Collisionless Heating Research Articles

Collisionless electron heating by radio-frequency plasma sheaths

Collisionless rf sheaths have been investigated in a self-consistent particle simulation. The one-dimensional simulation is bounded by an rf driven electrode on one side and quasineutral plasma on the other so that the sheath can be examined in isolation from other discharge processes. The simulations indicate that electron velocity distributions arriving at the electrode are distorted when the ratio of the maximum velocity of the moving electron front in the rf sheath to the thermal velocity is greater than ∼0.5. Both electron heating and power loss to the electrode increases as this ratio is increased. At ratios greater than ∼0.8–1 a positive net energy flux returning from the rf sheath is observed. Electron inertia is not negligible in this regime.

Collisionless electron heating in an inductively coupled discharge.

We present self-consistent simulations and analysis of the electron heating processes in an inductively coupled discharge. The results show that collisionless electron heating is predominant at pressures of 10 mTorr or less. The collisionless excitation mechanism is a warm plasma effect, analogous to the anomalous skin effect in metals.

Ultrahigh intensity laser–plasma interaction: A Lagrangian approach*

A Lagrangian analysis simplifies considerably the description of the ultrahigh intensity regime of laser–plasma interaction, and facilitates the identification of several new and important effects. First, the vacuum figure ‘‘8’’ orbit is shown to be unstable, with respect to a stochastic instability leading to collisionless heating. Second, in the generation of plasma wakes using ultrahigh intensity laser pulses, it can be shown that, for long-duration laser pulses, the plasma wake is insignificant, but, through proper phasing of a set of short-duration pulses, a dramatic amplification of the wake amplitude occurs. Third, in the generation of third-harmonic waves using ultrahigh intensity, long-duration laser pulses, it can be seen that a mismatch in the phase velocity limits severely the power conversion, but a conversion efficiency free from saturation might indeed be possible by employing either a density-modulated plasma or an ionized buffer gas.

Fluid closures which mimic wave-praticle interactions in strong Langmuir turbulence.

A new two-time-scale model of strong Langmuir turbulence has been constructed, using higher-moment fluid equations with dissipative closures designed to better simulate Vlasov theory predictions of linear wave properties, and to treat collisionless heating of particles by waves. Numerical solutions are carried out in a study of electron heating associated with collapse and burnout of a large-amplitude initial Langmuir wave and in a study of radiation-driven Langmuir turbulence interacting with ion-acoustic quasimodes in plasmas with ${\mathit{T}}_{\mathit{e}}$\ensuremath{\approxeq}${\mathit{T}}_{\mathit{i}}$.

Collisionless conductivity and stochastic heating of the plasma sheet in the geomagnetic tail

The chaotic single particle orbits in the geomagnetic tail are used to calculate the collisionless conductivity. It is shown that the stochasticity from inhomogeneous magnetic fields leads to a power law decay of the single particle correlation function similar to an elastic collisional process. The height‐integrated dissipative part of the collisionless conductivity governs the irreversible stochastic heating of the plasma sheet. Both exponentially growing reconnection type magnetic perturbations and a sinusoidal pulse with a half period up to 1 hour in duration are used to analyze the plasma sheet heating.

Heating and cooling in reverse shocks into pure heavy-element supernova ejecta

view Abstract Citations (44) References (38) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Heating nd cooling in reverse shocks into pure heavy-element supernova ejecta. Hamilton, A. J. S. ; Sarazin, C. L. Abstract Electron heating and cooling in reverse shocks into pure heavy-element supernova ejecta with shock velocities in the range of a few hundred to a few thousand km/s, are examined. Collisionless heating of electrons at a shock front in pure heavy-element ejecta tends to have a smaller, though still appreciable, effect than is the case for a cosmic-abundance plasma. This is mainly because only previously ionized electrons entering the shock front can be collisionlessly heated, whereas the majority of electrons are only subsequently ionized and must be heated by collisions. The preshock ionization state depends mainly on photoionizing emission from the reverse shock which can cause substantial photoionization at early times when the ejecta is optically thick to ionizing radiation. Cooling is important in pure heavy-element ejecta and may result in thermal instabilities and runaway cooling at early times. The results of numerical computations are presented for some particular case. Publication: The Astrophysical Journal Pub Date: December 1984 DOI: 10.1086/162687 Bibcode: 1984ApJ...287..282H Keywords: Electron Plasma; Heavy Elements; Plasma Cooling; Shock Fronts; Shock Heating; Supernova Remnants; Abundance; Computational Astrophysics; Electron Energy; Ionizing Radiation; Optical Thickness; Plasma Heating; Stellar Mass Ejection; Astrophysics full text sources ADS | data products SIMBAD (2)

Collisionless drift instability and ion heating in a current-carrying inhomogeneous plasma

Low-frequency collisionless drift waves grow intensively when electron currents parallel to a magnetic field are drawn in a single-ended Q machine. For a smaller electron drift velocity, the measured dispersion relations of the wave are consistent with the linear theory of the current-driven collisionless drift instability. The temperature of the ions is observed to increase anisotropically concomitant with the growth of the drift wave. The heating rate is found to be proportional to the wave energy estimated from the saturated frequency spectrum and its dependence on the electron drift is measured to be of the form (u/ve)4. A further increase in the electron drift results in the excitation of an ion acoustic wave and a flute-like instability.

Observation of Collisionless Heating and Thermalization of Ions in a Theta Pinch

Spectral line profiles from impurity ions in a small theta pinch have been measured and are interpreted as ion-velocity distribution functions. For antiparallel driving and bias fields, the ions attain a Maxwellian distribution corresponding to a perpendicular temperature of 3-4 keV in a time short compared to particle self-collision times. Thermalization is less rapid for parallel magnetic fields.

Resonances in the Collisionless Heating of a Plasma by Transit Time Magnetic Pumping

Using a general expression for the power absorbed by transit time magnetic pumping, the resonances in the heating, due to the three low-frequency electromagnetic waves which can propagate in a plasma in a magnetic field, are calculated. The strengths and widths of the three resonances are compared under conditions where the electrons absorb most of the power. The ion-acoustic resonance is the broadest and the magneto-acoustic (or compressional Alfvén) the strongest. The Alfvén (or shear Alfvén) wave is undamped when cyclotron damping and terms of order ω2/ωci2 are neglected. However, when terms of order ω2/ωci2 are included, the Alfvén wave is shown to have a stronger resonance than the ion-acoustic wave. Numerical results have also been obtained for the magneto-acoustic resonance under conditions where the ions are also heated and the width of the resonance is much broader than for pure electron heating.

The collisionless heating of a plasma by means of oscillating external currents

The transfer of power between an external circuit and a collisionless plasma is described. A very simple model is used which enables heating for arbitrary values of the frequency to be analyzed. Transit time magnetic pumping and ion cyclotron heating are described in detail. The simple model used enables the mechanism of magnetic pumping to be described much more precisely than has been done previously. The mechanism is two-dimensional, i.e. if only one dimensional variations are included there is no absorption. It is shown that for magnetic pumping the current parallel to the static magnetic field absorbs no power. It is also shown that the heating rate at the ion cyclotron frequency is very much greater than the magnetic pumping rate. Finally, the conditions are given for the electric field components (which give rise to the power absorption) to be vacuum fields.

Measurement of Light scattered from Density Fluctuations within a Collisionless Shock

WE have previously described a collisionless shock with low Alfven Mach number (MA), which propagates perpendicular to a magnetic field1–3. The shock is produced by the radial compression of an initial hydrogen plasma within a linear z-pinch. The initial plasma is 85 per cent ionized with electron density = 6.4 × 1020 m−3, and temperatures = = 1.2 eV, and is in an axial magnetic field = 0.12 Wb m−2. The shock propagates radially inwards through the initial plasma with a steady velocity Vs = 240 km s−1 (MA = 2.5), and with a steady structure of width Ls = 1.4 mm and compression ratio F = 2.5. The measured electron temperature behind the shock, = 44 eV, implies a resistivity within the shock about two orders of magnitude greater than the classical collisional value4. This demonstrates the collisionless nature of the shock. The effective mean resistivity (η), obtained from the power balance equation corresponds to a colision frequency The currently accepted theories of such shocks3,5,6 invoke ion wave turbulence7 to explain the structure and collisionless heating.

Observation of collisionless plasma heating by strong shock waves

The heating of a plasma by collisionless shock waves is investigated by measuring the variation of magnetic field (with magnetic probes), density and electron temperature (from Thomson scattering of laser light) in the shock waves. The compression waves are produced in a tube of 14 cm diameter by the fast rising magnetic field (12 kG in 0.5Μsec) of a theta pinch. For shocks with Mach numbers between 2 and 3 propagating into a hydrogen or deuterium plasma with a localΒ of about 1 (Β=ratio of particle pressure to magnetic pressure) the measured jump in density and magnetic field across the front is 2 to 4, and the electron temperature increases in the front from 3 to 50 eV with a further rise to between 100 and 250 eV in the piston region. Only about 20% of the measured electron heating can be explained by adiabatic heating and resistive heating based on binary collisions, indicating a high turbulent plasma resistance. Both the observed electron heating and the width of the shock front, which is about 0.6 ·c/Ω p, can be accounted for using an effective collision frequency close to the ion plasma frequencyΩ p. The ion heating in the almost stationary shock fronts can be inferred indirectly from the steady state conservation relations. For shock waves with Mach numbersM<M crit it seems to be consistent with an adiabatic heating process, whereas forM>M crit the calculated ion temperatures exceed those one would except for a merely adiabatic heating.

Erratum: Collisionless Heating of the Solar-Wind Plasma. I. Theory of the Heating of Collisionless Plasma by Hydromagnetic Waves

Erratum: Collisionless Heating of the Solar-Wind Plasma. I. Theory of the Heating of Collisionless Plasma by Hydromagnetic Waves

Collisionless Heating of the Solar-Wind Plasma. II. Application of the Theory of Plasma Heating by Hydromagnetic Waves

view Abstract Citations (110) References (23) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Collisionless Heating of the Solar-Wind Plasma. II. Application of the Theory of Plasma Heating by Hydromagnetic Waves Barnes, Aaron Abstract The theory of heating of collisionless plasma by damping hydromagnetic waves is applied in a qualitative model of solar-wind heating. It is proposed that an efflux of 5 X 1026 ergs sec', in the form of fast-mode magnetoacoustic waves, propagates outward into the outer corona. Most of this wave energy is transformed into electron and ion thermal energy through damping, within a few solar radii, and is ex- pected to enhance the velocity of the wind at the orbit of Earth A smaller amount of this wave energy will not be absorbed until it has propagated far from the Sun; the absorption of this part of the wave energy will enhance the temperature of the solar-wind ions, and because the ion-ion mean free path is long in this region, the ion temperature will remain high even at the orbit of Earth. The proposed heating model qualitatively accounts for the discrepancy between observed solar-wind velocities and ion tem- peratures, and those predicted by the Sturrock-Hartle two-fluid model of the solar wind Publication: The Astrophysical Journal Pub Date: January 1969 DOI: 10.1086/149866 Bibcode: 1969ApJ...155..311B full text sources ADS | Related Materials (1) Part 1: 1968ApJ...154..751B

Collisionless Heating of the Solar-Wind Plasma. I. Theory of the Heating of Collisionless Plasma by Hydromagnetic Waves

view Abstract Citations (95) References (13) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Collisionless Heating of the Solar-Wind Plasma. I. Theory of the Heating of Collisionless Plasma by Hydromagnetic Waves Barnes, Aaron Abstract In this, the first of a series of papers examining the role of collisionless heating in the solar wind, the general theory of heating of collisionless plasma by hydromagnetic waves is derived It is shown that damping of fast-mode hydromagnetic waves can heat both protons and electrons, enhancing the "com- ponent" of kinetic (ion or electron) temperature parallel to the mean magnetic field, but not affecting the transverse temperatures A numerical ca1cu~ation of the heating associated with fast-mode waves as a function of propagation direction is given, and a qualitative summary of the ways in which the heating depends on plasma conditions is presented Publication: The Astrophysical Journal Pub Date: November 1968 DOI: 10.1086/149794 Bibcode: 1968ApJ...154..751B full text sources ADS | Related Materials (1) Part 2: 1969ApJ...155..311B

Collisionless heating of ions and electrons in a turbulent toroidal plasma

Collisionless heating of ions and electrons in a turbulent toroidal plasma

Collisionless Heating and Wave Amplification through Interaction with a Density Gradient

Collisionless heating occurs when a magnetoacoustic wave travels at right angles to a magnetic field in a plasma whose density is increasing in the direction of travel. Inclusion of pressure terms in a fluid description leads to an interaction of the wave with the density gradient which allows a net transfer of energy from the wave to the plasma. The mechanism is, however, reversible. Consequently a wave traveling out of the plasma is amplified, and the plasma loses energy to it. A method for obtaining a net transfer of energy to the plasma from a wave originating externally by varying the magnetic field strength is discussed along with the effect of the density gradient on other heating mechanisms.

Heating a plasma by means of magnetic pumping

We present two models for the heating of a cylindrical plasma by an oscillating magnetic field. The model for collisional heating, applicable at low temperatures and high densities, is extended to include dissipative effects. Both linear and nonlinear numerical calculations yield heating times which agree for moderate values of the modulation index. A model for collisionless transit-time heating, applicable at high temperatures, is extended to include the self-consistent electric fields; the ions are treated by means of a Vlasov equation and the electrons are treated as a fluid in equilibrium. Inclusion of the electric fields enhances the heating rate by as much as a factor of four. Heating rates calculated from the two theories are in essential agreement when the mean free path of the ions is comparable to the length of the pumping section.

Quasi-linear theory of a plasma

In this work we present the fundamental ideas of a quasi-linear theory for a weakly turbulent plasma. We consider a number of plasma processes characterized by the excitation of collective degrees of reedom: the dynamics of the growth of noise in an unstable plasma, the interaction of a beam of charged particles with a plasma, and the damping of plasma waves. We discuss the properties of the stationary, weakly turbulent state that arises when a current flows through a plasma; the problem of anomalous plasma diffusion across a magnetic field is considered. We also investigate “threshold absorption” of high-amplitude waves, which is a mechanism for collisionless heating.

Quasi-linear plasma theory (theory of a weakly turbulent plasma)

The basic principles of the quasi-linear theory of a weakly turbulent plasma are presented. Several processes occurring in a plasma in which collective degrees of freedom are excited are considered: the dynamics of noise build-up in an unstable plasma, the interaction of a beam of charged particles with the plasma, the damping of the plasma waves. The properties of the stationary weakly turbulent state arising in a plasma when a current passes through it are discussed, and so also is the problem of the anomalous diffusion of the plasma across a magnetic field. The phenomenon of `threshold absorption' of large amplitude waves in a plasma, leading to the collisionless heating of the particles, is also examined.