Capillary Plasma Research Articles

Electron beam and plasma modes of a channel spark discharge operation

Parameters of a modified pulsed channel spark discharge (CSD), operating at a repetition rate up to 100 Hz at Ar gas pressures of 10−3 and 10−4 Torr and of the generated electron beam, were studied using different electrical, optical, and x-ray diagnostics. It was shown that efficient (up to ∼74%) transfer of the initially stored energy to the energetic electron beam is realized only at the pressure of 10−4 Torr. Conversely, at the pressure of 10−3 Torr, less than 10% of the stored energy is acquired by the energetic electrons. It was found that the energetic electron beam generation is limited by the expansion of the cathode and anode plasmas and by the formation of plasma inside the gap between the CSD capillary output and the anode. It was also found that the plasma, which acquires the hollow cathode potential, is already formed at the beginning of the CSD operation inside the capillary, and the electron emission occurs from the capillary output plasma boundary. Finally, it was shown that the electron beam energy spectrum differs significantly from the energy spectrum, which one may expect in the case of the planar diode operation.

Laser pulse guiding and electron acceleration in the ablative capillary discharge plasma

The results of experiments are presented for the laser electron acceleration in the ablative capillary discharge plasma. The plasma channel is formed by the discharge inside the ablative capillary. The intense short laser pulse is guided over a 4 cm length. The generated relativistic electrons show both the quasimonoenergetic and quasi-Maxwellian energy spectra, depending on laser and plasma parameters. The analysis of the inner walls of the capillaries that underwent several tens of shots shows that the wall deformation and blistering resulted from the discharge and laser pulse effects.

Yield of Opportunistic Targeted Screening for Type 2 Diabetes in Primary Care: The Diabscreen Study

In screening for type 2 diabetes, guidelines recommend targeting high-risk individuals. Our objectives were to assess the yield of opportunistic targeted screening for type 2 diabetes in primary care and to assess the diagnostic value of various risk factors. In 11 family practices (total practice population = 49,229) in The Netherlands, we conducted a stepwise opportunistic screening program among patients aged 45 to 75 years by (1) identifying high-risk individuals (=1 diabetes risk factor) and low-risk individuals using the electronic medical record, (2) obtaining a capillary fasting plasma glucose measurement, repeated on a separate day if the value was greater than 110 mg/dL, and (3) obtaining a venous sample if both capillary fasting plasma glucose values were greater than 110 mg/dL and at least 1 sample was 126 mg/dL or greater. We calculated the yield (percentage of invited patients with undiagnosed diabetes), number needed to screen (NNS), and diagnostic value of the risk factors (odds ratio and area under the receiver operating characteristic curve). We invited for a first capillary measurement 3,724 high-risk patients seen during usual care and a random sample of 465 low-risk patients contacted by mail. The response rate was 90% and 86%, respectively. Ultimately, 101 high-risk patients (2.7%; 95% confidence interval [CI], 2.2%-3.3%; NNS = 37) and 2 low-risk patients (0.4%; 95% CI, 0.1%-1.6%; NNS = 233) had undiagnosed diabetes (P <.01). The prevalence of diabetes among patients 45 to 75 years old increased from 6.1% to 6.8% as a result. Among diagnostic models containing various risk factors, a model containing obesity alone was the best predictor of undiagnosed diabetes (odds ratio = 3.2; 95% CI, 2.0-5.2; area under the curve=0.63). The yield of opportunistic targeted screening was fair; obesity alone was the best predictor of undiagnosed diabetes. Opportunistic screening for type 2 diabetes in primary care could target middle-aged and older adults with obesity.

Hollow cathode effects in the pre-breakdown phase of a pulsed capillary discharge

Experimental observations of the hollow cathode effect (HCE) in an open end pulsed capillary discharge (PCD) are presented. In the HCE axial electron beams emitted from a pre-breakdown plasma produced spontaneously in the hollow cathode region (HCR) assist ionization growth in the interelectrode volume. The PCD operates in argon at 0.6–1.4 Torr, ∼10 kV applied voltage. Time resolved spectroscopic measurements, with 15 ns time resolution, are used in conjunction with photomultiplier observations of light emission from the capillary ends, and Faraday cup measurements of axial electron beams, to characterize the pre- and post-breakdown processes in the HCR of the discharge. The HCR emission is found to be dominated by Ar II lines. Comparison between measured and synthetic spectra indicates that the pre-breakdown HCR plasma is characteristic of a collisional low pressure, low density plasma, whereas the post-breakdown HCR plasma, tens of nanoseconds after breakdown, is due to plasma ejection from the capillary volume. Experimental evidence of a zippering effect in post-breakdown capillary plasma heating, due to an initial axial pressure gradient, as predicted by computer simulations, has been found.

Capillary Plasma Electrode Discharge as an Intense and Efficient Source of Vacuum Ultraviolet Radiation for Plasma Display

The characteristic properties of microscale capillary plasma electrode structures were experimentally investigated and compared to the dielectric barrier discharge (DBD) structure. The vacuum ultraviolet (VUV) emission from the capillary plasma electrode discharges (CPEDs) was more intense and more efficient than the one from the DBD. Based on VUV emission characteristics, it is confirmed that the CPED-based plasma display could be a possible candidate to find the breakthrough in the luminance and luminous efficiency of plasma display.

Population Pharmacokinetics of Lumefantrine in Pregnant Women Treated with Artemether-Lumefantrine for Uncomplicated Plasmodium falciparum Malaria

Artemether-lumefantrine has become one of the most widely used antimalarial drugs in the world. The objective of this study was to determine the population pharmacokinetic properties of lumefantrine in pregnant women with uncomplicated multidrug-resistant Plasmodium falciparum malaria on the northwestern border of Thailand. Burmese and Karen women (n = 103) with P. falciparum malaria and in the second and third trimesters of pregnancy were treated with artemether-lumefantrine (80/480 mg) twice daily for 3 days. All patients provided five capillary plasma samples for drug quantification, and the collection times were randomly distributed over 14 days. The concentration-time profiles of lumefantrine were assessed by nonlinear mixed-effects modeling. The treatment failure rate (PCR-confirmed recrudescent infections at delivery) was high; 16.5% (95% confidence interval, 9.9 to 25.1). The population pharmacokinetics of lumefantrine were described well by a two-compartment open model with first-order absorption and elimination. The final model included interindividual variability in all pharmacokinetic parameters and a linear covariate relationship between the estimated gestational age and the central volume of distribution. A high proportion of all women (40%, 41/103) had day 7 capillary plasma concentrations of <355 ng/ml (which corresponds to approximately <280 ng/ml in venous plasma), a threshold previously associated with an increased risk of therapeutic failure in nonpregnant patients in this area. Predictive modeling suggests that a twice-daily regimen given for 5 days would be preferable in later pregnancy. In conclusion, altered pharmacokinetic properties of lumefantrine contribute to the high rates of failure of artemether-lumefantrine treatment in later pregnancy. Dose optimization is urgently needed.

Numerical Simulation of Capillary Convection with Encapsulated Phase-Change Particles

This study presents preliminary numerical simulations of forced convection with encapsulated phase-change material (EPCM) particles suspended in water, flowing through a square cross-section duct with top and bottom isoflux surfaces. The EPCM particles fit snugly in the channel, mimicking the flow of red blood cells and plasma in alveolar capillaries. Results for particles of different diameters show the snug fitting to yield enhanced heat transfer. The numerical results also seem to indicate the existence of an optimum number of particles for maximum heat transfer coefficient, a result of the interplay of flow circulation and heat transfer competition as the number of particles is changed in the channel.

Reduced red blood cell velocity in nail-fold capillaries as a sensitive and specific indicator of microcirculation injury in systemic sclerosis

To assess red blood cell velocity in finger nail-fold capillaries using video capillaroscopy in patients with SSc and other collagen diseases. This study included 127 patients with SSc as well as patients with SLE (n = 33), DM/PM (n = 21), RA (n = 13) and APS (n = 12), and 20 healthy subjects. Red blood cell velocity was evaluated using frame-to-frame determination of the position of capillary plasma gaps. The mean red blood cell velocity was significantly decreased in patients with SSc compared to healthy controls (63.0% reduction) and patients with other conditions. Mean blood velocity was similar between patients with dcSSc and lcSSc. Importantly, even SSc patients with normal or non-specific nail-fold video capillaroscopic (NVC) patterns or a scleroderma early NVC pattern exhibited a significantly lower red blood cell velocity compared to healthy controls (51.7 and 61.4% reduction, respectively) or patients with other conditions, despite normal or mild capillary changes. Patients with the scleroderma active and late NVC pattern showed a more decreased blood velocity (65.5 and 66.2% reduction, respectively). This reduced blood velocity was significantly associated with NVC findings, including capillary ramification and capillary loss. Although remarkably reduced velocity was observed in SSc patients with intractable digital ulcers (72.1% reduction), it was significantly improved by lipo-prostaglandin E(1) (lipo-PGE(1)) infusion. Our results suggest that reduced blood velocity is a hallmark of SSc. Furthermore, measurement of red blood cell velocity may be useful in evaluating therapeutic effects on microcirculation.

Development of a dielectric-barrier discharge enhanced microplasma jet

A low-power ultrahigh-frequency-driven inductively coupled microplasma (ICMP) source equipped with dielectric-barrier discharge (DBD) was developed to realize a low-temperature and high-density plasma in fine quartz capillaries with inner diameters of less than 1.0 mm. A stable plasma was generated and its sustainability was independent of the gas flow rate. This plasma jet had a longer plume than that of a thermoelectron-enhanced microplasma jet, and time-resolved characterization suggested interactions between ICMP and DBD jets. By optical emission spectroscopy characterization, the gas temperature and electron density inside a capillary were estimated to be 400–1000 K and 1013–1014 cm−3, respectively.

Independent two-photon measurements of albumin GSC give low values

Independent two-photon measurements of albumin GSC give low values

Progress on laser plasma accelerator development using transversely and longitudinally shaped plasmas

A summary of progress at Lawrence Berkeley National Laboratory is given on: (1) experiments on down-ramp injection; (2) experiments on acceleration in capillary discharge plasma channels; and (3) simulations of a staged laser wakefield accelerator (LWFA). Control of trapping in a LWFA using plasma density down-ramps produced electron bunches with absolute longitudinal and transverse momentum spreads more than ten times lower than in previous experiments (0.17 and 0.02 MeV/c FWHM, respectively) and with central momenta of 0.76±0.02MeV/c, stable over a week of operation. Experiments were also carried out using a 40 TW laser interacting with a hydrogen-filled capillary discharge waveguide. For a 15 mm long, 200 μm diameter capillary, quasi-monoenergetic bunches up to 300 MeV were observed. By detuning discharge delay from optimum guiding performance, self-trapping was found to be stabilized. For a 33 mm long, 300 μm capillary, a parameter regime with high energy bunches, up to 1 GeV, was found. In this regime, peak electron energy was correlated with the amount of trapped charge. Simulations show that bunches produced on a down-ramp and injected into a channel-guided LWFA can produce stable beams with 0.2 MeV/c-class momentum spread at high energies. To cite this article: W.P. Leemans et al., C. R. Physique 10 (2009). On présente un résumé des progrès obtenus au Lawrence Berkeley National Laboratory sur : (1) les expériences sur l'injection dans une rampe de densité décroissante ; (2) les expériences sur l'accélération dans des canaux de plasmas de décharges capillaires ; et (3) les simulations d'accélérateur par champ de sillage laser (LWFA) en configuration multi-étages. Le contrôle du piégeage dans un LWFA à l'aide de rampes de densité décroissante produit des paquets d'électrons avec des dispersions de moment cinétique longitudinal et transversal plus de dix fois plus faibles que dans des expériences antérieures (respectivement 0,17 and 0,02 MeV/c FWHM) avec une valeur centrale de 0,76±0,02MeV/c, stable sur la durée de la semaine d'expérience. Des expériences ont également été faites à l'aide d'un laser de 40 TW interagissant avec un guide d'onde constitué par une décharge capillaire d'hydrogène. Pour un capillaire de longueur 15 mm et de diamètre 200 μm, des électrons quasi-monoénergétiques atteignant 300 MeV ont été observés. En jouant sur le délai du temps d'allumage de la décharge et en s'écartant ainsi des performances optimales de guidage, l'auto piégeage a pu être stabilisé. Pour un capillaire de longueur 33 mm et de diamètre 300 μm, un régime de paramètres avec des électrons atteignant 1 GeV a été trouvé. Dans ce régime, l'énergie maximum des électrons a été corrélée avec la quantité d'électrons piégés. Les simulations ont montré que des paquets d'électrons produits dans une rampe de densité décroissante et injectés dans un guide dans un LWFA peuvent constituer des faisceaux stables de haute énergie avec des dispersions en moment de l'ordre de 0,2 MeV/c. Pour citer cet article : W.P. Leemans et al., C. R. Physique 10 (2009).

Effect of laser ablation on the mechanical impulse formation in capillary discharge plasma

Within studies on the creation of new types of engines for small-sized space vehicles, we have experimentally studied the effect of the laser ablation of an electrode (insulator) material on the mechanical impulse of capillary discharge plasma. It is demonstrated that laser pulses can be used to reliably initiate of lowvoltage capillary discharge at low pressures, that is, under conditions where the usual discharge initiation is complicated. The proposed combined scheme allows the weight and size characteristics of plasma thrusters operating in pulsed and pulse-train regimes to be reduced.

Capillary Discharge XUV Radiation Source

A device producing Z-pinching plasma as a source of XUV radiation is described. Here a ceramic capacitor bank pulse-charged up to 100 kV is discharged through a pre-ionized gas-filled ceramic tube 3.2 mm in diameter and 21 cm in length. The discharge current has amplitude of 20 kA and a rise-time of 65 ns. The apparatus will serve as experimental device for studying of capillary discharge plasma, for testing X-ray optics elements and for investigating the interaction of water-window radiation with biological samples. After optimization it will be able to produce 46.9 nm laser radiation with collision pumped Ne-like argon ions active medium.

Electrothermal-Chemical Ignition Research on 120-mm Gun in Korea

Electrothermal-chemical (ETC) propulsion with the control of a combustion process yet requires large electrical energies for an appreciable effect. Referring to the changed tendency of focusing ETC researches on the early ignition phase, the Agency for Defense Development (ADD), Korea, has been studying an electrothermal ignition for a 120-mm gun using a capillary plasma injector. Under the condition of a limited capillary geometry, design efforts with various liner materials have been done to achieve robust capillary discharges capable of transferring energies around 100 kJ. Electrical properties were estimated with the help of plasma theories and compared with experimental results. Experiments using a closed vessel and a gun-chamber simulator have been done to investigate the burning behaviors and the early phase of an electrothermal ignition, respectively. The closed vessel was designed for both a plasma and a conventional ignition. The burning rates could be obtained up to 70 MPa. The gun-chamber simulator was designed in the shape of the chamber of a 120-mm gun except for an acrylic chamber wall withstanding up to 30 MPa. Through prior tests using the closed vessel and the gun-chamber simulator, appropriate electrical energies and propellant have been selected. Firings of the full-scale 120-mm gun have been done using JA2 propellant. Electrical pulses of 1-2.5-ms duration in the energy from 20 to 120 kJ were applied. Aside from ignition capability, the results showed a possibility of a control on the peak pressure. Currently, ADD, Korea, continues the research to enhance the efficiency of the plasma injector, to compact the pulse forming network, and to investigate the electrothermal ignition properties of LOVA propellant.

Numerical Parametric Study of the Capillary Plasma Source for Electrothermal–Chemical Guns

This work expands upon previous research into developing a numerical model of a capillary plasma source for application to electrothermal chemical guns. The capillary model is comprised of a kinetic model simulating polyethylene ablation coupled to a one dimensional time-dependent hydrodynamic model to determine the capillary outflow parameters. As input the simulation requires the capillary internal radius, length, and applied electrical current. Previous work found that best agreement with experimentally measured ablated mass could be achieved with the application of a backflux parameter, representing the percentage of the ablated material that was allowed to return to the polyethylene surface and form a film. Using the model, a parameter study is conducted to determine the effects that varying the peak electrical current, internal capillary radius and backflux parameter have on the plasma temperature, peak outflow pressure, and total ablated mass. A sinusoidal electrical current is assumed in the present work, with the peak current and discharge time taken over a range typically encountered in electrothermal chemical gun application. Analysis of the dependence of total ablated mass and peak capillary pressure on the deposited electrical energy yield insight into non- linearities in the capillary energy equation.

Progress Towards an End-to-End Model of an Electrothermal Chemical Gun

Much progress has been made in the last few years toward the development of an end-to-end computer model of an electrothermal chemical gun. Phenomena that must be considered in an electrothermal chemical gun model include the initial capillary plasma properties, the plasma-air interaction, plasma sheath effects, and the plasma-propellant interaction itself. This paper presents an overview of recent progress made modeling these various phenomena. Also discussed are methods under consideration to incorporate surface chemistry effects into the plasma-propellant interaction model.

Determination of the charge of the plasma proteins and consequent Donnan equilibrium across the capillary barriers in the rat microvasculature

Due to the negatively charged proteins in plasma, a Donnan equilibrium will be formed between plasma and interstitium or, as in the glomerulus, between glomerular plasma and Bowman's space. The phenomenon is of great physiological significance in the sense that the electro-osmotic pressure offered by the small ions attracted to the proteins may account for an important part of the total colloid osmotic pressure and also as the electric potential consequent to the Donnan distribution will affect the transcapillary transport of all charged molecular compounds. The present study aimed at estimating the protein charge in rat plasma in order to validate its importance for colloid osmotic pressure and potential. The charge of the plasma proteins was determined in vitro from the concentration of sodium across a cellophane membrane separating a rat plasma sample from saline alone. However, in order to improve the sensitivity of the method, the studies were carried out at an ionic strength of 1/10 of physiological saline. The average charge of plasma was estimated at 0.23 +/- 0.003 mEq g(-1) protein (mean +/- SE), and the standard variation at +/-0.01 mEq g(-1), i.e. about 5%. At the normal protein concentration in Wistar rats of 50 g L(-1), the charge of the proteins in systemic plasma was calculated to be 11.5 mEq L(-1), whereas in glomerular and peritubular capillary plasma, the larger protein concentration increases the protein charge to 14.4 mEq L(-1). The results verify that the plasma protein charge accounts for about one-third of the total colloid osmotic pressure and that the obtained potential will constitute a major driving force for the transport of charged molecular compounds.

Does HbA1C predict isolated impaired fasting glycaemia in the oral glucose tolerance test in subjects with impaired fasting glycaemia?

To assess the usefulness of erythrocyte glycated haemoglobin (HbA1C) as a screening tool to identify those subjects with impaired fasting glycaemia (IFG) who do not have impaired glucose tolerance (IGT) or diabetes mellitus (DM) on a 75 g oral glucose tolerance test (OGTT). Design and methods All subjects undergoing an OGTT had HbA1C measured at baseline. Receiver operator characteristics analysis was used to identify optimal HbA1C cut-off values for diagnosing and excluding IGT and DM. We studied 140 subjects (69 women) with IFG (fasting capillary plasma glucose between 6.1-6.9 mmol/L). Using World Health Organisation criteria, 27 had isolated IFG, 56 had IGT and 57 had DM. HbA1C was higher (P < 0.001) in patients with DM (6.8 +/- 0.93%) when compared with those with IGT (6.3 +/- 0.68%) and isolated IFG (6.2 +/- 0.30%), but HbA1C was similar in those with IGT and isolated IFG. There was no HbA1C cut-off value differentiating isolated IFG from IGT or DM. None of the subjects with isolated IFG had HbA1C concentration of >6.8%, but 76% and 54% subjects with IGT and DM, respectively, had HbA1C of < or =6.8%. HbA1C measurement is of limited value in differentiating isolated IFG, IGT and DM in subjects with IFG. It cannot be used to identify which subjects with IFG do not require an OGTT.

Determination of Free Calcium and Calcium-Containing Species in Human Plasma by Capillary Electrophoresis-Inductively Coupled Plasma Optical Emission Spectrometry

A new method for the determination of free calcium concentration in human plasma was developed by online coupling capillary electrophoresis (CE) with inductively coupled plasma optical emission spectrometry (ICP-OES). Baseline separation of calcium-containing species was achieved by CE-ICP-OES in a 120-cm-long capillary with 100-microm internal diameter, at 20 kV applied voltage, with a 30 mmol/L Tris-HCl buffer at pH 7.4. A total of eight calcium-containing species were found in human plasma; the concentration of free calcium ion was found to be 41.9 mg/L. The concentrations of calcium for other seven calcium species, estimated from the calibration against Ca(2+) standard, were 3.14-15.6 mg/L. The precision (RSD, n = 10) ranged from 1.2 to 2.7% for the migration time and 2.8 to 3.9% for the peak area. The developed method was also applied to analyze plasma samples with recovery ranged from 94.5 to 102% for samples spiked with 40 mg/L free Ca(2+) ion.

Experimental observations in compact capillary discharges

We present experimental results on the characterization of a non-ablating fast pulsed capillary discharge, with a hollow cathode (HC) geometry, operating in argon below 1 Torr. Both the pre-breakdown and breakdown phase of the discharge are investigated with several diagnostics, which include electron beam monitoring, capacitive probe array and extreme ultraviolet (EUV) detector array. The pre-breakdown phase is found to be characterized by the emission of HC electron beams, which assist the propagation of a high speed ionization wave, with typical velocity in the 106–107 m s−1. Coinciding with electric breakdown a fast EUV radiation pulse is emitted. The leading edge of the radiation pulse is due to beam target emission by the HC electron beams. At the breakdown the radiation emission is mainly centered in the 5–15 nm spectral window, and is emitted from a capillary plasma which is being heated by a kiloampere level, 10 ns half-width current pulse.