Localized Power Deposition Research Articles

Local power deposition for the perpendicular propagation of an ordinary wave across the electron cyclotron resonance layer

It is shown how the concept of local power deposition can be identified with the time rate of increase of the particle kinetic energy density at second order in the linearization procedure. The secular behaviour of the second order part of the distribution function is also explicitly pointed out.

Electron cyclotron interaction in the lower hybrid heating regime

The analysis of the down shifted resonant interaction of electron cyclotron waves in a Tokamak, operating in the lower hybrid heating regime, has been performed by a numerical computation of the ray trajectories, the local relativistic power absorption and the driven current density profile. Top and equatorial launch have been considered. The conditions for localized power deposition and efficient current drive, suitable for current density profile modifications, have been investigated in terms of the injection and plasma parameters. The physical interpretation of the results has been given through the analysis of the electron resonance with both LH and EC waves in momentum space, of the corresponding spatial resonant regions and of the refractive effects. The results are applied to the injection of EC waves at 140 GHz in FTU.

A model for impedance determinations and power deposition characterization in three-electrode configurations for capacitive radio frequency hyperthermia--Part B: Current flow and power deposition.

The 2-D rectangular model for three-electrode radio frequency hyperthermia applicators established in Part A is applied to the determination of the current lines and the potential lines inside the system. Any electrode voltage distributions can be considered. Two figures illustrate the impact of the electric and the geometric parameters on these lines. They show that important changes in local current density, in electric field strength, and in electric field orientation are tied to the adjustments of the relevant parameters. Two successive sampling processes lead to the determination of the local power deposition. The figures which are displayed demonstrate the ability to move this deposition inside any useful area by means of proper trimming of the electrode voltage phases and magnitudes.

A Microwave Decoupled Electrode for the Electroencephalogram (Short Papers)

The recording of the electroencephalogram (EEG) in an amplitude-modulated microwave field presents two related but distinct problems when conventional electrodes are employed. The electrode and its associated conductors extract power from the incident radiation, resulting in increased local power deposition which confounds dosimetric arguments and imposes local thermalization; the electrode tissue interface is a nonlinear system that demodulates amplitude-modulated signals with the results that the demodulate is additively mixed with the EEG. The problems were studied in a series of bench tests with conventional and thin-film microwave integrated circuit (MIC) electrodes. The latter are decoupled from the magnetic component of the field by virtue of radically reduced dimensions of the thin-loop component of its geometry, and suppression of dipole (i.e., electric field interaction) currents by use of integrated Nichrome series resistance. The result is that the demodulation artifact is undetectable in the ensemble averaged-power spectrum from the in vitro electrode up to an S-band incident-power density of 100 mW/cm/sup 2/. Thermalization was studied in a dielectric brain phantom with high-resistance monofilament leads to the MIC with a result that 0.6/spl deg/C heating is attributable to the electrode with prolonged exposure to a 50-mW/cm/sup 2/ field.