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We have built a millimeter wave polarimeter which measures wave polarization parameters: the polarization angle, and the ellipticity including field spin direction in an evacuated high-power system. The polarimeter was applied to diagnose the 1 MW level electron-cyclotron plasma heating system at 110 GHz for the DIII-D tokamak. We have observed the time-dependent behavior of the gyrotrons and have characterized and calibrated the high-power transmission system which consists of grooved mirror polarizers, miter bends, switches, and corrugated wave guides. This article describes the principle of operation and the design method of the polarimeter and the examples of measurements.

The electron cyclotron emission (ECE) diagnostic system is installed on the large helical device (LHD). The system includes the following instruments: a heterodyne radiometer, a Michelson spectrometer, and a grating polychromator. A 63.5 mm corrugated waveguide system is fully utilized. Large collection optics and notch filters at the frequency of the LHD electron cyclotron heating (ECH) were developed for this system. In addition to these filters, the rectangular waveguide notch filters, the ECE measurement with the radiometer has been successfully performed during the ECH.

Fast Alfven waves radiated from the phased array antenna in the DIII‐D tokamak [L. G. Davis et al. in Proceedings of the 12th IEEE Symposium on Fusion Engineering, Piscataway, 1987 (Institute of Electrical and Electronics Engineers, New York, 1987), p. 991] and used for heating and current drive are studied by employing a B‐loop array mounted on the vacuum vessel wall. The wave propagation direction controlled by the antenna phasing is clearly observed. A small divergence of the rays arising from the anisotropic nature of the fast wave is found. Comparison with a ray tracing code confirms that the ray position calculated by the code is precise up to at least one toroidal turn of the rays. Conservation of ktR, which is a basic assumption in computer codes, is tested. Although the upshift of toroidal wave number kt at small major radius R is confirmed, ktR is not well conserved. The so‐called ‘‘eigenmode’’ is observed and the cause is identified. A mass density interferometer is demonstrated by employing t...

Reliable operation of discharges with negative central magnetic shear has led to significant increases in plasma performance and reactivity in both low confinement, L‐mode, and high confinement, H‐mode, regimes in the DIII‐D tokamak [Plasma Physics and Controlled Nuclear Fusion Research 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. 1, p. 159]. Using neutral beam injection early in the initial current ramp, a large range of negative shear discharges have been produced with durations lasting up to 3.2 s. The total noninductive current (beam plus bootstrap) ranges from 50% to 80% in these discharges. In the region of shear reversal, significant peaking of the toroidal rotation [fφ(0)∼30–60 kHz] and ion temperature [Ti(0)∼15–22 keV] profiles are observed. In high‐power discharges with an L‐mode edge, peaked density profiles are also observed. Confinement enhancement factors up to H≡τE/τITER‐89P∼2.5 with an L‐mode edge, and H∼3.3 in an edge localized mode (ELM)‐free H mode, are obtained. Transp...

We present a new technique to generate a high‐power pulse burst with a repetition rate of greater than 107 pulses per second. The circuit consists of transmission lines segmented by saturable inductors or ferrite‐filled coaxial cables in which an electromagnetic shock wave is driven. Small scale experiments have demonstrated that a burst of ten pulses can be easily generated.

It is shown that a nonlinear lumped‐circuit transmission line with a bandpass can transmit weak signals and reflect strong signals. Such nonlinear bandpass filters have an absolute limit on the power passed and may prove useful as circuit protectors.

We propose use of a fast Alfven wave interferometer and reflectometer as a tokamak diagnostic to measure the plasma mass density, D–T species mix profile, and density fluctuations. Utilizing the property that the phase velocity of the fast wave propagating across the magnetic field is the Alfven speed with thermal correction, this fast wave interferometer on the DIII-D tokamak was successfully used to obtain the line integrated density. Since the position of the ion–ion hybrid cutoff in tokamaks is uniquely determined by the species mix ratio and wave frequency, the reflectometer arrangement finds the species mix profile. The inversion method of reflectometry is discussed. The multiple chord interferometer also measures the mass density fluctuation profile.

Eletromagnetic solitions at a 10 MW level in a frequency band of several hundred megahertz are generated in a transmission line loaded by a nonlinear ceramic dielectric in the para‐ electric phase.

We point out that the creation of a soliton pulse train in a nonlinear‐dispersive system can be used for the generation of high‐power microwave bursts. A modulated transmission line with an appropriate nonlinear dielectric is proposed. The nonlinear wave evolution is analyzed and requirements for the dielectric material are found. Problems associated with the material are discussed. Low‐power experimental demonstrations of these concepts are presented.

Single electromagnetic pulses propagating in a spatially modulated nonlinear dielectric are compressed temporally. The system discussed may generate very short, high‐power electromagnetic pulses.

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.

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.

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.

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 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.

A hot electron plasma is produced in a magnetic‐mirror field by high‐power microwave discharges. When an instability is triggered in a hot electron plasma, it is observed that the instability is accompanied by a burst of energetic electrons escaping from the magnetic mirror, a fast rising x‐ray signal, a sudden increase of light intensity, and an intense burst of microwaves composed of harmonics of 2.1 GHz. This frequency cannot be explained in terms of the electron cyclotron frequencies associated with the magnetic field intensity within the plasma chamber.

The perturbed part of the ion distribution function is observed experimentally when an ion wave or ion wave echo is excited in a plasma. In the case of the wave the perturbed distribution is confirmed to survive, as predicted by Landau, after the wave damps away. In the case of the ion wave echo the features of the oscillations of the distribution function in velocity space are in agreement with the prediction of the perturbation theory carried to the second order. However the second‐order perturbed distribution function, which is responsible for the formation of the echo, is observed to undergo a strong reduction in amplitude after the appearance of the echo electric field.

Ion‐acoustic solitary wave (solitons) have been studied experimentally by employing a double‐plasma device. The solitary waves are found to be produced from both a single compressional pulse and a continuous wave. A rarefaction pulse also produces solitons if the pulse width is sufficiently wide. A theory based on the Schrodinger equation accounts for the number of solitons. Recurrence to the original state is observed when a continuous wave is launched. A simple wave‐wave coupling analysis for the recurrence of the original state is given.

Theory and experiments of spatial ion‐wave echoes are reported. In the collisionless approximation, the calculated line shape of the second‐order echo is found to be a universal function of Δx/δ, the distance from the expected position of the echo divided by the Landau damping length of the ion‐wave constituting the echo. Higher‐order echoes predicted by Gould are observed up to the fourth order with respect to the external fields at the predicted positions with the predicted dependence of their amplitude on the amplitude of the primary waves. In addition, new types of higher‐order echoes which result from the electric fields of other echoes are predicted and observed. Measurements of the peak amplitude of the second‐order echo as a function of the separation l between the two exciters indicates that the memory of the past excitation retained in the distribution function damps exponentially with the attenuation length proportional to the wavelength of the excited wave. The effect of ion‐neutral collisions...