INVESTIGATION OF POSITIVE COLUMN ABOVE CRITICAL FIELD

An experimental investigation, which includes detailed spatial correlation measurements, reveals that the helium positive column is dominated up to many times the critical magnetic field by a finite amplitude helical osculation. The equations describing this situation are solved by introducing into them experimental values for some of the variables. With this technique it is possible to avoid the use of unrealistic boundary conditions. The calculated values of axial wavelength, helical rotational frequency, and the magnitude of the radial flux of ions are in fair agreement with experimental values. The calculated growth rate is essentially zero up to four times the critical field, in agreement with the theory of Holter and Johnson, but increases steadily with further increase in magnetic field. A possible explanation of the latter region is that the previously stable helical oscillation turns into a helical relaxation oscillation. While the results of this investigation are contrary to the requirements of the turbulence theory of Kadomstev, there is a faint indication that the system may become turbulent at very high magnetic fields.