil current falls to zero and begins to rise again, possibly because the magnetic field limits the energy gained by free electrons and inhibits breakdown in the bulk of the gas and along the insulating wall. We performed 2-d magnetohydrodynamic simulations of this process with MACH2 using a physical model that allows us to control the time of ionization. These simulations show that the flux trapped inside the first ionized plasma is very small compared to the bias flux. Upon a moment's reflection it is easy to see that this must be true in the experiment since the magnetic field is near zero then. The subsequent rise of the current back to and above the bias level drives a theta pinch which is also experimentally observed. In this case, only the flux that diffuses into the plasma during that pinch is available for trapping in the FRC. Our simulated FRCs formed in this fashion trap only a modest fraction of the bias flux and are similar to those observed in experiments. They are also much less robust than those in simulations where the time of - irst ionization is artificially delayed until later in the preionization pulse when the magnetic field is high. We will show these simulations and comparisons to experiments. We hope the understanding gleaned from these simulations will help us trap more flux in our FRCs. Our simulated FRCs formed in this fashion trap only a modest fraction of the bias flux and are similar to those observed in experiments. They are also much less robust than those in simulations where the time of first ionization is artificially delayed until later in the preionization pulse when the magnetic field is high. We will show these simulations and comparisons to experiments. We hope the understanding gleaned from these simulations will help us trap more flux in our FRCs.
    Plasma Science (ICOPS), 2011 Abstracts IEEE International Conference on; 01/2011
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    ABSTRACT: Detailed calculations of the dynamics of the formation, guide, and mirror applied magnetic fields were conducted using a commercially available generalized finite element solver. As part of the integrated FRC compression heating experiment (FRCHX), an applied magnetic field forms, translates and finally captures the FRC in the liner region sufficiently long to enable compression. Large single turn coils are used in the formation region, and detailed information on the magnetic field greatly enhances the fidelity of 2-D magnetohydrodynamic simulations using MACH2. Solenoidal coils produce the necessary magnetic field for translation and capture of the FRC prior to liner implosion. Since the liner implosion is underway before the FRC is injected, the magnetic flux that diffuses into the liner is compressed, and the calculations must account for the liner motion. Design iterations were performed using the detailed magnetic field solver with MACH2 to achieve both the coil design and operating parameters which resulted in the highest likelihood of FRC capture prior to compression. This work is funded by the U.S. Department of Energy Office of Fusion Energy Sciences.
    11/2010;
  • Michael H. Frese, Sherry D. Frese
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    ABSTRACT: Over the next few years at AFRL, FRCs will be formed, translated into and captured in imploding liners, and compressed to fusion conditions to investigate magnetized plasma compression. Recent experiments have shown smaller differences between vacuum and plasma shot magnetic probe signals than predicted by MACH2 2-d r-z simulation, implying smaller FRC radii and entrained mass. Understanding the causes of this apparent mass loss could lead to making substantially more robust FRCs. MACH2 2-d r-theta simulations show gross asymmetries developing during the multiple theta-pinches of the preionization phase caused by the magnetic Rayleigh-Taylor instability. The asymmetric plasma configurations in these simulations strongly resemble axial-view visible light images from previous preionization experiments on FRCX at Los Alamos. In the simulations, plasma flows to the wall and could be lost there. These simulations strongly suggest that 3-d simulations will be necessary for complete understanding of the full process, and they are, in part, preparation for those.
    11/2010;
  • Sherry D. Frese, Michael H. Frese
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    ABSTRACT: Over the next few years, Los Alamos National Laboratory and the U. S. Air Force Research Laboratory Directed Energy Directorate will form, translate, capture, and compress a field reversed configuration (FRC) of magnetized deuterium plasma using an imploding solid liner to achieve magnetic fields more than 10^6 times that of the Earth and plasma pressures of 10^6 atmospheres. These experiments require multiple pulsed power events before FRC compression: formation of the FRC and its translation to and capture in a collapsing magnetic cavity. The FRC must be robust enough to have a long lifetime and yet be small enough to translate quickly and to enter the collapsing magnetic cavity. In early 2010 the team performed over 100 formation, translation, capture (FTC) experiments with a stationary liner and the first complete experiment with an imploding liner (FRCHX) in April. Working with the experimental team, NumerEx has performed integrated simulations of the FTC and FRCHX experiments to aid in the design of both, and to improve the simulations' fidelity. We will present comparisons of measurements from the simulations and experiments, as well as pre- and post-experiment analysis of the first FRCHX.
    11/2010;
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    ABSTRACT: Plasma guns offer opportunities to generate and direct plasma flows at high energy density. Typically, such guns comprise coaxial electrodes that are connected to high-current sources (e.g., capacitor banks, pulse lines, inductive stores, or magnetic-flux-compression generators). The basic interactions include ionization of materials such as injected gas or preinstalled wires/foils, acceleration of these materials by the Lorentz force, and expulsion of the resulting plasma flows. We review the use of a particular arrangement in the form of a plasma flow switch that acts as a multimegampere commutator, but it can also provide a magnetized-plasma target for compression by an imploding liner. In a quite separate concept, a plurality of quasi-steady plasma guns in a spherical array provides converging, collimated jets to compress plasma with stand-off from the plasma generators and chamber walls. Such stand-off in a repetitively pulsed system can be crucial for the development of fusion power reactors at megagauss energy densities.
    IEEE Transactions on Plasma Science 09/2010; · 0.87 Impact Factor
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    ABSTRACT: Summary form only given. Experiments on FRC formation and translation into the interior of a metal shell or liner have been conducted at AFRL. Flux exclusion, collimated light, and interferometer data on magnetized plasma injection will be presented. These are a pre-requisite for FRC compression by liner implosion, experiment progress on which will also be presented. FRC translation, capture, and compression experiments all use primarily axial ~ 2 Tesla guide and mirror fields established inside the liner, using ~ 5 millisecond rise time discharges into an array of pulsed magnet coils surrounding the liner implosion portion of the device. A 12 MA, 4.5 MJ axial discharge drives the liner implosion for compression experiments. The FRC capture experiments use 3 capacitor discharges into a segmented theta coil surrounding the FRC formation region to establish a bias field, accomplish pre-ionization of deuterium gas, and provide the reverse field main theta discharge (~ 1 Megamp) which forms the FRC. This is aided by two cusp field discharges. The guide and mirror fields enable translation of the FRC and its capture in the liner interior region. Diagnostics include pulsed power (current and voltage), magnetic field, field exclusion, He Ne laser interferometry, imaging and spectroscopy, radiography, and both activation and time-of-flight neutron detection. Design features and operating parameters are guided by 2D-MHD simulations.
    IEEE International Conference on Plasma Science 01/2010;
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    ABSTRACT: Summary form only given. The Los Alamos National Laboratory (LANL) collaboration with Air Force Research Laboratory (AFRL) collaboration is close to a physics demonstration of compressional heating in a Magneto Inertial Fusion (MIF) plasma target. These first Magnetized Target Fusion (MTF) experiments will use solid aluminum flux compressor shells. The experimental high density Field Reversed Configuration (FRC) can be made to translate fast enough so that FRC lifetime is not an issue. We show some initial translation data from the Los Alamos FRC experiment FRXL that characterize the translated target plasma. We have taken advantage of the LANL experience so that a near duplicate of FRXL has come up in several months. The solid liner MTF is only one of several magnetized, pulsed MIF fusion schemes that are being pursued. We outline the present status of MTF including target formation, translation to a trapping region, and compression results.
    IEEE International Conference on Plasma Science 01/2010;
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    Michael H. Frese, Sherry D. Frese
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    ABSTRACT: Plasmas with embedded high magnetic fields are less subject to thermal conduction losses and can therefore reach higher temperatures under compression. This effect offers a path to generation of neutrons by thermal collisions known as magnetized target fusion (MTF). Now also referred to as magneto-inertial fusion (MlF). Since MTF allows the use of slower drivers for compress ion, it should lower the cost of achieving intense neutron pulses. NumerEx's effort under this Task Order has focused on two different concepts for MTF. The first approach is the generation, stagnation, and compression of ultrahigh speed plasma (UHP) flow; the second is formation, translation, capture, and compression of a field-reversed magnetized plasma configuration (FRC). In both concepts, the ultimate compression is by an imploding liner driven by a fast capacitor bank. Here we will describe our achievements in simulating those two concepts. The first section will focus on simulations of the UHP target liner compression, and the second, on simulations of FRC compression.
    10/2009;
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    ABSTRACT: Summary form only given. We present and overview the experimental high density Field Reversed Configurationi (FRC) approach for application to a physics demonstration of magnetized target fusion (MTF). This MT target plasma continues to be developed at the Los Alamos FRC experiment FRXL. The first translated FRXL FRC data will be shown, where the translation speeds exceed 15cm/usec, which yields a translation time substantially shorter than the FRC lifetimes. The conical theta coil is expected to generate toroidal magnetic field and helicity and increase stability and lifetime. The implications of the present data for MTF experiments will be discussed, along with the hardware, diagnostics, and pre-compression plasma formation and trapping experiments.
    IEEE International Conference on Plasma Science 01/2009;
  • S. D. Frese, M. H. Frese
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    ABSTRACT: Summary form only given. Over the next three to five years, Los Alamos National Laboratory (LANL) and the U. S. Air Force Research Laboratory (AFRL) will form, translate, capture, and compress a field reversed configuration (FRC) of magnetized deuterium plasma using an imploding solid liner to achieve magnetic fields more than a million times that of the Earth and plasma pressures of one million atmospheres. These experiments require two pulsed power events before FRC compression: formation of the FRC and its translation to and capture in a collapsing magnetic cavity. Though the FRC must be robust enough to have a long lifetime and yet be small enough to translate quickly and to enter the collapsing magnetic cavity, its formation is a relatively well-behaved process.However, its translation and capture is at best a balancing act. The mirror field at the liner entrance must be small enough to allow the FRC to enter, and that at the exit must be large enough to reflect it back, after which the entrance mirror field must be large enough to keep it from bouncing back out again. This is complicated by the fact that the liner implosion will begin before FRC formation in order for the FRC to last through compression. Hence, the relevant mirror fields are dynamically created by partial liner compression. Working in close coordination with the electromechanical design team, NumerEx has performed integrated simulations of the FRC formation, translation, capture and compression to aid in the choice of field strengths, coil placement, and timing. We will describe this process by showing simulations of successful and unsuccessful designs. We will also describe improvements we made to our models to increase their fidelity and flexibility, so that as new coil designs and experimental measurements of translation and mirror fields have become available, we could quickly incorporate them.
    IEEE International Conference on Plasma Science 01/2009;