Science-Based Solutions for NNSA Mission Needs
Sandia's existence stems from its engineering support of the Manhattan Project during the 1940's to develop Nuclear Weapons (NWs), and its first and foremost mission remains engineering support for the NW program. This mission represents a significant fraction of the total effort at Sandia, which is administered by the National Nuclear Security Administration (NNSA). Not surprisingly, Center 1100 has had many core thrusts that have a rich history of contributing in important ways to NW mission needs. These past thrust activities have in many cases led to enduring applied research programs and unique capabilities with continuing important direct applications that support the evolving stockpile and nuclear nonproliferation. A significant fraction of the research in Center 1100 is therefore geared toward performing fore-front science that has either an immediate or the promise of future impact on the nation's nuclear arsenal. This R&D can be categorized under the following headings
- Enhanced Surveillance — To develop sensors, networking, &smp; monitoring technologies to support development &smp; deployment of new embedded methods for early detection of age-induced degradation in the stockpile.
- Corrosion Mechanisms
- Neutron Generator Science
- Plasma Physics
- Dynamic Material Properties — To provide a science and competency base for the incorporation of new technologies into weapon systems and address mechanical properties of materials, processing and performance in high pressure, shock, and plasma environments.
- Shock Physics of Ferroelectric Materials and Systems
- Shock Sensors
- Equation of State Theory
- Enhanced Surety —
- To provide a science and competency base for the incorporation of new technologies into weapon systems and stockpile stewardship operations.
- GaN photovoltaics
- Optical Sprytrons
- To provide a science and technology base for the incorporation of new lasers and optics technologies into weapon systems surety
- Direct Optical Initiation
- Remote Optical Sensing
- Optical-based Sensors, Communications, and Security.
- To provide a science and competency base for the incorporation of new technologies into weapon systems and stockpile stewardship operations.
- Readiness in Technical Base and Facilities — To Support the Center's main research facilities for NW research: The Compound Semiconductor Research Laboratory (CSRL — now the MESA Micro Fab/Lab), and the Ion Beam Laboratory (IBL).
- CSRL
- Prototype small periphery electronic and optoelectronic devices that utilizes compound semiconductor material, e.g. GaN/AlGaN High Electron Mobility Transistors.
- Integrated Nanotechnology Platforms
- IBL
- QASPR - Qualification Alternatives to the Sandia Pulsed Reactor system for weapons qualification in short-pulse neutron radiation environments.
- Radiation Effects Microscopy
- Applied Nuclear Physics — Ion Beam Analysis
- Defect Science
- CSRL
Neutron Generator Science
Our expertise and facilities in radiation plasma and shock physics have always been actively involved in supporting the design and development of neutron generators. This is especially true today, since Sandia now has total responsibility (design, development and production) for these critical components. Crucial current activities that we are involved in include:
- Neutron Tube Shotlife — Neutron tubes accelerate deuterium ions at high energies from a source into a tritiated target, producing neutrons through the T(d,n) fusion reaction. These tubes must operate multiple times to be certified for the stockpile, and this is called "shotlife". This shotlife was becoming marginal on a tube to be used in the W76-1. Research performed in our Ion Beam Laboratory (IBL) discovered that deuterium released during the "shot", was not getting regettered properly back into the source. A new Ion Beam Analysis (IBA) technique was invented for the purpose of this research. Engineers in the Neutron Generator Design Group proposed an approach to enhance this regettering, and this was tested in the IBL, validating models of this increased performance, leading to this approach being adopted by the Neutron Generator Facility (NGF) to manufacture the tube.
- Neutron Tube Physics — When the neutron tube production line was recently moved from Pinelas to Albuquerque, there were a number of challenges in restoring production that pointed to a fundamental lack of understanding of some aspects of the tube physics. This recognition by many members of the design and production teams led to a renewed interest in identifying and understanding fundamental issues related to plasma surface interactions, arc initiation and control, secondary electron generation, and surface contamination. Due to our expertise, we have played an important role in defining the problems, identifying solutions based upon experiments, and improving tube performance. Our contributions in this area have been recognized by both Sandia and DOE.
- Power Supply Materials and Physics — A new Chem Prep process is being developed to produce PZT 95/5 and new encapsulant formulations are being explored for the neutron generator power supply. Center 1100 is studying the shock responses of both the PZT and encapsulants to ensure adequate data bases and viability for this application. We are also heavily involved with Center 2500 in studying the characteristics of the power supply under laboratory conditions that mimic actual operation in order to understand and model device performance as well as to identify and remedy breakdown mechanisms over the full STS temperature range.
Ion Beam Analysis (IBA)
Two accelerator facilities in the Center are used for quantitative high-energy ion beam analysis of materials. These are the 2.5 MV Van de Graaff and the 6.5 MV Tandem Pelletron. Light elements (hydrogen to fluorine) are depth concentration profiled using heavy ion elastic recoil detection (ERD) and nuclear reaction analysis (NRA), while heavier elements are measured using backscattering spectrometry (e.g., RBS) and proton induced x-ray emission (PIXE). An external Micro Ion Beam Analysis (X-MIBA) capability enables multi-elemental analysis and ion irradiation of samples, which are vacuum incompatible or extraordinarily large, and is currently a main component of the Center's Homeland Security program where it is being used to detect radioactive particulates and measure compositional signatures. The Nuclear Microprobe with is used to study materials with 1 micron lateral resolution.
The capabilities of IBA are summarized in our IBA Periodic Table.
Plasma Physics
Plasma physics has been a part of the Laboratories research portfolio almost from the beginning of the laboratory. Recently, our historical expertise in this area has contributed to ongoing missions in the areas of fusion research, neutron generators, high power gas lasers, and microelectronics processing. In addition to our impact on Sandia missions, we have made significant contributions to external programs funded by private industry (Sematech, Applied Materials) and other governmental agencies.
The chemical complexity of most plasma systems coupled with the challenges of directly probing plasmas has led us to develop a portfolio of plasma diagnostic techniques that span the spectrum from dc to rf, microwaves, and light. In addition we have been instrumental in the development of a number of heavy particle beam and laser based techniques. Due to their complexity, many of these diagnostic techniques do not exist outside Sandia. We are recognized world leaders in the area of plasma diagnostics and are regularly invited to give talks reviewing our techniques, consult with a range of customers, and participate in program reviews.
Plasma physics is typically divided into high and low temperature regimes. The high temperature plasma work has primarily benefited the DOE Office of Science Program in Magnetic Fusion Energy (MFE). Early work in H retention in metals and nonmetals, including the low-Z materials used for Plasma Facing Components (PFCs) such as limiters and plates used in diverters, lead to physics models for this retention that was ultimately used to formulate the details of the successful DT Campaign at the Princeton Plasma Physics Lab so as to stay with a rather low tritium inventory limit. More recently, our work has been to understand and control impurity transport at the edge of current tokamaks (DIII-D and CMOD), and spherimaks (NSTX), and to perfect detached-plasma techniques that both benefit H recycling and reduce erosion of PFCs.
Low temperature plasma physics is typically defined as electron temperatures of less than 10 eV. In the commercial arena, plasmas of this type are critical for microelectronics plasma processing, fluorescent lighting, flat panel displays and televisions, remediation of toxic materials, surface cleaning, and atmospheric rf propagation effects in the ionosphere. Within Sandia, the current significant emphasis in the areas of neutron tube source design (see item on Neutron Generator Science below), microelectronics processing, and dusty plasmas. In what follows we highlight the latter two areas.
- Microelectronic Processing — Plasma processing is a critical technology used in the production of microelectronics devices. The historical role for our Center has been to generate a scientific understanding of the fundamental mechanisms responsible for rf sheath formation and plasma chemistry. That understanding is incorporated into the general knowledge base for this area in the form of models and scaling laws. Due to our reputation in this area, we are regularly solicited to consult with industry.
- Dusty Plasmas — Our work in dusty plasmas is a relatively new program funded by BES that is examining the close coupling between plasma and micron sized dust particles. The coupling leads to collective and long range interactions between the dust and plasma and the formation of regular dust arrangements, or plasma crystals. In addition to employing our range of established plasma diagnostics, we are developing new techniques to characterize and understand these collective, many body interactions. One goal is to exploit the inherent self assembly of the dust into 3D stable crystal assemblies to make structures with unique properties.
Thus, while plasma physics has been a part of the centers portfolio for a number of years, it continues to contribute to a range of laboratory missions. We are currently exploring new areas related to remediation of biomass, plasma-surface interactions, the use of plasmas for hypersonic aircraft control, and plasma assisted combustion for high altitude aircraft.
Shock Physics
Shockwave physics at Sandia was born in a predecessor organization of Center 1100. The early work centered in part on material strength and survivability of weapon components and systems and to a larger extent on the development of novel concepts and materials for shock-actuated small pulse power sources. These sources became the active components in impact fuses and in explosively-driven ferroelectric and ferromagnetic firesets, and neutron generator power supplies. Concomitantly, we developed Sandia's first gas gun facility for controlled shockwave research, (still in use today) as well as a variety of shock diagnostic capabilities for both laboratory and underground experiments. We also performed research and developed considerable understanding of the shock initiation of explosives and used this knowledge to understand and help develop families of bridge-wire and slapper detonators. In some of these areas (ferroelectrics, encapsulants and dynamic piezoelectric stress gauges) Center 1100 remains the primary organization with the unique expertise and capabilities to address continuing needs.
Because shock experiments are expensive and their assembly is time consuming, early on Center 1100 established a static high pressure laboratory to complement the shock effort. This laboratory, which is still active today, allowed us to study in detail the phase diagrams of ferroelectric, ferromagnetic and other materials as well as their properties under pressure. Much of what we know about the physics and mechanisms of fire sets and neutron generator power supplies came from work in this laboratory. Recent work has been on PZT 95/5 and encapsulants in support of NG development and on slim-loop ferroelectrics (or relaxors) in support of firesets. This laboratory is also a critical resource for our BES-supported research on the fundamental physics of disordered ferroelectrics and dielectrics.
A few highlights of recent work follow:
- Dynamic Stress Instrumentation — We developed the Sandia Quartz Gauge which was for many years the primary standard for dynamic stress-time measurement at the Nevada Test Site and in the laboratory. We later developed the lithium niobate stress gauge and more recently the thin-film, piezoelectric polymer (PVDF) gauge. The latter two gauges have found extensive recent uses in flight tests for the diagnostics of the simultaneity of detonators, in field tests and in laboratory research.
- Instrumentation of Full-Scale Hydrodynamic Field Tests — Using our PVDF and lithium niboate dynamic gauges we have developed unique expertise and are the organization responsible for shock instrumentation to assess the standoff needed for the survivability of key components. We work closely with LANL, LLNL and Sandia engineering and development organizations in this area.
- Ferroelectrics Ceramics — We have investigated and continue to study the shock and high pressure responses of the PZTs and PBZT used in pulse power supplies to understand the physics of shock depoling and to develop models and data bases for use in developing simulation tools. We have found that the slim loop material PBZT is a relaxor unlike the other PZTs of interest that are normal ferroelectrics, and its shock depoling mechanism is different. These findings were very important for the modeling/simulation efforts.
Remote Optical Sensing
The goal of Sandia's remote optical sensing program is to characterize and identify material located at some distance from the sensor. In the current program, the materials span the full range of radiological, chemical and biological materials located on the ground or in airborne plumes at distances from feet to UAV and satellite based systems. The huge span of this laboratory wide effort is rooted in our Center's historical investment in gas phase molecular spectroscopy and laser development.
When started more than a decade ago, this work initially focused on nuclear nonproliferation issues. Based upon our previous research in molecular spectroscopy, a UV laser based system was proposed, despite a prevailing opinion outside the laboratory that UV would not work. Exploiting our investment in nonlinear laser optics, a frequency agile UV laser with unprecedented performance was fielded. That fully mobile system not only proved the validity of UV laser-based remote sensing but is now the technique of choice for this work. Our success and subsequent mission growth into other areas has firmly established Sandia as leader in remote sensing technologies. We are regularly called upon to consult with a range of governmental agencies and serve on review panels. In keeping with our tradition of national service, our work in this area has been little reported in the general literature due to sensitive aspects of the program and technology.
While the current generation of tools has enabled a broad range of remote sensing missions, there remain a number of potential technologies and outstanding science questions that could be pursued to enable the next generation of systems. For example, compact and easily deployed micro-optical systems that contain the functionality of the larger laboratory systems would be of widespread interest. In addition, the general nature of UV laser based remote sensing makes it a flexible technology base to address the ever-widening array of national threats. Our work in these areas continues.
Radiation Effects Microscopy (REM)
We have facilities for nuclear microscopy and radiation effects microscopy based on a 6.5 MV tandem Pelletron ion accelerator and 1.9 MeV/amu Radio Frequency Quadrupole LINAC Booster. We generate ion species from hydrogen to gold for radiation effects research The Sandia Nuclear Microprobe with micrometer size high-energy ion beams is used to microscopically study radiation effects in devices ranging from discrete transistors to state of the art integrated circuits. Three advanced diagnostic techniques were invented at Sandia: Single-Event-Upset Imaging, Ion-Beam-Induced-Charge-Collection Imaging (IBICC), and time-resolved IBICC. A recent development is the Ion Electron and Ion Photon Emission Microscopes (2001 and 2005 R & D-100 Award winners), which can perform radiation microscopy using very highly ionizing particles without focusing the ion beam. Most recently we have developed a dedicated endstation to expose discrete transistors to intense pulses of high energy heavy ions, e.g., 40 MeV Si ions, to simulate and study neutron damage effects using in situ Deep Level Transient Spectroscopy (DLTS).
REM was started at Sandia in 1990 with the invention of Single Event Upset (SEU)-Imaging. Since that time it has been used in three modes: (1) to perform basic research into the induction of charges into the circuit of an IC by energetic ions, (2) the pre-production testing of prototype circuits for SEUs, and (3) the post-production analysis of IC failures due to low resistance to SEUs. REM has had a significant impact on radhard IC design and manufacturing because of accomplishments using all three of these modes. Three selected examples are given here.
- Charge Induction Research — SEU Images of Sandia's most advanced generation of ICs, CMOS7r that uses Silicon on Insulator (SOI) technology, showed charge collection and upsets from ion strikes of gates of SRAM FETs as expected, but also saw upsets and high charge collection in "off" drains of these FETs that was unexpected. Further measurements on test capacitors confirmed that charge deposited in the substrate Si diffused to a region of depletion, and electric field, near the oxide — Si interface that induced considerable charge into the capacitor electrode on the surface through the Gunn theorem. The DAVINCI code used at Sandia to model ion strikes on advanced electronics and to pre-confirm the rad hardness of IC designs was found not able to handle the physics of this charge induction (i.e., displacement currents) properly. Efforts treating this deficiency in the DAVINCI code have been made.
- Prototype Testing — Sandia manufactured a British ASIC IC using the CMOS7r SOI generation prior to completing the design of the Permafrost ASIC Controller chip for the W76-1. SEU cross section measurements at the Brookhaven National Lab (BNL) found that these ICs had a low charge deposition (LET) threshold to SEUs (i.e., light ions such as Cl could cause upsets), but BNL could not pinpoint the cause of this radiation softness. These parts were then brought to our REM system at SNL, and SEU-Images quickly revealed that ion strikes to the "off" drains of latches (flip flops consisting of two coupled SRAMs) used to transfer data on to and off of the ASIC were the cause of these upsets. The DAVINCI code was used to model three alternative designs of these latches, and a test chip utilizing these alternatives was manufactured in the MDL and tested on the REM system. SEU-Images confirmed that eliminating two resistors from the design of these latches corrected the problem. It was this new latch design that was incorporated into the Permafrost Controller, resulting in "first pass success" of the manufacture of this important radhard IC.
- SEU Failure Analysis — The FAQ (focal plane array ASIC) chip is part of the BDYE satellite burst detector system manufactured by Sandia. Our SEU-Imaging found that RAM address decoder circuitry in this chip could register inaccurate data from the analog-digital circuits (ADCs) due to ion strikes. This radiation softness problem is still under review.