119 research outputs found
The Professional Learning Motivation Profile (PLMP): A Tool for Assessing Instructional Motivation
This article chronicles the collaboration of administrators from six districts and three college professors as they assessed professional learning during the first year of teaching. The examination led to the development of a Professional Learning Motivation Profile. Results from the profile indicated a traditional model of professional development was not effective in growing the professional learning motivation of beginning teachers. Anecdotal data shared includes how administrators used the data to inform conversations designed to support teachers in their journey toward courageous, effective instruction
Fast-ignition design transport studies: realistic electron source, integrated PIC-hydrodynamics, imposed magnetic fields
Transport modeling of idealized, cone-guided fast ignition targets indicates
the severe challenge posed by fast-electron source divergence. The hybrid
particle-in-cell [PIC] code Zuma is run in tandem with the
radiation-hydrodynamics code Hydra to model fast-electron propagation, fuel
heating, and thermonuclear burn. The fast electron source is based on a 3D
explicit-PIC laser-plasma simulation with the PSC code. This shows a quasi
two-temperature energy spectrum, and a divergent angle spectrum (average
velocity-space polar angle of 52 degrees). Transport simulations with the
PIC-based divergence do not ignite for > 1 MJ of fast-electron energy, for a
modest 70 micron standoff distance from fast-electron injection to the dense
fuel. However, artificially collimating the source gives an ignition energy of
132 kJ. To mitigate the divergence, we consider imposed axial magnetic fields.
Uniform fields ~50 MG are sufficient to recover the artificially collimated
ignition energy. Experiments at the Omega laser facility have generated fields
of this magnitude by imploding a capsule in seed fields of 50-100 kG. Such
imploded fields are however more compressed in the transport region than in the
laser absorption region. When fast electrons encounter increasing field
strength, magnetic mirroring can reflect a substantial fraction of them and
reduce coupling to the fuel. A hollow magnetic pipe, which peaks at a finite
radius, is presented as one field configuration which circumvents mirroring.Comment: 16 pages, 17 figures, submitted to Phys. Plasma
Report from the Integrated Modeling Panel at the Workshop on the Science of Ignition on NIF
This section deals with multiphysics radiation hydrodynamics codes used to design and simulate targets in the ignition campaign. These topics encompass all the physical processes they model, and include consideration of any approximations necessary due to finite computer resources. The section focuses on what developments would have the highest impact on reducing uncertainties in modeling most relevant to experimental observations. It considers how the ICF codes should be employed in the ignition campaign. This includes a consideration of how the experiments can be best structured to test the physical models the codes employ
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Progress on the physics of ignition for radiation driven inertial confinement fusion (ICF) targets
Extensive modeling of proposed National Ignition Facility (NIF) ignition targets has resulted in a variety of targets using different materials in the fuel shell, using driving temperatures which range from 250-300 eV, and requiring energies from < 1 MJ up to the full 1. 8 MJ design capability of NIF. Recent Nova experiments have shown that hohlraum walls composed of a mixture of high-z materials could result in targets which require about 20% less energy. Nova experiments are being used to quantify benefits of beam smoothing in reducing stimulated scattering processes and laser beam filamentation for proposed gas-filled hohlraum targets on NIF. Use of Smoothing by Spectral Dispersion with 2-3 {Angstrom}of bandwidth results in <4-5% of Stimulated Raman Scattering and less than about 1% Stimulated Brillouin Scattering for intensities less than about 2x10{sup 15}W/cm{sup 2} for this type of hohlraum. The symmetry in Nova gas- filled hohlraums is affected by the gas fill. A large body of evidence now exists which indicates that this effect is due to laser beam filamentation which can be largely controlled by beam smoothing. We present here the firs 3-D simulations of hydrodynamic instability for the NIF point design capsule. These simulations, with the HYDRA radiation hydrodynamics code, indicate that spikes can penetrate up to 10 {mu}m into the 30{mu}m radius hot spot before ignition is quenched. Using capsules whose surface is modified by laser ablation, Nova experiments have been used to quantify the degradation of implosions subject to near NIF levels of hydrodynamic instability
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3D Simulations of line emission from ICF capsules
Line emission from ICF implosions can be used to diagnose the temperature of the DT fuel and provides an indication of the distortion in the fuel-pusher interface. 2D simulations have provided valuable insights into the usefulness of argon and titanium dopants as diagnostics of instabilities. Characterizing the effects of drive asymmetries requires 3D modeling with large demands for computer time and memory, necessitating the use of parallel computers. We present the results of some 3D simulations achieved with a code utilizing both shared memory and distributed parallelism. We discuss the code structure and related performance issues
Cone-Guided Fast Ignition with no Imposed Magnetic Fields
Simulations of ignition-scale fast ignition targets have been performed with
the new integrated Zuma-Hydra PIC-hydrodynamic capability. We consider an
idealized spherical DT fuel assembly with a carbon cone, and an
artificially-collimated fast electron source. We study the role of E and B
fields and the fast electron energy spectrum. For mono-energetic 1.5 MeV fast
electrons, without E and B fields, the energy needed for ignition is E_f^{ig} =
30 kJ. This is about 3.5x the minimal deposited ignition energy of 8.7 kJ for
our fuel density of 450 g/cm^3. Including E and B fields with the resistive
Ohm's law E = \eta J_b gives E_f^{ig} = 20 kJ, while using the full Ohm's law
gives E_f^{ig} > 40 kJ. This is due to magnetic self-guiding in the former
case, and \nabla n \times \nabla T magnetic fields in the latter. Using a
realistic, quasi two-temperature energy spectrum derived from PIC laser-plasma
simulations increases E_f^{ig} to (102, 81, 162) kJ for (no E/B, E = \eta J_b,
full Ohm's law). This stems from the electrons being too energetic to fully
stop in the optimal hot spot depth.Comment: Minor revisions in response to referee comment
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