Plasma Lifetime Research Articles

Multiaperture ion beam extraction from gas-dynamic electron cyclotron resonance source of multicharged ions

Electron cyclotron resonance ion source with quasi-gas-dynamic regime of plasma confinement (ReGIS), constructed at the Institute of Applied Physics, Russia, provides opportunities for extracting intense and high-brightness multicharged ion beams. Despite the short plasma lifetime in a magnetic trap of a ReGIS, the degree of multiple ionization may be significantly enhanced by the increase in power and frequency of the applied microwave radiation. The present work is focused on studying the intense beam quality of this source by the pepper-pot method. A single beamlet emittance measured by the pepper-pot method was found to be approximately 70 pi mm mrad, and the total extracted beam current obtained at 14 kV extraction voltage was approximately 25 mA. The results of the numerical simulations of ion beam extraction are found to be in good agreement with experimental data.

Equilibrium rotation in field-reversed configurations

The turbulence that drives anomalous transport in field-reversed configurations (FRCs) is believed to break the otherwise closed magnetic surfaces inside the separatrix. This places electrons in the core of the plasma in electrical contact with those in the periphery. This effect was proposed and investigated in the context of spheromaks [D. D. Ryutov, Phys. Plasmas 14, 022506 (2007)]. The opening up of internal magnetic field lines serves to regulate the electrostatic potential in the interior of the plasma, and in turn drives ion rotation. In effect, “end-shorting,” a well-known phenomenon in the FRC scrape-off layer, also extends into the plasma interior. For conditions relevant to experiments, the ion rotation can be expressed in terms of equilibrium properties (density and temperature gradients) and as such is the “equilibrium” rotation. This theory is incomplete in that it neglects evolving, transport-related effects that modify the equilibrium and, indirectly, the rotation rate. Consequently, the equilibrium rotation theory is only partially successful in predicting experimental results: although it predicts the average rotation well, the estimated degree of rotational shear seems unlikely, especially at late times in the plasma lifetime.

Observation of tilting activities in translated field reversed configuration plasma using computer tomography at two different cross sections

Tilting activities of field reversed configuration (FRC) plasma were observed in translation experiments using computer tomography (CT) at two different cross sections in the FRC injection experiment (FIX) machine [S. Okada et al., Nucl. Fusion 47, 677 (2007)]. In these experiments, two sets of CT devices were installed at the upstream and downstream sides of the confinement chamber of the FIX. Each CT device was composed of three arrays of detectors sensitive to the near-infrared radiation. The peak of the reconstructed emission profile at one side was displaced from the center of the cross section of the chamber. On the other hand, the reconstructed profile at the other side was located around the center. This result suggests that the FRC plasma was tilting in the axial direction. The occurrence of the observed tilting activities had almost no effect on the lifetime of the FRC plasma.

Using Three-Body Recombination to Extract Electron Temperatures of Ultracold Plasmas

Three-body recombination, an important collisional process in plasmas, increases dramatically at low electron temperatures, with an accepted scaling of Te(-9/2). We measure three-body recombination in an ultracold neutral xenon plasma by detecting recombination-created Rydberg atoms using a microwave-ionization technique. With the accepted theory (expected to be applicable for weakly coupled plasmas) and our measured rates, we extract the plasma temperatures, which are in reasonable agreement with previous measurements early in the plasma lifetime. The resulting electron temperatures indicate that the plasma continues to cool to temperatures below 1 K.

New Results in the Theory of Multiple Mirror Plasma Confinement

Theory of plasma confinement in a multiple mirror trap is extended. Plasma lifetime is estimated for new regimes with partially devastated loss-cone, which occur at the stage of plasma decay in GOL-3 multiple mirror after termination of relativistic electron beam injection.

Interaction of piroxicam with mitochondrial membrane and cytochrome c

Modulation of surface properties of biomembranes by any ligand leading to permeabilization, fusion, rupture, etc. is a fundamental requirement for many biological processes. In this work, we present the interaction of piroxicam, a long acting Non-Steroidal Anti-Inflammatory Drug (NSAID) with isolated mitochondria, membrane mimetic systems, intact cells and a mitochondrial protein cytochrome c. Dye permeabilization study on isolated mitochondria indicates that piroxicam can permeabilize mitochondrial membrane. Direct imaging by Scanning Electron Microscope (SEM) shows that piroxicam induces changes in mitochondrial membrane morphology leading to fusion and rupture. Transmission Electron Microscope (TEM) imaging of piroxicam treated DMPC vesicles and mixed micelles formed from CTAB and SDS show that causing membrane fusion is a general property of piroxicam at physiological pH. In intact cells viz., V79 Chinese Hamster lung fibroblast, piroxicam is capable of releasing cytochrome c from mitochondria into the cytosol in a dose dependent manner along with the enhancement of downstream proapoptotic event viz., increase in caspase-3 activity. We have also shown that piroxicam can reduce cytochrome c within a time frame relevant to its lifetime in blood plasma. UV-visible spectroscopy has been used to study the reaction mechanism and kinetics in detail, allowing us to propose and validate a Michaelis–Menten like reaction scheme. CD spectroscopy shows that small but significant changes occur in the structure of cytochrome c when reduced by piroxicam.

Tomographic Reconstruction of Internal Instability in a Field-Reversed Configuration

Rotational instability with toroidal mode number n = 2 has been known as a destructive instability which limits the configuration lifetime in a field-reversed configuration plasma. In recent experiments using tomographic technique, the spatial distribution of plasma radiation (bremsstrahlung) was measured with a newly developed multi-purpose optical diagnostic system. Global deformation of the cross-sectional structure of a FRC and its time evolution were investigated by a computed tomography (CT) reconstruction technique (ART method) [T. Asai et al., Physics of Plasmas 13, 072508]. These results indicate that the FRC plasma has an internal deformation, which has different phase from the deformation of separatrix surface. These two different toroidal deformations are difficult to be observed by spatially integrated methods, for example, magnetic probes, end-on camera and so on. In this work, detailed features of this internal behavior have been investigated by a newly improved tomographic reconstruction method.

Concept, techniques, deposition mechanism of impulse plasma deposition — A short review

At the beginning of 80s last century, our research group gathered around Professors Mieczyslaw and Aleksandra Sokolowski recognized that the application of non-equilibrium plasma is necessary in synthesis of monotropic phases of high melting materials. It was evident for us that impulse plasma ensures both the highest level of non-equilibrity and highest level of vapour ionisation. These conditions seemed to be especially suitable for synthetizing the phases with high energetic barrier of nucleation process. The method of deposition of high melting materials layers by the use of impulse plasma was called the Impulse Plasma Deposition (IPD). The IPD device consists of the condenser battery charged to the voltage of order of kVs, plasma coaxial accelerator, ignitron setup, vacuum chamber and substrate holder. Plasma is generated with the frequency of 10 − 1 –10 Hz. The life time of plasma in each impulse is of order of 10 − 4 s. During the discharge of condensers individual plasmoids are being accelerated in the coaxial generator by the Ampere force to the speed of the order of 10 4 m s − 1 and directed to the substrate. The substrate is nonheated from any external heat source prior, during and after the plasma process. Experiments showed that the nucleation of phases takes place on ions of plasma and layer is constituted by the limited coalescence of the subnano- or nano particles on the substrate surface. Layers of DLC, c-BN, oxides, interstitial phases and complex metallic alloys with nano- or amorphous/nano-crystalline structure are produced with the use of IPD. In 1989 the IPD method was implemented to the industry for deposition of TiN layers on cutting tools.

Equilibrium and stability studies of oblate field-reversed configurations in the Magnetic Reconnection Experiment

The equilibrium and stability of oblate field-reversed configurations (FRCs) have been studied in the Magnetic Reconnection Experiment [M. Yamada et al., Phys. Plasmas 4, 1936 (1997)]. In the absence of a passive stabilization, tilt and shift instabilities often become unstable, with the tilt in particular limiting the plasma lifetime. The tilt instability can be mitigated by either including a passive stabilizing conductor, or by forming very oblate plasmas. Large perturbations (n=2 and 3) may still remain after passive stabilization is applied. These perturbations have the characteristics of co-interchange modes, which have never been observed, and can lead to the early termination of the plasma. The co-interchange modes can be minimized through the formation of plasmas with a very oblate shape, leading to the maximum FRC lifetime. A code has been developed to calculate equilibria for these plasmas. A rigid-body model explains the improved stability of oblate plasmas to n=1 tilt modes. Numerical calculations indicate improved stability to n⩾2 co-interchange modes for the very oblate plasma shapes.

Preparation of silicon thin films by intense pulsed ion-beam evaporation method with low temperature process

We have succeeded in preparing polycrystalline silicon thin films by the intense pulsed ion-beam evaporation method without impurities on substrates of silicon and quartz. Good crystallinity and high deposition rate were achieved without thermal processing such as heating the substrates. The crystallinity of poly-Si film has been improved by increasing the density of the ablation plasma. Since the lifetime of the ablation plasma, which was obtained by a pulsed ion beam with 50-ns pulse width, is of the order of 20 μs, the instantaneous deposition rate is in the region of cm/s. The crystallinity was increased by increasing the number of shots. The crystallization and the deposition rate of poly-Si thin films prepared on different substrate positions were investigated.

J/ψ gluonic dissociation revisited: III. Effects of transverse hydrodynamic flow

In a recent paper [B.K. Patra, V.J. Menon, Eur. Phys. J. C 44, 567 (2005)] we developed a very general formulation to take into account explicitly the effects of the hydrodynamic flow profile on the gluonic breakup of J/ψs produced in an equilibrating quark–gluon plasma. Here we apply that formulation to the case when the medium is undergoing a cylindrically symmetric transverse expansion starting from RHIC or LHC initial conditions. Our algebraic and numerical estimates demonstrate that the transverse expansion causes enhancement of the local gluon number density ng, affects the pT-dependence of the average dissociation rate \(\langle\tilde{\Gamma}\rangle\) through a partial-wave interference mechanism and makes the survival probability S(pT) to change with pT very slowly. Compared to the previous case of a longitudinal expansion the new graph of S(pT) is pushed up at LHC but develops a rich structure at RHIC, due to a competition between the transverse catch-up time and the plasma lifetime.

Transient Ion Sheath in Pulsed Plasmas

In plasma-based ion implantation and deposition (PBII&D), the use of pulsed-plasma sources such as a shunting arc might have some advantages over a conventional plasma source used to produce high-density plasmas. It is desirable for a conformal implantation into the materials (targets) with complicated surfaces. In some cases, the pulsed plasmas may be surrounded by a vacuum region in the vessel, when the lifetime of each pulsed plasma is short compared with the plasma-expansion time. When a target is immersed in such isolated plasmas and a negative voltage pulse is applied for ion implantation, the ion-sheath potential may be different from what is expected in a plasma contacting the vacuum vessel of the ground potential. The ion-sheath potential, the difference between the plasma space potential and the target potential, determines the maximum energy of the implanted ions. A simplified one-dimensional model, in which the target is immersed in a plasma surrounded by a vacuum (or low density) region and an outside vessel of the ground potential, has been developed. It is shown that, when a negative high-voltage pulse is applied to the target for ion implantation, the resultant sheath potential can be substantially lower than the applied potential depending upon the ion current to the target and the distance of the plasma edge from the vessel wall. This effect on the ion current and implanted-ion energy distribution is discussed in this paper

High-density field-reversed configuration plasma for magnetized target fusion

Field reversed theta pinch technology is employed with programmed cusp fields at the theta coil ends to form high-density field-reversed configuration (FRC) plasmas. The well-formed FRC plasmas have volume-averaged density of 2-4/spl times/10/sup 22/ m/sup -3/, total temperature (T/sub e/+T/sub i/) of 300-500 eV, and plasma lifetime between 10-20 /spl mu/s in 50-70 mtorr of deuterium static gas fill. The achieved FRC parameters are very close to the desired target plasma requirements for magnetized target fusion.

Ion and neutral energy distributions to the MgO surface and sputtering rates in plasma display panel cells

One of the factors limiting the lifetime of plasma display panels (PDPs) is sputtering of the MgO layer deposited on the dielectric covering the electrode. The goal of the work reported here is to evaluate the influence of different operating conditions on the sputtering rate of the MgO layer in PDPs operating with Xe/Ne mixtures. Sputtering is caused by the ions and fast neutral atoms impacting the surface. Starting with results from a fluid model, we use a Monte Carlo simulation to calculate energy distributions of the ion and fast neutrals arriving on the MgO coated surface for a set of baseline conditions. Estimates of the sputtering yield of MgO are then combined with the energy distributions to evaluate the sputtering rates for matrix and coplanar geometries. Parametric calculations in a simple geometry were performed to examine the effect of gas mixture, gas pressure, cell capacitance, and applied voltage on the sputtering rate of the MgO layer. Our main result is the prediction of longer lifetime for mixtures containing about 20%Xe for both matrix and coplanar geometries.

Long lifetime plasma channel in air generated by multiple femtosecond laser pulses and an external electrical field

The lifetime of a plasma channel produced by self-guiding intense femtosecond laser pulses in air is largely prolonged by adding a high voltage electrical field in the plasma and by introducing a series of femtosecond laser pulses. An optimal lifetime value is realized through adjusting the delay among these laser pulses. The lifetime of a plasma channel is greatly enhanced to 350 ns by using four sequential intense 100fs(FWHM) laser pulses with an external electrical field of about 350kV/m, which proves the feasibility of prolonging the lifetime of plasma by adding an external electrical field and employing multiple laser pulses.

Influence of negative leader propagation on the triggering and guiding of high voltage discharges by laser filaments

The triggering and guiding of negative discharges using filaments induced by a femtosecond-terawatt laser pulse have been studied in sphere-plane gaps up to 4.5 meters. Fast-frame camera pictures allow the evaluation of the influence of the negative leader propagation on the triggering and guiding process. We show that the plasma channel can either trigger a space-leader discharge or act as a guiding path for the negative leader head. For the latter case the results suggest a linear dependence of the guided lengths up to 2.4 m, while the formation of a space-leader reduces this guided length by up to 50%. This effect is explained by the limited plasma lifetime of the filament that is measured to be about 1 μs.

L55P Transthyretin Accelerates Subunit Exchange and Leads to Rapid Formation of Hybrid Tetramers

Transthyretin is a tetrameric protein associated with the commonest form of systemic amyloid disease. Using isotopically labeled proteins and mass spectrometry, we compared subunit exchange in wild-type transthyretin with that of the variant associated with the most aggressive form of the disease, L55P. Wild-type subunit exchange occurs via both monomers and dimers, whereas exchange via dimers is the dominant mechanism for the L55P variant. Because patients with the L55P mutation are heterozygous, expressing both proteins simultaneously, we also analyzed the subunit exchange reaction between wild-type and L55P tetramers. We found that hybrid tetramers containing two or three L55P subunits dominate in the early stages of the reaction. Surprisingly, we also found that, in the presence of L55P transthyretin, the rate of dissociation of wild-type transthyretin is increased. This implies interactions between the two proteins that accelerate the formation of hybrid tetramers, a result with important implications for transthyretin amyloidosis.

Self-consistent turbulent convection in a magnetized plasma

It has been shown that low-frequency vortex convection, which is self-consistently developed in a magnetized plasma, may lead to nondiffusive transport processes similar to those observed in various systems of the plasma magnetic confinement. To theoretically analyze such a convection, an approach is proposed on the basis of the direct computer simulation of the quasi-two-dimensional dynamics of a weakly dissipative plasma with the use of adiabatically reduced hydrodynamic-type equations. The derived equations ensure the description of both relatively fast nonlinear convective flows and slower resulting transport processes and allow the simulation of the plasma evolution at sufficiently long times comparable with the plasma lifetime. The simulation shows that the development of the convection leads to the formation of nonlinear large-scale stochastic vortex structures, which exhibit broad power-law frequency and wavenumber spectra, as well as the non-Gaussian statistics of fluctuations, and corresponds to the notion of structure turbulence. The resulting transport processes are nonlocal and nondiffusive and have a number of characteristic properties similar to those observed in real experiments. The self-consistency of the pressure and density profiles in the plasma, L-H transitions, impurity pinch, etc., are among these properties.

Equations for nonlinear MHD convection in shearless magnetic systems

A closed set of reduced dynamic equations is derived that describe nonlinear low-frequency flute MHD convection and resulting nondiffusive transport processes in weakly dissipative plasmas with closed or open magnetic field lines. The equations obtained make it possible to self-consistently simulate transport processes and the establishment of the self-consistent plasma temperature and density profiles for a large class of axisymmetric nonparaxial shearless magnetic devices: levitated dipole configurations, mirror systems, compact tori, etc. Reduced equations that are suitable for modeling the long-term evolution of the plasma on time scales comparable to the plasma lifetime are derived by the method of the adiabatic separation of fast and slow motions.

Macroscopic separation of charges in a pulsed electric discharge

The possibility of separating charges in an ordinary electric discharge was demonstrated. The luminous object formed after the end of the discharge was found to exist over a few hundred milliseconds, or six orders of magnitude longer than the lifetime of an ideal plasma of the same volume. It is shown that the luminous object has a negative electric charge and has no free charged particles of opposite sign.