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.
Stability of laminar electron layers
The stability of a finite thickness, laminar cylindrical shell of electrons rotating azimuthally and enclosed in a coaxial waveguide is considered. The equilibrium rotation of the electrons is supported either by a radial electric field, an axial magnetic field, or a combination of both. The stability problem is formulated exactly as an eigenvalue problem, including all relativistic and electromagnetic effects as well as all effects of self and applied equilibrium fields. An approximate dispersion relation, valid for thin beams, is obtained analytically and the classical results for the ‘‘longitudinal’’ modes, i.e., the negative mass, cyclotron maser, and diocotron instabilities and for the ‘‘transverse’’ mode are recovered in appropriate limits. The dispersion relation is relatively simple and is valid for arbitrary values of the equilibrium electric and magnetic fields and for arbitrary beam energy. It therefore provides a ready comparison of the small signal properties of such devices as the Astron, gy...
Negative Mass Instability with Bθ Field
Earlier negative mass instability calculations with a mirror magnetic field have been extended to also include a Bθfield. The plasma is contained in a torus, of elliptical cross section, which is radially thin. From a new dispersion relation it is found that: (a) for a cold plasma the negative mass instability persists even for large Bθ, although the growth rate goes as Bθ−1; (b) for a finite velocity spread plasma, the addition of a Bθ field allows much higher densities, because the stability criterion becomes independent of density. These results appear to explain the beam disruption observed on the Stevens Institute plasma betatron surprisingly well.