Lawson criterion for ignition exceeded in an inertial fusion experiment

For more than half a century, researchers around the world have been engaged in attempts to achieve fusion ignition as a proof of principle of various fusion concepts. Following the Lawson criterion, an ignited plasma is one where the fusion heating power is high enough to overcome all the physical processes that cool the fusion plasma, creating a positive thermodynamic feedback loop with rapidly increasing temperature. In inertially confined fusion, ignition is a state where the fusion plasma can begin "burn propagation" into surrounding cold fuel, enabling the possibility of high energy gain. While "scientific breakeven" (i.e., unity target gain) has not yet been achieved (here target gain is 0.72, 1.37 MJ of fusion for 1.92 MJ of laser energy), this Letter reports the first controlled fusion experiment, using laser indirect drive, on the National Ignition Facility to produce capsule gain (here 5.8) and reach ignition by nine different formulations of the Lawson criterion

Data from: Effects of environmental factors on sucker catch rate, size structure, species composition, and precision from boat electrofishing

This data is associated with the article "Effects of environmental factors on sucker catch rate, size structure, species composition, and precision from boat electrofishing." The data consists of two XLSX files and one README file associated with the methodology and documentation to allow for replication and verification of findings.Catostomidae (catostomids) are suckers of the order Cyprinifores and the majority of species are native to North America; however, species in this group are understudied and rarely managed. The popularity in bowfishing and gigging for suckers in the United States has increased concerns related to overfishing. Little information exists about the relative gear effectiveness for sampling catostomids. Our study objective was to evaluate the relative effectiveness of boat electrofishing for sampling Black Redhorse Moxostoma duquesnei, Golden Redhorse M. erythrurum, Northern Hogsucker Hypentelium nigricans, White Sucker, and Spotted Sucker populations in Lake Eucha, OK. We used an information theoretic approach to determine the abiotic variables related to sucker catch per effort (C/f). Our analysis indicated that sucker C/f was highest during night and decreased with increasing water temperature. Sucker size structure was significantly different between daytime and nighttime samples; however, effect size estimates for size structure comparisons indicated size distributions exhibited moderate overlap. Distributional comparisons indicated daytime and nighttime samples were similar for fish >180 mm total length (TL). Effect size estimates also suggested little association between the proportion of each species captured and time of day or water temperature. Night electrofishing at water temperatures from 16-25 ⁰C yielded the most precise C/f estimates. If managers are interested in precision, then we recommend night electrofishing suckers in reservoirs at water temperatures from 16-25 ⁰C; though, if total number of suckers is more important than precision, samples taken at night from 6-15 ⁰C are recommended. Further study of the relationship between abiotic variables and catostomid catchability using various gears would be beneficial to agencies interested in these populations.Natural Resource Ecology and Managemen

Flashover of a vacuum-insulator interface: A statistical model

We have developed a statistical model for the flashover of a 45° vacuum-insulator interface (such as would be found in an accelerator) subject to a pulsed electric field. The model assumes that the initiation of a flashover plasma is a stochastic process, that the characteristic statistical component of the flashover delay time is much greater than the plasma formative time, and that the average rate at which flashovers occur is a power-law function of the instantaneous value of the electric field. Under these conditions, we find that the flashover probability is given by 1-exp(-E_{p}^{β}t_{eff}C/k^{β}), where E_{p} is the peak value in time of the spatially averaged electric field E(t), t_{eff}≡∫[E(t)/E_{p}]^{β}dt is the effective pulse width, C is the insulator circumference, k∝exp(λ/d), and β and λ are constants. We define E(t) as V(t)/d, where V(t) is the voltage across the insulator and d is the insulator thickness. Since the model assumes that flashovers occur at random azimuthal locations along the insulator, it does not apply to systems that have a significant defect, i.e., a location contaminated with debris or compromised by an imperfection at which flashovers repeatedly take place, and which prevents a random spatial distribution. The model is consistent with flashover measurements to within 7% for pulse widths between 0.5 ns and 10   μs, and to within a factor of 2 between 0.5 ns and 90 s (a span of over 11 orders of magnitude). For these measurements, E_{p} ranges from 64 to 651  kV/cm, d from 0.50 to 4.32 cm, and C from 4.96 to 95.74 cm. The model is significantly more accurate, and is valid over a wider range of parameters, than the J. C. Martin flashover relation that has been in use since 1971 [J. C. Martin on Pulsed Power, edited by T. H. Martin, A. H. Guenther, and M. Kristiansen (Plenum, New York, 1996)]. We have generalized the statistical model to estimate the total-flashover probability of an insulator stack (i.e., an assembly of insulator-electrode systems connected in series). The expression obtained is consistent with the measured flashover performance of a stack of five 5.72-cm-thick, 1003-cm-circumference insulators operated at 100 and 158  kV/cm. The expression predicts that the total-flashover probability is a strong function of the ratio E_{p}/k, and that under certain conditions, the performance improves as the capacitance between the stack grading rings is increased. In addition, the expression suggests that given a fixed stack height, there exists an optimum number of insulator rings that maximizes the voltage at which the stack can be operated. The results presented can be applied to any system (or any set of systems connected in series) subject to random failures, when the characteristic statistical delay time of a failure is much greater than its formative time