Steady-State Orbitron Emissions
The Orbitron maser has been operated at a pressure of 2 × 10-6 in the steady state. Electrons are supplied to the device by an oxide-coated tungsten cathode placed inside the cylindrical cavity. The plasma-free emission corresponded to harmonically related steady-state narrow lines. The fundamental (lowest frequency) line corresponds to a resonance in the cavity system, which could be observed with a grid-dip meter.
Millimeter microwave emission from a maser by use of plasma-produced electrons orbiting a positively charged wire
Plasma-produced electrons have been trapped for long periods of time in orbits around a positively charged wire. Since the frequency of rotation of each electron increases if it loses kinetic energy and sinks into the positive-potential well, phase bunching resulting in intense microwave emission can be easily excited.
New Low-Profile Applicators for Local Heating of Tissues
A new type of low-profile applicator is described giving efficient power transfer to tissue with low leakage. It consists of a resonant element spaced from a ground plane by low-loss material having high relative permittivity and some relative permeability. This combination is covered by similar material which can be placed in direct contact with the tissue to be heated, or separated from it by a water bolus as required. Laboratory measurements using phantom materials show that these applicators are well matched and produce well defined and relatively uniform heating profiles. Applicators having maximum dimensions of 3-15 cm covering the frequency range 1000-100 MHz, respectively, are described. Penetration depths of at least 4 cm at 100-200 MHz are achieved. Tests on anesthetised pigs and some clinical assessment have confirmed the usefulness of this compact low-frequency type of applicator and have shown that performance compares favorably with that of other recently reported types. The design can be optimized for treatment of specific sites, and suitable choice of dimensions and electrical characteristics of the layer material allow the low-profile concept to be extended over a wide range of operating frequencies.