[en] We investigate the radiation properties of an antenna that was formed by a hybrid combination of a monopole radiation source and a cavity built around a dielectric layer-by-layer three-dimensional photonic crystal. We measured a maximum directivity of 310, and a power enhancement of 180 at the resonant frequency of the cavity. We observed that the antenna has a narrow bandwidth determined by the cavity, where the resonant frequency can be tuned within the band gap of the photonic crystal. The measured radiation patterns agree well with our theoretical results. (c) 2000 American Institute of Physics

[en] The radiation of a vertical electric dipole over an electrically homogeneous sphere is considered anew, starting with a novel mathematical formulation. Both the dipole and the point of observation are assumed to lie on the spherical interface. The analysis is valid for a sphere whose radius is much larger than the wavelength in the outside region. Contributions to the value of the fields come, on the one hand, from the waves that propagate along the interface and, on the other hand, from the waves that propagate through the sphere by successive reflections. (c) 2000 American Geophysical Union

[en] Preliminary high power tests have been performed on a folded waveguide (FWG) ICRF launcher with a curved coupling faceplate installed. Two alternative faceplate configurations have been built and tested at low power and will be tested at high power in the near future. The new designs include a dipole plate which provides a 0-π launch spectrum and a more transparent, flexible monopole face plate configuration. This FWG design is a 12 vane, 57 MHz design with a 0.31 m square cross section. The FWG can be installed with either fast wave or ion-Bernstein wave polarization and can also be retracted behind a vacuum isolation valve. A 1x4 FWG array optimized for fast wave current drive on DIII-D has been conceptualized. (c) 1999 American Institute of Physics

No abstract available

[en] The 30 MHz high harmonic fast wave (HHFW) antenna array for NSTX consists of 12 current straps, evenly spaced in the toroidal direction. Each pair of straps is connected as a half-wave resonant loop and will be driven by one transmitter, allowing rapid phase shift between transmitters. A decoupling network using shunt stub tuners has been designed to compensate for the mutual inductive coupling between adjacent current straps, effectively isolating the six transmitters from one another. One half of the array, consisting of six full-scale current strap modules, three shunt stub decouplers, and powered by three phase-adjustable rf amplifiers had been built for electrical testing at ORNL. Low power testing includes electrical characterization of the straps, operation and performance of the decoupler system, and mapping of the rf fields in three dimensions

[en] The rotating polarization wave (RPW) communication technique uses two different waves that have very closely related carrier frequencies. The sum of these carriers provides a beat wave with an envelope that oscillates at a frequency that is half of the difference of the two carrier frequencies. The RPW consists of the first beat wave transmitted from the first linearly polarized antenna and a second beat wave transmitted with a 90° delay (with respect to the envelope oscillating frequency) from the second linearly polarized antenna, which is spatially perpendicular to the first antenna.

[en] A coaxial antenna for the heating of toroidal plasmas has been conceived and constructed. Being wholly metallic (stainless steel), the several coaxial ceramic passages assuring the transit of the H.F. energy into vacuum being situated far from the plasma, the use of such antennas can be envisaged in next generation machines where the environment is particularily severe. The coaxial design (having a lower internal impedance than a wave guide) reduces the electric fields present in the antenna-plasma interface, assuring, at the same time, a spatial uniformity of the fields making possible a substantial reduction in the transmitted power density. The main technological advantages (with respect to a wave guide grill structure) are: (a) simplification of the construction especially in multi-channel systems (b) quasi-elimination of the problems associated with the ceramic windows transmitting the H.F. energy (c) absence of a low frequency cut-off making possible to place launching structures in vertical chimneys where space is limited (d) an eventual reduction of certain phenomena inherent to this type of heating such as particle acceleration, space charge separation, pondemotive forces etc

[en] In this paper we study the underlying physics for the radiation from simple metallic antennas—the role played by the microscopic motion of the charge within the conductor forming the antenna. On the macroscopic scale, the radiation from the antenna is shown to be due to the time derivative of the volume density of current, which on the microscopic scale is caused by the spatial average for the acceleration of the electrical charges that make up the conductor. To provide additional insight for this general result, a specific microscopic model for the conductor is examined: the classical free-electron model for a metal. (paper)

[en] A complete analysis of an ICRH antenna system is given yielding practical criteria for design optimisation relevant to large machines. After having analysed the screening effect of an electrostatic shield, a solution is presented for the field distribution around an electrostatically shielded antenna from which the effect of the plasma on the loading and the reactance of the antenna can be obtained. A general procedure for the application of these results to multple antennae system is outlined and practical rules are derived for optimizing the rf power unit antenna surface coupled to the plasma

No abstract available