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This study exemplifies the use of TappingModeTM atomic force microscopy (AFM) surface morphology imaging to investigate and optimise the metalorganic chemical vapour deposition (MOCVD) growth conditions and post-growth stability of thin (

We summarize recent applications of two real-time optical diagnostic techniques, reflectance difference spectroscopy (RDS) and spectroellipsometry (SE), to epitaxial growth on GaAs and atomic layer epitaxy (ALE) in particular. Using RDS, we obtain the first real-time spectroscopic data of the evolution of the (001) GaAs surface to cyclic and non-cycle exposures of atmospheric pressure H 2 , H 2 and trimethylgallium, and H 2 and arsine, which simulate growth by ALE. None of our observations is consistent with any previously proposed simple model, emphasizing the necessity of real-time measurements for the analysis of complex surface reactions. Using SE we have constructed a closed-loop system for controlling the compositions of Al x Ga 1− x As layers grown by chemical beam epitaxy. We have produced various graded-compositional structures, including parabolic quantum wells 200 A wide where the composition was controlled by analysis of the running outermost 3 A (about 1 monolayer) of depositing material.

The primary transmission electron microscopy (TEM) imaging methods which are currently used to analyse III–V compound semiconductor heterostructures are discussed. InGaAs/AlGaAs/GaAs heteroepitaxial layers grown by molecular beam epitaxy were studied by cross-sectional TEM and energy dispersive spectroscopy (EDS). The presence of interfacial roughness, fine periodic striation contrast due to Al composition oscillations, layer contrast in the lattice images, and defects observed by TEM in selected samples are discussed. EDS on TEM was of limited utility in determining the composition of thin epitaxial layers and comparing the composition near and away from a defect.

The design of a tantalum nozzle for group V hydride cells in gas source molecular beam epitaxy is presented. The nozzle, which determines the flux distribution from the group V cell is optimized for uniformity and maximum flux utilization. Arsine cracking efficiency and relative concentrations of various gas species are measured by a quadrupole mass analyzer. The operating temperature for the source cell is determined as the region where maximum dimeric arsenic is available for growth.

A variety of optical methods is now available for studying surface processes and for monitoring layer thicknesses and compositions during semiconductor crystal growth by molecular beam epitaxy, organometallic chemical vapor deposition, and related techniques. New capabilities for surface analysis are provided by new techniques such as reflectance‐difference spectroscopy, which use intrinsic symmetries to suppress ordinarily dominant bulk contributions. Bulk and microstructural properties such as compositions and layer thicknesses can be determined directly by techniques such as spectroellipsometry, which return information integrated over the penetration depth of light. Proven capabilities suggest new applications to interrupted growth and to metastable materials systems involving self‐ordering and strain relaxation. The first closed‐loop system for controlling semiconductor crystal growth, which uses a spectroellipsometer as the monitoring element, is briefly described.

In this study, we investigate the dependence of GaN surface morphology on the absolute strain values for thin (c-plane sapphire substrates of various miscut angles towards the m-plane. Results indicate an excellent correlation between the surface roughness observed employing an AFM tool and epilayer strain values. An overall increase of surface roughness (decrease of atomic terrace width) is found with decreasing compressive strain (epilayer vs. bulk value). In addition, sapphire substrates with increasing miscut angle (0.30 deg) appear to relax the inherent, built-in strain differently in the vertical (growth) direction when compared to just (0.00 deg) substrates. Strain relaxation by typical V-shaped, hexagonal pits is directly imaged through the comparison of surface features inside and outside of pits in the thin GaN epilayer films.

The authors have studied the formation of InAlAs/InP interfaces grown by organometallic-MBE (molecular-beam epitaxy). They analyzed the photoluminescence emission at 5 K of a series of InAlAs/InP samples with different interface growth procedures, taking advantage of recombination across the type II interface which is very sensitive to the interface characteristics. Samples grown with different growth-halts, special interfaces with thin binary layers between the InP and InAlAs layers, and InP samples with an intermediate surface exposure to As/sub 2/ were investigated. TEM (transmission electron microscopy) and ellipsometry measurements are presented. The results are interpreted in terms of a P-As exchange effect during the InAlAs/InP formation. The most stable interface is obtained with the incorporation of a thin AlP interfacial layer, which can be understood by bond strength considerations. >

Nondestructive room temperature photoluminescence of the InGaAs channel of a pseudomorphic high electron mobility transistor is presented as a function of bias applied to a semitransparent gate. The channel electron sheet concentration is evaluated via line‐shape fitting of the photolumin‐ escence spectrum. Excellent agreement with electrically derived values of the channel charge was found. Information on the symmetry of the channel potential is also provided by the results of the photoluminescence line‐shape fit.

We report properties of the InAlAs/InP interface and its formation during growth by organometallic molecular beam epitaxy. Taking advantage of the photoluminescence emission occurring at this type II interface, we were able to directly investigate the interface characteristics for different growth conditions. A shift is observed in the energy of the interface recombination transition which we interpret as evidence of a P‐As exchange effect dependent on the specific growth sequence. This effect was further investigated by growing interfaces with thin layers (InAs, AlAs, AlP) between the InP and InAlAs. The results can be understood in terms of a model based on bond strength considerations. We predicted and demonstrated that the most stable interface is obtained with incorporation of a thin AlP interfacial layer.

Selective area growth (etching) by low‐pressure organometallic chemical vapor deposition (LP‐OMCVD) is utilized to intentionally modulate the local growth (etch) rate by choosing the pattern of dielectric‐masked areas, thereby defining III‐V semiconductor structures in situ. This technique is applied to tune the emission wavelength of a GaAs/AlGaAs quantum well structure, and to obtain InP/InGaAs superlattice structures tapered in thickness with growth rate increases as high as 800%, suitable for integrated optics applications. In contrast, selective deposition by organometallic molecular beam epitaxy (OMMBE) does not produce growth rate enhancements, thereby preventing similar in situ definition schemes but allowing to integrate structures with optimized nominal thicknesses.

Using spectroellipsometry, we obtain information on the near‐surface composition x of epitaxial AlxGa1−xAs layers during crystal growth by organometallic molecular beam epitaxy and use this information to regulate the flow of triethylaluminum to the growth surface. The resulting closed‐loop control system maintains the imaginary part of the dielectric response of thick AlxGa1−xAs films constant to an equivalent compositional precision better than ±0.001 over extended periods of time.

We report the first use of ellipsometry as a real‐time monitor of III‐V semiconductor crystal growth by molecular beam epitaxy, specifically growth of GaAs and AlGaAs from arsine, triethylgallium, and triethylaluminum sources. Our results provide new insight into the oxide desorption process and show a sensitivity of ±0.03 in compositions x>0.2 for 10 A thickness increments of AlxGa1−xAs during initial deposition on GaAs.

We investigate the formation of inAs-rich layers at the interface between InP and arsenicbased Ill-V alloys grown by chemical beam epitaxy (CBE). In-situ spectroscopic ellipsometry, low temperature photoluminescence, secondary ion mass spectrometry and transmission electron microscopy were used to characterize the formation of these layers. We present evidence for interfacial layer roughness that depends strongly on growth temperature and on the presence of surface steps, and show that modifications of the interface chemistry and of the gas-switching sequence can reduce interfacial layer thicknesses.

AlGaAs/InGaAs/GaAs heteroepitaxial layers grown by molecular beam epitaxy were studied by cross-sectional transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS). The presence of waviness/roughness, fine periodic striation contrast due to Al composition oscillations, and defects were observed by TEM in selected samples. EDS on the TEM was of limited utility in determining the composition of thin epitaxial layers and in comparing the composition near and away from a defect. Arguments are presented to rationalize these results.

A variety of optical methods are now available for studying surface processes and for monitoring layer thicknesses and compositions during semiconductor crystal growth by molecular beam epitaxy (MBE), organometallic chemical vapor deposition (OMCVD), and related techniques. New capabilities for surface analysis are being provided by developing techniques such as reflectance-difference spectroscopy (RDS), which use intrinsic symmetries to suppress ordinarily dominant bulk contributions. Bulk and microstructural properties such as compositions and layer thicknesses can be determined by techniques such as spectroellipsometry (SE), which return information integrated over the penetration depth of light. Recent advances include the application of reflectance to monitor dynamic surface processes, RDS to characterize (001) GaAs surfaces in OMCVD environments, and SE to control growth of AlxGa1-x, As materials and structures.

Using closed‐loop ellipsometric feedback control, we have grown a variety of epitaxial AlxGa1−xAs structures by chemical beam epitaxy where compositions x vary continuously with thickness according to a given input function. Present limits are exemplified by a 200 A parabolic quantum well structure grown using compositions determined from the outermost running ∼3 A (∼1 monolayer) of depositing material.

We present the growth habits of GaAs and InGaAs quantum wells grown by organometallic‐molecular‐beam epitaxy (OM‐MBE) on (100) GaAs substrates with micron‐range corrugations aligned along the [011] direction. The growth habits resemble those obtained by molecular‐beam epitaxy, but with several obvious differences, which are discussed on the basis of their different growth mechanisms. These differences reduce the importance of the geometric factors for OM‐MBE which dominate in MBE. We observe lateral compositional variations in the InGaAs quantum well. The patterned samples exhibit enhanced luminescence efficiency compared to reference flat samples.

We use a backdiffracted beam from a grating to establish accurately ellipsometric angles of incidence in configurations where samples cannot be accessed directly.

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.

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: $\frac{(1\ensuremath{-}{\ensuremath{\sigma}}_{J1})b}{{\ensuremath{\nu}}_{d}}$ equals 0.773527\ifmmode\pm\else\textpm\fi{}0.000016, ${c}_{p}$ is 85 600\ifmmode\pm\else\textpm\fi{}18 cps, ${c}_{d}$ equals 13 122\ifmmode\pm\else\textpm\fi{}11 cps, ${d}_{1}$ is 17 761\ifmmode\pm\else\textpm\fi{}12 cps, ${d}_{2}$ equals 22 454\ifmmode\pm\else\textpm\fi{}6 cps, and $\frac{f}{{H}^{2}}$ is (-26.90\ifmmode\pm\else\textpm\fi{}0.40)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}6}$ cps ${\mathrm{gauss}}^{\ensuremath{-}2}$. From these values of the interaction constants are derived the following physical quantities: the HD rotational magnetic moment $^{\mathrm{HD}}_{0}〈\frac{{\ensuremath{\mu}}_{J}}{J}〉_{1}$ equals 0.663211\ifmmode\pm\else\textpm\fi{}0.000014 nuclear magneton, the quadrupole moment $Q$ of the deuteron is (2.738\ifmmode\pm\else\textpm\fi{}0.014)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}27}$ ${\mathrm{cm}}^{2}$, the rotational magnetic field ${{H}_{p}}^{\ensuremath{'}}$ at the proton is 19.879\ifmmode\pm\else\textpm\fi{}0.006 gauss and ${{H}_{d}}^{\ensuremath{'}}$ at the deuteron is 20.020\ifmmode\pm\else\textpm\fi{}0.028 gauss, the internuclear spacing in the zeroth vibrational and first rotational state is such that $^{\mathrm{HD}}_{0}{〈{R}^{\ensuremath{-}3}〉}_{1}^{\ensuremath{-}\frac{1}{3}}$ equals (0.74604\ifmmode\pm\else\textpm\fi{}0.00010)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}8}$ cm, and the dependence of the diamagnetic susceptibility on molecular orientation (${\ensuremath{\xi}}_{\ifmmode\pm\else\textpm\fi{}1}\ensuremath{-}{\ensuremath{\xi}}_{0}$) is -(3.56\ifmmode\pm\else\textpm\fi{}0.20)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}31}$ erg ${\mathrm{gauss}}^{\ensuremath{-}2}$ ${\mathrm{molecule}}^{\ensuremath{-}1}$. 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, $^{\mathrm{HD}}_{0}〈{\ensuremath{\xi}}^{\mathrm{hf}}〉_{1}=(1.675\ifmmode\pm\else\textpm\fi{}0.005)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}31}$ erg ${\mathrm{gauss}}^{\ensuremath{-}2}$ ${\mathrm{molecule}}^{\ensuremath{-}1}$; the quadrupole moment of the electron distribution relative to the internuclear axis, $^{\mathrm{HD}}_{0}〈{Q}_{e}〉_{1}=(0.324\ifmmode\pm\else\textpm\fi{}0.010)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}16}$ ${\mathrm{cm}}^{2}$; and the high-frequency contribution to the magnetic shielding constant for HD, $^{\mathrm{HD}}_{0}〈{\ensuremath{\sigma}}^{\mathrm{hf}}〉_{1}=(\ensuremath{-}0.594\ifmmode\pm\else\textpm\fi{}0.030)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}.$

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.

An electron‐bombardment detector developed for the detection of noncondensable as well as condensable molecular beams is described. The ionization efficiency for a hydrogen deuteride beam is in the range of 10−5 to 10−4. Auxiliary components include: vacuum buffer chambers for source background gas reduction; a mass spectrometer for ion mass selection; an electron multiplier, electrometer, and phase‐sensitive detector combination for signal observation. Modulation techniques for beam and magnetic resonance detection are discussed. Efficiencies, background problems, and relevant noise sources are included in a discussion of operational characteristics. A resonance line trace produced by at most 3% of a total HD beam is presented to demonstrate the signal to noise ratio at low signal levels. The system has effectively detected beams of permanent gases such as HD, D2, and Ne.

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.

Three potential applications for the “ladder” siloxanes in photonic technologies are discussed. These are: (1) as a silica fiber cladding material for which a silica fiber core-siloxane cladding index depression (Δn) of 0.04 is observed; (2) as a fiber coating material to provide mechanical and environmental protection for which a siloxane coated silica core fiber is observed to have improved properties over a fiber coated with an epoxy-acrylate or linear siloxane. Thus, the ladder siloxane can serve a dual coating/cladding function; and (3) as the passive lightguiding element in planar optoelectronics for which the index depression (Δn), as compared to silica, is 0.04 for the cured siloxane. 0.02 for a fenestrated silica obtained by removing the organic component from the siloxane, or values between 0.02 and 0.0 obtained by sintering this fenestrated silica.

Results from the first end-stopping experiment on a high-energy (T/sub i/ approx. 1.5 keV, n approx. 10/sup 16/ cm/sup -3/) theta pinch are reported. The experiment was done with quartz end plugs. The results show that the insertion of the plugs improves plasma stability, reduces particle end loss out of the device, and improves the energy confinement.

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.)

Silicon nitride films deposited from silane-nitrogen and silane-ammonia mixtures by PECVD contain large amounts of hydrogen. We have determined that adding argon to the gas mixture reduces the amount of hydrogen in the resulting films. Differences in film composition are obviously due to changes in the chemistry of the discharge which was characterized by line-of-sight mass spectrometry, optical emission spectroscopy and plasma double probe measurements. Substrate temperature was fixed at 325°C, pressure was 500 mtorr, the RF power was 0.25 watts cm−2, the silane to nitrogen ratio was varied from 0.003 to 0.02, the silane to ammonia ratio was varied from 0.01 to 0.5, and the argon additions were 10% of the total gas flow. Argon additions to the discharge increased the plasma density in both nitrogen and ammonia plasmas. Optical emission from N2 and Si-H species increased upon the addition of 10% argon to the silane-nitrogen discharge, whereas the N-H emission decreased upon addition of argon to the silane-ammonia discharge. Infrared transmission spectra of films deposited with and without argon show no change in peak position or intensity of Si-H and N-H absorption bands in the spectral range studied, despite a large (over 20%) reduction in hydrogen content, as determined by nuclear profiling, upon the addition of argon. These results suggest that a substantial fraction of the hydrogen in the films is not infrared active. We propose that the reduction in hydrogen content is due to bombardment of the growing film by argon ions, which sputter the adsorbed hydrogen molecules.

The pyrolytic conversion of an organosilsesquioxane (Owens-Illinois resin GR650) to SiO2 is characterized by ir spectroscopy, thermogravimetry and evolved gas analysis (line-of-sight mass spectroscopy). Scanning calorimetry, ramping at 10°C/min, on the as-received (room temperature annealed) resin indicates a glass transition temperature of 67°C which decreases to 58°C for an unrelaxed sample. The ir spectra have bands which can be assigned to Si-CH3 and Si-O-Si modes. For 30 minute isothermal anneals at temperatures above 420°C there is a continuous decrease in the bands associated with the Si-CH3 groups such that after 30 minutes at 650°C the ir spectrum has evolved to that for SiO2. Evolved gas analysis indicates that there are four major components evolving. Over the temperature range (ramping at 10°C/min) ∼180 to ∼500°C we observe C2H5OH and H2O, both of which are condensation reaction products from the curing reaction. Methane is a major evolving species over the temperature range ∼500 to ∼800°C and the thermal spectrum is double peaked which we attribute to CH3+ bound to the inside and outside of the polymer cage structures. The final major component detected was H2, over the temperature range ∼600 to ∼1100°C, which was attributed to pyrolysis of the organic components, both trapped and evolving. The features of the weight loss curve can be accounted for by the measured evolving species spectra.

The properties necessary for a material to be useful as a fiber cladding (appropriate Δn) and/or coating (provide mechanical protection) were evaluated for an organosilsesquioxane (Owens-Illinois Resin GR 650). The samples were 120 μm silica fibers coated with 12 μm of the cured organosilicon polymer. We observe, from an index profile of the clad fiber, that Δn = 0.04. The tensile strength measured in air (65% RH, 25 °C) was 765 ksi and the dynamic fatigue constant determined under the same ambient conditions was 29, both of which are typical of a mechanically protected fiber. From aging experiments in 90 °C distilled water we observe that the onset for a marked loss of strength with time is ∼1 day for an epoxy-acrylate coated fiber and slightly more than a week for the organosilicon polymer coated fiber, a notable improvement.

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.