National Nuclear Security Administration

About: National Nuclear Security Administration is a government organization based out in Washington D.C., District of Columbia, United States. It is known for research contribution in the topics: Capacitor & Neutron. The organization has 130 authors who have published 114 publications receiving 1269 citations. The organization is also known as: NNSA & Nuclear Security Administration.

Conceptual designs of two petawatt-class pulsed-power accelerators for high-energy-density-physics experiments

Abstract: Here, we have developed conceptual designs of two petawatt-class pulsed-power accelerators: Z 300 and Z 800. The designs are based on an accelerator architecture that is founded on two concepts: single-stage electrical-pulse compression and impedance matching [Phys. Rev. ST Accel. Beams 10, 030401 (2007)]. The prime power source of each machine consists of 90 linear-transformer-driver (LTD) modules. Each module comprises LTD cavities connected electrically in series, each of which is powered by 5-GW LTD bricks connected electrically in parallel. (A brick comprises a single switch and two capacitors in series.) Six water-insulated radial-transmission-line impedance transformers transport the power generated by the modules to a six-level vacuum-insulator stack. The stack serves as the accelerator’s water-vacuum interface. The stack is connected to six conical outer magnetically insulated vacuum transmission lines (MITLs), which are joined in parallel at a 10-cm radius by a triple-post-hole vacuum convolute. The convolute sums the electrical currents at the outputs of the six outer MITLs, and delivers the combined current to a single short inner MITL. The inner MITL transmits the combined current to the accelerator’s physics-package load. Z 300 is 35 m in diameter and stores 48 MJ of electrical energy in its LTD capacitors. The acceleratormore » generates 320 TW of electrical power at the output of the LTD system, and delivers 48 MA in 154 ns to a magnetized-liner inertial-fusion (MagLIF) target [Phys. Plasmas 17, 056303 (2010)]. The peak electrical power at the MagLIF target is 870 TW, which is the highest power throughout the accelerator. Power amplification is accomplished by the centrally located vacuum section, which serves as an intermediate inductive-energy-storage device. The principal goal of Z 300 is to achieve thermonuclear ignition; i.e., a fusion yield that exceeds the energy transmitted by the accelerator to the liner. 2D magnetohydrodynamic (MHD) simulations suggest Z 300 will deliver 4.3 MJ to the liner, and achieve a yield on the order of 18 MJ. Z 800 is 52 m in diameter and stores 130 MJ. This accelerator generates 890 TW at the output of its LTD system, and delivers 65 MA in 113 ns to a MagLIF target. The peak electrical power at the MagLIF liner is 2500 TW. The principal goal of Z 800 is to achieve high-yield thermonuclear fusion; i.e., a yield that exceeds the energy initially stored by the accelerator’s capacitors. 2D MHD simulations suggest Z 800 will deliver 8.0 MJ to the liner, and achieve a yield on the order of 440 MJ. Z 300 and Z 800, or variations of these accelerators, will allow the international high-energy-density-physics community to conduct advanced inertial-confinement-fusion, radiation-physics, material-physics, and laboratory-astrophysics experiments over heretofore-inaccessible parameter regimes.« less

Elevation change of the Antarctic ice sheet, 1995-2000, from ERS-2 satellite radar altimetry

Abstract: We analyzed Antarctic ice-sheet elevation change (dH/dt) from 1995 to 2000 using 123 million elevation change measurements from European Remote Sensing 2 ice-mode satellite radar altimeter data covering an area of about 7.2 million km/sup 2/. Almost all drainage basins in east Antarctica had average dH/dt values within /spl plusmn/3.0 cm/year, whereas drainage basins in west Antarctica had substantial spatial variability with average dH/dt values ranging between -11 to +12 cm/year. The east Antarctic ice sheet had a five-year trend of 1/spl plusmn/0.6 cm/year, where 13 out of the 14 basins had either a positive trend or a trend that was not significantly different than zero. The west Antarctic ice sheet had a five-year trend of -3.6/spl plusmn/1.0 cm/year due largely to strong negative trends of around 10 cm/year for basins in Marie Byrd Land along the Pacific sector of the Antarctic coast. The continent as a whole had a five-year dH/dt trend of 0.4/spl plusmn/0.4 cm/year. Finally, time series constructed for the Pine Island, Thwaites, De Vicq, and Land glaciers in west Antarctic showed five-year dH/dt trends from -26 to -135 cm/year that were significantly more negative than the average dH/dt trends in their respective basins. The strongly negative dH/dt values for these coastal glacier outlets are consistent with recently reported results indicating increased basal melting at these glaciers' grounding lines caused by ocean thermal forcing.