Plasma Low Density Research Articles

Serum Lipid, Amino Acid and Acylcarnitine Profiles of Obese Cats Supplemented with Dietary Choline and Fed to Maintenance Energy Requirements.

Simple SummaryResearch has estimated that the majority of domestic cats are overweight or obese. Current weight-loss plans tend to have disappointing outcomes and are not without risk. During periods of severe energy restriction, obesity predisposes cats to developing fatty liver. Choline has been linked to fat metabolism in other animals but has not been studied in cats. Twelve obese cats were split into two groups and were fed a control diet (n = 6; 4587 mg choline/kg dry matter) or a high choline diet (n = 6; 18,957 mg choline/kg DM) for 5 weeks. Cats were fed to maintain body weight. Choline increased serum cholesterol, triacylglycerides, lipoproteins, and plasma methionine. It also decreased serum blood urea nitrogen and alkaline phosphatase as well as the ratio of plasma acylcarnitine to free carnitine. The results suggest that choline supplementation may increase fat transport out of the liver and help maintain liver health in obese cats. Choline supplementation may prove useful for safe weight loss in obese cats by minimizing the risks of fatty liver.Obesity is a health concern for domestic cats. Obesity and severe energy restriction predispose cats to feline hepatic lipidosis. As choline is linked to lipid metabolism, we hypothesized that dietary choline supplementation would assist in reducing hepatic fat through increased lipoprotein transport and fatty acid oxidation. Twelve obese cats (body condition score [BCS] ≥ 8/9) were split into two groups. Cats were fed a control (n = 6; 4587 mg choline/kg dry matter [DM]) or a high choline diet (n = 6; 18,957 mg choline/kg DM) for 5 weeks, for adult maintenance. On days 0 and 35, fasted blood was collected, and the body composition was assessed. Serum lipoprotein and biochemistry profiles, plasma amino acids and plasma acylcarnitines were analyzed. The body weight, BCS and body composition were unaffected (p > 0.05). Choline increased the serum cholesterol, triacylglycerides, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, very low-density lipoprotein cholesterol and plasma methionine (p < 0.05) and decreased the serum blood urea nitrogen and alkaline phosphatase (p < 0.05). Choline also reduced the plasma acylcarnitine to free carnitine ratio (p = 0.006). Choline may assist in eliminating hepatic fat through increased fat mobilization and enhanced methionine recycling.

Study on control of hypersonic aerodynamic force by quasi-DC discharge plasma energy deposition

This paper reports an active method for aerodynamic force control of a hypersonic spacecraft via shock wave mitigation with plasma energy deposition. The energy deposition was generated by quasi-direct current discharge at two positions in the streamwise direction on a flat plate upstream a compression surface. Wind tunnel experiments of visualizing a Mach 6 flow over a ramp with high-speed schlieren imaging were performed to verify the method's effect on diluting a shock wave. Meanwhile, the Reynolds averaged Navier-Stokes equations, with a source term of simulating plasma heating due to discharge, were solved to evaluate the method's control abilities. From the experimental results, low-density plasma layers can be formed by quasi-DC discharge, which were continuously weakening the shock wave induced by the ramp. The numerical results predicted flow topology under control well with the experimental schlieren images, with the corresponding force reduction rate as high as 58%, which mainly depends on the amount of energy injection, instead of arrangement of heating zones in this study.

Estimate of pre-thermal quench non-thermal electron density profile during Ar pellet shutdowns of low-density target plasmas in DIII-D

The radial density profile of pre-thermal quench (pre-TQ) early-time non-thermal (hot) electrons is estimated by combining electron cyclotron emission and soft x-ray data during the rapid shutdown of low-density (ne≲1019 m−3) DIII-D target plasmas with cryogenic argon pellet injection. This technique is mostly limited in these experiments to the pre-TQ phase and quickly loses validity during the TQ. Two different cases are studied: a high (10 keV) temperature target and a low (4 keV) temperature target. The results indicate that early-time, low-energy (∼10 keV) hot electrons form ahead of the argon pellet as it enters the plasma, affecting the pellet ablation rate; it is hypothesized that this may be caused by rapid cross field transport of argon ions ahead of the pellet or by rapid cross field transport of hot electrons. Fokker–Planck modeling of the two shots suggests that the hot electron current is quite significant during the pre-TQ phase (up to 50% of the total current). Comparison between modeled pre-TQ hot electron current and post-TQ hot electron current inferred from avalanche theory suggests that hot electron current increases during the high-temperature target TQ but decreases during the low-temperature target TQ. The uncertainties in this estimate are large; however, if true, this suggests that TQ radial loss of hot electron current could be larger than previously estimated in DIII-D.

Dynamics of laser produced plasma from foam targets for future nanolithography devices and X-ray sources

Foam targets are expected to be more efficient candidates than solid targets for laser produced plasma (LPP) for extreme ultraviolet (EUV) and X-ray radiation sources due to the expected plasma conditions that can be optimized regarding plasma opacities, volumetrics heating effects, and the produced ions debris characteristics. In this paper, a comparison of ion dynamics between low-density foam and solid Ni plasma was systematically investigated at CMUXE. The foam Ni target (density 0.6 g/cm3) and solid Ni target (density 8.9 g/cm3) were irradiated with 1064 nm Nd:YAG laser in vacuum. A Faraday cup (FC) was used to record the ion flux and time-of-flight (TOF) signals. A lower and wider TOF signal was observed for foam Ni plasma on the time scale. The average ion energy and peak of the TOF signal of solid Ni plasma were much higher than that of the foam Ni plasma. However, the total charge values between foam and solid Ni plasma were comparable indicating a more volumetric absorption of laser energy for foam Ni. The average ion energy and peak of the TOF signal of solid Ni showed a stronger angular and laser energy dependence than that of foam Ni. The plume shape of the solid Ni plasma appeared as an oblong ellipse at each time, while that of foam Ni plasma tended to be more circular, especially at early times. The results of mass ablation rate were consistent with the FC signals and showed a more intense plasma shielding for solid Ni.

Trapped-electron-mode property and role for the L-H transition in L-mode edge plasmas with relatively high electron temperature and weak ion temperature gradient

When the low-confinement mode (L-mode) edge has relatively high electron temperature and weak ion temperature gradient, for example, as observed in the ECH-heated low-density plasmas, the trapped electron mode (TEM) can play an important role in the low to high confinement (L-H) transition as well as the L-mode edge transport, instead of the resistive ballooning or ion temperature gradient mode (RBM or ITG). Motivated by this, a study is first presented about, among several types of the TEM, which one is the most dominant in the above L-mode edge condition, showing that it is dominated by a mixture of the density gradient driven and dissipative TEMs. The parameter dependence of the growth rate of this dominant TEM type is then checked, showing that it has the scaling qualitatively similar to the H-mode threshold power one observed in plasmas where the TEM can be a dominant mode. Closely related to this, a discussion is also given about the L-H transition expected in plasmas where the TEM is assumed to be dominant. Unlike the typical L-H transition that is believed to occur in the RBM-dominant plasmas, it is conjectured to take place in one-step form, with no generation or negligible role of the limit-cycle-oscillation, thus requiring a larger threshold power.

Ultrafast x-ray imaging of pulsed plasmas in water

Pulsed plasmas in liquids exhibit complex interaction between three phases of matter (liquids, gas, plasmas) and are currently used in a wide range of applications across several fields, however significant knowledge gaps in our understanding of plasma initiation in liquids hinder additional application and control; this area of research currently lacks a comprehensive predictive model. To aid progress in this area experimentally, here we present the first-known ultrafast (50 ps) X-ray images of pulsed plasma initiation processes in water (+25 kV, 10 ns, 5 mJ), courtesy of the X-ray imaging techniques available at Argonne National Laboratory's Advanced Photon Source (APS), with supporting nanosecond optical imaging and a computational X-ray diffraction model. These results clearly resolve narrow (~10 micron) low-density plasma channels during initiation timescales typically obscured by optical emission (<100 ns), a well-known and difficult problem to plasma experiments without access to state-of-the-art X-ray sources such as the APS synchrotron. Images presented in this work speak to several of the prevailing plasma initiation hypotheses, supporting electrostriction and bubble deformation as dominant initiation phenomena. We also demonstrate the plasma setup used in this work as a cheap ($<$US\$100k), compact, and repeatable benchmark imaging target (29.1 km/s, 1 TW/cm$^2$) useful for the development of next-generation ultrafast imaging of high-energy-density physics (HEDP), as well as easier integration of HEDP research into synchrotron-enabled facilities.

Large closed-field corona of WX Ursae Majoris evidenced from radio observations

The space-weather conditions that result from stellar winds significantly impact the habitability of exoplanets. The conditions can be calculated from first principles if the necessary boundary conditions are specified, namely the plasma density in the outer corona and the radial distance at which the plasma forces the closed magnetic field into an open geometry. Low frequency radio observations (ν ≲ 200 MHz) of plasma and cyclotron emission from stars probe these magneto-ionic conditions. Here we report the detection of low-frequency (120–167 MHz) radio emission associated with the dMe6 star WX UMa. If the emission originates in WX UMa’s corona, we show that the closed field region extends to at least ≈10 stellar radii, which is about a factor of a few larger than the solar value, and possibly to ≳20 stellar radii. Our results suggest that the magnetic-field structure of M dwarfs is in between Sun-like and planet-like configurations, where compact over-dense coronal loops with X-ray emitting plasma co-exist with a large-scale magnetosphere with a lower plasma density and closed magnetic geometry.

Low jitter parabolic profile low density plasma channel in 3D printed gas filled capillary

A parabolic profile plasma channel formed by an electric discharge inside a gas filled capillary are currently used to achieve optimal conditions for laser guiding and electron acceleration. Acceleration of high quality externally injected electron beam by laser induced wake field requires precise synchronization between several systems. In our experiment the measured jitter in plasma ignition was on the scale of 1 ns, providing possibility for the synchronization with high intensity laser and other auxiliary systems (e.g injectors). We confirmed the existence of a parabolic density plasma profile inside the capillary using an 84 MHz oscillator laser and found its duration to be approximately 300 ns.

Laser-assisted graphene growth directly on silicon

Controlled graphene growth on a substrate without the use of catalysts is of great importance for industrial applications. Here, we report thickness-controlled graphene growth directly on a silicon substrate placed in a low-density microwave plasma environment using a laser. Graphene is relatively easy to grow in high-density plasma; however, low-density plasma lacks the sufficient energy and environment required for graphene synthesis. This study reports that laser irradiation on silicon samples in a low-density plasma region nucleates graphene, and growth is controlled with laser exposure time and power. A graphene–silicon junction is thus formed and shows an enhanced (1.7 mA) short-circuit current as compared to one grown in high-density plasma (50 μA) without the laser effects. Synthesized graphene is characterized by Raman spectroscopy, atomic force microscopy to investigate surface morphology and Hall effect measurements for electronic properties. The key aspect of this report is the use of a laser to grow graphene directly on the silicon substrate by ensuring that the bulk resistance of the silicon is unaffected by ion bombardment. Additionally, it is observed that graphene grain size varies in proportion to laser power. This report can help in the growth of large-area graphene directly on silicon or other substrates at reduced substrate temperatures with advanced electronic properties for industrial applications.

Development of high-efficiency capacitive discharge using magnetic resonance wireless power transfer systems

We developed a high-efficiency source in a capacitively coupled plasma using magnetic resonance wireless power transfer (MRWPT) systems, which has the advantage that the matcher efficiency is very high at low gas pressures (2 mTorr to 20 mTorr) and high density plasmas (about 1 × 1010 cm−3 to 5 × 1010 cm−3). At the non-resonance conditions, most of the RF power is dissipated by the transmitter coil and the plasma is not discharged. However, at the resonance condition, the plasma is discharged as the current flowing through the transmitter coil rapidly decreases, and the matcher efficiency is higher than 90% in all experiments. For analysis, the transformer model with MRWPT systems is developed. The experimental result is consistent with the model, and the results are discussed with the relevant physical mechanisms.

Creation of an axially uniform plasma channel in a laser-assisted capillary discharge

Dissipative capillary discharges form plasma channels which allow for high power laser guiding, enabling efficient electron acceleration in a laser wakefield accelerator. However, at the low plasma densities required to produce high-energy electrons, in order to avoid capillary wall damage, high power lasers need a tighter transverse confinement that cannot be achieved by the capillary discharge powered by Ohmic heating alone. The introduction of an additional laser for heating of the plasma leads to deeper and narrower plasma channels. Here we investigate the formation of laser-heated axially uniform plasma channels. We show that a high degree of longitudinal uniformity can be achieved despite significant evolution of the heater laser during its propagation through the channel.

Features and quantitative characteristics of the interaction of benzo[a]pyrene with fractions of the human blood plasma lipoproteins

The paper considers the features and quantitative characteristics of the interaction of human blood plasma low (LDL), very low (VLDL) and high density lipoproteins (HDL) with a polycyclic aromatic hydrocarbon benzo[a]pyrene (B[a]P). Material and methods. The studies were performed using preparative ultracentrifugation of human plasma lipoprotein fractions and fluorescence spectroscopy. Results. The spectral characteristics of tryptophan fluorescence of VLDL, LDL and HDL fractions during titration with B[a]P solution are presented. The interaction of LP fractions with B[a]P was accompanied by quenching of tryptophanil fluorescence: the greatest decrease in fluorescence at saturating concentrations of B[a]P was noted for the HDL fraction — over 80 %; the effect of B[a]P was weaker for LDL (65-74 %) and for VLDL (50-60 %) of the initial level. Based on the results of the tryptophan fluorescence quenching curves and taking into account the molecular weights, quantitative characteristics of the interaction of the LP fractions with B[a]P were obtained: the association constants were of the order of (1.3 - 2.5) × 10-6 M, and the number of binding sites for B[a] P on LP particles ranged from 19 for HDL and up to 43 for VLDL. Conclusion. The quantitative characteristics of the interaction obtained for the complexes of LP with B[a]P allow us to consider the LP of blood plasma as real transport forms for B[a]P and other hydrophobic compounds into the cells of organs and tissues of the body.

Generation of attosecond electron bunches and x-ray pulses from few-cycle femtosecond laser pulses

Laser-plasma electron accelerators can be used to produce high-intensity x-rays, as electrons accelerated in wakefields emit radiation due to betatron oscillations. Such x-ray sources inherit the features of the electron beam; sub-femtosecond electron bunches produce betatron sources of the same duration, which in turn allow probing matter on ultrashort time scales. In this paper we show, via Particle-in-Cell simulations, that attosecond electron bunches can be obtained using low-energy, ultra-short laser beams both in the self-injection and the controlled injection regimes at low plasma densities. However, only in the controlled regime does the electron injection lead to a stable, isolated attosecond electron bunch. Such ultrashort electron bunches are shown to emit attosecond x-ray bursts with high brilliance.

Plasma-assisted discharges and charging in EUV-induced plasma

In the past years, EUV lithography scanner systems have entered high-volume manufacturing for state-of-the-art integrated circuits (IC), with critical dimensions down to 10 nm. This technology uses 13.5-nm EUV radiation, which is transmitted through a near-vacuum H2 background gas, imaging the pattern of a reticle onto a wafer. The energetic EUV photons excite the background gas into a low-density H2 plasma. The resulting plasma will locally change the near-vacuum into a conducting medium and can charge floating surfaces and particles, also away from the direct EUV beam. We will discuss the interaction between EUV-induced plasma and electrostatics, by modeling and experiments. We show that the EUV-induced plasma can trigger discharges well below the classical Paschen limit. Furthermore, we demonstrate the charging effect of the EUV plasma on both particles and surfaces. Uncontrolled, this can lead to unacceptably high voltages on the reticle backside and the generation and transport of particles. We demonstrate a special unloading sequence to use the EUV-induced plasma to actively solve the charging and defectivity challenges.

Ablated precursor plasma and evolution of magnetic field of exploding cylindrical thin liner

The formation of precursor plasma and ablation dynamics of Al thin liner explosion are investigated in this manuscript. The size of 12 mm in diameter, 10 μm in thickness Al liners are exploded on the Qin-1 facility (about 450 ns, 450 kA). An axial laser shadowgraphy and interferometry platform is set up to observe the plasma dynamics inside the liner. To solve the problem that the inside plasma density of the liner cannot be absolutely calibrated due to the lack of a zero plasma density area, we have established a CW laser interference system using a streak camera which can trace the interference lines over time. Low-density (10−7−10−6 g cm−3) precursor plasma is generated from the interior wall and flows towards the center with a velocity of about 150–200 km s−1, thus forming a column with high electron density by accumulation. Simultaneously, a high-density plasma layer flows toward the center at about 10 km s−1. The electron density of the central plasma column rises up rapidly after the precursor reaches the center and achieves 2.5 × 1018 cm−3 at 280 ns after the current starts. To fully understand the process, we have used the resistive magnetohydrodynamic code FLASH to realize a simulation to study interior precursor dynamics. We compared these simulation results with our experiments. Finally, we measured the voltage for the whole process and derived the inductance change and effective current radius. We compared the simulated current density distribution with the experimental result which proves that a considerable amount of current flows through the center plasma column, making the effective radius of current become smaller over time.

Formation, Focusing and Transport of Highintensity, Low-Energy Metal Ion Beams

High-intensity implantation of low-energy ions into various materials demonstrates the formation of long, ionalloyed layers having a thickness of tens and hundreds of micrometers. A deep incorporation of alloying elements in materials is achieved, first of all, due to a stronger radiation-induced ion diffusion at ultrahigh current densities and radiation fluence ranging from 1020 to 1022 cm2, when the diffusion coefficient exceeds its classical value derived from Arrhenius theory by several orders of magnitude. Nevertheless, the generation of low-energy ions with energies of several or a few kiloelectronvolts at high current densities of several hundreds of milliamperes per square metre and their effective transport, is a sophisticated problem. The paper studies the ballistic focusing of high-intensity pulsed ion beams at 2 kV accelerating voltage, 800 μs pulse time, 0.8 duty cycle, and their propagation through the preliminary injected low-density background plasma.

Expansion of ultracold neutral plasmas with exponentially decaying density distributions

We present a study of the expansion of an ultracold neutral plasma (UCNP) with an initial density distribution that decays exponentially in space, created by photoionizing atoms shortly after their release from a quadrupole (or biconic cusp) magnetic trap. A characteristic ion acoustic timescale is evident in the evolution of the plasma size and velocity, indicating that the dynamics are reasonably well described by a model of hydrodynamic expansion of a quasi-neutral plasma. However, for low plasma density and high initial electron temperature, excess ion kinetic energy in the vicinity of the central density peak suggests significant local non-neutrality at early times. Observations are compared to the well-understood self-similar expansion of a UCNP with an initial Gaussian density distribution, and a similar scaling law describes the evolution of plasma size for both cases.

Towards the optimisation of direct laser acceleration

Experimental measurements using the OMEGA EP laser facility demonstrated direct laser acceleration (DLA) of electron beams to (505 ± 75) MeV with (140 ± 30) nC of charge from a low-density plasma target using a 400 J, picosecond duration pulse. Similar trends of electron energy with target density are also observed in self-consistent two-dimensional particle-in-cell simulations. The intensity of the laser pulse is sufficiently large that the electrons are rapidly expelled along the laser pulse propagation axis to form a channel. The dominant acceleration mechanism is confirmed to be DLA and the effect of quasi-static channel fields on energetic electron dynamics is examined. A strong channel magnetic field, self-generated by the accelerated electrons, is found to play a comparable role to the transverse electric channel field in defining the boundary of electron motion.

New Ritz Wavelengths and Transition Probabilities of Parity-forbidden [Mn II] Lines of Astrophysical Interest.

We report a comprehensive list of accurate Ritz wavelengths and calculated transition probabilities for parity-forbidden [Mn II] lines. Ritz wavelengths have been derived from experimentally established energy level values resulting from an extensive analysis of a high-resolution Fourier-transform emission spectrum of singly ionized manganese. Our analysis includes transitions between all known metastable and other long-lived levels of Mn II giving a total of 1130 [Mn II] Ritz wavelengths. Our entire list of derived Ritz wavelengths for [Mn II] lines ranges between 237 nm and 170 μm (42,125-58 cm-1). The accurate Ritz wavelengths and calculated transition probabilities for forbidden lines in this paper are useful in the study and diagnostics of nebulae and other low-density astrophysical plasmas.

Gyroresonant wave-particle interactions with chorus waves during extreme depletions of plasma density in the Van Allen radiation belts.

The Van Allen Probes mission provides unique measurements of the most energetic radiation belt electrons at ultrarelativistic energies. Simultaneous observations of plasma waves allow for the routine inference of total plasma number density, a parameter that is very difficult to measure directly. On the basis of long-term observations in 2015, we show that the underlying plasma density has a controlling effect over acceleration to ultrarelativistic energies, which occurs only when the plasma number density drops down to very low values (~10 cm-3). Such low density creates preferential conditions for local diffusive acceleration of electrons from hundreds of kilo-electron volts up to >7 MeV. While previous models could not reproduce the local acceleration of electrons to such high energies, here we complement the observations with a numerical model to show that the conditions of extreme cold plasma depletion result in acceleration up to >7 MeV.