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The probe noise in quiescent plasmas has been studied experimentally. The observing frequency f normalized to the electron plasma frequency f p e is between 10 -3 and 1. In the low frequency range, f / f p e ≪1, the probe noise consists of the shot noise for the electron collecting region of the Langmuir probe, even when the probe potential is higher than the space potential. The shot noise arising from the probe electron current suffers a reduction due to the transit time effect near the electron plasma frequency. In this frequency range the thermal noise is observed instead of the shot noise. Resonant increases of the noise current are found at the sheath-plasma resonance and at the plasma wave resonance frequencies. On the other hand the noise current arising from the probe ion current is smaller than the full shot noise level. The reduction factor for the noise is found to depend on f / f p i , where f p i is the ion plasma frequency. A mechanism for the reduction of the ion shot noise is proposed.

The formation and propagation of ion-acoustic solitons are observed experimentally. The character of a solitary pulse is observed to follow the predictions of the Kortewegde Vries equation with respect to the shape and velocity of the soliton. The interaction between two solitons is modified significantly by dissipation. However, the nonlinear nature of the interactions is confirmed for solitons moving in the same direction. Solitons moving in the opposite direction and colliding have very little effect on each other.

The DP (or double plasma) device consists of two essentially collisionless plasmas that are separated from each other (for electrons only) by a negatively biased grid. Large cross section beams of ions are produced in one plasma by raising the potential of the other. Ion waves or shocks are produced in one plasma by oscillatory or large sudden (or ramp) potential changes in the other. Electrons emitted from two electrically separate spatial arrays of small filaments produce the two plasmas with densities in the range from below 108 to ∼1010 ion/cm3 with noise levels 〈δn/n〉≈5×10−4.

The ion acoustic wave response to an impulse disturbance is experimentally examined for two different exciting mechanisms. The differences and similarities are noted for the double-plasma (D-P) and plate excitation methods. The observed response agrees well with that predicted from a self-similar study of a fluid equation model which includes the effects of Poisson's equation.

An experimental technique is described which allows one to easily measure and rapidly display the particle distribution function in phase-space in nonlinear wave-plasma interaction experiments. An application to the study of Pseudowaves is also presented.

Self-modulation of the high-frequency electric field is observed when its frequency is near the electron plasma frequency. The localized field due to the self-modulation is found to make deprossions in the plasma density, and to be trapped in the deniiity dip which moves with the ion-acoustic speed. The depth of the dip reaches to 20% of the unperturbed density. The maximum amplitudes of the high-frequency field and the density dip are linearly proportional to each other. All these features are quantitatively explained by the results of the theory of coupled electron-plasma and ion-acoustic solitary waves.

The two-dimensional nonlinear interaction of two planar ion-acoustic solitons has been studied experimentally. When the angle between the wave vectors of the two interacting solitons is small and the soliton amplitudes approach a critical value, a resonant three-soliton interaction occurs.

X rays emitted by electrons channeling through a periodically distorted lattice are studied. The lattice distortion works as a wiggler. The intensity of the radiation due to the resonance scattering of the wiggler field can be made comparable with that of the channeling radiation.

Electrostriction effects are considered in a high power dielectric loaded transmission line designed to generate solitons. The Cerenkov emission of elastic waves from the metal‐dielectric interface produces the largest strain among the strain producing mechanisms. The expression for strain as a function of electric field strength is found. The signal loss due to the emission of elastic waves is shown to be insignificant.

We present experimental and numerical evidence of temporal contraction of electromagnetic pulses propagating in nonuniform, nonlinear dispersive transmission lines. The pulses are both contracted and amplified by orders of magnitude.

Large-amplitude electron plasma waves in a bounded plasma are observed to steepen and to form shock waves with trailing wave trains. For larger-amplitude shocks, however, the trailing wave trains are found to disappear.

The resonant ion-beam-driven electrostatic ion cyclotron instability is identified. Measured dispersion relation and onset vs. beam energy and density agree with numerical calculations based on a theory which includes beam acoustic terms. After amplitude saturation, velocity space diffusion of the beam ions is observed. (auth)

Deformation of the charged surface of liquid 4He is studied by optical means. Near the dimple crystal formation point we observe saturation effects and a stripe structure exhibiting hysteresis. We compare data to existing theories of nonlinear equilibrium.

The shot noise to a probe immersed in a plasma is observed to be reduced by electron-neutral atom collisions in the probe sheath.

The ion acoustic wave and a fast propagating signal are observed in a cesium plasma. The latter is considered to be a burst of accelerated plasma due to excitation of grid.

Phase velocities of ion waves are found to be almost frequency-independent at frequencies close to the ion plasma frequency in a plasma of equal electron and ion temperatures as is predicted by the theory.

An experiment is described in which free-streaming particles are launched by a grid. The damping of the signal satisfies the Hirshfield-Jacob criterion for wave propagation.

Complicated behaviors of large-amplitude ion acoustic waves are shown experimentally and are discussed qualitatively.

The electron temperature of a quiescent plasma in a metal discharge chamber, where the walls serve as the anode, can be raised by introducing a second anode consisting of 0.0025‐cm‐diam tungsten wires held at potentials as high as 100 V with respect to the walls. Hot electrons orbit the wires and return to the plasma. Cold electrons are absorbed. Smooth temperature variation, without introduction of noise, has been achieved between 0.5 and 4.0 eV.

The frequency of the electron drift waves is observed to increase with electron temperature and the experimental values of the frequency are quantitatively compared with the theoreetical values.

Externally imposed resonant magnetic islands may be used to slow down the growth rate of the tearing mode via Rutherford’s mechanism. However, this is effective only if the harmonic number of the externally imposed islands is sufficiently high.

The nonlinear evolution of an ion‐acoustic wave packet is studied. Experimentally, it is found that (i) nonlinear phase modulation develops in the wave packet; (ii) the phase modulation, together with the dispersion effect, causes expansion and breaking of the wave packet; (iii) the ions trapped in the troughs of the wave potential introduce self‐phase modulation; and (iv) the ion‐acoustic wave is stable with respect to the modulational instability. Computer simulations have reproduced the experimental results. The physical picture and the model equation describing the wave evolution are discussed.

A nonlinear theory of the capillary waves accounts for the macroscopic lattice formation on the electron-charged surface of liquid helium observed in a recent experiment. The lattice allows both shear and compressional lattice waves to propagate.

A poloidal quadrupole field is applied to a tokamak discharge in order to study the magnetic field‐line reconnection. Elongation of the poloidal cross‐section of the plasma is observed when the quadrupole field strength is below a critical value. As the quadrupole field is increased above this critical field strength, reconnection occurs and the magnetic axis changes from being the center of elliptic magnetic surfaces (i.e., an ’’O’’ point) to the center of symmetry of hyperbolic surfaces (an ’’X’’ point). The reverse process is also observed.

The detailed identification of two instabilities driven by an ion beam injected parallel to the confining magnetic field, a resonant ion cyclotron instability, and a nonresonant ion cyclotron drift wave driven by the density gradient of the beam, is reported. Experimental results are in good agreement with numerical calculations based on the kinetic Vlasov equations. Quasi‐linear velocity space diffusion of the beam ions by wave‐particle interaction is observed, demonstrating enhanced energy transfer. The relevancy of these results to tokamak neutral beam injection heating is discussed.

Small particles in plasmas can form a coulomb lattice. The conditions for solidification in a laboratory plasma are discussed.

The steepening and breaking of the velocity‐modulated ion beam in phase space is observed experimentally. Depending on the range of velocity perturbation amplitude, three different types of beam evolution are identified. A simple theory which takes into account the ion‐temperature effect explains the observed behavior of the beam.

The response of electrons in a collisionless plasma to a fast‐rising voltage step is investigated experimentally and theoretically. At small amplitudes the step generates a wave train, the leading edge of which propagates along the column at the long‐wavelength electron plasma wave velocity. At large step amplitudes a fast burst of electrons is observed, with kinetic energy roughly proportional to the step amplitude, followed by a nonlinear electron plasma wave signal which shows solitonlike behavior.

Growth of two types of sideband waves has been observed experimentally when a relatively large‐amplitude ion‐acoustic wave propagates in a collisionless plasma having the electron‐to‐ion temperature ratio Te/Ti≈20. The observed frequency spectrum and growth rate, as well as the frequency and amplitude ranges of the large‐amplitude wave for which the sideband wave growth is observed are in good agreement with the theory of trapped particle instabilities. The sidebands extract the energy from the large‐amplitude wave and cause it to be heavily damped.

Low‐frequency electrostatic waves which propagate across the magnetic field are studied experimentally. The observed dispersion relation agrees with that of the ion cyclotron harmonic wave. Strong damping of the wave is observed.