We report an improved measurement of the free neutron lifetime τ n using the UCNτ apparatus at the Los Alamos Neutron Science Center. We count a total of approximately 38 × 10 6 surviving ultracold neutrons (UCNs) after storing in UCNτ's magnetogravitational trap over two data acquisition campaigns in 2017 and 2018. We extract τ n from three blinded, independent analyses by both pairing long and short storage time runs to find a set of replicate τ n measurements and by performing a global likelihood fit to all data while selfconsistently incorporating the β-decay lifetime. Both techniques achieve consistent results and find a value τ n ¼ 877.75 AE 0.28 stat þ 0.22= − 0.16 syst s. With this sensitivity, neutron lifetime experiments now directly address the impact of recent refinements in our understanding of the standard model for neutron decay.

A.; Makela, M.; Bagdasarova, Y.; et al., "Performance of the Los Alamos National Laboratory spallation-driven solid-deuterium ultra-cold neutron source," Rev. Sci. Instrum. 84, 013304 (2013); http://dx.doi.org/10.1063/1.4770063 REVIEW OF SCIENTIFIC INSTRUMENTS 84, 013304 (2013) Performance of the Los Alamos National Laboratory spallation-driven solid-deuterium ultra-cold neutron source In this paper, we describe the performance of the Los Alamos spallation-driven solid-deuterium ultracold neutron (UCN) source. Measurements of the cold neutron flux, the very low energy neutron production rate, and the UCN rates and density at the exit from the biological shield are presented and compared to Monte Carlo predictions. The cold neutron rates compare well with predictions from the Monte Carlo code MCNPX and the UCN rates agree with our custom UCN Monte Carlo code. The source is shown to perform as modeled. The maximum delivered UCN density at the exit from the biological shield is 52(9) UCN/cc with a solid deuterium volume of ∼1500 cm 3 .

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The US Fusion Energy Sciences Advisory Committee (FESAC) was charged 'to identify the most promising transformative enabling capabilities (TEC) for the U.S. to pursue that could promote efficient advance toward fusion energy, building on burning plasma science and technology.' A subcommittee of U.S. technical experts was formed, and received community input in the form of white papers and presentations on the charge questions. The subcommittee identified four 'most promising transformative enabling capabilities': • Advanced algorithms • High critical temperature superconductors • Advanced materials and manufacturing • Novel technologies for tritium fuel cycle control In addition, one second tier TEC, defined as a 'promising transformative enabling capability' was identified: fast flowing liquid metal plasma facing components. Each of these TECs presents a tremendous opportunity to accelerate fusion science and technology toward power production. Dedicated investment in these TECs for fusion systems is 1 needed to capitalize on the rapid advances being made for a variety of non-fusion applications, to fully realize their transformative potential for fusion energy.

We develop a mini gas gun system for simultaneous, single-pulse, x-ray diffraction and imaging under high strain-rate loading at the beamline 32-ID of the Advanced Photon Source. In order to increase the reciprocal space covered by a small-area detector, a conventional target chamber is split into two chambers: a narrowed measurement chamber and a relief chamber. The gas gun impact is synchronized with synchrotron x-ray pulses and high-speed cameras. Depending on a camera's capability, multiframe imaging and diffraction can be achieved. The proof-of-principle experiments are performed on single-crystal sapphire. The diffraction spots and images during impact are analyzed to quantify lattice deformation and fracture; fracture is dominated by splitting cracks followed by wing cracks, and diffraction peaks are broadened likely due to mosaic spread. Our results demonstrate the potential of such multiscale measurements for studying high strain-rate phenomena at dynamic extremes.

The UCNA experiment was designed to measure the neutron β-asymmetry parameter A 0 using polarized ultracold neutrons (UCN). UCN produced via downscattering in solid deuterium were polarized via transport through a 7 T magnetic field, and then directed to a 1 T solenoidal electron spectrometer, where the decay electrons were detected in electron detector packages located on the two ends of the spectrometer. A value for A 0 was then extracted from the asymmetry in the numbers of counts in the two detector packages. We summarize all of the results from the UCNA experiment, obtained during run periods in which ultimately culminated in a 0.67% precision result for A 0 .

A shower of 50-ptm-diameter carbon dust grains has been accelerated to speeds up to 6 km/s in laboratory for the first time. A coaxial plasma gun is used for dust acceleration. A distinctive feature of this plasma accelerator is that it can use any gas and can operate with microparticles having any shape. Deuterium gas and carbon dust is chosen to be compatible with fusion plasmas as a diagnostic tool. The measured voltages and discharge currents of the plasma gun are up to 10 kV and 230 kA, respectively. The plasma ejected from the gun by JxB forces at speeds of about 28 km/s is well collimated for a distance of about 2 m. A hydrodynamic model, as well as a direct collision model which accounts for direct collisions of ions with the grains, is used to explain the dust acceleration. The drag force depends on the ratio of the plasma density to the dust material density. The plasma density and the electron and ion temperatures in the models are of the order of 10 19 m-3, and about 1 eV, respectively. Possible applications of hypervelocity dust are studies of dust-plasma interaction and magnetic field mapping in fusion plasmas.

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