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The formation, confinement and stability of two types of compact toroids, spheromaks and field reversed configurations (FRC), are reviewed. Spheromaks, which contain both toroidal and poloidal magnetic fields, have been formed with magnetized coaxial plasma guns, by a combination of Z- and θ-pinch techniques and by an electrodeless slow induction technique, and trapped in both prolate and oblate flux conservers. As predicted by theory, the prolate configuration is unstable to the tilt mode, but the oblate configuration with a conducting wall is stable. Configuration lifetimes of up to 0.8 ms are observed. The FRC is a high-beta, highly prolate compact toroid formed with field-reversed theta-pinch techniques and having purely poloidal magnetic field. Theory predicts unstable fluting and internal tilting modes, but they are not observed experimentally. Configurations with high densities ~ 1015 cm-3 and with lifetimes of 50–120 μs are terminated by an n = 2 rotational mode of instability.

The identification of a sharp low-wavelength cutoff in the spectrum of x rays emitted from deuterium discharges in Scylla has resulted in the assignment of an electron temperature of 240\ifmmode\pm\else\textpm\fi{}40 ev at the time of peak magnetic field compression. Simultaneous time-resolved absolute intensity determinations in the visible continuum, when coupled with the temperature measurement, yield an upper limit electron number density of (5\ifmmode\pm\else\textpm\fi{}1)\ifmmode\times\else\texttimes\fi{}${10}^{16}$/${\mathrm{cm}}^{3}$ at peak compression. The absolute value of $\frac{\mathrm{dE}}{d\ensuremath{\lambda}}$ in the soft x ray region is two hundred times larger than bremsstrahlung from a pure deuterium plasma at the temperature and density quoted, and it is postulated that the large experimental $\frac{\mathrm{dE}}{d\ensuremath{\lambda}}$ is the result of recombination radiation from about 2% of oxygen contaminant from the discharge tube walls.

The Scylla plasma experiment, which employs a rapidly rising magnetic field in a cylindrical mirror geometry to produce and heat a deuterium plasma, is described. Experimental studies of the reproducible neutron emission from the hot plasma show that the neutrons are emitted (1) in a symmetrical, bell-shaped time distribution centered on the maximum of the magnetic field, (2) from a limited region with a 2-cm axial length and a 1.5-cm diameter centered in the compression coil, and (3) in the radial direction with a narrow spread of energies and no significant anisotropy. The time distribution of the neutron emission is shown to be in agreement with a thermonuclear yield curve calculated for an adiabatic compression by the observed magnetic field. The neutron yield has been studied as a function of deuterium pressure, capacitor-bank voltage, and nitrogen impurity. Observations of the space-time distribution of the visible light emission with a streak camera show that (1) a strong radial "shock" occurs at the beginning of the second half-cycle, (2) very little light is emitted from the plasma "fireball" during the time of neutron emission, and (3) an intense luminous flux is produced during the later stages of the discharge. The energy absorbed in each half-cycle of the discharge by the gas is presented as calculated from the incremental damping of the driving magnetic field. Observations of hard x-ray emission (\ensuremath{\sim}200 kev) at times of maximum $\frac{\mathrm{dB}}{\mathrm{dt}}$ for operating pressures in the 5- to 50-micron range are contrasted with the characteristics of the neutron emission in regard to time distribution, pressure, impurities, and rf pre-excitation. Magnetic probe studies of the Scylla discharge are reported and evidence is given that the perturbing effects of the probe dominate the plasma temperature.

A diagnostic experiment has been carried out on the $d\ensuremath{-}d$ reactions produced by fast magnetic compression of a deuterium plasma. A determination of the velocity spectra of protons and of tritons from the $d\ensuremath{-}d$ reaction was made by magnetic analysis and nuclear plate detection of the particles. The observed distributions are Gaussian, with widths which correspond to a deuteron temperature of 1.3 kev. Comparison of the mean proton and triton momenta indicates that no plasma drift in the (axial) direction of observation is present, nor any potential difference between the source plasma and detector greater than a few volts. These results, coupled with previous ones on the neutron yield, duration, source extent, and lack of circumferential drift argue against any of the simple, physically plausible non-Maxwellian acceleration mechanisms for the $d\ensuremath{-}d$ reactions so far proposed.

Neutrons were produced from a deuterium plasma compressed by a rising axial magnetic field. The device used, named Scylla, at present employs three single-turn coils. The emission of both x rays and neutrons were observed during the second and to a lesser extent later compressions. X rays, when observed, occur during the beginning and the end of a compression cycle when the electric fleld is high. In contrast, neutrons occur only in summetrical bursts lasting about 1 mu sec centered on the instant of compression. (M.H.R.)

An experiment is described which was designed to measure directly the ion temperature in Scylla. By studying the velocity spectrum of products of the reaction D(d,p)T, the mean square velocity of the d-d system center-of-mass was measured, and the plasma temperature was inferred. A temperature of T = 1.3 kev was determined. (W.D.M.)

End‐loss experiments on the high‐energy (Te+Ti=3.3 keV, ne=1.5×1016 cm−3) 5 m Scylla IV‐P theta pinch are reported. The evolution of the theta‐pinch plasma parameters in the presence of axial losses and the behavior of the exhausting plasma near the ends of the device have been investigated. The measured decay of the theta‐pinch plasma electron temperature agrees with code predictions based on classical axial thermal conduction losses. However, the axial ion heat flux is found to be unmeasurably small in the collisionless ion plasma. Energy‐line‐density measurements at the coil midplane also agree with code predictions and provide evidence of inward traveling rarefaction‐like waves. At the theta‐pinch ends, the exhausting plasma is comprised of a collimated plasma core which remains radially confined for tens of centimeters, strongly convects magnetic fields, and contains the bulk of the ejected plasma. This collimated core is surrounded by a plasma annulus that expands rapidly to the walls after leaving the theta‐pinch coil. The radially confined exhaust plasma is successfully modeled as one‐dimensional flow through a converging‐diverging nozzle. The new results obtained in Scylla IV‐P have led to a re‐analysis of the particle end‐loss data obtained in previous experiments. The subsequent comparison of experiments and theory shows that the normalized particle end‐loss time is independent of both the plasma beta and collisionality regime.

Small helical fields have been added to the main compression field of a 3‐m long theta pinch, both by grooving the main compression coil and by adding helical windings driven by capacitor banks. The equilibrium and stability of the theta‐pinch plasma column and the interference force produced by a combination of helical fields have been studied and are found to be in agreement with theory.

The injection of the plasma, produced by the collision of two D plasmas from coaxial guns, into the Scylla magnetic compression device is studied. The plasma formed by the two guns generally has fast and slow components. The neutron production obtalned by trapping each of these components is measured for the cases in whlch the guidlng magnetic field is parallel or antiparallel to the compression field. These measurements are also made using only one of the plasma guns. The use of this plasma injection device is compared with the older Scylla method. (T.F.H.)

The effects of strong preionization and the application of steady bias magnetic fields on the operation of the magnetic compression device Scylla are studied. It is shown that both strong preionization and a bias field B0 antiparallel to the main compression field Bz are necessary to produce neutrons during the first half‐cycle of Bz. Other aspects of the plasma activity are also shown to depend strongly upon the sign of B0. Application of bias fields with weak preionization leads to production of hard x rays which occur on the half‐cycle of the discharge which precedes that of neutron emission. When hard x rays are produced the plasma is not hydromagnetic. The hard x rays are extinguished when there is strong preionization, leading to a hydromagnetic plasma. In the case of the hydromagnetic plasma it is concluded that antiparallel B0 plays its role early in a given half‐cycle and affects the plasma primarily during its preheating, ionization phase, rather than during the adiabatic‐compression phase which follows it. An interpretation is given in terms of a plasma sheath which has special properties when it separates magnetic fields of opposite signs.

A hexapole magnetic field has been superimposed on the fast magnetic mirror compression field of the Scylla III θ pinch in an attempt to stabilize an observed plasma instability. The instability is of the flute type with a superimposed rotation. The effect of the hexapole field on the plasma stability was studied with streak camera photography and through observation of the neutron emissions. Under certain conditions the hexapole ``stabilizing'' field has an observable effect on the instability. Its main effect is to symmetrize the rotation about the axis of the compression coil and to produce a delay in the onset of the instability. There is at most a small effect tending to symmetrize the time distribution of neutron emission and to increase the neutron yield.An ionized deuterium plasma is produced by a fast, low energy capacitor bank coupled directly to the single‐turn compression coil of the Scylla III device. The ``afterglow'' of this preionization discharge, uniformly permeated by a magnetic bias fi...

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

Faraday rotation measurements have been combined with Mach‐Zehnder interferometer measurements to yield the value of the internal magnetic field Bi in the Scylla IV plasma as a function of time and radius. Since the Faraday rotation is proportional to ∫ Bi(l)ne(l) dl and the Mach‐Zehnder interferometer provides ∫ ne(l) dl, the data give the average value of the internal magnetic field Bi(r) which exists over the plasma length l at the radius r. The measurements of Bi(r) are combined with those of the external magnetic field Be to determine the average plasma β as a function of radius, β = 1 − Bi2(r)/Be2. The Faraday rotation measurement employs a 1.5‐mm diam beam of visible radiation (6328 A) from a He‐Ne gas laser as a plasma magnetic‐field probe and a calcite Wollaston prism as the polarization analyzer with silicon diode detectors. In the low‐pressure plasma regime (10‐25 mTorr) the β values in the central plasma‐core (∼5‐mm diameter) range in value between 0.9 and 1.0 with initial reversed bias magnetic fields and between 0.7 and 0.95 without bias fields. Radial profiles of β averaged over the plasma length have been obtained at various times during the discharge. A combination of β, n, and Te in the simple pressure balance yields ion temperatures in the 2‐ 6‐keV region.