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Experiments are reported on helical plasma equilibrium and stability in the Scyllac toroidal θ-pinch sectors (120°) which have major radii of 2.375 and 4.0 m with coil arc lengths of 5.0 and 8.4 m, respectively. In these experiments the outward toroidal drift force was compensated by a combination of ℓ = 1 helical and ℓ = 0 bumpy fields which are generated by shaping the inner surface of the compression coil or by driven ℓ = 1 windings. Time-resolved measurements were made of the gross plasma-column motion, the plasma radius, the magnetic flux excluded by the plasma, the external magnetic field, the plasma density, the electron and ion temperatures, and the plasma β at axial locations of minimum and maximum plasma radius. These data are used to study the approach to the theoretically predicted toroidal equilibrium (including axial pressure equilibrium). The plasma column remained in stable equilibrium for 7 – 10 μs in the 8-m sector compared with 4 – 7 μs in the 5-m experiment, at which times the onset of a terminating m = 1, k ≈ 0 sideways motion occurred. The results show that the plasma achieved axial pressure equilibrium (nkT = const) in 4 – 6 μs, while maintaining equilibrium in the toroidal plane for 10 μs or longer. The measurements of the plasma radius, β and magnetic field in the various experiments have confirmed in detail the stable toroidal equilibrium observed in the streak photographs during the first 4-10 μs of the discharge. The observed toroidal equilibria of the high-β, θ-pinch plasma are in quantitative agreement with MHD sharp-boundary theory and confirm the theoretical scaling of the equilibrium field between the 5-m and the 8-m sector experiments.

A neutron-producing plasma with ion energy ∼3–4 keV has been produced at filling densities 10–50 μHg without negative bias magnetic fields in a 570-kJ theta pinch. Axial interferograms, taken with a ruby-laser-illuminated Mach—Zehnder interferometer show that a stable compressed plasma core exists throughout the magnetic half cycle with no ionized impurities outside the core, and no drift toward the wall. The interferograms give peak plasma densities of 2 to 5 × 1016 cm-3, and also indicate a loss of particles as a function of time. Plasma containment times (e-folding times of N) before peak compression are 6 to 30 μsec. The observed loss rates are approximately in agreement with predictions of free flow through an orifice whose radius is equal to an ion Larmor radius. Soft x-ray measurements yield ∼300 eV electron temperature for all filling pressures. Absolute intensities of the soft x-ray emissions show the impurity level to be <0.1%. The ion energy for the low-pressure regime deduced from pressure balance between plasma and magnetic field (assuming β = 1) is about a factor two higher than the ion energy deduced from the measured neutron yield for a Maxwell distribution. The discrepancy suggests that the distribution is more nearly monoenergetic than Maxwellian.

Molecular beam observations have been made of the radiofrequency spectra corresponding to reorientations of the deuteron, proton, and rotational magnetic moments in the HD molecule. For HD in the zeroth vibrational and first rotational state, these observations were made in magnetic fields of approximately 1700, 3400, and 4800 gauss. The results are found to be consistent with the theory of heteronuclear diatomic molecules. The direct result of these experiments is the determination of the Hamiltonian interaction constants: (1-crji)b/vd equals 0.773527 ±0.000016, c p is 85 600±18 cps, c d equals 13 122iU cps, di is 17 761±12 cps, d 2 equals 22 454±6 cps, and f/H 2 is (-26.90 ±0.40) X10 -6 cps gauss -2 . From these values of the interaction constants are derived the following physical quantities: the HD rotational magnetic moment KD O(JJ.J/J)I equals 0.663211 ±0.000014 nuclear magneton, the quadrupole moment Q of the deuteron is (2.738±0.014)X10~2 7 cm 2 , the rotational magnetic field B v ' at the proton is 19.879±0.006 gauss and H/ at the deuteron is 20.020±0.028 gauss, the internuclear spacing in the zeroth vibrational and first rotational state is such that HD o(i?~3)r* equals (0.74604±0.00010)X10~8 cm, and the dependence of the diamagnetic susceptibility on molecular orientation (£±i -£o) is -(3.56±0.20)X10~3 1 erg gauss -2 molecule -1 . Combining these values with Ramsey's theory on zero-point vibration and centrifugal stretching in molecules gives the high-frequency contribution to the molecular susceptibility, HD o(£ hf )i= (1.675±0.005) X10~3 1 erg gauss -2 molecule -1 ; the quadrupole moment of the electron distribution relative to the internuclear axis, HD o(&)i = (0.324±0.010)X10 -16 cm 2 ; and the high-frequency contribution to the magnetic shielding constant for HD, HD^hf)^ (-0.594±0.030)X10 -5 .

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