Small-scale Plasma Research Articles

Microwave scattering by turbulent plasma

Microwave transmission across a column of turbulent plasma is strongly influenced by the presence of small-scale plasma density inhomogeneities. In devices such as ZETA, fluctuations of 10-25% about mean densities of 1014 cm-3 have been observed with correlation lengths of up to 5-10 cm and time scales of 10-5 s. Scattering measurements have used microwaves with a free-space wavelength of 2 mm (corresponding to a critical density of 2.5*1014 cm-3) and in ZETA multiple scattering processes are important. A numerical solution for the transport theory formulation of multiple scattering is used to interpret the measurements and good agreement with Langmuir probes is obtained.

Plasma Injection into a Magnetic Field of Cusped Geometry

A plasma stream was directed from a field-free region along the axis of symmetry into a magnetic field of biconical cusped geometry. No evidence was found to support the hypothesis that a directed plasma stream can not penetrate a magnetic field whose value exceeds Bc2 = 12πρv2, where ρ is the plasma density and v its directed velocity. As the plasma penetrated the magnetic field, the plasma and field were found to intermix. Large quantities of the plasma which entered the containment region through one point cusp were found to leave promptly through the second point cusp and through the line cusp. Bombardment of the vacuum chamber walls in the vicinity of the line cusp generated sufficient secondary ions to mask any small scale plasma trapping. However, there was no evidence of gross trapping of the injected plasma.