Measurements are described of the behaviour of 100-200 kA discharges in a variety of configurations of the general pinch and hard-core type. The systems were studied using a variety of internal and external magnetic probes, by electrostatic double probes and by fast photography. Correlation of the magnetic field fluctuations measured by the various coils enabled the axial wave number k and azimuthal mode number m of the perturbation to be deduced. In both pinch and hard-core cases the predominant mode number was m = 1 and the sign and magnitude of k were such that the perturbation was helical with a direction parallel to that of the mean magnetic field. Framing camera pictures of the discharge supported these results. Increasing the azimuthal magnetic field at all radii in the hard-core case was found to reduce the amplitude of the magnetic fluctuations and a discharge stable on this basis was achieved. By contrast, increasing the axial field at all radii had a slight de-stabilizing effect. Programming the axial field so as to have a null at some radius made the discharge violently unstable. Electric field measurements in stable and unstable hard-core discharges showed irreproducible fluctuations in the latter case of similar 10 V/cm and frequencies 500 kc/s - 1 Mc/s. Langmuir probe measurements of the plasma density in pinch and hard-core discharges showed a well-confined plasma only in the hard-core case. These results are shown to be in good agreement with the theory of hydromagnetic stability when, and only when, the effect of finite electric conductivity is included.
No takes yet. Share an insight, caveat, or question.
Aitken et al. (1964) studied this question.