Plasma Fluctuations Research Articles

Single- and Multiple-Dose Pharmacokinetics and Pharmacodynamics of PN-943, a Gastrointestinal-Restricted Oral Peptide Antagonist of α4β7, in Healthy Volunteers.

PN‐943 is an orally stable, gastrointestinal‐restricted peptide that binds specifically to α4ß7 integrin on leukocytes, blocking leukocyte trafficking to and activation in the gut, inhibiting colon inflammation and reducing signs and symptoms of active ulcerative colitis. Two pharmacokinetic/pharmacodynamic studies were conducted in healthy volunteers. Study 1 was a first‐in‐human study with 40 male subjects receiving PN‐943, 100 to 1400 mg or placebo, as single doses and 57 male subjects receiving PN‐943, 100 to 1000 mg or placebo, as multiple doses. Study 2 was a randomized, crossover study comparing multiple doses of 450‐mg PN‐943 twice daily as a liquid solution and as an immediate‐release tablet in 10 subjects. No subjects discontinued due to treatment‐emergent adverse events. Consistent with the gastrointestinal‐restricted nature of the peptide, systemic exposure was minimal; there was an approximate dose‐proportional increase in area under the plasma concentration–time curve. There was minimal accumulation with once‐daily dosing and an absence of time‐dependent changes in pharmacokinetics. Administration of PN‐943 after a high‐fat meal reduced peak plasma concentration and area under the plasma concentration–time curve. There was minimal (<0.1%) urinary excretion of intact drug, and there was a dose‐related increase in fecal excretion of intact PN‐943. Dose‐dependent increases in blood receptor occupancy and reduction in blood receptor expression were observed, supporting target engagement. Twice‐daily dosing resulted in sustained receptor occupancy with low plasma fluctuations (143%). PN‐943 was generally well tolerated following single and multiple oral doses with low systemic exposure. Twice‐daily dosing resulted in sustained pharmacokinetics and pharmacodynamics, supporting further investigation in efficacy studies.

Ionospheric Plasma Fluctuations Induced by the NWC Very Low Frequency Signal Transmitter

AbstractThe Australian NWC (North West Cape) signal transmitter is known to strongly interfere with the topside ionosphere. We analyze 456 conjunctions between Swarm A, B and NWC, in addition to 58 conjunctions between NorSat‐1 and NWC. The in‐situ measurements provided by these satellites include the 16 Hz Swarm Advanced Plasma Density data set, and the novel 1,000 Hz plasma density measurements from the m‐NLP system aboard NorSat‐1. We subject the data to a detailed PSD analysis and subsequent superposed epoch analysis. This allows us to present comprehensive statistics of the NWC‐induced plasma fluctuations, both their scale‐dependency, and their climatology. The result should be seen in the context of VLF signal transmitter‐induced plasma density fluctuations, where we find counter‐evidence for the existence of turbulent structuring induced by the NWC transmitter.

Subluminal electrostatic noise in isotropic space plasmas. General formulas and nonrelativistic thermal limit

The properties of the collective subluminal electrostatic fluctuations in isotropic plasmas are investigated using the covariant kinetic theory of linear fluctuations based on the correct momentum–velocity relation. The covariant theory correctly accounts for the differences in subluminal and superluminal fluctuations in contrast to the non-covariant theory. The general formalism developed here is valid in unmagnetized plasmas and in magnetized plasmas for wavevectors of electrostatic waves parallel to the direction of the uniform magnetic field. Of particular interest are potential differences between the covariant and the non-covariant approach and the consequences of these differences in modifying observational predictions. For thermal particle distributions of protons and electrons with nonrelativistic equal temperatures, the covariant and non-covariant theories yield exactly the same dispersion function and relation for weakly damped electrostatic waves. Also, the quasi-equilibrium wavenumber spectrum of collective thermal electrostatic noise agrees in both theories apart from the important wavenumber restriction |k|&amp;gt;kc=ωp,e/c. While the non-covariant analysis also yields eigenmode fluctuations at small wavenumbers with superluminal phase speeds, the correct covariant analysis indicates that subluminal electrostatic fluctuations are only generated at wavenumbers |k|&amp;gt;kc by spontaneous emission of the plasma particles. As a consequence, the nonrelativistic thermal electrostatic noise wavenumber spectrum is limited to the wavenumber range ωp,e≤|k|≤kmax. Within a linear fluctuation theory, superluminal electrostatic noise cannot be generated.

Self-adaptive diagnostic of radial fast-ion loss measurements on the ASDEX Upgrade tokamak (invited).

A poloidal array of scintillator-based Fast-Ion Loss Detectors (FILDs) has been installed in the ASDEX Upgrade (AUG) tokamak. While all AUG FILD systems are mounted on reciprocating arms driven externally by servomotors, the reciprocating system of the FILD probe located just below the midplane is based on a magnetic coil that is energized in real-time by the AUG discharge control system. This novel reciprocating system allows, for the first time, real-time control of the FILD position including infrared measurements of its probe head temperature to avoid overheating. This considerably expands the diagnostic operational window, enabling unprecedented radial measurements of fast-ion losses. Fast collimator-slit sweeping (up to 0.2 mm/ms) is used to obtain radially resolved velocity-space measurements along 8cm within the scrape-off layer. This provides a direct evaluation of the neutral beam deposition profiles via first-orbit losses. Moreover, the light-ion beam probe (LIBP) technique is used to infer radial profiles of fast-ion orbit deflection. This radial-LIBP technique is applied to trapped orbits (exploring both the plasma core and the FILD stroke near the wall), enabling radial localization of internal plasma fluctuations (neoclassical tearing modes). This is quantitatively compared against electron cyclotron emission measurements, showing excellent agreement. For the first time, radial profiles of fast-ion losses in MHD quiescent plasmas as well as in the presence of magnetic islands and edge localized modes are presented.

Quiescent regions below the X-point in ASDEX upgrade

Probe measurements of plasma fluctuations in the divertor region of ASDEX Upgrade reveal the existence of two quiescent regions close to the separatrix: one on the low field side scrape-off layer and one on the high field side of the private flux region. The X-point manipulator at ASDEX Upgrade provides the unique possibility of obtaining continuous measurements of the ion-saturation current from the low field side scrape-off layer through the private flux region and into the high field side scrape-off layer.

On the Origin of High–Frequency Magnetic Fluctuations in the Interplanetary Medium: A Brownian–like Approach

Low–frequency fluctuations in the interplanetary medium have been extensively investigated and described in the framework of turbulence, and the observed universal scaling behavior represents a clear signature of the underlying energy cascade. On the contrary, the interpretation of observations of plasma fluctuations at high frequencies, where wave–wave coupling, collisionless dissipation, and anomalous plasma heating play a key role, still represents a challenge for theoretical modeling. In this paper the high frequency fluctuations occurring in the interplanetary space are described through a Brownian–like approach, where the plasma dynamics at small scales is described through a stochastic process. It is shown that a simple model based on this framework is able to successfully reproduce the main features of the spectrum of the observed magnetic fluctuations. Moreover, the Fluctuation-Dissipation Relation, derived by our model, leads to a power law between dissipation rate and temperature, which is compatible with the occurrence of Landau damping, interpreted thus as the main mechanism of dissipation in the solar wind plasma.

Temporally and spatially resolved study of laser-induced plasma generated on coals with different volatile matter contents

Volatile matter content is one of the important characteristics of coal, which would inevitably influence the laser-coal interaction process. In this work, the coal samples with different volatile matter contents were carried out by laser induced breakdown spectroscopy (LIBS) in argon atmosphere. The temporal and spatial evolution of spectra was captured along with the plasma evolution to investigate the mechanism of the volatile matter effects. The results showed that the spectral emissions for the species that abundant in volatile matter were intense at the plasma front, which indicated that the volatile matter vaporized preferentially as laser irradiating and pushed toward the upper part of the plasma. The distribution characteristics of the atomic carbon emission and ionic calcium emission of different coals demonstrated that the amount of vaporization increased with the volatile content. The more abundant dissociated volatile matter in the plasma plume benefited the generation of molecular carbon (CN and C2) formed by several pathways, resulting in an enhancement on the corresponding emissions. Moreover, effects of volatile content on ablation process contributed to the difference in plasma structure and composition, which would be magnified during the plasma expansion and fluctuation process, contributing to greatly diverse plasma morphology and parameter distribution. Consequently, a conceptual laser-coal interaction model was proposed based on the comprehensive analysis of the measurements to describe the initiation and propagation of the effects of volatile matter on coal plasma.

A study of the electrical characteristics of a double plug probe aimed to the measurement of plasma fluctuations in a toroidal magnetized plasma.

We have analyzed the electrical characteristics of a plug probe as a function of the orientation relative to the local magnetic field. Our aim was to demonstrate that the probe characteristic, besides a better evaluation of the plasma potential, retains the capability to reliably estimate the electron temperature and density. This feature could be exploited with a multi-pin probe to measure simultaneously the fluctuations of all plasma parameters.

Development of the gas puffing imaging diagnostic on J-TEXT tokamak.

Edge turbulence is important for plasma confinement, so the gas puffing imaging (GPI) diagnostic was proposed on the J-TEXT tokamak for the two-dimensional measurement of turbulence in the edge region. GPI is a diagnostic of plasma turbulence that uses a puff of neutral gas at the plasma edge to increase the local visible light emission for improved space-time resolution of plasma fluctuations. Considering the conditions of J-TEXT, the observation area is 21° away from the position of the optical system in the toroidal direction, and the observation area is 10 cm × 10cm inside and outside the last closed flux surface. To have a lower divergence of the gas flow, the gas puff nozzle is specially designed. An interface has been developed for operation. To photograph the line radiation generated by the neutral gas cloud along the magnetic field lines, the optical system is designed. It is composed of a quartz glass, mirrors, commercial lenses, filters, and high-speed cameras. The high-speed camera can capture the line radiation with a speed up to 180 000 frames/s with 256 pixels × 256 pixels and an exposure time of 5 µs. In a recent experiment, the new GPI diagnostic has obtained some preliminary pictures.

Electric-field induced fluctuations in laser generated plasma plume

The effect of an external electric field on laser-generated plasma has been studied. It is observed that the laser-generated plasma can be used for the ignition of a spark in the presence of a low voltage external electric field. An eight-fold emission intensity enhancement in Cu I spectral lines are measured as compared to the signal intensity in the absence of an external electric field. The plasma parameters remain the same initially, up to a few microseconds after the generation of plasma, and this feature makes it more interesting for the quantitative analysis of any sample using laser induced breakdown spectroscopy (LIBS). In the presence of an external electric field, fluctuations (contraction and expansion) in the laser-generated plasma are observed which increase the plasma decay time and consequently result in enhanced signal intensity.

High β-Glucan Barley Improves Postprandial Hyperglycemia after Meal Loading in Patients with Type 2 Diabetes

Objective: We investigated whether barley with a high β-glucan content (7.2 g per 100 g) improves postprandial plasma glucose levels and fluctuations using a meal tolerance test and Continuous Glucose Monitoring (CGM) in patients with type 2 diabetes. Methods: A meal tolerance test (500 kcal) was conducted using two types of test meals: one with white rice (WR diet) and one with white rice mixed 1:1 with high β-glucan-containing barley (BR diet). Both meals included the same side dish. Plasma glucose changes over 180 minutes were compared after ingestion of the test meals. In addition, participants wore a CGM device for the 2 study days, to measure the daily variations in glucose levels when the WR or BR diet as staple food was provided 3 times a day with the same side dish in both meals. Results: Twenty-nine patients with type 2 diabetes (age 52.5 ± 15.1 years, BMI 27.5 ± 4.7 kg/m2, HbA1c 8.1 ±1.8 %) were included in this study. The incremental area under the curve of plasma glucose levels after BR diet ingestion was significantly lower than that after WR diet ingestion (7934.0 ± 4151.2 vs 9434.0 ± 4701.2 mg·min/dL). CGM showed a 24-hour standard deviation of blood glucose after the BR diet was significantly lower than that after the WR diet. Conclusion: These results suggest that postprandial plasma glucose elevation and fluctuation in patients with type 2 diabetes are suppressed by adding high-β-glucan barley to white rice in meals.

Sub-grid-scale effects in magnetised plasma turbulence

In the present paper, we use a coarse-graining approach to investigate the nonlinear redistribution of free energy in both position and scale space for weakly collisional magnetised plasma turbulence. For this purpose, we use high-resolution numerical simulations of gyrokinetic (GK) turbulence that span the proton–electron range of scales, in a straight magnetic guide field geometry. Accounting for the averaged effect of the particles’ fast gyro-motion on the slow plasma fluctuations, the GK approximation captures the dominant energy redistribution mechanisms in strongly magnetised plasma turbulence. Here, the GK system is coarse grained with respect to a cut-off scale, separating in real space the contributions to the nonlinear interactions from the coarse-grid scales and the sub-grid scales (SGS). We concentrate on the analysis of nonlinear SGS effects. Not only does this allow us to investigate the flux of free energy across the scales, but also to now analyse its spatial density. We find that the net value of scale flux is an order of magnitude smaller than both the positive and negative flux density contributions. The dependence of the results on the filter type is also analysed. Moreover, we investigate the advection of energy in position space. This rather novel approach for GK turbulence can help in the development of SGS models that account for advective unstable structures for space and fusion plasmas, and with the analysis of the turbulent transport saturation.

Test bench for calibration of magnetic field sensor prototypes for COMPASS-U tokamak

Magnetic field sensors are fundamental for control and physics exploitation of fusion devices. Their inductive nature implies high dynamic ranges and a broad bandwidth, thus a precise characterization and calibration of these probes is paramount. COMPASS-U will have a completely new set of magnetic diagnostics, from sensors to data acquisition. Sensors installed in-vessel will operate at 300–500 °C and should survive transients of even higher temperatures and thus materials used should be high-temperature compatible. These design limitations will have an impact on the dynamic range and bandwidth of the sensors, which needs to be reliably quantified, optimally with the same test bench for all sensor types. The first part of this work presents a test bench and the process of how to calibrate the effective area using a large solenoidal coil and frequency response of the magnetic sensor prototypes with a Helmholtz coil. In the second part, test results of the sensor prototypes are presented and discussed in detail. The low-bandwidth sensors made of mineral insulated cable (MIC), intended for plasma control and machine protection, show negligible attenuation up to 10 kHz, sufficient for their role. For fast coils consisting of bare wire wound on ceramic mandrel and Thick Printed Copper (TPC) sensors the negligible attenuation measured below 1 MHz is again sufficient for their intended purpose of detecting fast coherent plasma fluctuations. Resonances introduced by the capacitance of long cables from the vacuum vessel feedthroughs to the data acquisition systems are measured, to model their influence on the signal.

LOFAR Observations of a Jet-driven Piston Shock in the Low Solar Corona

Abstract The Sun produces highly dynamic and eruptive events that can drive shocks through the corona. These shocks can accelerate electrons, which result in plasma emission in the form of a type II radio burst. Despite the large number of type II radio burst observations, the precise origin of coronal shocks is still subject to investigation. Here, we present a well-observed solar eruptive event that occurred on 2015 October 16, focusing on a jet observed in the extreme ultraviolet by the Atmospheric Imaging Assembly (SDO/AIA), a streamer observed in white light by the Large Angle and Spectrometric Coronagraph (SOHO/LASCO), and a metric type II radio burst observed by the LOw Frequency Array (LOFAR). LOFAR interferometrically imaged the fundamental and harmonic sources of a type II radio burst and revealed that the sources did not appear to be cospatial, as would be expected from the plasma emission mechanism. We correct for the separation between the fundamental and harmonic using a model that accounts for scattering of radio waves by electron density fluctuations in a turbulent plasma. This allows us to show the type II radio sources were located ∼0.5R ⊙ above the jet and propagated at a speed of ∼1000 km s−1, which was significantly faster than the jet speed of ∼200 km s−1. This suggests that the type II burst was generated by a piston shock driven by the jet in the low corona.

A Gyrokinetic simulation model for low frequency electromagnetic fluctuations in magnetized plasmas

We present a new model for simulating the electromagnetic fluctuations with frequencies much lower than the ion cyclotron frequency in plasmas confined in general magnetic configurations. This novel model (termed as GK-E&B) employs nonlinear gyrokinetic equations formulated in terms of electromagnetic fields along with momentum balance equations for solving fields. It, thus, not only includes kinetic effects, such as wave-particle interaction and microscopic (ion Larmor radius scale) physics; but also is computationally more efficient than the conventional formulation described in terms of potentials. As a benchmark, we perform linear as well as nonlinear simulations of the kinetic Alfvén wave; demonstrating physics in agreement with the analytical theories.

The first observation of 4D tomography measurement of plasma structures and fluctuations

A tomography system is installed as one of the diagnostics of new age to examine the three-dimensional characteristics of structure and dynamics including fluctuations of a linear magnetized helicon plasma. The system is composed of three sets of tomography components located at different axial positions. Each tomography component can measure the two-dimensional emission profile over the entire cross-section of plasma at different axial positions in a sufficient temporal scale to detect the fluctuations. The four-dimensional measurement including time and space successfully obtains the following three results that have never been found without three-dimensional measurement: (1) in the production phase, the plasma front propagates from the antenna toward the end plate with an ion acoustic velocity. (2) In the steady state, the plasma emission profile is inhomogeneous, and decreases along the axial direction in the presence of the azimuthal asymmetry. Furthermore, (3) in the steady state, the fluctuations should originate from a particular axial position located downward from the helicon antenna.

High-Speed Video Analysis of the Process Stability in Plasma Spraying

In plasma spraying, instabilities and fluctuations of the plasma jet have a significant influence on the particle in-flight temperatures and velocities, thus affecting the coating properties. This work introduces a new method to analyze the stability of plasma jets using high-speed videography. An approach is presented, which digitally examines the images to determine the size of the plasma jet core. By correlating this jet size with the acquisition time, a time-dependent signal of the plasma jet size is generated. In order to evaluate the stability of the plasma jet, this signal is analyzed by calculating its coefficient of variation cv. The method is validated by measuring the known difference in stability between a single-cathode and a cascaded multi-cathode plasma generator. For this purpose, a design of experiment, covering a variety of parameters, is conducted. To identify the cause of the plasma jet fluctuations, the frequency spectra are obtained and subsequently interpreted by means of the fast Fourier transformation. To quantify the significance of the fluctuations on the particle in-flight properties, a new single numerical parameter is introduced. This parameter is based on the fraction of the time-dependent signal of the plasma jet in the relevant frequency range.

Harmonic Radio Emission in Randomly Inhomogeneous Plasma

Abstract In the present paper, we describe a theoretical model of the generation of harmonic emissions of type III solar radio bursts. The goal of our study is to fully take into account the most efficient physical processes involved in the generation of harmonic electromagnetic emission via nonlinear coupling of Langmuir waves in randomly inhomogeneous plasma of solar wind ( ). We revisit the conventional mechanism of coalescence of primarily generated and back-scattered Langmuir waves in quasihomogeneous plasma. Additionally, we propose and investigate another mechanism that generates harmonic emission only in a strongly inhomogeneous plasma: the nonlinear coupling of incident and reflected Langmuir waves inside localized regions with enhanced plasma density (clumps), in the close vicinity of the reflection point. Both mechanisms imply the presence of strong density fluctuations in plasma. We use the results of a probabilistic model of beam–plasma interaction and evaluate the efficiency of energy transfer from Langmuir waves to harmonic emission. We infer that harmonic emissions from a quasihomogeneous plasma are significantly more intense than found in previous studies. The efficiency of Langmuir wave conversion into electromagnetic harmonic emission is expected to be higher at large heliospheric distances for the mechanism operating in quasihomogeneous plasma and at small heliocentric distances for the one operating in inhomogeneous plasma. The evaluation of emission intensity in quasihomogeneous plasma may also be applied for type II solar radio bursts. The radiation pattern in both cases is quadrupolar, and we show that emission from density clumps may efficiently contribute to the visibility of harmonic radio emission.

Poloidally resolved measurements of the perpendicular propagation velocity of density fluctuations in ASDEX Upgrade L-mode plasmas

Poloidal asymmetries of the propagation velocity of density fluctuations perpendicular to the magnetic field measured with Doppler reflectometry have been reported in several magnetic confinement plasma devices. Careful analysis of a large variety of different low confinement mode plasma scenarios performed at the ASDEX Upgrade tokamak does not reveal such an asymmetry outside the uncertainties of the evaluation process of the measurement data. The perpendicular velocity is investigated between mid-radius and the plasma edge and follows the poloidal dependence of the E × B drift velocity regardless of the probed turbulence structure size. Compared to measurements of a charge exchange recombination spectroscopy diagnostic this points towards a significantly smaller phase velocity than the E × B drift velocity. The analysis technique is presented in a representative discharge together with a sensitivity study of the impact of density, magneto hydrodynamic equilibrium and diagnostic alignment on the interpretation of the measured Doppler shift using ray tracing and thus on poloidal asymmetries. Three more highly different plasma scenarios with poloidally symmetric velocity profiles are shown.

Development of a collective scattering system and its application to the measurement of multiscale fluctuations in KSTAR plasmas

A four-channel collective scattering system (CSS) has been developed to extend the current turbulence measurement capability (poloidal wavenumber 3 cm−1) beyond the ion gyroscale in the KSTAR tokamak. By utilizing a 300 GHz probe beam and four-channel detector array, the CSS can measure electron density fluctuations of four distinct poloidal wavenumbers from 14 to 26 cm−1 at a high sampling rate (typically 10 MS s−1). In between discharges the radial measurement location can be varied from the plasma center to the outer edge with the remote control of the optical system. In this paper, the details of the major components and laboratory evaluation of the optical system are described. Several initial measurements such as (1) the broadband turbulence reduction during L–H transition, (2) the broadband turbulence increase in H-mode when the amplitude of edge-localized mode crashes is reduced by increased density, (3) the amplification of a quasi-coherent mode by additional heating in high-performance H-mode, and (4) the appearance of high-frequency magnetohydro-dynamical modes during slow L–H transition, are briefly presented. The possibility of the CSS as a hybrid system (of a scattering system and fluctuation interferometer), which complicates the interpretation of the CSS data, is also discussed.