A wide range of targets with laser energies spanning two orders of magnitude have been shot at the National Ignition Facility (NIF). The National Ignition Campaign (NIC) targets are cryogenic with Si ...supports and cooling rings attached to an Al thermo-mechanical package (TMP) with a thin (30 micron) Au hohlraum inside. Particular attention is placed on the low-energy shots where the TMP is not completely vaporized. In addition to NIC targets, a range of other targets has also been fielded on NIF. For all targets, simulations play a critical role in determining if the risks associated with debris and shrapnel are acceptable. In a number of cases, experiments were redesigned, based on simulations, to reduce risks or to obtain data. The majority of these simulations were done using the ALE-AMR code, which provides efficient late-time (100-1000X the pulse duration) 3D calculations of complex NIF targets.
Vacuum scattering of electrons by an intense laser field is considered. This phenomenon is shown in many cases to be a polarization independent effect for arbitrary angle of incidence by an electron ...on a linearly polarized laser pulse. As the laser intensity grows and the focal volume shrinks, however, this independence fails. The corresponding electron energy and laser intensity transition is derived here for the first time. Such vacuum scattering is found to be driven by several mechanisms that occur over several scale lengths. Using both plane wave and focused laser field models, the relative importance of each is probed. In addition to extending the state of the art TEM00 to eighth order in the diffraction angle, an independent solution to the full Maxwell wave equation is also derived here based on the spectral methodology in which the imposed transverse laser fields are purely Gaussian in the focal plane. This is compared to the series expansion and found to be a distinct solution. Finally, this method is extended to allow for an arbitrary super-Gaussian transverse field profile boundary condition in the focal plane. After addressing these fundamental physics problems, some discussion of applications is given. First, the Thomson scattering cross section is derived for all laser intensities and electron energies. This allows the total amount of energy scattered by a Maxwellian electron beam to be computed: a useful experimental quantity. Following this, a simple, intuitive model is developed to calculate the brightness of a Thomson light source in a given frequency band. This is then compared to experiment and used to estimate the brightness of such a source driven by Z-Beamlet. Finally, a tunable infrared source is theoretically demonstrated. Electrons trapped in a standing electromagnetic wave tend to oscillate within the ponderomotive potential well. This bounce frequency and the laser frequency mix creating several intermodulation products that are manifested in the Thomson scattered spectra. For intensities on the order of 1017 W/cm2 , this phenomenon will scatter light along the laser polarization in the near infrared regime.
NIF experiments with Be capsules have followed a path of the highly successful "high-foot" CH capsules. Several keyhole and ConA targets preceeded a DT layered shot. In addition to backscatter ...subtraction, laser drive multipliers were needed to match observed X-ray drives. Those for the picket (0.95), trough (1.0) and second pulse (0.80) were determined by VISAR measurements. The time dependence of the Dante total x-ray flux and its fraction > 1.8 keV reflect the time dependence of the multipliers. A two step drive multiplier for the main pulse can match implosion times, but Dante measurements suggest the drive multiplier must increase late in time. With a single set of time dependent, multi-level multipliers the Dante data are well matched. These same third pulse drive multipliers also match the implosion times and Dante signals for two CH capsule DT. One discrepancy in the calculations is the X-ray flux in the picket. Calculations over-estimate the flux > 1.8 keV by a factor of ~100, while getting the total flux correctly. These harder X-rays cause an expansion of the Be/fuel interface of 2-3 km/s before the arrival of the first shock. VISAR measurements show only 0.2 to 0.3 km/s. The X-ray drive on the DT Be capsule was further degraded by a random decrease of 9% in the total picket flux. This small change caused the capsule fuel to change from an adiabat of 1.8 to 2.3 by mistiming of the first and second shocks. With this shock tuning and adjustments to the calculation, the first NIF Be capsule implosion achieved 29% of calculated yield, comparable to the CH DT capsules of 68% and 21%. Inclusion of a large M1 asymmetry in the DT ice layer and mixing from instability growth may help explain this final degradation. In summary when driven similarly the Be capsules performed like CH capsules. Performance degradation for both seems to be dominated by drive and capsule asymmetries.
We report the theoretical prediction and experimental verification of polarization independence of direct laser scattering of free electrons in vacuum. Simulations show multi-MeV electron scattering ...is possible. The focal volume requirement for independence is derived.
