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A dense plasma focus (DPF) is a relatively compact coaxial plasma gun, which completes its discharge as a Z-pinch. These devices are designed to operate at a variety of scales to produce short (

The sheared-flow-stabilized (SFS) Z-pinch is a promising confinement concept for the development of a compact fusion reactor. The Z-pinch has been theoretically and experimentally shown to be stabl...

The fusion Z-pinch experiment (FuZE) is a sheared-flow stabilized Z-pinch designed to study the effects of flow stabilization on deuterium plasmas with densities and temperatures high enough to drive nuclear fusion reactions. Results from FuZE show high pinch currents and neutron emission durations thousands of times longer than instability growth times. While these results are consistent with thermonuclear neutron emission, energetically resolved neutron measurements are a stronger constraint on the origin of the fusion production. This stems from the strong anisotropy in energy created in beam-target fusion, compared to the relatively isotropic emission in thermonuclear fusion. In dense Z-pinch plasmas, a potential and undesirable cause of beam-target fusion reactions is the presence of fast-growing, “sausage” instabilities. This work introduces a new method for characterizing beam instabilities by recording individual neutron interactions in plastic scintillator detectors positioned at two different angles around the device chamber. Histograms of the pulse-integral spectra from the two locations are compared using detailed Monte Carlo simulations. These models infer the deuteron beam energy based on differences in the measured neutron spectra at the two angles, thereby discriminating beam-target from thermonuclear production. An analysis of neutron emission profiles from FuZE precludes the presence of deuteron beams with energies greater than 4.65 keV with a statistical uncertainty of 4.15 keV and a systematic uncertainty of 0.53 keV. This analysis demonstrates that axial, beam-target fusion reactions are not the dominant source of neutron emission from FuZE. These data are promising for scaling FuZE up to fusion reactor conditions.

The sheared-flow stabilized $Z$-pinch has demonstrated long-lived plasmas with fusion-relevant parameters. This Letter presents the first experimental results demonstrating sustained, quasi-steady-state neutron production from the Fusion $Z$-pinch Experiment (FuZE), operated with a mixture of 20% deuterium/80% hydrogen by volume. Neutron emissions lasting approximately $5~\mu$s are reproducibly observed with pinch currents of approximately $200$ kA during an approximately $16~\mu$s period of plasma quiescence. The average neutron yield is estimated to be $\left ( 1.25\pm 0.45 \right )\times 10^{5}$ neutrons/pulse and scales with the square of the deuterium concentration. Coincident with the neutron signal, plasma temperatures of $1-2$ keV, and densities of approximately $10^{17}$ cm$^{-3}$ with $0.3$ cm pinch radii are measured with fully-integrated diagnostics., Comment: 5 pages and 6 figures

This work presents a study of the region of nanoparticle growth in an atmospheric pressure carbon arc. The nanoparticles are detected using the planar laser-induced incandescence technique. The measurements revealed large clouds of nanoparticles in the arc periphery bordering the region with a high density of diatomic carbon molecules. Two-dimensional computational fluid dynamic simulations of the arc combined with thermodynamic modeling show that this is due to the interplay of the condensation of carbon molecular species and the convection flow pattern. These results show that the nanoparticles are formed in the colder, peripheral regions of the arc and describe the parameters necessary for coagulation.

A novel approach using multiple scintillator detectors is applied to measure temporally- and spatially-resolved neutron production in the Fusion Z-pinch Experiment (FuZE) device, a Sheared-Flow Stabilized (SFS) Z-pinch. Diagnosing neutron production from FuZE is important for determining if fusion is thermonuclear and whether the FuZE device can be scaled toward reactor conditions. Absolute yields of up to 2 × 10 5 neutrons per discharge are measured with calibrated plastic scintillator detectors operating in pulse-counting mode. Neutron emission durations of up to ∼ 8 μ s are inferred by recording the time difference between the first and last pulses for each discharge. Multiple scintillator detectors located at different positions with respect to the fusing plasma are used to demonstrate that the axial extent of the neutron producing region is comparable to the device volume. Scintillator detectors are well-suited as neutron diagnostics for FuZE and other plasma devices with similar yields and emission durations. Increasing the neutron yield, duration, and volume of the neutron emitting region within the plasma column are significant experimental objectives for FuZE.

Experiments were performed to maximize the neutron yield from a 2 kJ dense plasma focus (DPF) and characterize the amount of copper sputtered from the surface of an anode by varying the diameter of the anodes’ on-axis hollow. The hollow is a void in the copper material along the longitudinal axis of the anode. All the anodes had an outer diameter of 1.2 in. and the diameter of the hollow varied from 0 in. (no hollow) to 1 in. The anodes with a hollow produced a greater number of neutrons per discharge than the anode without a hollow. Over 40 discharges, the hollow anode that yielded the most neutrons (9.1 ±0.4 ×10 6 neutrons per discharge produced with the 0.75 in. hollow) produced >6 times more neutrons than the anode with no hollow. A qualitative observation of the anodes after 130 discharges showed less surface damage on anodes with a larger hollow. Quantitative sputter measurements were performed by characterizing the amount of copper sputtered onto on-axis quartz targets for three newly machined anodes, each with a particular hollow diameter. The quantitative results matched the qualitative observations: the copper sputter was reduced using larger hollows. The largest hollow sputtered 17 ±1.0 nm/sr/discharge of copper, a reduction of 69 % compared to the anode with the most damage.Experiments were performed to maximize the neutron yield from a 2 kJ dense plasma focus (DPF) and characterize the amount of copper sputtered from the surface of an anode by varying the diameter of the anodes’ on-axis hollow. The hollow is a void in the copper material along the longitudinal axis of the anode. All the anodes had an outer diameter of 1.2 in. and the diameter of the hollow varied from 0 in. (no hollow) to 1 in. The anodes with a hollow produced a greater number of neutrons per discharge than the anode without a hollow. Over 40 discharges, the hollow anode that yielded the most neutrons (9.1 ±0.4 ×10 6 neutrons per discharge produced with the 0.75 in. hollow) produced >6 times more neutrons than the anode with no hollow. A qualitative observation of the anodes after 130 discharges showed less surface damage on anodes with a larger hollow. Quantitative sputter measurements were performed by characterizing the amount of copper sputtered onto on-axis quartz targets for three newly machined ano...

Developments in the recent application of in situ diagnostics to improve understanding of nanomaterial synthesis processes in carbon arc plasma are summarized. These diagnostics measure the plasma conditions in the arc core and the precursor species to nanoparticle formation and the presence and sizes of nanoparticles in the synthesis region surrounding the hot arc core. They provide information that could not be obtained by the ex situ diagnostics used in previous studies of nanomaterial synthesis in arc plasma. The following diagnostics are covered: optical emission spectroscopy, planar laser induced fluorescence, laser induced incandescence, fast frame imaging, coherent Rayleigh Brillouin scattering, and the nanomaterial extractor probe. The diagnostic measurements are consistent with a recently developed two-dimensional fluid model of nanomaterial synthesis in the arc plasma.

Background— Acetyltransferase p300 is essential for cardiac development and is thought to be involved in cardiac myocyte growth through MEF2- and GATA4-dependent transcription. However, the importance of p300 in the modulation of cardiac growth in vivo is unknown. Methods and Results— Pressure overload induced by transverse aortic coarctation, postnatal physiological growth, and human heart failure were associated with large increases in p300. Minimal transgenic overexpression of p300 (1.5- to 3.5-fold) induced striking myocyte and cardiac hypertrophy. Both mortality and cardiac mass were directly related to p300 protein dosage. Heterozygous loss of a single p300 allele reduced pressure overload–induced hypertrophy by ≈50% and rescued the hypertrophic phenotype of p300 overexpressers. Increased p300 expression had no effect on total histone deacetylase activity but was associated with proportional increases in p300 acetyltransferase activity and acetylation of the p300 substrates histone 3 and GATA-4. Remarkably, a doubling of p300 levels was associated with the de novo acetylation of MEF2. Consistent with this, genes specifically upregulated in p300 transgenic hearts were highly enriched for MEF2 binding sites. Conclusions— Small increments in p300 are necessary and sufficient to drive myocardial hypertrophy, possibly through acetylation of MEF2 and upstream of signals promoting phosphorylation or nuclear export of histone deacetylases. We propose that induction of myocardial p300 content is a primary rate-limiting event in the response to hemodynamic loading in vivo and that p300 availability drives and constrains adaptive myocardial growth. Specific reduction of p300 content or activity may diminish stress-induced hypertrophy and forestall the development of heart failure.

Coherent population trapping (CPT) is theoretically examined as a magnetic-field diagnostic for high-\ensuremath{\beta} hydrogen plasma. Time-dependent quantum mechanical Bloch equations, which describe the evolution of the 2$s$ and 3$p$ level populations of the hydrogen atom under CPT conditions, were solved numerically. When the frequency difference of two copropagating lasers equals the energy difference between the atoms' levels subject to the local magnetic field, a discernable CPT dark line in the H\ensuremath{\alpha} emission is predicted, enabling the possibility of noninvasive, localized magnetic-field measurements. The effects of fine and hyperfine level structure, Doppler broadening, plasma-generated electric fields, and degree-of-hydrogen ionization are included in the model. A shift in dark-line position of 15$%$ of the linewidth is predicted to be caused by contributions from the entire H\ensuremath{\alpha} manifold. The laser-induced H\ensuremath{\alpha} fluorescence is estimated to be an order of magnitude stronger than the background H\ensuremath{\alpha} emission.

An adjusted form of thermionic emission is applied to calculate emitted current from laser-heated nanoparticles and to interpret time-resolved laser-induced incandescence (TR-LII) signals. This adjusted form of thermionic emission predicts significantly lower values of emitted current compared to the commonly used Richardson-Dushman equation, since the buildup of positive charge in a laser-heated nanoparticle increases the energy barrier for further emission of electrons. Thermionic emission influences the particle's energy balance equation, which can influence TR-LII signals. Additionally, reports suggest that thermionic emission can induce disintegration of nanoparticle aggregates when the electrostatic Coulomb repulsion energy between two positively charged primary particles is greater than the van der Waals bond energy. Since the presence and size of aggregates strongly influences the particle's energy balance equation, using an appropriate form of thermionic emission to calculate emitted current ma...

We observed temporal laser-induced incandescence (LII) signals from multiwalled carbon nanotubes (MWCNTs) suspended in ambient air. Unlike previous LII experiments with soot particles, which showed that primary particles with larger diameters cool at slower timescales relative to smaller particles, we observed that thicker MWCNTs with larger outer diameters (ODs) cool at faster timescales relative to thinner MWCNTs with smaller ODs. We suggested a simple explanation of this effect, based on the solution of one-dimensional nonstationary heat conduction equation for the initial non-uniform heating of MWCNTs with ODs greater than the skin depth.