ROTATIONAL INSTABILITY IN THE THETA PINCH
An experimental study of the rotation and associated instability was made in a theta pinch with a peak field of 85 kG reached in 2.3 mu sec. The starting deuterium gas pressure was in the range 50 to 150 mu Hg, and for operation on the second half-cycle of the sinusoidal driving field the magnetic flux trapped within the plasma varied between plus or minus 100 kMx. In most conditions the circular cross section of the plasma became perturbed along its length by the growth of two flutes which rotated at an angular velocity of up to 6 x 10/sub 7/ rad/sec. It is deduced from measurenrents on the rotation that the plasma acquires its angular momentum at the start of the half-cycle, and the results are interpreted on the basis that the angular momentum is initially in a diamagnetic (azimuthal) ion current. A model is described for establishing this current as a consequence of contact between the plasma and the walls. Results on the time of onset of the instability, and on the growth rate of the flutes, point to the existence of some damping or stabilizing process; it is found that field diffusion, or a rapid axial contraction of the plasma (due to closed reversed field loops), can lead to instability, and when these are reduced the stable time is increased. The possible influence of finite Larmor radius stabilization is discussed. The stability condition, originally derived for low BETA but recently shown to have more general validity, is in qualitative agreement with the results. (auth)
- Research Organization:
- United Kingdom Atomic Energy Authority, Aldermaston, Berks, Eng.
- Sponsoring Organization:
- USDOE
- NSA Number:
- NSA-17-036786
- OSTI ID:
- 4660605
- Journal Information:
- Physics of Fluids (U.S.), Journal Name: Physics of Fluids (U.S.) Vol. Vol: 6; ISSN PFLDA
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
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