Multimode Hydrodynamic Instability Growth of Preimposed Isolated Defects in Ablatively Driven Foils.

The Nike KrF laser facility was used to study the evolution of isolated defects with characteristic sizes of <1 to 10s of µm in laser-accelerated plastic foils. The experimental platform permitted, for the first time, the systematic study of localized perturbation growth, which is inherently multimode, through ablative Richtmyer-Meshkov and Rayleigh-Taylor stages and into the strongly nonlinear regime. Initial target defects were relatively large amplitude, but spatially localized, and emulated tent, fill-tube, and other nonuniformities that are present in inertial confinement fusion capsules. Face-on x-ray radiography indicated initial growth of the perturbation in both depth and width, followed by its apparent closure due to oblique spike growth. Hollow jetlike profiles of laterally expanding, rising, Rayleigh-Taylor bubbles were observed on the rear surface of the target from each isolated defect. Radiation hydrodynamic simulations provided insight into the mechanism of the closure and other features of the bubble and spike evolution specific to isolated defects.

Direct drive with the argon fluoride laser as a path to high fusion gain with sub-megajoule laser energy.

Argon fluoride (ArF) is currently the shortest wavelength laser that can credibly scale to the energy and power required for high gain inertial fusion. ArF's deep ultraviolet light and capability to provide much wider bandwidth than other contemporary inertial confinement fusion (ICF) laser drivers would drastically improve the laser target coupling efficiency and enable substantially higher pressures to drive an implosion. Our radiation hydrodynamics simulations indicate gains greater than 100 are feasible with a sub-megajoule ArF driver. Our laser kinetics simulations indicate that the electron beam-pumped ArF laser can have intrinsic efficiencies of more than 16%, versus about 12% for the next most efficient krypton fluoride excimer laser. We expect at least 10% 'wall plug' efficiency for delivering ArF light to target should be achievable using solid-state pulsed power and efficient electron beam transport to the laser gas that was demonstrated with the U.S. Naval Research Laboratory's Electra facility. These advantages could enable the development of modest size and lower cost fusion power plant modules. This would drastically change the present view on inertial fusion energy as being too expensive and the power plant size too large. This article is part of a discussion meeting issue 'Prospects for high gain inertial fusion energy (part 1)'.

Publisher's Note: Demonstration of Fuel Hot-Spot Pressure in Excess of 50 Gbar for Direct-Drive, Layered Deuterium-Tritium Implosions on OMEGA [Phys. Rev. Lett. 117, 025001 (2016)].

This corrects the article DOI: 10.1103/PhysRevLett.117.025001.

Demonstration of Fuel Hot-Spot Pressure in Excess of 50 Gbar for Direct-Drive, Layered Deuterium-Tritium Implosions on OMEGA.

A record fuel hot-spot pressure P_{hs}=56±7 Gbar was inferred from x-ray and nuclear diagnostics for direct-drive inertial confinement fusion cryogenic, layered deuterium-tritium implosions on the 60-beam, 30-kJ, 351-nm OMEGA Laser System. When hydrodynamically scaled to the energy of the National Ignition Facility, these implosions achieved a Lawson parameter ∼60% of the value required for ignition [A. Bose et al., Phys. Rev. E 93, 011201(R) (2016)], similar to indirect-drive implosions [R. Betti et al., Phys. Rev. Lett. 114, 255003 (2015)], and nearly half of the direct-drive ignition-threshold pressure. Relative to symmetric, one-dimensional simulations, the inferred hot-spot pressure is approximately 40% lower. Three-dimensional simulations suggest that low-mode distortion of the hot spot seeded by laser-drive nonuniformity and target-positioning error reduces target performance.

Observation of strong oscillations of areal mass in an unsupported shock wave.

An experimental study of hydrodynamic perturbation evolution in a strong unsupported shock wave, which is immediately followed by an expansion wave, is reported. A planar solid plastic target rippled on the front side is irradiated with a 350-450 ps long laser pulse. The perturbation evolution in the target is observed using face-on monochromatic x-ray radiography during and for up to 4 ns after the laser pulse. The theoretically predicted large oscillations of the areal mass in the target are observed for the first time. Multiple phase reversals of the areal mass modulation are detected.

Hybrid target design for imprint mitigation in direct-drive inertial confinement fusion.

A target design for mitigating the Rayleigh-Taylor instability is proposed for use in high energy density and direct-drive inertial confinement fusion experiments. In this scheme, a thin gold membrane is offset from the main target by several-hundred microns. A strong picket on the drive beams is incident upon this membrane to produce x rays which generate the initial shock through the target. The main drive follows shortly thereafter, passing through the ablated shell and directly driving the main target. The efficacy of this scheme is demonstrated through experiments performed at the OMEGA EP facility, showing a reduction of the Rayleigh-Taylor instability growth which scales exponentially with frequency, suppressing development by at least a factor of 5 for all wavelengths below 100 µm. This results in a delay in the time of target perforation by ∼40%.

[Treatment of pediatric femur fractures by immediate reduction and spica cast application--clinical and economical feasibility in the Israeli medical system].

BACKGROUND: Pediatric femur fractures are common injuries necessitating immediate application of spica cast or surgical stabilization. Currently, neither conservative nor operative fixation shows superior results; nevertheless, operative intervention has become more common lately. The current study retrospectively investigates short term results of immediate spica cast application, as well as the economic consequences of this treatment. METHODS: All cases of pediatric (6 months - 6 years) femur fractures treated in a single medium-sized hospital during 3 years were reviewed. Characteristics of fracture treatment and economical aspects were analyzed. RESULTS: Twenty four patients (17 boys and 7 girls, mean age 2.5 years, range 9 months to 5.5 years), were treated during the study period by immediate closed reduction and spica cast application. Eleven patients were also treated for medical reasons. All cases achieved acceptable alignment and shortening after cast removal. Two patients were re-admitted to the hospital Emergency Room but no changes in treatment were needed, one patient needed re-reduction. Mean hospital stay was 2.75 days. Calculated cost of such treatment is estimated to be almost equal to the compensation given by insurance companies (based on hospital stay in Israel). CONCLUSIONS: Immediate application of spica cast for pediatric femur fractures, achieves its goals of appropriate fracture-alignment and acceptable complication rates. The authors believe that the compensation should be procedure-based and not hospital-stay based, in a way that will encourage higher efficacy of medical treatment and shortened hospital stay.

Measurements of electron density and temperature profiles in plasma produced by Nike KrF laser for laser plasma instability research.

A grid image refractometer (GIR) has been implemented at the Nike krypton fluoride laser facility of the Naval Research Laboratory. This instrument simultaneously measures propagation angles and transmissions of UV probe rays (λ = 263 nm, Δt = 10 ps) refracted through plasma. We report results of the first Nike-GIR measurement on a CH plasma produced by the Nike laser pulse (∼1 ns FWHM) with the intensity of 1.1 × 10(15) W/cm(2). The measured angles and transmissions were processed to construct spatial profiles of electron density (ne) and temperature (Te) in the underdense coronal region of the plasma. Using an inversion algorithm developed for the strongly refracted rays, the deployed GIR system probed electron densities up to 4 × 10(21) cm(-3) with the density scale length of 120 µm along the plasma symmetry axis. The resulting n(e) and T(e) profiles are verified to be self-consistent with the measured quantities of the refracted probe light.

Hepatobiliary and pancreatic infections in AIDS: Part one.

Infections of the liver and biliary tract are common during the course of AIDS. A variety of viral, bacterial, fungal, and other opportunistic infections can present with hepatobiliary involvement as either the primary site of infection or secondary to a disseminated process. Coinfection with hepatitis B and C are particularly common due to the shared means of transmission of these viruses with HIV. The typical presenting features of hepatobiliary infections are right upper quadrant (RUQ) pain and abnormal liver function tests. Initial evaluation should include an RUQ ultrasonogram, which will usually identify abnormalities in the biliary tract and may demonstrate some parenchymal abnormalities as well. A liver biopsy is necessary to determine the etiology of focal hepatic lesions or opportunistic infections within hepatic parenchyma when other less invasive tests are negative or inconclusive. Special stains and culture techniques are required to identify specific organisms in the biopsy specimen. HIV-related biliary disorders include acalculous cholecystitis, which is a potentially serious condition requiring prompt recognition and gallbladder decompression. AIDS-cholangiopathy is a form of cholangitis involving the intra- and/or extrahepatic biliary tree. Endoscopic retrograde cholangio-pancreatography (ERCP) is the test of choice, demonstrating the stricturing, dilatation, and beading of bile ducts seen in this condition. Endoscopic sphincterotomy of the papilla of Vater may provide symptomatic relief for patients with papillary stenosis. Opportunistic infections of the pancreas have been reported. Evaluation should include a computerized tomogram of the abdomen and possible pancreatic tissue aspiration or biopsy. Management of pancreatitis is supportive.

Hepatobiliary and pancreatic infections in AIDS: Part II.

In the first part of our review, we discussed the general evaluation and clinical presentation of the various hepatic infections occurring in patients with AIDS. In addition, we focused on specific hepatic parenchymal infections. In this article, we will discuss the major clinical syndromes arising from opportunistic infections affecting the gallbladder (acalculous cholecystitis), biliary tree (AIDS-cholangiopathy), and pancreas (pancreatitis). Acalculous cholecystitis can develop in patients with AIDS who have not experienced the severe precipitating physiologic stresses normally required in patients without AIDS. The most common presentation is with right upper quadrant (RUQ) pain and tenderness. The diagnosis is a clinical one since there is no standard test, other than surgery. Cholecystectomy is the treatment of choice. The most common AIDS-associated infective complication of the biliary tree is AIDS-cholangiopathy. This is best viewed as a form of secondary sclerosing cholangitis resulting from a variety of opportunistic infections within the biliary tree. Affected persons present with RUQ pain and have marked elevations in the canalicular enzymes, alkaline phosphatase, and gamma-glutamyl transferase. Morphologic abnormalities are identified by endoscopic retrograde cholangiopancreatography. These include stricturing, dilatation, and beading of the biliary tract. Endoscopic sphincterotomy of the papilla of Vater may provide symptomatic relief for patients with papillary stenosis. Opportunistic infections within the pancreas gland have been documented in both pre- and postmortem studies. However, the true incidence of pancreatitis related to infections is unknown. The presentation is similar to that of pancreatitis from other causes. A computerized tomogram of the abdomen is the investigation of choice. Tissue aspiration or biopsy of the pancreas is required to demonstrate the presence of an opportunistic infection. The management is usually supportive, as it is rare that a specific infection is identified and treated.

Selecting a small business computer.

In this age of information, growing businesses have the opportunity at a very early stage to computerize their operations. Today's entrepreneurs must choose what computer services to buy amid a bewildering variety of products and programs, each proclaimed, brassily, as the best, the latest, or the next generation. In this article, the author advises entrepreneurs and managers to make sure that the computer can handle everyday demands. He counsels that good software, service, and support are more important than the latest hardware.

Implementation of focal zooming on the Nike KrF laser.

In direct drive inertial confinement laser fusion, a pellet containing D-T fuel is imploded by ablation arising from absorption of laser energy at its outer surface. For optimal coupling, the focal spot of the laser would continuously decrease to match the reduction in the pellet's diameter, thereby minimizing wasted energy. A krypton-fluoride laser (λ = 248 nm) that incorporates beam smoothing by induced spatial incoherence has the ability to produce a high quality focal profile whose diameter varies with time, a property known as focal zooming. A two-stage focal zoom has been demonstrated on the Nike laser at the Naval Research Laboratory. In the experiment, a 4.4 ns laser pulse was created in which the on-target focal spot diameter was 1.3 mm (full width at half maximum) for the first 2.4 ns and 0.28 mm for the final 2 ns. These two diameters appear in time-integrated focal plane equivalent images taken at several locations in the amplification chain. Eight of the zoomed output beams were overlapped on a 60 µm thick planar polystyrene target. Time resolved images of self-emission from the rear of the target show the separate shocks launched by the two corresponding laser focal diameters.

Basic hydrodynamics of Richtmyer-Meshkov-type growth and oscillations in the inertial confinement fusion-relevant conditions.

In inertial confinement fusion (ICF), the possibility of ignition or high energy gain is largely determined by our ability to control the Rayleigh-Taylor (RT) instability growth in the target. The exponentially amplified RT perturbation eigenmodes are formed from all sources of the target and radiation non-uniformity in a process called seeding. This process involves a variety of physical mechanisms that are somewhat similar to the classical Richtmyer-Meshkov (RM) instability (in particular, most of them are active in the absence of acceleration), but differ from it in many ways. In the last decade, radiographic diagnostic techniques have been developed that made direct observations of the RM-type effects in the ICF-relevant conditions possible. New experiments stimulated the advancement of the theory of the RM-type processes. The progress in the experimental and theoretical studies of such phenomena as ablative RM instability, re-shock of the RM-unstable interface, feedout and perturbation development associated with impulsive loading is reviewed.

Stability of a shock-decelerated ablation front.

Experimental study of a shock-decelerated ablation front is reported. A planar solid plastic target is accelerated by a laser across a vacuum gap and collides with a lower-density plastic foam layer. While the target is accelerated, a fast Rayleigh-Taylor (RT) growth of the seeded single-mode perturbation at the ablation front is observed. After the collision, the velocity of the ablation front is seen to remain constant. The reshock quenches the RT growth but does not trigger any Richtmyer-Meshkov growth at the ablation front, which is shown to be consistent with both theory and simulations.

Experimental evidence of impact ignition: 100-fold increase of neutron yield by impactor collision.

We performed integrated experiments on impact ignition, in which a portion of a deuterated polystyrene (CD) shell was accelerated to about 600 km/s and was collided with precompressed CD fuel. The kinetic energy of the impactor was efficiently converted into thermal energy generating a temperature of about 1.6 keV. We achieved a two-order-of-magnitude increase in the neutron yield by optimizing the timing of the impact collision, demonstrating the high potential of impact ignition for fusion energy production.

Successful treatment of chylous ascites secondary to Mycobacterium avium complex in a patient with the acquired immune deficiency syndrome.

Chylous ascites is a rare form of ascites, the presence of which generally denotes a very poor long term prognosis. We report the case of a patient with acquired immune deficiency syndrome (AIDS) and massive chylous ascites secondary to Mycobacterium avium complex (MAC) infection, identified in the ascitic fluid by a DNA probe assay. With multidrug anti-MAC therapy the ascites resolved completely, and the patient has survived for >21 months. Diagnosis and treatment of MAC-related chylous ascites are reviewed.

Direct observation of mass oscillations due to ablative Richtmyer-Meshkov instability in plastic targets.

We report the first direct experimental observation of the ablative Richtmyer-Meshkov instability. It manifests itself in oscillations of areal mass that occur during the shock transit time, which are caused by the "rocket effect" or dynamic overpressure characteristic of interaction between the laser absorption zone and the ablation front. With the 4-ns-long Nike KrF laser pulse and our novel diagnostic technique (monochromatic x-ray imaging coupled to a streak camera) we were able to register a peak and a valley of the areal-mass variation before the observed onset of the Rayleigh-Taylor growth.

Direct observation of feedout-related mass oscillations in plastic targets.

"Feedout" means the transfer of mass perturbations from the rear to the front surface of a driven target. When a planar shock wave breaks out at a rippled rear surface of the target, a lateral pressure gradient drives sonic waves in a rippled rarefaction wave propagating back to the front surface. This process redistributes mass in the volume of the target, forming the feedout-generated seed for ablative Rayleigh-Taylor (RT) instability. We report the first direct experimental observation of areal-mass oscillation associated with feedout, followed by the onset of exponential RT growth.