Lawrence Livermore National Laboratory

Featuring some of our top Engineering innovations

New, ultrahigh-speed railgun design earns patent

Historically, railguns have been considered theoretically capable of delivering ultrahigh-velocity (>10 km/s) projectiles, but have never reached their potential. Typically, trailing "restrike" arcs would form at velocities greater than about 5 km/s, progressively sapping the drive current from behind the armature. This ultimately limited peak performance to no more than about 7 km/s. As part of the Ultra-High-Velocity LDRD, we designed a hybrid armature, which starts with a solid armature and progresses to a mixed solid armature/plasma brush. The armature was designed for use in a rail configuration with open sidewalls and in vacuum conditions. A version of the design was tested at IAP Research in 2010, with some initial positive results. In 2012, this "solid-to-hybrid transitioning armature railgun with non-conforming-to-prejudice bore profile" design was issued a patent. The invention could lead to ultrahigh-velocity railgun designs that attain payload speeds over 8 km/s. Applications for such a design would include equation-of-state research and launching projectiles from positions in the upper atmosphere or from orbital platforms. Jerome Solberg;

Continued advancement of the neural interface technology efforts to restore sight and hearing

Ongoing work by the Center for Micro and Nano Technology's (CMNT) neural interface technology team continued to yield significant recognition and advancement for the Artificial Retina and Cochlear Implant efforts. Having previously won numerous awards, including the 2009 R&D100 Editor's Choice Award and the 2010 Popular Mechanics Breakthrough Award, the Artificial Retina effort was recognized with the LLNL Director's S&T Award in 2012. Additionally, this project has led to numerous patents for LLNL and has established us as a leader in the neural prosthetic field. It has also led to a unique capability in the CMNT for developing biomedical devices, which has been leveraged to obtain additional WFO funding and establish the Biotechnology Core Competency at LLNL. Sat Pannu;

Advances in pillar structured thermal neutron detector

LLNL's neutron "Pillar Detector" fabrication technology uses semiconductor-based micro-structured elements as an electrical signal generation medium for the detection of neutrons. These materials, in the form of semiconductor "pillars" embedded in a matrix of high cross-section neutron converter materials (such as boron), emit charged particles upon interaction with neutrons. These charged particles in turn generate electron-hole pairs and thus detectable electrical current in the semiconductor micro-structured elements. Recent results demonstrate a highest measured efficiency of up to 48.5 %, reproducible at 40%, for 50-µm pillars. This is the highest efficiency rating achieved by any solid-state device. Further advances should enable us to reach the DNDO sponsor goal of 50% efficiency. Another significant achievement for 2012 was the demonstration of using the detector technology for multiplicity counting for mass extraction and isotope identification, wherein we were able to successfully identify a Californium sample. We also participated in DNDO-sponsored neutron test campaigns. Rebecca Nikolic;

Phoenix advances high-energy, explosive pulse-power generator systems

Phoenix is a Weapons and Complex Integration project to reduce the uncertainties in the equation-of-state models of weapon materials currently in the stockpile and assess updated materials that may be required as part of stockpile life extension programs. Phoenix has demonstrated a 3-million atmosphere ramp pressure drive in copper using a compact, explosive-driven flat-plate generator and is optimizing this system to produce a 5-million atmosphere drive for plutonium in FY15 at the U1a facility at the Nevada National Security Site. The ultimate objective of this project is to utilize the project's large 60-million-joule, explosive-driven pulsed power generator to drive material samples isentropically to pressures greater than 10 million atmospheres.

The Phoenix leverages 2-D and 3-D physics/engineering design codes, a number of which are unique to LLNL, to model the complex hydrodynamics, magneto-hydrodynamics, and plasma physics of the generators, power flow structures, and dynamic loads. These codes—combined with a dedicated group of scientists, engineers, and technical staff—have allowed this project to make significant advances in the use of explosive pulsed power as a reliable, repeatable tool for advancing the scientific objectives of the Stockpile Stewardship Program. Scott McAllister;

Additive manufacturing of new microstructured materials

Rapid developments within the Additive Manufacturing (AM) initiative were routine in 2012, as materials scientists and engineers sought to design and build new materials that will open up new spaces on many Ashby material selection charts, such as those for stiffness and density as well as thermal expansion and stiffness. Using projection microstereolithography, direct ink writing, and electrophoretic deposition technologies, we were able to: fabricate what is believed to be the highest stiffness-to-weight ratio material in the world; fabricate energy absorbing materials with designed and gradient properties (silicone foams); and demonstrate controlled energy release rates of thermite materials via microarchitecture, resulting in energy release rates spanning two orders of magnitude by design. Additionally, at the end of the year, two new metals powder AM machines were installed and commissioned in the B321C machine shop. With these new machines, we will be able to produce parts using common AM metals (tool steel, stainless steel, titanium, aluminum) as well as a wide range of development materials. Chris Spadaccini;

AMT diagnostic for NIF verifies AM is kept low, and reduces hardware costs

NIF laser pulses are frequency modulated (FM) to create bandwidth that prevents power from concentrating in any one spectral band and initiating a parasitic mechanism known as Stimulated Brillouin Scattering. On a high-energy laser system, this extra bandwidth is challenging to manage. In the presence of uncorrected spectral distortions in the laser amplifier chain, it can convert into amplitude modulation (AM), which can damage the final optics. The Amplitude Modulation Temporal (AMT) system verifies that the AM is kept below 10% on every NIF shot. Measuring the AM of all 48 NIF quads on a single-shot basis requires state-of-the-art oscilloscopes and detectors that cost $300,000 per channel. In order to reduce the cost of the overall system, the AMT team designed and deployed an optical–electronic–optical multiplexing scheme. The method converts the 1053-nm light to a voltage signal, which in turn modulates a 1550-nm telecom carrier signal and makes use of a wavelength division multiplexing (WDM) scheme to combine all 48 signals onto a single oscilloscope. This innovation saved the NIF project $14 million in direct hardware costs. However, perhaps the greater benefit is the time and personnel savings in verifying that the AM is low when NIF makes a wavelength change. John Heebner;

Precision engineering for NIF targets

Two dedicated clean assembly lines were added to the NIF target assembly area. One of the lines is to fabricate thin film "tents" to secure and center the capsules inside the hohlraum of cryogenic targets. The other line is to handle the capsule fill-tube assemblies (CFTA). The CFTA line has individual stations to leak test the capsule, thread it into a vacuum chuck for future handling steps, clean the surface of the capsule with a 100 micron diameter solvent stream, map the full surface (4 pi steradians) of the capsule and ready the capsule for insertion into a target. The scale of the CFTA is a 2-mm-diameter capsule held with a 10-micron-diameter glass fill tube that increases in diameter up to 150 microns. This requires very precise handling and moving steps to minimize loads on the CFTA and to provide the incremental motion needed for the confocal microscope to map individual 100-micron patches of the surface. A clean and well-characterized capsule is critical to ignition targets to avoid and understand the effects of isolated defects on the implosion symmetry and mix of the ablator and fuel. Beth Dzenitis;

Develpment of new NIF target platforms

Sixteen new types of NIF targets were developed and deployed in FY12. The Compton radiography target provided a new x-ray backlighter to image the cold fuel in a layered target during an implosion. The ConAwide and ConA2D targets both provided a larger diagnostic opening to measure symmetry earlier in the implosion cycle. The View Factor target, which has a larger laser entrance opening, provided an enhanced view into the hohlraums. The 3-axis keyhole target allowed simultaneous measurement of the shock timing in three directions. The THDKey target allowed shock timing in a layered target to validate the surrogacy of liquid D2-filled versus solid hydrogen in keyhole targets. Each of the new targets required a precision engineering effort to design and fabricate the individual components and specialized tooling to handle the micron-scale components for target assembly. Beth Dzenitis;

Simulation and experiments explore using dynamic z-pinches for high-gradient, high-current particle acceleration

Particle accelerators, which use electromagnetic fields to propel charged particles to high speeds and to contain them in well-defined beams, have become ubiquitous in our society. They form the engineering basis for applications ranging from fundamental physics research to proton therapy cancer treatments. State-of-the art accelerator technology using RF-driven, vacuum-based columns has reached its limit of about 0.3 MV/cm because of available RF sources and vacuum breakdown limits. In Engineering, we are investigating a new type of accelerator based on understanding and exploiting empirically observed acceleration fields in z-pinch plasmas, which can reach multiple MV/cm while driving kiloamps of current. Such notably higher acceleration gradients could enable many applications that require both very high particle energy and compact size.

Last year, we took significant steps in understanding these z-pinches through the first fully kinetic simulations that model the plasma particle by particle. The simulations for the first time self-consistently reproduced key features of these z-pinch plasmas, such as MeV particle beams emitted from centimeter-long plasmas. Experimentally, we have produced record acceleration gradients of greater than 0.5 MV/cm for sub-kilojoule, tabletop z-pinch plasmas, and are exploring the injection of a probe beam into the z-pinch to demonstrate using the plasma as a high-gradient acceleration stage. This work has already led to Program applications and to multiple published articles, including in Physical Review Letters. Vince Tang;

Advances in compact neutron source technology

(A) Neutrons can be employed for finding a variety of illicit materials such as explosives and special nuclear materials. Commercial applications range from well-logging to radiography. A highly portable and compact neutron source would enable important multiple detection capabilities in the field. In an effort supported by NA-22, Engineering is developing a palm-size neutron source with sufficient strength (1e7 DT n/s) for finding hidden nuclear materials in the field. New accelerator technologies that requires less power and space, such as the use of field ionization sources, are being researched and developed to enable this source. Our R&D has already produced the highest recorded neutron yields and fluence produced by field ionization sources, and we recently developed a new neutron target fabrication technique that could double the yield of neutron generators in general. A Record of Invention and a patent have been filed. Moving forward, we expect to have the technology basis for a palm-size neutron source developed by FY14.

(B) X-ray and gamma radiography can provide nondestructive evaluation (NDE) of complex, shielded objects and both are used routinely in all fields. Neutron radiography, although less common because of the lack of compact high-intensity sources, can provide orthogonal, complementary information since neutrons are heavily attenuated by low-Z materials while x-rays are stopped easily by high-Z materials. In partnership with sponsors including WCI and NA-22, we are developing portable radiography sources and techniques for various potential applications. The ultimate goal is to employ both photon and neutron radiography simultaneously in a highly portable format for a complete picture of an object, and to do this without isotope-based sources (since they cannot be turned off.) In particular, we have experimentally demonstrated—using a carbon target on our new 4-MV deuterium accelerator in B431—the possibility of dual neutron and gamma radiography through deuterium–carbon reactions that produce both MeV-level neutrons and gammas. We have produced the first radiographs using this new target. In the analysis and techniques area, we have shown that it is possible to reduce the deleterious effect of blurring from thick but efficient radiography scintillators through maximum entropy-based reconstruction routines. We have also recently developed and validated a new hybrid radiography model that allows us to predict the effectiveness of new types of sources through simulation. Through combined R&D efforts in both radiography accelerator systems and analysis routines, we expect to advance the state of the art in what can be effectively radiographed in the field. Vince Tang;

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