Helium gas at a pressure of 60 mtorr is contained in a discharge tube of 4.8 cm dia. and 49 cm length which is equipped with end electrodes and is situated within a multi-turn solenoid. The gas is preionized by means of an axial current pulse of 9.5 kA amplitude and 32 μsec duration. Following the preionization pulse, two high power r.f. generators, each capable of delivering pulses of 7 periods at a frequency of 3.10 Mc/s, are triggered. One generator produces an oscillating axial current in the preionized plasma while the other induces an oscillating azimuthal current. The generators are adjusted to give equal B θ and B z peak amplitudes at the inner wall of the discharge tube. These peak amplitudes reach a maximum value of 2.2 kG. When the two oscillating currents are dephased by 90°, the plasma experiences the continuous magnetic pressure exerted by a rotating field. Streak photographs show that the plasma separates from the tube wall and implodes towards the axis. Framing pictures show that cylindrical symmetry is maintained during this implosion. The implosion stage of the pinch is shown to be well represented by a solution of the appropriate snowplow equation. 1.1 μsec after the initiation of the r.f. discharge, luminosity again appears in the region of the tube wall and stays there for the remainder of the discharge. This light is associated with the production of conducting material at the wall and a subsequent growth of currents in this material. Measurements made of the time variation of the inductance of the pinch support this conclusion.
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Jones et al. (1968) studied this question.