Measuring the principal Hugoniot of inertial-confinement-fusion-relevant TMPTA plastic foams.

Wetted-foam layers are of significant interest for inertial-confinement-fusion capsules, due to the control they provide over the convergence ratio of the implosion and the opportunity this affords to minimize hydrodynamic instability growth. However, the equation of state for fusion-relevant foams are not well characterized, and many simulations rely on modeling such foams as a homogeneous medium with the foam average density. To address this issue, an experiment was performed using the VULCAN Nd:glass laser at the Central Laser Facility. The aim was to measure the principal Hugoniot of TMPTA plastic foams at 260mg/cm^{3}, corresponding to the density of liquid DT-wetted-foam layers, and their "hydrodynamic equivalent" capsules. A VISAR was used to obtain the shock velocity of both the foam and an α-quartz reference layer, while streaked optical pyrometry provided the temperature of the shocked material. The measurements confirm that, for the 20-120 GPa pressure range accessed, this material can indeed be well described using the equation of state of the homogeneous medium at the foam density.

Automation and control of laser wakefield accelerators using Bayesian optimization.

Laser wakefield accelerators promise to revolutionize many areas of accelerator science. However, one of the greatest challenges to their widespread adoption is the difficulty in control and optimization of the accelerator outputs due to coupling between input parameters and the dynamic evolution of the accelerating structure. Here, we use machine learning techniques to automate a 100 MeV-scale accelerator, which optimized its outputs by simultaneously varying up to six parameters including the spectral and spatial phase of the laser and the plasma density and length. Most notably, the model built by the algorithm enabled optimization of the laser evolution that might otherwise have been missed in single-variable scans. Subtle tuning of the laser pulse shape caused an 80% increase in electron beam charge, despite the pulse length changing by just 1%.

A spectrometer for ultrashort gamma-ray pulses with photon energies greater than 10 MeV.

We present a design for a pixelated scintillator based gamma-ray spectrometer for non-linear inverse Compton scattering experiments. By colliding a laser wakefield accelerated electron beam with a tightly focused, intense laser pulse, gamma-ray photons up to 100 MeV energies and with few femtosecond duration may be produced. To measure the energy spectrum and angular distribution, a 33 × 47 array of cesium-iodide crystals was oriented such that the 47 crystal length axis was parallel to the gamma-ray beam and the 33 crystal length axis was oriented in the vertical direction. Using an iterative deconvolution method similar to the YOGI code, modeling of the scintillator response using GEANT4 and fitting to a quantum Monte Carlo calculated photon spectrum, we are able to extract the gamma ray spectra generated by the inverse Compton interaction.

Characteristics of White Leghorn chickens selected for heat tolerance.

A series of studies was conducted to identify and delineate factors associated with responses of chickens to high ambient temperatures. Two populations of birds were used which had been selected divergently for tolerance to stress at 40.6 degrees C. and 75% R.H. and at 5 weeks of age. After four generations of selection for survival time the lines had separated by 28 minutes: 58 vs. 86 minutes for the low and high, respectively. Egg production, hatchability, Haugh units and specific gravity did not differ between lines. Egg weight was greater in the low line. The body temperature of chicks at 30 minutes of heat stress was correlated (r = -0.454; P less than 0.05) to survival time. Body weight was correlated (r = -0.325) with resistance to heat stress while loss of body weight during heat stress was correlated (r = +0.478) with resistance. There was no apparent difference between lines in respect to resistance of 16-day old embryos to heat stress.

Relationship of heat tolerance and oxygen consumption in chickens.

Chicks from lines genetically selected for high or low heat tolerance were compared to lines selected for high or low oxygen consumption. Oxygen consumption, survival time, respiration rate, lung capacity and body weight were determined. Selection for high oxygen consumption ahd high heat tolerance resulted in birds with similar characteristics. The high line birds for both heat tolerance and oxygen consumption had greater oxygen consumption, survival time and lung capacity but lower body weight.