Cryogenic Ice Research Articles

Modifying the Pore Size of Resorcinol Formaldehyde Aerogels for Fabrication of Hollow Spheres for Direct Drive ICF Experiments

AbstractThis work investigates an alternative way to modify the pore size of a 100 mg/cc resorcinol formaldehyde (R/F) aerogel without any significant change to the aerogel target density. This was successfully accomplished by an addition of hydrophilic polymer additive [Poly Vinyl Alcohol (PVA) or Poly Acrylic Acid (PAA)] to the R/F precursor solution which acts as an impurity in the reaction. The polymer can modify the cross linking or aggregation of the primary particles which can change the structure formation of the aerogel, thus changing the pore size. This paper will discuss this process modification and the fabrication of hollow, large pore R/F aerogel spheres that are used for direct drive inertial confinement fusion (ICF) cryogenic ice layering experiments at the University of Rochester Laboratory for Laser Energetics (LLE). The aerogels were characterized using scanning electron microscopy (SEM), nitrogen gas adsorption, and ultra small angle x-ray scattering (USAXS).

Freeze/thaw induced demulsification of water-in-oil emulsions with loosely packed droplets

Freeze/thaw treatment has been widely investigated for phase separation of oil-in-water (O/W) emulsions. However, it is a new application for destroying the inverted emulsions, water-in-oil (W/O) emulsions. In this study, freeze/thaw treatment was used to break the W/O emulsions with loosely packed droplets that were produced from the oils generally adopted as membrane phase in emulsion liquid membrane (ELM) process. The effects of emulsion system parameters and freezing conditions on demulsification performance were investigated. A near linear relationship was observed between demulsification performance and water content (30–65%). Demulsification performance greatly increased with the increase of droplet size (2.7–7.3 μm), while it was slightly affected by oil type. Four freezing methods were employed including freezing in refrigerator, cryogenic bath, dry ice and liquid nitrogen. The best freezing method for water removal was freezing in cryogenic or dry ice, and its efficiency was over 70% for all experimental systems with 60% water content regardless of droplet size and oil phase type. Furthermore, microscopic process of demulsification was monitored using optical microscope and the coalescence of droplets was simulated. From the experiments, the gradual demulsification process induced by freeze/thaw was proven and a collision mechanism was proposed. Meanwhile, the volume expansion of water turning to ice and interfacial tension of oil–water interface were determined as main driving forces of demulsification. The proposed mechanism and driving forces can explain the influences of various parameters on demulsification performance well.

Computer modeling of hydrogen and methane transport in cellular nanostructures of amorphous ice

New computer modeling of the condensed state of water is offered. Mechanisms of polyamorphic transformations of high-density amorphous (HDA) and low-density amorphous (LDA) phases of cryogenic ice and their properties to accumulate methane and hydrogen are studied. As have shown essential distinction in the average size of compact clusters (H2O)n in the cryogenic HDA-ice (n ∼105 ) and LDA-ice (n ∼30) allows to change a share of methane accumulation inside clusters of amorphous ice. In HDA-ice large clusters can accumulate a lot more methane molecules than in the case of LDA-ice. Density jumps on polyamorphic transition of ice allows obtaining reversible accumulation of methane inside cellular nanostructures of cryogenic amorphous ice.

Diagnosing radiation drive asymmetry and absorbed energy in ignition Hohlraums using gas-filled capsules

The shape of the x-ray self-emission image from an imploded inertial confinement fusion capsule has been used to diagnose Hohlraum radiation drive asymmetry [L. J. Suter et al., Phys. Rev. Lett. 73, 2328 (1994); A. Hauer et al., Rev. Sci. Instrum. 66, 672 (1995); A. Hauer et al., Phys. Plasmas 2, 2488 (1995); N. D. Delameter et al., Phys. Plasmas 3, 2022 (1996)]. Timing of neutron yield from the implosion can also be used to diagnose the absorbed radiation drive energy. We propose a set of beryllium capsules filled with gas, rather than layered cryogenic ice, to diagnose asymmetry and absorbed energy in ignition Hohlraums. Capsules with a range of initial shell thickness have a corresponding range of implosion times, allowing sampling of drive conditions throughout an ignition pulse. For example a 12μm thick shell implodes during the foot of the ignition pulse, sampling the drive up to about 10ns. For such capsules, the foot pulse is a high-adiabat drive and leads to implosions that are rather robust against instability and mixing. In these capsules, the best time to record images for diagnosing asymmetry may be several hundred picoseconds after peak x-ray brightness, when the image distortion is increasing rapidly.

Three-Dimensional Characterization of Cryogenic Target Ice Layers Using Multiple Shadowgraph Views

Backlit optical shadowgraphy is the primary diagnostic for D2 ice layer characterization of cryogenic targets for the OMEGA Laser System at the Laboratory for Laser Energetics (LLE). Reflection and refraction of light passing through the ice layer produce characteristic rings. The position of the most prominent of the shadowgraph rings, known as the bright ring, can be resolved to ∼0.1-pixel rms, corresponding to about 0.12 μm for typical LLE target shadowgraphs. Measurement of the bright ring position in conjunction with ray-trace model predictions determines the ice layer thickness and the Fourier-mode spectrum of the ice roughness for that view. The LLE target characterization stations use two camera angles and target rotation to record target shadowgraphs from many different views. Combining these views allows construction of a 3-D ice layer representation, an estimation of the global surface roughness, and a determination of a Legendre-mode spectrum suitable for implosion modeling. The standard operating procedure is to construct a 3-D ice layer representation using the analysis of 48 separate shadowgraphic views. The 3-D ice surface is then decomposed in terms of spherical harmonics, allowing the determination of low-mode number (ℓ ≤ to 10) elements of a Legendre-mode power spectrum. Higher-mode number elements of the Legendre power spectrum are determined by mapping the Fourier-mode power spectrum averaged over all views

Direct-drive, cryogenic target implosions on OMEGA

Direct-drive spherical implosions of cryogenic, D2-filled capsules are performed on the 60-beam OMEGA laser system [T. R. Boehly, D. L. Brown, R. S. Craxton, R. L. Keck, J. P. Knauer, J. H. Kelly, T. J. Kessler, S. A. Kumpan, S. J. Loucks, S. A. Letzring, F. J. Marshall, R. L. McCrory, S. F. B. Morse, W. Seka, J. M. Soures, and C. P. Verdon, Opt. Commun. 133, 495 (1997)]. The targets are energy scaled from the base line ignition design developed for the National Ignition Facility [W. J. Hogan et al., Nucl. Fusion 41, 567 (2001)]. Thin-walled (∼4μm), ∼860μm diam deuterated polymer shells are permeation filled with D2 gas and cooled to the triple point (∼18.7K). Cryogenic ice layers with a uniformity of ∼2μm rms are formed and maintained. The targets are imploded with high-contrast pulse shapes with full single-beam smoothing (1THz bandwidth, two-dimensional smoothing by spectral dispersion with polarization smoothing) to study the effects of the acceleration- and deceleration-phase Rayleigh–Taylor growth on target performance. Two-dimensional hydrocode simulations show good agreement with the experimental observations. Scattered-light and neutron-burn-history measurements are consistent with predicted absorption and hydrodynamic coupling calculations. Time-resolved and static x-ray images show the progress of the imploding shell, the shape, and temperature of the stagnating core. Particle-based instruments measure the fusion yield and rate, the ion temperature in the core, and the fuel areal density at the time of neutron production. These experiments have produced fuel areal densities of up to ∼100mg∕cm2, primary neutron yields of ∼4×1010, and secondary neutron yields of 1% to 2% of the primary yield. These results validate the hydrocode predictions for the direct-drive ignition-point design, giving increasing confidence in the direct-drive approach to inertial confinement fusion ignition.

Sticky Ice Grains Aid Planet Formation: Unusual Properties of Cryogenic Water Ice

There is limited time for the dust in the nebula around a newborn star to form planetesimals: in a few million years or less the star's stellar winds will disperse most of the unagglomerated dust. It has been difficult to explain the efficiency by which dust grains must have agglomerated to form planetesimals in circumstellar disks. A major obstacle is the fragility of aggregates, leading to collisional fragmentation, which makes it difficult for them to grow to, and beyond, meter-sized bodies. The distinct properties of cryogenic (5-100 K) amorphous water ice, which composes or coats the grains in the cooler parts of the nebulae (≳Jovian distances), may be able to account for the rapid agglomeration. Measurements are presented that show that this ice readily acquires persistent macroscopic electric dipoles, strongly enhancing grain-grain adhesion. In addition, measurements were made showing that vapor-deposited amorphous water ice is also highly mechanically inelastic (≈10% rebound). Together these may explain this efficient net sticking and net growth. Similar properties of higher temperature grains may aid agglomeration in the inner regions of the nebulae.

Design of the OMEGA Laser Target Chamber Tritium Removal System

Preparations are currently underway at the OMEGA laser at the University of Rochester Laboratory for Laser Energetics (UR/LLE) to conduct direct drive laser implosion campaigns with inertial confinement fusion targets containing deuterium-tritium (DT) cryogenic ice layers. The OMEGA Cryogenic Target Handling System will fill plastic targets with high-pressure DT (150 MPa) at 300 to 500 K, cool them down to cryogenic temperature (<25 K), form the DT ice layer, and transport the targets to the OMEGA laser target chamber. Targets will then be shot with the 60-beam 30-kJ OMEGA laser. A tritium removal system has been designed to remove tritium from effluents associated with operation of the target chamber and its associated diagnostic antechambers, vacuum pumping systems, and target insertion systems. The design of the target chamber tritium removal system (TCTRS) is based on catalytic oxidation of DT and tritiated methane to tritiated water (DTO), followed by immobilization of DTO on molecular sieves. The design of the TCTRS presented a challenge due to the low tritium release limits dictated by the tritium license at UR/LLE. Aspen Plus, a commercial software package intended for the simulation and design of chemical processing systems operating at steady state, was used to simulate and design the TCTRS. A second commercial software package, Aspen ADSIM, was used to simulate and design the TCTRS molecular sieve beds, which operate at unsteady state. In this paper, we describe the design of the TCTRS and the benefits that were realized by use of the Aspen Plus and Aspen ADSIM software packages.

Development of the Los Alamos National Laboratory Cryogenic Pressure Loader

Targets for inertial fusion research and ignition at OMEGA, the National Ignition Facility, LMJ, and future facilities rely on beta-radiation-driven layering of spherical cryogenic DT ice layers contained within plastic or metal shells. Plastic shells will be permeation filled at room temperature then cooled to cryogenic temperatures before removal of the overpressure. The cryogenic pressure loader (CPL) was recently developed at Los Alamos National Laboratory as a testbed for studying the filling and layering of plastic target shells with DT. A technical description of the CPL is provided. The CPL consists of a cryostat, which contains a high-pressure permeation cell, and has optical access for investigating beta layering. The cryostat is housed within a tritium glovebox that contains manifolds for supplying high-pressure DT. The CPL shares some design elements with the cryogenic target handling system at the OMEGA facility to allow testing of tritium issues related to that system. The CPL has the capability to fill plastic targets by permeation to pressures up to 100 MPa and to cool them to 15 K. The CPL will accommodate a range of targets and may be modified for future experiments.

Pathways to Glycine and Other Amino Acids in Ultraviolet-irradiated Astrophysical Ices Determined via Quantum Chemical Modeling

A recent experimental study reported that glycine and other amino acids were formed when cryogenic H2O ice containing small amounts of CH3OH, NH3, and HCN was subjected to ultraviolet (UV) irradiation. Quantum chemical calculations were employed to evaluate the viability of various pathways to the formation of glycine, alanine, and serine in dilute H2O ice containing CH3OH and HCN. Under the experimental processing conditions of deposition and UV irradiation at 15 K followed by heating to room temperature, amino acids can form by recombining radicals produced by dehydrogenating H2O and CH3OH and subsequently hydrogenating HCN. The study indicates that isotopic substitution experiments would identify CH3OH as the source of the C atom in the COOH carboxylic acid group of the amino acids observed in the irradiation experiments, with the CO+OH reaction playing an important role. The remaining C and N atoms in glycine are predicted to originate from HCN via sequential hydrogenation to yield CH2NH2. Formation pathways for alanine and serine are also discussed.

Impact penetrometry on a comet nucleus — interpretation of laboratory data using penetration models

The first — and possibly deepest — in situ science measurements on the 46P/Wirtanen nucleus will be made by two sensors of the Rosetta Lander's MUPUS experiment. A piezoelectric shock accelerometer (ANC-M) and a resistance temperature sensor (ANC-T) will be mounted in the Lander's harpoon anchor. This will be shot into the surface at about 60 m s −1 on touchdown, reaching a final depth of between a few centimetres and about 2.5 m, depending on the hardness of the ground and the maximum available cable length. Early indications of the strength of the surface material and any distinct layers should prove valuable to subsequent depth-sensitive investigations, including the MUPUS thermal probe, seismic sounding experiments, the sampling drill and composition analyses of the extracted material. Interpretation of the ANC-M data will help to constrain models of the formation and evolution of the material found at the landing site and document the mechanical and structural context of nearby sampled material. We report on the results of recent test shots performed with a prototype anchor into several porous materials: two types of glass foam, H 2O ice and CO 2 ice. With the help of data from direct shear tests and quasi-static penetration tests, we interpret the processed deceleration data using a cavity-expansion penetration model. Layers of distinctly different strengths can be detected and located, and the deceleration profiles are in reasonable agreement with the profiles obtained by quasi-static tests. The anchor projectile's long sharp tip tends to smear out the boundaries, however. In applying the penetration model we found that the coefficient of sliding friction and the target's volumetric strain have a much stronger influence on the deceleration profile than the initial target density and angle of internal friction. Very small values of volumetric strain (corresponding to high ‘drag coefficient’) were required to fit deceleration profiles to the measured data for the glass foam, contrary to what we initially expected by inspecting the thin layer of crushed material around the walls of the penetrated channel. We interpret this to mean that such brittle, porous materials as the glass foam (and perhaps highly porous, brittle, cryogenic ice) do not exhibit plastic deformation before failing completely by the crushing of cell walls. The decelerating forces are thus thought to be dominated by momentum transfer to the crushed material and by the crushing strength of the cellular microstructure, rather than by the force required to deform the target plastically. The cavity-expansion model seems to be well-suited to the ice shots, but for the brittle, cellular glass foam, alternative approaches, taking into account the material's microstructure, are needed. As a first step in this direction, a microstructural model linking textural properties of the material (pore and grain size, and relative contact area between grains) is applied to the glass foam data, obtained from quasi-static penetration tests and from direct shear strength tests. It is demonstrated that the dependence of strength on porosity can be well represented by the model suggested. A microstructural model for sintered ices, relating strength properties to porosity and thermal properties, would be useful for interpretation of MUPUS ANC-M data in the context of other physical properties measurements. The work presented here may also have some relevance to the design of future comet landers or penetrators. The harpoon anchor/penetrometer approach could be employed on other minor body landing missions, while the modelling technique is similar in many ways to that appropriate for other penetrometers/penetrators.

Carbonic acid in the gas phase and its astrophysical relevance

In outer space, high-energy irradiation of cryogenic ice mixtures of abundant water and carbon dioxide is expected to form solid carbonic acid. Experiments and thermodynamic analyses show that crystalline carbonic acid sublimates without decomposition. Free-energy considerations based on highly accurate molecular quantum mechanics, in combination with vapor pressures resulting from experimental sublimation rates, suggest that in the gas phase, a monomer and dimer of carbonic acid are in equilibrium, comparable to that of formic acid. Gaseous carbonic acid could be present in comets, on Mars and outer solar system bodies, in interstellar icy grains, and in Earth's upper atmosphere.

Mobilization of cryogenic ice in outer Solar System satellites

Voyager images of the uranian satellites show a diversity of geological features, including clear evidence for the ‘softening’ and mobilization of ice on Miranda and Ariel. Some of these features are similar to those seen on jovian and saturnian satellites, where the mobile material is believed to be water or a water–ammonia mixture. However, the extremely low temperatures and probable unavailability of large energy sources within the uranian satellites lead us to consider flow mechanisms that operate at very low temperature (T ≤ 100 K). We propose here a form of pressure-solution creep, in which very fine-grained water ice or clathrate hydrate is mobilized by a small amount of intergranular cryogenic fluid (CH_4, CO or N_2). Viscosities as low as 10^(12) P are possible for a limited time, sufficient to allow flooding of rift valleys and perhaps even substantial lateral flows (glaciers).

Internal defects—use of ultrasonic flaw detectors: Light Metals and Metal Industry, 28, No. 326, 47 (1965)

In the present article frozen and deeply chilled water-ice particles, with a temperature of around −100 °C, act as a blasting abrasive. For accelerating cryogenic ice particles the process of injector blasting is used. The advantage of this abrasive at these low temperatures lies in the complete absence of residues after processing. Abrasive water-ice particles turn back to water by melting. Possible applications for this innovative process are especially complex components that can be easily deburred and cleaned. The production process of deep frozen ice particles will be described and first practical deburring test results will be shown.