Effects of Lower-Hybrid Heating on the Hot Electrons in an Electron-Cyclotron-Resonance Plasma

Experiments were performed on an electron cyclotron resonance plasma in a dc magnetic mirror to determine the effects of lower hybrid resonance radiation on the anisotropy of the plasma. It was found that the anisotropy of the plasma hot electrons decreased, the flux of hot electrons escaping through the mirror throats decreased and the midplane wall bremsstrahlung rate slightly increased as lower hybrid resonance power was increased. This is explained by observing that cold plasma, expelled by the lower hybrid radiation, decreases the number of scattering centers in the midplane, which results in a deeper diamagnetic well for the hot electrons.     

Electron Heating of the Cluster Plasma by an Ultrashort Laser Pulse

JETP Letters - The interaction of an ultrashort (~10 fs) laser pulse with a relativistic intensity (≳1018 W/cm2) with a cluster medium characterized by a random distribution of large,...     

Lower Hybrid Heating of an Electron-Cyclotron-Resonance Plasma in a Canted Magnetic Mirror

Plasma heating at the lower hybrid resonance was studied experimentally in a canted magnetic mirror in order to determine the effects of magnetic field curvature on heating efficiency. Heating occurred mainly on what would be the "outside" of an equivalent torus, peaking near the hybrid resonant layer. The best conditions for heating were seen to be a relatively flat density profile of magnitude slightly below that where hybrid resonance would be expected. The density profile was seen to move "outward" as cant angle was increased, while the hybrid layers were seen to move oppositely, toward what would be the inside of the torus. No significant deleterious effects on the efficiency of the lower hybrid resonant heating (LHRH) were observed as the canting was changed.     

Excitation of an Additional Region of Short-Wavelength Plasma Oscillations in Ionospheric Heating Experiments

We discuss transfer of plasma waves, excited by a powerful radio wave due to its scattering on artificial ionospheric irregularities, into an additional region of very short plasma oscillations polarized almost perpendicular to the magnetic field. Such a region can exist in the magnetized ionospheric plasma due to the strong spatial dispersion. We take into account the plasma-wave diffusion over the spectrum caused by multiple scattering on irregularities, as well as the nonlinear process of plasma-wave interaction due to induced scattering by ions. The latter process leads to the transfer of primary plasma waves into the additional region. The induced scattering is considered in the differential approximation valid for sufficiently smooth plasma-wave spectra. The numerical calculations are performed for a Maxwellian plasma in which suprathermal electrons are absent. It is shown that in this case, the additional region of plasma waves is excited if the pump frequency is close to but slightly less than the fourth electron gyroharmonic, so that the absorption of primarily excited plasma waves becomes sufficiently strong. Application of our calculations to the results of ionospheric experiments is discussed.     

Plasmon Mechanism of Overdense Plasma Heating

This paper attempts to introduce an effective mechanism of plasma heating of an overdense plasma layer. This mechanism is directly related to the phenomena of anomalous transparency of an overdense plasma layer. High temperature is achieved due to the resonant excitation of the coupled surface waves on both sides of the plasma layer. The dissipative energy of the collisional effects appears as an effective heating source in this mechanism. The solutions of the heat equation under the resonant situations are obtained in the steady and unsteady states conditions. The main factors, affecting the considered plasma heating mechanism, are also discussed. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Hot Ion Plasma Heating Experiments in SUMMA

Initial empirical results are presented for the hot-ion plasma heating experiments conducted in the new SUMMA (Superconducting Magnetic Mirror Apparatus) at NASA Lewis Research Center. A discharge was formed by applying a radially inward DC electric field near the mirror throats. Data were obtained at midplane magnetic flux densities from 1.0 to 3.5 tesla. Charge-exchange neutral particle energy analyzer data were reduced to ion temperatures using a plasma model that included a Maxwellian energy distribution super-imposed on an azimuthal drift, finite ion orbits, and radial variations in density and electric field. Using this plasma model, the highest ion temperatures computed were 5 keV, 1.2 keV, and 1 keV for He+, H2+, and H+, respectively. These were obtained at a mid-plane magnetic flux density of 1.6 T. Ion temperature was found to scale roughly as (P/B)n, where P/B is the ratio of power input to magnetic flux density and n is about 1 for hydrogen and 2 for helium. Optical spectroscopy line-broadening measurements yielded ion temperatures about 15 percent higher than the charge-exchange neutral particle analyzer results for hydrogen and about 50 percent higher for helium. Spectroscopically obtained electron temperatures ranged from 3 to 30 eV.     

Turbulent Heating Experiments in a Plasma Betatron

The various experiments carried out with the University of Saskatchewan plasma betatron are reviewed. The apparatus, having a major/minor radius of 19 cm/3 cm, a toroidal magnetic field B? ? 0.4 T and a heating field E? ? 12 kV/m, has been operated in different modes ? designated as betatron, tokamak and reversed - B?. The characteristics of the turbulently heated plasma and the physical processes occurring in each mode are discussed.     

Beat Heating of Collisional and Magnetised Plasma

The heating of a plasma by stimulating plasma electrons as well as plasma ions with two anti-parallel electromagnetic waves under the influence of a uniform static magnetic field is studied using Maxwell's equations and equations of motion. A formula for the power absorption per unit volume of the plasma is derived and effects of collisions and magnitude and orientation of the magnetic field on the beat heating are examined numerically. It is observed that the average power absorption in the absence of ion-neutral collisions in the plasma barely exceeds unity in the units of pure Langmuir mode excitation where as in the presence of ion-neutral collisions the power absorption immediately shoots up to a very high value.     

Ion Heating in Dusty Plasma of Noble Gas Mixtures

Ion heating in dusty plasma of noble gas mixtures is studied by the observation of dust particles in stratified glow discharge. The particles and their formations can be used as a “contact‐free” probe of the ion flows. It is shown that under condition of experiments transition of dust particles into crystalline state in pure gases occur at much lower pressures in comparison to the case of gas mixtures. This observation is also supported by the evaluation of “effective” kinetic temperature of dust particles as defined from the velocity distribution function at the same set of discharge parameters. Absolute value of temperature of dust component in the mixture of helium and argon indicates important role of argon ionization process (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

X-Ray Measurements during Whistler-Mode Electron Cyclotron Resonance Plasma Startup and Heating in an Axisymmetric Magnetic Mirror

New measurements and analyses of whistler-mode electron cyclotron resonant heating (ECRH) startup and heating in an axisymmetric magnetic mirror are presented. Experimental studies of startup are presented which include the effects of initial neutral gas pressure on density and energy buildup rates, the effects of electron-beam-generated seed plasma on startup times, and a possible density threshold for the absolute whistler instability. Results of two types of analyses are presented. The first is a Fokker-Planck finite-element simulation the principal result of which is the prediction of the creation of a sloshing electron velocity distribution in the first 10 ?s after microwave power is applied. The second simulation uses rate equations to predict buildup, with rate coefficients based on a model sloshing-electron distribution function. Both results are consistent with experimental observations. Measurements of X-ray emission provided information about plasma transport, the sloshing electron spatial distribution, and the hot-electron average energy. The foil ratio technique gave average energies of 1-3 keV during whistler-mode ECRH, in agreement with afterglow measurements of hot electron decay. Possible applications of whistler-mode ECRH plasma production and heating are for plasma soft X-ray sources and plasma potential modification in tandem mirror machines.     

Zero-Dimensional Model to Study the Effectiveness of Plasma Heating and Thermal Energy Confinement in Globus-M Tokamak in Ohmic Heating Modes

Experimental study of thermal energy confinement in magnetic confinement devices is one of the fundamental problems in plasma physics. The data processing technique covering kinetic and magnetic measurements performed for the Globus-M tokamak is described. A zero-dimensional code has been developed on the basis of this approach making it possible to calculate important discharge parameters during the experiment (between discharges): the electron and ion stored thermal energy content, plasma effective charge, and confinement time. Good agreement of the zero-dimensional calculations and ASTRA modeling indicates that this approach can be applied for routine data processing in Globus-M in view of the specifics of the device.     

Numerical Analysis of the Joule Heating Effect on Plasma Heat Transfer

The application of thermal plasmas particularly in the field of plasma chemistry and plasma material processing requires a basic understanding of the heat transfer process. This paper is concerned with an analysis of the heat transfer to a positively biased body exposed to a plasma flow. Because of the induced current flow due to the biasing potential, the plasma surrounding the biased body will experience an increase in temperature caused by Joule heating. The fraction ? of the dissipated heat which is transferred to the body is calculated for an atmospheric argon plasma flow at temperatures between 104 and 2 × 104K and Reynolds numbers of 40 and zero. The results indicate that ? increases with increasing plasma temperature for Re = 40 and decreases slightly with increasing plasma temperature for Re = 0. As the Re number increases at constant plasma temperature ? decreases.     

Production of Mixed Powders of Actinide Dioxides by Thermal Reductive Denitration Using Microwave Heating

Physics of Atomic Nuclei - The use of microwave heating to produce solid solutions of actinide oxides in the processes of thermal denitration of model nitric acid solutions formed in reducing...     

Effect of Flat Top Electron Distribution on the Turbulent Heating of a Plasma

Expressions for anomalous resistivity and energy transfer collision frequency in the presence of ion-acoustic instability have been derived. It is found that the rapid electron heating may be attributed to the flattening of the top of the electron distribution function to a high degree. Results are valid under the situation when krr_c « 1 where τ_c is the correlation time for turbulence.     

In Situ Dimensional Characterization of Magnetic Nanoparticle Clusters during Induction Heating

The study and fundamental understanding of magnetic nanoparticle induction heating remains critical for the advancement of magnetic hyperthermia technologies. Complete characterization of not only the nanoparticles themselves but their interparticle behavior in a sample matrix is necessary to accurately predict their heating response. Herein, an in situ method for measuring the extent of nanoparticle clustering during induction heating using small-angle and ultrasmall-angle neutron scattering facilities at the National Institute of Standards and Technology Center for Neutron Research is described and implemented by comparing two sets of iron oxide nanoparticles with differing structures and magnetic properties. By fitting the scattering profiles to a piecewise model covering a wide Q-range, the magnitude of nanoparticle clustering during induction heating is quantified. Observations of the low-Q intensity before and after heating also allow for relative measurement of the cluster volume fraction during heating. The use of this method can prove to be advantageous in both developing more encompassing models to describe magnetic nanoparticle dynamics during heating as well as optimizing nanoparticle synthesis techniques to reduce aggregation during heating.     

Heating by absorption in the focus of an objective lens

We derive an integral solution for the local heating of a linearly absorbing, uniform medium exposed to strongly focused light. Numerical results for local heating under typical multiphoton microscopy and optical trapping conditions are presented for various aperture angles. In contrast with common Gaussian beam approximations, our model employs the focal-intensity distribution as described by the point spread function of the lens. In this way, the model also accounts for axial heat transportation, which results in a lower prediction for the temperature increase. For an aperture of 1.2 (water immersion), irradiation with 100 mW of 850-nm light for 1 s increases the local temperature of water by 0.2 K. Heating of water by linear absorption can be ruled out as a limiting factor in standard multiphoton-excitation microscopy.