Unstable Plasma Research Articles

Measurements of the imploding plasma sheath in triple-nozzle gas-puff z pinches

Gas-puff z-pinch implosions are characterized by the formation of a dense annular plasma shell, the sheath, that is driven to the axis by magnetic forces and therefore subject to the magneto-Rayleigh–Taylor instability. Here, the conditions within these sheaths are measured on the 1-MA COBRA generator at Cornell University [Greenly et al., Rev. Sci. Instrum. 79, 073501 (2008)] for various gas species and initial fill densities. The gas-puff loads are initialized by a 7 cm diameter triple-nozzle gas valve assembly with concentric outer and inner annular nozzles and a central gas jet. Thomson scattering and laser interferometry provide spatially resolved flow, temperature, and electron density profiles midway through the implosion, while extreme ultraviolet pinhole cameras record the evolution of the plasma column and photoconducting diodes measure x-ray emission. Analysis of the scattering spectra includes a means of discriminating between thermal and non-thermal broadening to test for the presence of hydrodynamic turbulence. Two types of sheath profiles are observed, those with sharp discontinuities at the leading edge and those with smooth gradients. In both cases, non-thermal broadening is generally peaked at the front of the sheath and exhibits a characteristic decay length that roughly scales with the sheath ion mean free path. We demonstrate that this non-thermal broadening term is inconsistent with laminar velocity gradients and is more consistent with dissipative turbulence driven by unstable plasma waves in a collisionless shock. The resulting differences in sheath profile are then set by the sheath ion collisionality in a manner consistent with recent 1D kinetic simulations [Angus et al., Phys. Plasmas 28, 010701 (2021)].

Experimental study of single- vs two-close-frequency heating impact on confinement and loss dynamics in ECR ion source plasmas by means of x-ray spectroscopy and imaging

We hereby report a study on confinement and electron loss dynamics in the magnetic trap of an electron cyclotron resonance ion source using a special multi-diagnostic setup that has allowed the simultaneous collection of plasma radio-self-emission and x-ray images in the range 500 eV–20 keV. Argon plasmas were generated in single- and two-close-frequency heating (SFH and TCFH) modes. Evidence of turbulent regimes has been found: for stable and unstable configurations quantitative characterizations of the plasma radio self-emission have been carried out, then compared with local measurements of plasma energy content evaluated by x-ray imaging. This imaging method is the only one able to clearly separate x-ray radiation coming from the plasma from that coming from the plasma chamber walls. X-ray imaging has also been supported and benchmarked by volumetric spectroscopy performed via silicon drift and high-purity germanium detectors. The obtained results in terms of x-ray intensity signal coming from the plasma core and from the plasma chamber walls permit the estimation of the average ratio: plasma vs. walls (i.e. plasma losses) as a function of input RF power and pumping wave frequency, showing an evident increase (above the experimental errors) of the intensity in the 2–20 keV energy range due to the plasma losses in the case of unstable plasma. This ratio was well correlated with the strength of the instabilities, in SFH operation mode; in TCFH mode, under specific power balance conditions and frequency combinations, it was possible to damp the instabilities, and thus the plasma losses were observed to decrease and a general reconfiguration of the spatial plasma structure occurred (the x-ray emission was more concentrated in the center of the plasma chamber). Finally, a simplified model was used to simulate electron heating under different pumping frequencies, prompting discussion of the impact of velocity anisotropy vs the onset of the instability, and the mechanism of particle diffusion in the velocity space in stable and unstable regimes.

Design of a high energy density experiment to measure the suppression of hydrodynamic instability in an applied magnetic field

A transverse magnetic field can suppress the hydrodynamic instability growth of an unstable plasma interface. This effect, of interest to inertial confinement fusion and astrophysics, has mostly been studied via simulation. Here, we present the design of an experiment at the National Ignition Facility (NIF) to demonstrate this effect in a laboratory. Simulations indicate that the timescale for the diffusion of the magnetic field across the mixing region should be at least comparable to the timescale of the instability growth in order to have a measurable suppression effect. This motivates the use of lower density target materials than usual high energy density (HED) hydrodynamics experiments to permit faster hydrodynamics and higher plasma conductivities (through higher temperature), for a given laser drive and magnetic field. We discuss a target design for creating a Rayleigh–Taylor unstable HED plasma interface that uses 320 mg/cc iodine-doped carbon foam as the heavy material, 20 mg/cc carbon foam as the light material, and a 6 μm amplitude, a 120 μm wavelength ripple machined at the interface, which shows a measurable suppression effect with a nominal NIF drive and a 30 T magnetic field (the present facility limit). Models indicate lower density foams that may display even larger suppression effects, as the Hohlraum drive also radiatively preheats the foam to permit even higher temperatures and, hence, higher conductivities.

Influence of axial mirror ratios on the kinetic instability threshold in electron cyclotron resonance ion source plasma

Electron Cyclotron Resonance (ECR) ion source plasmas are prone to kinetic instabilities. The onset of the instabilities manifests as emission of microwaves, bursts of electrons expelled from the plasma volume, and the collapse of the extracted highly charged ion (HCI) currents. Consequently, the instabilities limit the HCI performance of ECR ion sources by limiting the parameter space available for ion source optimization. Previous studies have shown that the transition from stable to unstable plasma regime is strongly influenced by the magnetic field structure, especially the minimum field value inside the magnetic trap (Bmin). This work focuses to study the role of the magnetic confinement on the onset of the kinetic instabilities by probing the influence of the injection and extraction mirror field variation on the instability threshold. The experiments have been performed with a room-temperature 14.5 GHz ECR ion source with an axially movable middle coil that provides flexible control over the axial field profile and especially the Bmin, which was used to quantify the variation in the instability threshold. The experimental results show that variation of the extraction field Bext, which defines the weakest magnetic mirror, correlates systematically with the variation of the instability threshold; decreasing the Bext allows higher threshold Bmin. The result demonstrates the importance of electron confinement and losses on the plasma stability. The connection between the weakest mirror field and the onset of instabilities is discussed taking into account the variation of magnetic field gradient and resonance plasma volume.

Experience Verification of 63 Cases of Liver Transplantation Anesthesia Management

Background: We reviewed the intraoperative management of previous liver transplantation (LT) cases to identify an optimal anesthetic method, which may affect patient outcomes and lead to faster postoperative recovery for future recipients. Methods: This single-center retrospective study reviewed 63 patients who underwent LT, including 51 living donor LT (LDLT), seven deceased donor LT (DDLT), and five simultaneous liver-kidney transplantation patients. We examined the patients’ backgrounds, intraoperative management (anesthetic method, water balance, and catecholamine dosage), and postoperative courses (hospitalization period, length of intensive care unit stay, renal function). Results: All patients received general anesthesia using inhalational anesthetics, either sevoflurane or desflurane, and both drugs were administered similarly. Rocuronium was administered at its usual dose despite liver failure. All patients undergoing preoperative dialysis due to acute kidney injury were successfully withdrawn from dialysis after surgery. The albumin infusion volume was 32% of the total infusion and transfusion volume. The five-year survival rate was 88% and graft failure occurred in one case. Conclusion: The anesthetic management of LT is currently conducted empirically in our institution, and we could not identify an optimal anesthetic method. However, we drew some conclusions. First, the use of human atrial natriuretic peptide as a drug infusion and appropriate transfusion management was expected to restore renal function. Second, the infusion volume of albumin was high. Third, the usual dose of rocuronium was required because excessive bleeding may cause unstable plasma drug concentration. Our results will be useful in future multi-institutional studies or meta-analyses and further improving the outcomes of future transplant recipients.

Stabilization of vertical plasma position in the PHiX tokamak with saddle coils

Saddle coils (SCs) are proposed as coils with a stabilizing effect of a vertical plasma position. This effect comes from an average magnetic field along a magnetic field line. Magnetic field line tracing was performed to investigate the structure and the quantitative values of the averaged magnetic field generated by SCs and toroidal magnetic field coils (TFCs). Experiments to stabilize the vertical position of the plasma were also carried out in a small tokamak device, PHiX. It was experimentally demonstrated that the averaged magnetic field generated with SCs and TFCs could stabilize the vertically unstable plasmas. In addition, three-dimensional equilibrium calculation using VMEC suggested that the plasmas were vertically elongated on the toroidal average when the vertical positions were stabilized by SCs. From the above results, it was shown that the non-axisymmetric magnetic fields generated by SCs could realize the plasmas with stable vertical position and an elongated cross-section.

Correlation of bremsstrahlung and energy distribution of escaping electrons to study the dynamics of magnetically confined plasma

A combination of electron and bremsstrahlung diagnostics was used to study the properties of the highly charged plasma of an electron cyclotron resonance ion source (ECRIS). The bremsstrahlung radiation in both axial and radial directions was correlated with the energy distribution of the electrons escaping axially from the confined plasma, i.e. the lost electron energy distribution (LEED), to achieve a more comprehensive view of the plasma. The evolution of the bremsstrahlung spectra and the LEED were determined as a function of the main operating parameters of the ion source. Also, the effects of the transition from a stable to an unstable plasma regime were determined for the bremsstrahlung and LEED changes in the shape of the measured LEED were found to correlate with changing bremsstrahlung spectral temperature. It was also found that the magnetic field has a strong impact on the axial and radial bremsstrahlung spectra and the LEED affecting the bremsstrahlung intensity, spectral temperatures and the LEED high energy local maximum. A comprehensive discussion is provided to explain the observed different behaviour of axial and radial bremsstrahlung emissions with varying magnetic field based on the directionality of plasma bremsstrahlung in ECRIS specific magnetic confinement scheme. Furthermore, it was observed that the onset of kinetic plasma instabilities has a clear impact on the shape of the LEED

Probes of the quark-gluon plasma and plasma instabilities

Penetrating probes in heavy-ion collisions, like jets and photons, are sensitive to the transport coefficients of the produced quark-gluon plasma, such as shear and bulk viscosity. Quantifying this sensitivity requires a detailed understanding of photon emission and jet-medium interaction in a nonequilibrium plasma during the hydrodynamic stages of heavy-ion collisions. Up to now, such an understanding has been hindered by plasma instabilities. These instabilities arise out of equilibrium and lead to spurious divergences when evaluating the rate of interaction of hard probes with the plasma. In this paper, we show that taking into account the time evolution of an unstable plasma cures these divergences. Specifically, we calculate the time evolution of gluon two-point correlators in a setup with a small initial momentum anisotropy and show that the gluon occupation density at first grows exponentially. Based on this calculation, we argue for a phenomenological prescription where instability poles are subtracted. Finally, we show that in the Abelian case instability fields do not affect medium-induced photon emission to our order of approximation.

Analytic quasi-steady evolution of marginally unstable kinetic plasma instabilities in the presence of drag and scattering

The 1D bump-on-tail problem is studied in order to determine the influence of drag on quasi-steady solutions near marginal stability (1−γd/γL≪1) when effective collisions are much larger than the instability growth rate (ν≫γ). In this common tokamak regime, it is rigorously shown that the paradigmatic Berk–Breizman cubic equation for the nonlinear mode evolution reduces to a much simpler differential equation, dubbed the time-local cubic equation, which can be solved directly. It is found that in addition to increasing the saturation amplitude, drag introduces a shift in the apparent oscillation frequency by modulating the saturated wave envelope. Excellent agreement is found between the analytic solution for the mode evolution and both the numerically integrated Berk–Breizman cubic equation and fully nonlinear 1D Vlasov simulations. Experimentally isolating the contribution of drag to the saturated mode amplitude for verification purposes is explored but complicated by the reality that the amount of drag cannot be varied independently of other key parameters in realistic scenarios. While the influence of drag is modest when the ratio of effective drag to effective scattering α/ν is very small, it can become substantial when α/ν≳0.5, suggesting that drag should be accounted for in quantitative models of fast-ion-driven instabilities in fusion plasmas.

The effect of the plasma density gradient on current filamentation instability

AbstractThe filamentation instability is one of the basic beam‐plasma instabilities that play a significant role in the energy deposition mechanism of the relativistic electrons generated by the laser‐plasma interaction in the fast ignition scenario. In this paper, the effect of the density gradient into plasma on the filamentation instability was investigated in the Weibel unstable plasma, where the plasma temperature anisotropy can play an important role. Results indicated that the density gradient enhances the instability growth rate so that decreasing the density gradient from the critical surface to the core of fuel leads to instability for longer regions in k space. Also, investigations in the region close to the critical surface showed that for decreasing the beam number density nb ≤ 0.01n0, the instability occurs for while this can be different for higher values. Increasing the beam relativistic factor causes a decreasing peak of instability growth rate because of a reduction in beam current, whereas the initial thermal spread of plasma amplifies the filamentation instability.

Design of an edge tapered 915 MHz/TM021 microwave plasma reactor by numerical analysis

Microwave plasma reactor is often of particular interest due to their wide range of industrial applications, especially in high-end manufacturing. However, there exist problems of unstable plasma and small discharge area in conventional microwave reactors at 2.45 GHz. An edge tapered 915 MHz/TM021 microwave reactor evolved from reactors at 2.45 GHz is presented to improve the strength, area, and uniformity of microwave field for plasma applications. An electromagnetic model of a microwave reactor with the new coupling antenna composed of a tapered platform and a coaxial inner conductor is simulated. The simulation results show that the electric field strength in the new reactor with a size optimized coupling structure is more concentrated compared to similar reactors. A 2D axisymmetric hydrogen plasma discharge model based on self-consistent fluid simulation of this new reactor is presented. The obtained results show that this kind of model can lead to a better understanding of the physical processes occurring in these kinds of microwave reactors.

Mirror Instabilities in the Inner Magnetosphere and Their Potential for Localized ULF Wave Generation.

Results from the NASA Van Allen Probes mission indicate extensive observations of mirror/drift‐mirror (M/D‐M hereafter) unstable plasma regions in the night‐side inner magnetosphere. Said plasmas lie on the threshold between the kinetic and frozen‐in plasma regimes and have favorable conditions for the formation of M/D‐M modes and subsequent ultralow frequency (ULF) wave signatures in the surrounding plasma. We present the results of a climatological analysis of plasma‐γ (anisotropy measure) and total plasma‐β (ratio of particle to magnetic field pressure) in regard to the satisfaction of instability conditions on said M/D‐M modes under bi‐Maxwellian distribution assumption, and ascertain the most likely region for such plasmas to occur. Our results indicate a strong preference for the premidnight sector of the night‐side magnetosphere, with events ranging in time scales from half a minute (roughly 200 km in scale size) to several hours (multiple Earth radii). The statistical distribution of these plasma regions explicitly identifies the source region of “storm time Pc5 ULF waves” and suggests an alternative mechanism for their generation in the night‐side inner magnetosphere.

Measurement of electron density in transient spark discharge by simple interferometry

In this work, the electron density in an atmospheric-pressure Ar transient spark (TS) discharge was measured using an interferometric method. The discharge was operated in a pin-to-plate electrode configuration by applying DC voltages of 7–10 kV. The TS discharge current occurred within a short duration of less than 100 ns, and the peak current was as high as ~ 3 A. Below 8 kV, the TS discharge had weak, irregular emission, making it difficult to measure the electron density using Stark broadening. Here, we developed a simple He–Ne laser Michelson interferogram method for estimating the electron density of unstable TS discharge. Above 8 kV, the electron density values obtained from Stark broadening and the Michelson interferogram were similar and proportional to the dissipated energy. This interferogram method could be adopted to measure the electron density of unstable discharge plasmas, which was measured to be 1 × 1016 cm−3 at 7.0 kV in this experiment.

Redistribution of energy in a viscous heat-conductive medium during the interaction of a shock wave with a temperature layered plasma region

Experimental data on the creation of ionization unstable gas discharge plasma with large-scaled and small-scaled ionisation strata are presented. The redistribution of kinetic and internal energy between a stratified energy source and the area behind a shock wave is numerically studied on the base of the system of Navier-Stokes equations. Generation of the Richtmyer-Meshkov instabilities at many points is obtained which bend the shock wave front and, in some cases, completely destroy it (in density fields). The influence of heat conductivity on the obtained flow structures has been studied. For viscous heat conducting medium it was established the possibility to obtain local high energy zones behind the shock wave with values of energies several times higher than those for a non-stratified energy source with the same total energy. The values of energies in these zones were shown to be possibly controlled via the rarefaction parameter/temperature of a gas in the layers of a stratified energy source or by its geometry.

Repeatability improvement in laser induced plasma emission of particle flow by aberration-diminished focusing

Laser-induced breakdown spectroscopy (LIBS) analysis of particle flow is limited by plasma emission fluctuation due to unstable plasma excitation. The present work established two focusing configurations with different spherical aberration. Plasma emission characteristics and plasma morphology was investigated and compared. The results indicated that aberration-diminished focusing was good for laser-particle coupling. At the optimal lens-to-sample distance, the relative standard deviation (RSD, %) of plasma area decreased from 41.15% to 29.18%, the standard deviation of plasma position decreased from 1.84 mm to 1.25 mm. Based on the stabilization of plasma morphology, the signal RSD decreased from 15.85% to 8.24%. Furthermore, the laser-particle coupling under different focusing configuration was discussed in details. Aberration-diminished focusing shrunk the focal region along the beam path, leading to less fluctuated plasma position. Based on the feasibility of aberration-diminished focusing, it was applied to surface-stabilized LIBS scheme to establish an integrated scheme to stabilize LIBS analysis of particle flow. The signal RSD achieved by the integrated scheme is 4.60%, which was comparable to the signal repeatability in LIBS analysis of other solid sample forms.

Mechanism of signal uncertainty generation for laser-induced breakdown spectroscopy

Relatively large measurement uncertainty severely hindered wide application for laser-induced breakdown spectroscopy (LIBS), therefore it is of great importance to understand the mechanism of signal uncertainty generation, including initiation and propagation. It has been found that the fluctuation of plasma morphology was the main reason for signal uncertainty. However, it still remains unclear what mechanism leads to laser-induced plasma morphology fluctuation. In the present work, we employed three fast-imaging cameras to capture three successive plasma images from a same laser-induced Titanium alloy plasma, which enables us to understand more clearly of the plasma evolution process especially for the early plasma evolution stage when plasma and surrounding gases interact drastically. Seen from the images, the plasma experienced an increasing morphological fluctuation as delay time increased, transforming from a “stable plasma” before the delay time of 100 ns to a “fluctuating plasma” after the delay time of 300 ns. Notably, the frontier part of plasma showed a significant downward motion from the delay time of 150 ns to 200 ns and crashed with the lower part of the plasma, making the plasma flatter and later even splitting the plasma into two parts, which was considered as a critical process for the transformation of “stable plasma” to “unstable plasma”. By calculating the correlation coefficient of plasma image pairs at successive delay times, it was found that the higher the similarity between two plasma at early stage, the more similar at later stage; this implied that the tiny plasma fluctuation earlier than the critical delay time (150–200 ns) was amplified, causing a large plasma fluctuation at the later stage as well as LIBS measurement uncertainty. The initiation of slight fluctuation was linked with Rayleigh-Taylor Instability (RTI) due to the drastic material interpenetration at the plasma-ambient gas interface at earlier stage (before 50 ns). That is, the uncertainty generation of LIBS was proposed as: plasma morphology fluctuation was inevitably trigged by RTI at the early stage and the tiny fluctuation was amplified by the back pressed downward process of plasma frontier material, leading to severe morphology fluctuation as well as LIBS signal uncertainty.

Rotating ion beam effects on temperature gradient instability in completely ionized plasmas.

The aim of this paper is to investigate the effects of a rotating ion beam on the temperature gradient instability (TGI) in completely ionized plasmas. The interplay of the temperature and density gradients provides the basis for experiencing an unstable inhomogeneous plasma medium due to TGI taken under consideration. The density and temperature gradients are considered perpendicular to the magnetic field where a nonrelativistic rotating ion beam such as O^{+} is present. By implementing the kinetic theory together with a zeroth-order approximation of geometrical optics, the dielectric permittivity tensor of the inhomogeneous plasma is obtained where by a suitable linear eikonal equation, the growth rate of the TGI in the collisional regime is calculated in the presence of a rotating ion beam. In such a configuration an unstable condition is experienced in regions with opposite electron density and temperature gradients, where it is destabilized by the temperature and plasma density gradients and the frequent electron collisions. As a consequence, the results reveal that the TGI can be damped or modified through interaction with the rotating ion beam depending on the characteristics of the ion beam, namely, velocity and density.

Molecularly Imprinted Polymers Doped with Carbon Nanotube with Aid of Metal-Organic Gel for Drug Delivery Systems.

The incidence of breast cancer worldwide has been on the rise since the late 1970s, and it has become a common tumor that threatens women's health. Aminoglutethimide (AG) is a common treatment of breast cancer. However, current treatments require frequent dosing that results in unstable plasma concentration and low bioavailability, risking serious adverse reactions. Our goal was to develop a molecularly imprinted polymer (MIP) based delivery system to control the release of AG and demonstrate the availability of this drug delivery system (DDS), which was doped with carbon nanotube with aid of metal-organic gel. Preparation of MIP was optimized by key factors including composition of formula, ratio of monomers and drug loading concentration. By using multi-walled carbon nanotubes (MWCNT) and metal-organic gels (MOGs), MIP doubled the specific surface area, pore volume tripled and the IF was 1.6 times than the reference. Compared with commercial tablets, the relative bioavailability was 143.3% and a more stable release appeared. The results highlight the influence of MWCNT and MOGs on MIP, which has great potential as a DDS.

Spatial channeling in toroidal plasmas: overview and new results

Energy and momentum transfer by eigenmodes in tokamaks and stellarators, which arises when eigenmodes are destabilized by superthermal ions in a region that does not coincide with the damping region, is considered. This phenomenon, named spatial channeling (SC), may play an important role in toroidal plasmas. It may affect plasma energy confinement, plasma rotation, heating of the electron and ion components, and features of eigenmodes. The work contains both an overview and new results. In particular, it is found that SC may affect structure of Toroidicity-induced Alfvén Eigenmodes (TAE modes); the analysis is carried out for a low-mode-number TAE. It is concluded that high-frequency modes, with frequencies above and around the ion cyclotron frequency (fast magnetoacoustic modes and Alfvén modes), are more likely to affect plasma energy balance for reasonable values of mode amplitudes than low-frequency Alfvén modes. SC can also have strong influence on sheared rotation for reasonable values of mode amplitudes, and this effect does not depend on mode frequency. The overview is restricted to modes naturally occurring in unstable plasmas.

Peeling-ballooning stability of tokamak plasmas with applied 3D magnetic fields

The poloidal harmonics of the toroidal normal modes of an unstable axisymmetric tokamak plasma are employed as basis functions for the minimisation of the 3D energy functional. This approach presents a natural extension of the perturbative method considered in Anastopoulos Tzanis et al (2019 Nucl. Fusion 59 126028). This variational formulation is applied to the stability of tokamak plasmas subject to external non-axisymmetric magnetic fields. A comparison of the variational and perturbative methods shows that for D-shaped, high βN plasmas, the coupling of normal modes becomes strong at experimentally relevant applied 3D fields, leading to violation of the assumptions that justify a perturbative analysis. The variational analysis employed here addresses strong coupling, minimising energy with respect to both toroidal and poloidal Fourier coefficients. In general, it is observed that ballooning unstable modes are further destabilised by the applied 3D fields and field-aligned localisation of the perturbation takes place, as local ballooning theory suggests. For D-shaped high βN plasmas, relevant to experimental cases, it is observed that the existence of intermediate n unstable peeling-ballooning modes, where a maximum in the growth rate spectrum typically occurs, leads to a destabilising synergistic coupling that strongly degrades the stability of the 3D system.