Description: Based on the first principles [i.e., (i) by balancing the magnetic field advection with the term containing electron pressure tensor nongyrotropic components in the generalized Ohm’s law; (ii) using the conservation of mass; and (iii) assuming that the weak magnetic field region width, where electron meandering motion supports electron pressure tensor off-diagonal (nongyrotropic) components, is of the order of electron Larmor radius] a simple model of magnet...

By: Frank Verheest, Manfred A. Hellberg, and Ioannis Kourakis

Description: Large nonlinear acoustic waves are discussed in a four-component plasma, made up of two superhot isothermal species, and two species with lower thermal velocities, being, respectively, adiabatic and cold. First a model is considered in which the isothermal species are electrons and ions, while the cooler species are positive and/or negative dust. Using a Sagdeev pseudopotential formalism, large dust-acoustic structures have been studied in a systematic way, ...

Description: Ion collisionality is known to be a major factor which determines the magnitude of the surface (floating) potential of an individual particle immersed in a plasma. In this paper a simple interpolation formula for the ion flux collected by such a particle in the entire range of ion collisionality is proposed. The dependency of the floating potential on ion collisionality calculated using this formula as well as using other analytic approximations developed re...

By: I. U. Uzun-Kaymak, P. N. Guzdar, R. Clary, R. F. Ellis, A. B. Hassam et al

Description: The Maryland Centrifugal Experiment [ R. F. Ellis et al., Phys. Plasmas 12, 055704 (2005) ] is a mirror machine designed to have a plasma axially confined by supersonic rotation and dominantly interchange stable by the radial shear in the azimuthal velocity. Nevertheless, residual fluctuations still persist. To investigate the presence of such fluctuations, an azimuthal array of 16 magnetic pickup coils at the edge region of the plasma has been employed. A c...

Description: Anomalous ion and impurity heating in reversed field pinch plasmas is addressed. Previous work [ N. Mattor et al., Comments Plasma Phys. Controlled Fusion 15, 65 (1992) ], which calculated the heating of bulk ions by gyro and Landau resonances with turbulent fluctuations cascading from unstable tearing modes, is extended to impurity species measured in Madison symmetric torus (MST). The heavier mass of impurities allows gyro-resonant heating at lower frequen...

By: S. Efimov, A. Fedotov, S. Gleizer, V. Tz. Gurovich, G. Bazalitski et al

Description: Results of ∼ 200 kbar pressure generation at 50 μm distance from the implosion axis of the converging shock wave produced by an underwater electrical explosion of a cylindrical wire array are reported. The array was exploded using a submicrosecond high-current generator (stored energy of ∼ 4.2 kJ, current amplitude of ∼ 325 kA, rise time of ∼ 1 μs). Multiframe shadow imaging of the shock wave was used to determine its time of flight. These data were applied ...

By: A. Scipioni, P. Rischette, G. Bonhomme, and P. Devynck

Description: The understanding of turbulence in magnetized plasmas and its role in the cross field transport is still greatly incomplete. Several previous works reported on evidences of long-time correlations compatible with an avalanche-type of radial transport. Persistence properties in time records have been deduced from high values of the Hurst exponent obtained with the rescaled range R/S analysis applied to experimental probe data acquired in the edge of tokamaks. ...

Description: The solution for space-charge-limited (SCL) currents in electron vacuum diodes with monoenergetic initial velocity is extended to the relativistic regime. Two types of solutions are found: Type I corresponds to zero steady state surface electric field (field emission with high enhancement factor), and Type II corresponds to a finite steady state surface electric field (other emission mechanisms). Our solution compares well to the classical space-charge-limit...

By: R. E. Madden, S. C. Bott, D. Haas, Y. Eshaq, U. Ueda et al

Description: Studies of the late time diode gap formation in two- and four-wire tungsten x-pinches using an 80 kA, 50 ns current pulse are presented. Quantitative measurements of the coronal plasma density are recovered using interferometry simultaneously with laser shadowgraphy. Axial expansion of the gap occurs at ∼ 106 cm/s for both two- and four-wire systems and is likely to be driven by an axial J×B force resulting from radial current flow in the plasma minidiode “e...

By: D. Bruno, M. Capitelli, C. Catalfamo, and A. Laricchiuta

Description: Transport coefficients of equilibrium hydrogen plasma have been calculated by using different cutoffs of electronic partition functions and different sets of transport cross sections of electronically excited states. The selection of both the cutoff criterion and transport cross sections deeply affects the transport coefficients of the H, H+, e plasma mixture in the temperature range of 10 000–50 000 K and in the pressure interval of 1–1000 atm.

By: N. A. Yampolsky, N. J. Fisch, V. M. Malkin, E. J. Valeo, R. Lindberg et al

Description: A plasma-based resonant backward Raman amplifier/compressor for high power amplification of short laser pulses might, under ideal conditions, convert as much as 90% of the pump energy to the seed pulse. While the theoretical highest possible efficiency of this scheme has not yet been achieved, larger efficiencies than ever before obtained experimentally (6.4%) are now being reported, and these efficiencies are accompanied by strong pulse compression. Based o...

Description: The results of Doppler spectroscopy of hydrogen Balmer lines from a stainless steel (SS) and copper (Cu) hollow cathode (HC) glow discharge in ammonia and argon-ammonia mixture are reported. The experimental profiles in ammonia discharge are fitted well by superposing three Gaussian profiles. The half widths, in energy units, of narrow and medium Gaussians are in the ranges 0.3–0.4 eV and 3–4 eV, respectively, for both hollow cathodes what is expected on the...

Description: A classical trajectory Monte Carlo study is reported regarding the motion of a charged particle that is caused to drift across a magnetic field toward an artificially structured boundary, which produces a spatially periodic electrostatic potential. It is found that, for the system studied, the drift toward the boundary is inhibited if the particle’s speed associated with motion parallel to the magnetic field is much larger than the particle’s speed associate...

Description: A new three-dimensional model for the warm-ion turbulence at the tokamak edge plasma and in the scrape-off layer is proposed, and used to study the dynamics of plasma blobs in the scrape-off layer. The model is based on the nonlinear interchange mode, coupled with the nonlinear resistive drift mode, in the presence of the magnetic curvature drive, the density inhomogeneity, the electron dynamics along the open magnetic field lines, and the electron-ion and e...

By: S. K. Maharaj, R. Bharuthram, S. V. Singh, S. R. Pillay, and G. S. Lakhina

Description: The nonlinear evolution of driven low-frequency electrostatic waves is investigated in a three-component magnetized dusty plasma comprised of a warm dust fluid, electrons, and ions. Electrons as well as ions are considered to have Boltzmann distributions. The fluid equations for the dust along with the quasineutrality condition are used to obtain a single nonlinear differential equation for the electric field. Periodic solutions of the nonlinear differential...

Description: A kinetic theory of weakly damped Alfvén eigenmode solutions strongly interacting with the continuum is developed for tokamak plasmas with reversed magnetic shear. It is shown that finite Larmor radius (FLR) effects are required for global eigenmode solutions. FLR effects induce multiple kinetic subeigenmodes and collisionless radiative damping. The theory explains the existence of experimentally observed Alfvénic instabilities with frequencies sweeping down...

Description: The collective backscattering of intense laser radiation by energetic electron beams is considered. Exact solutions for the radiation field are obtained, for arbitrary electron pulse shapes and laser intensities. The electron beams act as imperfect nonlinear mirrors on the incident laser radiation. This collective backscattering process can lead to the development of new sources of ultrashort pulse radiation in the gamma-ray domain. Numerical examples show t...

By: N. Chakrabarti, P. N. Guzdar, R. G. Kleva, V. Naulin, J. J. Rasmussen et al.

Description: Presented in this paper is a mode-coupling analysis for the nonlinear excitation of the geodesic acoustic modes (GAMs) in tokamak plasmas by finite beta drift waves. The finite beta effects give rise to a strong stabilizing influence on the parametric excitation process. The dominant finite beta effect is the combination of the Maxwell stress, which has a tendency to cancel the primary drive from the Reynolds stress, and the finite beta modification of the d...

By: Alexey Mishchenko, Roman Hatzky, and Axel Könies

Description: Global linear gyrokinetic particle-in-cell (PIC) simulations of electromagnetic modes in pinch and tokamak geometries are reported. The global Alfvén eigenmode, the mirror Alfvén eigenmode, the toroidal Alfvén eigenmode, and the kinetic ballooning modes have been simulated. All plasma species have been treated kinetically (i.e., no hybrid fluid-kinetic or reduced-kinetic model has been applied). The main intention of the paper is to demonstrate that the glob...

By: Jiamin Yang, Zhimin Hu, Jiyan Zhang, Tuo Zhu, Yang Zhao et al

Description: The K-shell x-ray spectra from the aluminum plasmas generated by the interaction of the 120 TW, 30 fs laser with aluminum targets have been measured by defocusing the laser beam. Laser energy-normalized intensity of the He-a line increases with the laser intensity approximately as a power law ε∝ILγ with the much smaller exponent of γ = 0.062 compared to γ = 0.2 ∼ 0.5 in the previous experiments, which is caused by the stronger radial thermal diffusivity in t...