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The ability to understand and predict the response of matter at extreme conditions requires knowledge of a materials equation-of-state (EOS) including the location of phase boundaries, transition kinetics, and accurate measurements of temperature at pressure. Recent developments in optical pyrometry have provided methods for measuring temperature in the shocked state, and these have been used to study the phase diagram for some metals including cerium. Cerium has received significant attention because it exhibits a rich phase diagram that includes an anomalous melt boundary and a low-pressure shock-melt transition. In this work, we continue our study of shock-melting using optical pyrometry to measure the temperature and stress states for two-phase cerium (γ-Ce and β-Ce) shocked into the high-pressure liquid phase. Details of the experimental methods, analysis, and results are presented. [ABSTRACT FROM AUTHOR]

We report recent results of reactive and nonreactive metal fragments–ejecta–transporting in vacuum, and reactive and nonreactive gases. We postulate that reactive ejecta transporting in a reactive gas, such as D2, will rapidly break up into smaller fragments in situations where they are otherwise hydrodynamically stable in a nonreactive gas such as He. The ejecta were formed through explosive loading of thin Sn (nonreactive) and Ce (reactive) coupons that included machined periodic perturbations on their backsides, which interfaced with vacuum, He or D2. Coupon surface hydrodynamics, ejecta mass- and size-velocity distributions, and ejecta temperatures were diagnosed with laser doppler velocimetry, piezoelectric transducers, Mie scattering and infrared imaging (IR). In addition, particle imaging velocimetry was applied for the first time to evaluate ejecta transport to study ejecta sheet breakup dynamics. The IR data demonstrate that rapid reactions of Ce ejecta transporting in D2 occur. [ABSTRACT FROM AUTHOR]

Shocked Ce metal in contact with a reactive gas such as H2 or D2 produces a distribution of ejecta particles that react with the gas to form Ce hydrides or deuterides. We present an average particle reaction diffusion model to calculate particle and gas temperatures and reaction fractions. We compare model results with recent HE driven Ce experiments into reactive D2 and non-reactive He gases for a variety of initial gas pressures from 2–8 atmospheres at initial temperatures of 300 K. We find consistent agreement with radiance temperature measurements as a function of time using particle distributions from Mie scattering data resulting in Ce deuteride mass conversion fractions in D2 gas of order 10 – 20 %. [ABSTRACT FROM AUTHOR]

The database at http://www.radiopurity.org is the world's largest public database of material radio-purity measurements. These measurements are used by members of the low-background physics community to build experiments that search for neutrinos, neutrinoless double-beta decay, WIMP dark matter, and other exciting physics. This paper summarizes the current status and the future plan of this database. [ABSTRACT FROM AUTHOR]

Inertial confinement fusion research at Los Alamos National Laboratory is focused on high-leverage areas of thermonuclear ignition to which LANL can apply its historic strengths and that are complementary to high-energy-density-physics topics. Using the Trident and Omega laser facilities, experiments are pursued in laser-plasma instabilities, symmetry, Be technologies, neutron and fusion-product diagnostics, and defect hydrodynamics. [ABSTRACT FROM AUTHOR]

The decay of common radioactive gases, such as radon, produces stable isotopes by a sequence of daughter particles with varied half-lives. These daughter particles are a significant source of gamma, neutron, and alpha (_) particle backgrounds that can mimic desired signals in dark matter and neutrinoless double beta decay experiments. In the LUMINA Laboratory at Southern Methodist University (SMU), studies of radon plate-out onto copper samples are conducted using one of XIA's first five UltraLo 1800 alpha counters. We present results from investigations into various mitigation approaches. A custom-built copper holder (in either plastic or metal) has been designed and produced to maximize the copper's exposure to 220Rn. The 220Rn source is a collection of camping lantern mantles. We present the current status of control and experimental methods for addressing radon exposure levels. [ABSTRACT FROM AUTHOR]

Rejection and protection from background is a key issue for the next generation SuperCDMS SNOLAB experiment that will have a cross-section sensitivity of better than 8 × 10-46 cm2 for spin-independent WIMP-nucleon interactions. This paper presents the details of the methods used to reject electromagnetic backgrounds using the new iZIP detectors that are currently operated in the Soudan Underground Laboratory, MN and the methods the collaboration is investigating to protect against neutron background in the next generation SuperCDMS experiment. [ABSTRACT FROM AUTHOR]

Southern Methodist University houses one of five existing commercially available UltraLo 1800 production model alpha counters made by XIA LLC. The instrument has an electron drift chamber with a 707 cm2 or 1800 cm2 counting region which is determined by selecting the inner electrode size. The SMU team operating this device is part of the SuperCDMS screening working group, and uses the alpha counter to study the background rates from the decay of radon in materials used to construct the SuperCDMS experiment. We have studied four acrylic samples obtained from the MiniCLEAN direct dark matter search with the XIA instrument demonstrating its utility in low background experiments by investigating the plate-out of 210Pb and comparing the effectiveness of cleaning procedures in removing 222Rn progenies from the samples. [ABSTRACT FROM AUTHOR]

The low-background physics community has been performing assays of material radiopurity for decades and many thousands of such measurements exist. Some are available in publications and others in databases, but most are still communicated informally. No standard data format exists for encoding material assays and there is no central location to store them. The aim of the work reported here is to address this long-standing problem, through the creation of a concise and flexible material assay data format and powerful database software to use it. A public installation of this software may serve as a long-term repository for the community's material assay data. It is available at http://www.radiopurity.org. [ABSTRACT FROM AUTHOR]

Matter, as we know it, makes up less than 5% of the Universe. Various astrophysical observations have confirmed that one quarter of the Universe and most of the matter content in the Universe is made up of Dark Matter. The nature of Dark Matter is yet to be discovered and is one of the biggest questions in Physics. Particle Physics combined with astrophysical measurements of the abundance gives rise to a Dark Matter candidate called Weakly Interacting Massive Particle (WIMP). The low density of WIMPs in the galaxies and the extremely weak nature of the interaction with ordinary matter make detection of the WIMP an extraordinarily challenging task, with abundant fakes from various radioactive and cosmogenic backgrounds with much stronger electromagnetic interaction. The extremely weak nature of the WIMP interaction dictates detectors that have extremely low naturally occurring radioactive background, a large active volume (mass) of sensitive detector material to maximize statistics, a highly efficient detector based rejection mechanism for the dominant electromagnetic background and sophisticated analysis techniques to reject any residual background. This paper describes the status of the SuperCDMS experiment. [ABSTRACT FROM AUTHOR]

The CDMS collaboration utilizes Ge detectors for their Weakly Interacting Massive Particle (WIMP) search at the Soudan mine, Minnesota. The final data run of CDMS II is complete and a detector upgrade for SuperCDMS has commenced. A SuperTower of five 1-inch thick Ge crystals has been installed and undergoing commissioning. Its surface-event rejection capability should allow SuperCDMS to continue to run background free for the next proposed phases: 15 kg Ge deployment at Soudan, and up to 150 kg Ge deployment at SNOLAB. Recent detector advances to allow a 1 tonne Ge experiment are also discussed. [ABSTRACT FROM AUTHOR]

SuperCDMS employs 1-inch thick germanium crystals operated below 50mK in a dilution cryostat. Each detector produces ionization and phonon signals. Ionization signals are amplified by JFETs operating at 150K within an assembly mounted on the 4K cryostat stage. These high impedance signals are carried to the FETs by superconducting “vacuum coaxes” which minimize thermal conductivity, stray capacitance, and microphonics. Transition edge sensors produce low-impedance phonon signals, amplified by SQUID arrays mounted on a 600mK stage. Detectors are mounted in a six-sided wiring configuration called a “tower”, which carries signals from 40mK to 4K. A flex circuit 3 meters in length carries amplified signals for each detector from 4K to a vacuum bulkhead. We describe the methods used to support the detectors, wiring and amplifier elements at various thermal stages, minimizing electrical noise and thermal loads. [ABSTRACT FROM AUTHOR]

The Cryogenic Dark Matter Search experiment (CDMS) is using Phonon+Ionization detectors to search for Dark Matter in the form of Weakly Interactive Massive Particles (WIMPs). We report on new results from the operation of CDMS five “towers” at Soudan underground laboratory. With new and more massive detectors, SuperCDMS project has been started since March 2009. We report on the current status of SuperCDMS and its perspective. [ABSTRACT FROM AUTHOR]

The Cryogenic Dark Matter Search (CDMS) searches for Weakly Interacting Massive Particles (WIMPs) with cryogenic germanium particle detectors. These detectors discriminate between nuclear-recoil candidate and electron-recoil background events by collecting both phonon and ionization energy from interactions in the crystal. Incomplete ionization collection results in the largest background in the CDMS detectors as this causes electron-recoil background interactions to appear as false candidate events. Two primary causes of incomplete ionization collection are suface and bulk charge trapping. Recent work has been focused on reducing surface trapping through the modification of fabrication methods for future detectors. Analyzing data taken with test devices shows that hydrogen passivation of the amorphous silicon blocking layer does not reduce the effects of surface trapping. Other data shows that the iron-ion implantation used to lower the critical temperature of the tungsten transition-edge sensors increases surface trapping, causing a degradation of the ionization collection. Using selective implantation on future detectors may improve ionization collection for events near the phonon side detector surface. Bulk trapping is minimized by neutralizing ionized lattice impurities. Detector investigations at testing facilities and at the experimental site in Soudan, MN have provided methods to optimize the neutralization process and monitor running conditions to maintain maximal ionization collection. [ABSTRACT FROM AUTHOR]

The newly commissioned SuperCDMS Soudan experiment aims to search for WIMP dark matter with a sensitivity to cross sections of 5×10-45cm2 and larger (90% CL upper limit). This goal is facilitated by a new set of germanium detectors, 2.5 times more massive than the ones used in the CDMS-II experiment, and with a different athermal phonon sensor layout that eliminates radial degeneracy in position reconstruction of high radius events. We present characterization data on these detectors, as well as improved techniques for correcting position-dependent variations in pulse shape across the detector. These improvements provide surface-event discrimination sufficient for a reach of 5×10-45cm2. [ABSTRACT FROM AUTHOR]

For its dark matter search the SuperCDMS collaboration has developed new Ge detectors using the same athermal phonon sensors and ionization measurement technology of CDMS II but with larger mass, superior sensor performance and increased fabrication efficiency. The improvements in fabrication are described, a comparison of CDMS II and SuperCDMS detector production yield is reported, and future scalability addressed. [ABSTRACT FROM AUTHOR]

We have conducted a series of free surface shock experiments on cerium metal at peak shock pressures from 0.9–7.6 GPa. These experiments were done to examine the elastic-plastic behavior, the solid-solid phase transition occurring at 0.7–0.8 GPa, and the spall strength of the material as a function of peak stress. The elastic and low-pressure plastic waves exhibit long rise times while the post-transition plastic wave is sharp. Spallation wave profiles obtained using optical techniques are presented and discussed. [ABSTRACT FROM AUTHOR]

The mixing between fuel and shell materials in Inertial Confinement Fusion implosion cores is a topic of great interest. Mixing due to hydrodynamic instabilities can affect implosion dynamics and could also go so far as to prevent ignition. We have demonstrated that it is possible to extract information on mixing directly from experimental data using spectroscopic arguments. In order to compare this data-driven analysis to a theoretical framework, two independent mix models, Youngs’ phenomenological model and the Haan saturation model, have been implemented in conjunction with a series of clean hydrodynamic simulations that model the experiments. The first tests of these methods were carried out based on a set of indirect drive implosions at the OMEGA laser. We now focus on direct drive experiments, and endeavor to approach the problem from another perspective. In the current work, we use Youngs’ and Haan’s mix models in conjunction with hydrodynamic simulations in order to design experimental platforms that exhibit measurably different levels of mix. Once the experiments are completed based on these designs, the results of a data-driven mix analysis will be compared to the levels of mix predicted by the simulations. In this way, we aim to increase our confidence in the methods used to extract mixing information from the experimental data, as well as to study sensitivities and the range of validity of the mix models. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

We use the Quasi-static Particle-In-Cell code QuickPIC to model laser wake field acceleration, in both uniform and parabolic plasma channels within current state of the art experimental laser and plasma parameters. QuickPIC uses the quasi-static approximation, which allows the separation of the plasma and laser evolution, as they respond in different time scales. The laser is evolved with a larger time step, that correctly resolves distances of the order of the Rayleigh length, according to the ponderomotive guiding center approximation, while the plasma response is calculated through a quasi-static field solver for each transverse 2d slice. We have performed simulations that show very good agreement between QuickPIC and three dimensional simulations using the full PIC code OSIRIS. We have scanned laser intensities from those for which linear plasma waves are excited to those for which the plasma response is highly nonlinear. For these simulations, QuickPIC was 2–3 orders of magnitude faster than OSIRIS. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Laser Wakefield Accelerators (LWFA), in the resonant regime, require use of an injected electron beam. Several optical methods for generating electron bunches exist e.g., Laser Ionization and Ponderomotive Acceleration (LIPA) and Self-Modulated LWFA among others. Each of these schemes produces an electron bunch with a characteristic energy distribution. We examine the trapping characteristics in a resonant LWFA for an injection electron beam with a broad energy spread that can be characterized using a Boltzmann distribution with an “effective temperature”. We present results of both analytic calculations and simulations which provide a methodology for optimizing the resulting accelerated electron bunch characteristics i.e., energy and energy spread, for a given LWFA configuration. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

The standard regime for the laser wakefield accelerator (LWFA) usually requires external injection of MeV electrons. Ideally, the injected electron bunch should be injected into the proper phase of the accelerating wake, have a bunch length that is small compared with the plasma wavelength, and a low emittance and energy spread. This paper reports Hamiltonian analysis and simulation studies of two ‘nonideal’ injection schemes that demonstrate strong phase bunching and good accelerated beam quality in a channel-guided laser wakefield accelerator. For the case of monoenergetic, unphased (long bunch) injection, there is an optimum range of injection energies for which the LWFA can trap a significant fraction of the injected pulse while producing an ultrashort, high-quality accelerated pulse. Phased and unphased injection in a channel-guided LWFA with a broad injected energy spread has also been simulated. Although the trapping fraction is generally much smaller than in the monoenergetic case, some simulations exhibit final accelerated bunches with remarkably small energy spread. These results suggest that relatively poor quality injection pulses may still be useful in LWFA demonstration experiments. Implications for planned LWFA experiments at NRL are discussed. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]