Stabilization of Liner Implosions via a Dynamic Screw Pinch.

Magnetically driven implosions are susceptible to magnetohydrodynamic instabilities, including the magneto-Rayleigh-Taylor instability (MRTI). To reduce MRTI growth in solid-metal liner implosions, the use of a dynamic screw pinch (DSP) has been proposed [P. F. Schmit et al., Phys. Rev. Lett. 117, 205001 (2016)PRLTAO0031-900710.1103/PhysRevLett.117.205001]. In a DSP configuration, a helical return-current structure surrounds the liner, resulting in a helical magnetic field that drives the implosion. Here, we present the first experimental tests of a solid-metal liner implosion driven by a DSP. Using the 1-MA, 100-200-ns COBRA pulsed-power driver, we tested three DSP cases (with peak axial magnetic fields of 2 T, 14 T, and 20 T) and a standard z-pinch (SZP) case (with a straight return-current structure and thus zero axial field). The liners had an initial radius of 3.2 mm and were made from 650-nm-thick aluminum foil. Images collected during the experiments reveal that helical MRTI modes developed in the DSP cases, while nonhelical (azimuthally symmetric) MRTI modes developed in the SZP case. Additionally, the MRTI amplitudes for the 14-T and 20-T DSP cases were smaller than in the SZP case. Specifically, when the liner had imploded to half of its initial radius, the MRTI amplitudes for the SZP case and for the 14-T and 20-T DSP cases were, respectively, 1.1±0.3 mm, 0.7±0.2 mm, and 0.3±0.1 mm. Relative to the SZP, the stabilization obtained using the DSP agrees reasonably well with theoretical estimates.

Performance Scaling in Magnetized Liner Inertial Fusion Experiments.

We present experimental results from the first systematic study of performance scaling with drive parameters for a magnetoinertial fusion concept. In magnetized liner inertial fusion experiments, the burn-averaged ion temperature doubles to 3.1 keV and the primary deuterium-deuterium neutron yield increases by more than an order of magnitude to 1.1×10^{13} (2 kJ deuterium-tritium equivalent) through a simultaneous increase in the applied magnetic field (from 10.4 to 15.9 T), laser preheat energy (from 0.46 to 1.2 kJ), and current coupling (from 16 to 20 MA). Individual parametric scans of the initial magnetic field and laser preheat energy show the expected trends, demonstrating the importance of magnetic insulation and the impact of the Nernst effect for this concept. A drive-current scan shows that present experiments operate close to the point where implosion stability is a limiting factor in performance, demonstrating the need to raise fuel pressure as drive current is increased. Simulations that capture these experimental trends indicate that another order of magnitude increase in yield on the Z facility is possible with additional increases of input parameters.

Controlling Rayleigh-Taylor Instabilities in Magnetically Driven Solid Metal Shells by Means of a Dynamic Screw Pinch.

Magnetically driven implosions of solid metal shells are an effective vehicle to compress materials to extreme pressures and densities. Rayleigh-Taylor instabilities (RTI) are ubiquitous, yet typically undesired features in all such experiments where solid materials are rapidly accelerated to high velocities. In cylindrical shells ("liners"), the magnetic field driving the implosion can exacerbate the RTI. We suggest an approach to implode solid metal liners enabling a remarkable reduction in the growth of magnetized RTI (MRTI) by employing a magnetic drive with a tilted, dynamic polarization, forming a dynamic screw pinch. Our calculations, based on a self-consistent analytic framework, demonstrate that the cumulative growth of the most deleterious MRTI modes may be reduced by as much as 1 to 2 orders of magnitude. One key application of this technique is to generate increasingly stable, higher-performance implosions of solid metal liners to achieve fusion [M. R. Gomez et al., Phys. Rev. Lett. 113, 155003 (2014)]. We weigh the potentially dramatic benefits of the solid liner dynamic screw pinch against the experimental tradeoffs required to achieve the desired drive field history and identify promising designs for future experimental and computational studies.

Experimental demonstration of fusion-relevant conditions in magnetized liner inertial fusion.

This Letter presents results from the first fully integrated experiments testing the magnetized liner inertial fusion concept [S. A. Slutz et al., Phys. Plasmas 17, 056303 (2010)], in which a cylinder of deuterium gas with a preimposed 10 Taxial magnetic field is heated by Z beamlet, a 2.5 kJ, 1 TW laser, and magnetically imploded by a 19 MA, 100 ns rise time current on the Z facility. Despite a predicted peak implosion velocity of only 70 km = s, the fuel reaches a stagnation temperature of approximately 3 keV, with T(e) ≈ T(i), and produces up to 2 x 10(12) thermonuclear deuterium-deuterium neutrons. X-ray emission indicates a hot fuel region with full width at half maximum ranging from 60 to 120 µm over a 6 mm height and lasting approximately 2 ns. Greater than 10(10) secondary deuterium-tritium neutrons were observed, indicating significant fuel magnetization given that the estimated radial areal density of the plasma is only 2 mg = cm(2).

Understanding fuel magnetization and mix using secondary nuclear reactions in magneto-inertial fusion.

Magnetizing the fuel in inertial confinement fusion relaxes ignition requirements by reducing thermal conductivity and changing the physics of burn product confinement. Diagnosing the level of fuel magnetization during burn is critical to understanding target performance in magneto-inertial fusion (MIF) implosions. In pure deuterium fusion plasma, 1.01 MeV tritons are emitted during deuterium-deuterium fusion and can undergo secondary deuterium-tritium reactions before exiting the fuel. Increasing the fuel magnetization elongates the path lengths through the fuel of some of the tritons, enhancing their probability of reaction. Based on this feature, a method to diagnose fuel magnetization using the ratio of overall deuterium-tritium to deuterium-deuterium neutron yields is developed. Analysis of anisotropies in the secondary neutron energy spectra further constrain the measurement. Secondary reactions also are shown to provide an upper bound for the volumetric fuel-pusher mix in MIF. The analysis is applied to recent MIF experiments [M. R. Gomez et al., Phys. Rev. Lett. 113, 155003 (2014)] on the Z Pulsed Power Facility, indicating that significant magnetic confinement of charged burn products was achieved and suggesting a relatively low-mix environment. Both of these are essential features of future ignition-scale MIF designs.

Nonlinear amplification and decay of phase-mixed waves in compressing plasma.

Through particle-in-cell simulations, we show that plasma waves carrying trapped electrons can be amplified manyfold via compressing plasma perpendicularly to the wave vector. These simulations are the first ab initio demonstration of the conservation of nonlinear action for such waves, which contains a term independent of the field amplitude. In agreement with the theory, the maximum of amplification gain is determined by the total initial energy of the trapped-particle average motion but otherwise is insensitive to the particle distribution. Further compression destroys the wave; electrons are then untrapped at suprathermal energies and form a residual beam. As compression continues, the bump-on-tail instability is triggered each time one of the discrete modes comes in resonance with this beam. Hence, periodic bursts of the electrostatic energy are produced until a wide quasilinear plateau is formed.

Negative-mass instability in nonlinear plasma waves.

The negative-mass instability, previously found in ion traps, appears as a distinct regime of the sideband instability in nonlinear plasma waves with trapped particles. As the bounce frequency of these particles decreases with the bounce action, bunching can occur if the action distribution is inverted in trapping islands. In contrast to existing theories that also infer instabilities from the anharmonicity of bounce oscillations, spatial periodicity of the islands turns out to be unimportant, and the particle distribution can be unstable even if it is flat at the resonance. An analytical model is proposed that describes both single traps and periodic nonlinear waves and concisely generalizes the conventional description of the sideband instability in plasma waves. The theoretical results are supported by particle-in-cell simulations carried out for a regime accentuating the negative-mass instability.

Plasma-based accelerator with magnetic compression.

Electron dephasing is a major gain-inhibiting effect in plasma-based accelerators. A novel method is proposed to overcome dephasing, in which the modulation of a modest [~O(10 kG)], axial, uniform magnetic field in the acceleration channel leads to densification of the plasma through magnetic compression, enabling direct, time-resolved control of the plasma wave properties. The methodology is broadly applicable and can be optimized to improve the leading acceleration approaches, including plasma beat wave, plasma wakefield, and laser wakefield acceleration. The advantages of magnetic compression are compared to other proposed techniques to overcome dephasing.

Driving sudden current and voltage in expanding and compressing plasma.

A magnetized plasma preseeded with an initially undamped Langmuir wave is shown to transition suddenly to a collisionless damping regime upon expansion of the plasma perpendicular to the background magnetic field. The resulting anisotropic fast-particle distribution then leads to an electrical current and dc voltage induction. The current drive efficiency of this effect in nonstationary plasmas is shown to depend on the rate of expansion of the plasma, the time-varying collisionality, and the plasma L/R time. Subsequent recompression of the plasma enhances this current drive effect by reducing further the collision rate of the current-carrying electrons.

Controlling hot electrons by wave amplification and decay in compressing plasma.

Through particle-in-cell simulations, it is demonstrated that a part of the mechanical energy of compressing plasma can be controllably transferred to hot electrons by preseeding the plasma with a Langmuir wave that is compressed together with the medium. Initially, a wave is undamped, so it is amplified under compression due to plasmon conservation. Later, as the phase velocity also changes under compression, Landau damping can be induced at a predetermined instant of time. Then the wave energy is transferred to hot electrons, shaping the particle distribution over a controllable velocity interval, which is wider than that in stationary plasma. For multiple excited modes, the transition between the adiabatic amplification and the damping occurs at different moments; thus, individual modes can deposit their energy independently, each at its own prescribed time.

CT angiography of the artery of Adamkiewicz with 64-section technology: first experience in children.

BACKGROUND AND PURPOSE: Preoperative localization of the artery of Adamkiewicz (AKA) may be useful in selected children in prevention of ischemic spinal complications of spinal or thoracoabdominal aortic surgery. The aim of our study was to investigate the ability of 64-section CT for assessing the AKA in children. MATERIALS AND METHODS: Forty children (mean age, 7.5 +/- 5 years) underwent thoracic imaging with a 64-section CT scanner after intravenous injection of 1.5 mL/kg of contrast agent. Volumetric reconstructions were obtained for every patient. Identification of the AKA was performed on the basis of continuity from the aorta to the anterior spinal artery with a characteristic hairpin turn. Identification of the AKA and determination of its origin and course were analyzed by 2 independent radiologists. RESULTS: The AKA was successfully visualized in 38 patients (95%). Twenty-seven (71.1%) AKAs originated on the left side, whereas 11 (28.9%) originated on the right side. It was seen to originate at the level of the left 5th intercostal artery in 1 patient, the left 8th in 4, the left 9th in 15, the left 10th in 5, the left 11th in 2, the right 8th in 2, the right 9th in 6, the right 10th in 2, and the right 12th in 1. CONCLUSION: Sixty-four-section CT angiography depicted the AKA in a very high percentage (95%) of children. The results of this study suggest that 64-section CT angiography is a viable noninvasive technique that could be an alternate to selective angiography for delineating the AKA.

Ductal lavage for detection of cellular atypia in women at high risk for breast cancer.

BACKGROUND: Breast cancer originates in breast epithelium and is associated with progressive molecular and morphologic changes. Women with atypical breast ductal epithelial cells have an increased relative risk of breast cancer. In this study, ductal lavage, a new procedure for collecting ductal cells with a microcatheter, was compared with nipple aspiration with regard to safety, tolerability, and the ability to detect abnormal breast epithelial cells. METHODS: Women at high risk for breast cancer who had nonsuspicious mammograms and clinical breast examinations underwent nipple aspiration followed by lavage of fluid-yielding ducts. All statistical tests were two-sided. RESULTS: The 507 women enrolled included 291 (57%) with a history of breast cancer and 199 (39%) with a 5-year Gail risk for breast cancer of 1.7% or more. Nipple aspirate fluid (NAF) samples were evaluated cytologically for 417 women, and ductal lavage samples were evaluated for 383 women. Adequate samples for diagnosis were collected from 111 (27%) and 299 (78%) women, respectively. A median of 13,500 epithelial cells per duct (range, 43-492,000 cells) was collected by ductal lavage compared with a median of 120 epithelial cells per breast (range, 10-74,300) collected by nipple aspiration. For ductal lavage, 92 (24%) subjects had abnormal cells that were mildly (17%) or markedly (6%) atypical or malignant (<1%). For NAF, corresponding percentages were 6%, 3%, and fewer than 1%. Ductal lavage detected abnormal intraductal breast cells 3.2 times more often than nipple aspiration (79 versus 25 breasts; McNemar's test, P<.001). No serious procedure-related adverse events were reported. CONCLUSIONS: Large numbers of ductal cells can be collected by ductal lavage to detect atypical cellular changes within the breast. Ductal lavage is a safe and well-tolerated procedure and is a more sensitive method of detecting cellular atypia than nipple aspiration.

Enhancement of cortical Na+,K+-ATPase by increased oxygen tensions: evidence of a new controlling mechanism.

This study describes the preliminary isolation of substances from beef brain cortex which are required to produce an oxygen-induced enhancing effect on Na, K-ATPase. Evidence is presented that at least 3 fractions--a heat stable, low molecular weight proteinaceous substance, a cholesterol rich, membranous component, and an as yet unidentified substance--are required to produce oxygen enhancement of Na, K-ATPase activity. These findings have specific ramifications in neurocellular physiology, especially as related to seizures.

Cecectomy for complicated appendicitis.

BACKGROUND: Cecal leak or disruption after appendectomy for complicated appendicitis is a consequence of severity of disease and is related to residual abscess cavity, inflammation, phlegmon, and nonviable intestine. In an attempt to improve results, we have begun to resect the cecum and other localized infected tissue in instances of complicated appendicitis in which the viability of the appendiceal base and adjacent cecum is questionable. STUDY DESIGN: This is a prospective series of all patients who have undergone resectional therapy for complicated appendicitis in the last four years. Patients with other inflammatory conditions of the right colon have been specifically excluded. RESULTS: Seventeen patients have undergone resectional therapy for complicated appendicitis. Thirteen (76.5 percent) were men; the mean age was 42.4 years. The mean temperature and leukocyte count were 37.8 degrees C and 16.1 x 10(9) per L, respectively. These patients presented with a mean of 6.8 days of abdominal pain. Nine had a palpable abdominal mass, and all had tenderness in the right lower quadrant. In ten patients an abscess was encountered at operation. While the extent of the resection varied, it generally included the cecum, part of the right colon, and 5 to 7 cm of terminal ileum. Fourteen patients had a primary anastomosis, while the other three had the creation of an ileostomy. Complications were encountered in only two patients: one wound infection and one pulmonary embolus. There were no instances of postoperative intra-abdominal abscess, intestinal obstruction, or fecal fistula. All patients had a benign postoperative course and were discharged on the average of 9.9 days postoperatively. The ileostomies in three patients have been closed and no complications have occurred on follow-up examination. CONCLUSIONS: We conclude that aggressive resectional therapy of the cecum during appendectomy in selected patients with complicated appendicitis is effective therapy and can be performed safely.

Analysis of risk factors of postappendectomy intra-abdominal abscess.

BACKGROUND: Postappendectomy intra-abdominal abscesses (PAIAA) complicate the recovery of a small but significant fraction of patients with advanced appendicitis. STUDY DESIGN: A retrospective review of 1,184 patients with appendicitis was undertaken to define the clinical characteristics and risk factors associated with PAIAA. RESULTS: Thirty-three patients with 36 PAIAAs were found, an incidence of 2.8 percent. The mean age of patients with PAIAA was less than the overall group (16.9 versus 23.1 years, p = 0.002), and the mean core temperature of the PAIAA group was significantly higher (38.5 versus 38.2 degrees C). The incidence of PAIAA increased as the degree of appendiceal pathology worsened. The incidence of PAIAA was six (3.2 percent) of 190 in patients with gangrenous appendicitis and was 27 (8.7 percent) of 309 among patients with perforated appendicitis. Logistic regression analysis showed that independent predictors for the occurrence of PAIAA were young age and perforation. Although children presented with a higher rate of perforated appendicitis, this did not account for the younger age of the patients with PAIAA. Children (less than ten years of age) with perforation had PAIAA in ten (14 percent) of 69 cases compared with the incidence in the older patients with perforation of 17 (7.1 percent) of 240. CONCLUSIONS: These findings improve the surgeon's ability to identify patients at risk for PAIAA. Alterations in the perioperative management of perforated appendicitis, particularly in the pediatric patient, may reduce the occurrence of PAIAA.

Surgical approach to cecal diverticulitis.

BACKGROUND: Cecal diverticulitis is a rare condition in the Western world, with a higher incidence in people of Asian descent. The treatment for cecal diverticulitis has ranged from expectant medical management, which is similar to uncomplicated left-sided diverticulitis, to right hemicolectomy. STUDY DESIGN: A retrospective chart review was conducted of the 49 patients treated for cecal diverticulitis at Olive View-UCLA Medical Center from 1976 to 1998. This was the largest-ever single-institution review of cecal diverticulitis reported in the mainland US. RESULTS: The clinical presentation was similar to that of acute appendicitis, with abdominal pain, low-grade fever, nausea/vomiting, abdominal tenderness, and leukocytosis. Operations performed included right hemicolectomy in 39 patients (80%), diverticulectomy in 7 patients (14%), and appendectomy with drainage of intraabdominal abscess in 3 patients (6%). Of the 7 patients who had diverticulectomy, 1 required right hemicolectomy at 6 months followup for continued symptoms. Of the three patients who underwent appendectomy with drainage, all required subsequent hemicolectomy for continued inflammation. Of the 39 patients who received immediate hemicolectomies, there were complications in 7 (18%), with no mortality. CONCLUSIONS: We endorse an aggressive operative approach to the management of cecal diverticulitis, with the resection of all clinically apparent disease at the time of the initial operation. In cases of a solitary diverticulum, we recommend the use of diverticulectomy when it is technically feasible. When confronted with multiple diverticuli and cecal phlegmon, or when neoplastic disease cannot be excluded, we advocate immediate right hemicolectomy. This procedure can be safely performed in the unprepared colon with few complications. Excisional treatment for cecal diverticulitis prevents the recurrence of symptoms, which may be more common in the Western population.

Imaging of fungal, viral, and parasitic musculoskeletal and spinal diseases.

There are many nonbacterial infections that have musculoskeletal manifestations and radiologic findings. These infections produce a limited range of tissue responses, depending on the organism, the tissue compartment affected, and the immune competence of the host. Diagnosis is dependent on obtaining an appropriate travel or geographic history, the clinical and laboratory features, and on occasion the specific radiologic findings.

Biliary disease during pregnancy.

BACKGROUND: Biliary disease during pregnancy is rare and the need for surgery in these cases is controversial. We evaluated our experience with biliary disease during pregnancy with regard to outcome and cost containment. PATIENTS AND METHODS: We reviewed the clinical course of pregnant women with biliary disease at the University of California at Los Angeles and Olive View-UCLA Medical Centers from 1988 to 1993. RESULTS: Seventy-two of 46,075 pregnant women presented with biliary disease (incidence 0.16%). Sixteen underwent surgery while pregnant, 5 in the first and 11 in the second trimester. No maternal or fetal deaths occurred secondary to medical or surgical management of biliary disease. Patients who were treated medically at initial presentation had a 69% rate of relapse prior to delivery, compared to no relapses in those treated surgically (P < 0.01). Patients who experienced relapse spent an average of 3.0 additional days in hospital. CONCLUSION: Surgical therapy for biliary disease performed in the second trimester of pregnancy does not increase morbidity and may help reduce relapses and additional days in hospital.

Compliance of normal, dystrophic and transplanted mouse muscles.

Parallel and series compliances have been studied in extensor digitorum longus (fast) and soleus (slow) muscles in normal (strain C57BL/10) and dystrophic (strain mdx) mice, and in muscles regenerated after transplantation. Resting elasticity was analysed by measuring the tension-length relationship in unstimulated muscles. Passive tension is larger in mdx and in transplanted muscles than in their normal controls: at 1.15L0, passive tension is 0.12P0 in controls, 0.32P0 in mdx, and 0.40P0 in transplanted muscles. The differences are statistically significant. This indicates that passive tension is mainly determined by the amount of connective tissue. The stress-strain relationship of the series compliance was analysed by the method of isotonic releases during tetani. It is adequately described by a single exponential equation, with a rate constant of about 8P0/P. No difference was found between the various muscles studied. Extension of the series compliance at P0 is 0.02L0. Compliance is about 3% (L0/P0) at 0.2P0, and is not significantly different from zero at P0. Series compliance is thus very low in mouse muscles, substantially lower than in frog and rat muscles. Consequently, it can be neglected in studies of whole mouse muscle in which tension is higher than 0.4P0.

Internal fracture of a pediatric broviac catheter.

Indwelling central venous catheters have become an integral part of the care of bone marrow transplant patients. Current technology provides the physician with repeated, reliable accesses to the central venous system via centrally placed silastic (Broviac) catheters. This report describes an unusual mechanical complication and a method for catheter salvage.