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The rapid onset of quasiparticle tunneling current in superconductor-insulator-superconductor (Josephson) junctions at voltages above 2 delta/e is being used for millimeter wave heterodyne mixing. Junctions with 2 micron diameter and RN = 50 ohms have little capacitive shunting at the signal frequency of 36 GHz. Because there is no series resistance, residual capacitance can be tuned out. Single sideband conversion efficiencies of 0.18 and mixer noise temperatures as low as TM approximately 14K have been observed. Both results agree with shot noise limited mixer theory. Photon assisted tunneling effects are seen which indicate the approach to photon noise limited operation. (Author), Prepared in cooperation with National Bureau of Standards, Boulder, CO.

This paper studies the propagation of weakly nonlinear waves. The analysis is applicable to plasma waves, surface water waves, the interaction of laser beams with matter, particle accelerators, etc. The specific motivation for this work is, however, the study of internal waves in the ocean. Hamilton's principle is used to write the fluid equations in Hamiltonian form in terms of linear eigenmode amplitudes. Numerical studies are made of the effect of Fourier grid size and resonance widths. Statistical information is generated from an ensemble of initial states of the random wave field. (Author)

The results of extensive analog computer simulations of a Josephson junction used as a mixer with an external local oscillator are presented. The Resistively Shunted Junction model was used throughout, and the effects of intrinsic junction noise were included. When the source impedance is much greater than the junction resistance R our simulations permit predictions of conversion efficiency, noise temperature, and saturation level to be made for a wide range of experimental parameters. The possibility of harmonic mixing has also been considered. With a source resistance comparable to R (i.e., conventional matching) the behavior of the system is too complicated to permit such general predictions of performance. From the results of simulations for a particular set of parameters it appears that the best noise temperature will usually be achieved for a source impedance somewhat greater than R. An upper limit for the mixer noise temperature is approximately 40 T over a broad range of junction parameters, where T is the effective temperature of the junction. The Conversion efficiency under these circumstances should be comparable to what is potentially available from Schottky diode mixers. Our simulations show that with stronger microwave coupling it is possible to obtain conversion gain - i.e., a conversion efficiency exceeding unity. This, however, will probably be at the expense of a higher mixer noise temperature.

The properties of point contact Josephson junctions operated as mixers with an external local oscillator at 130 GHz have been studied, and the results compared with predictions of the resistively shunted junction model. It was found that the junctions output noise could be within a factor 1.5 of the model prediction based on thermal driving noise. When the coupling to the rf source was optimized, a factor two discrepancy was typical. The measured conversion efficiency agreed with the model, within the experimental uncertainty in the equivalent microwave circuit. The best coupling was achieved in full-height waveguide. The best overall performance, measured using the hot/cold source technique, was a single side band conversion efficiency of 0.30 and mixer noise temperature of 180 K (both + or - 20%). The best junctions were made of Nb, with carefully prepared points. Nonideal behavior in other junctions is ascribed to heating effects. There is some evidence that junctions whose resistance exceeds a threshold value of approx. 60 ohms are no longer well described by the RSJ model. A discussion is given of possible improvements in performance with better junctions or improved rf matching. (Author)

Significant progress has been made during the past two years in the development of millimeter wave superconducting devices. The present status of bolometric detectors and mixers, Josephson effect mixes, quasiparticle mixers, and Josephson effect parametric amplifiers will be reviewed. (Author)

We have observed doubly degenerate parametric amplification and oscillation at 36 GHz from a single point contact Josephson junction. The experimental results agree qualitatively with theoretical calculations based on the resistively shunted junction model. The estimated noise temperature of an amplifier with 11 dB net gain is consistent with zero, but has an upper limit of 50 K. Attempts to observe parametric amplification in the singly degenerate mode with a pump frequency of 72 GHz were not successful. (Author)

Josephson junctions are highly nonlinear and respond up to infrared frequencies. A wide variety of high frequency applications have been explored. In addition, several high frequency superconducting devices are being developed which do not use the Josephson effect. These include a superconducting version of the Schottky barrier diode for use as a heterodyne mixer and a video detector, and also a composite superconducting bolometer. In this review, the state of development of superconducting mixers, detectors, and parametric amplifiers at microwave, millimeter, and submillimeter wavelengths is discussed. Emphasis will be placed on developments which have taken place since 1974 when a previous review was circulated., Presented at the International Conference on Quantum Interference Devices, 4-8 Oct 76, Berlin (West Germany).

The goal of this research is to produce quantum limited SIS quasiparticle heterodyne receivers at submillimeter wavelengths. The approach is to compare the performance of waveguide and planar lithographed quasi-optical SIS mixers in W-band (lambda approx. 3mm) in order to understand the factors which upgrade the performance of the latter. This information will be used to optimize the planar quasi-optical mixers. Finally, these optimized designs will be scaled to submillimeter wavelengths. Systematic tests of both types of mixers have been carried out during the second grant year. Improved designs of planar quasi-optical mixers gave been designed and fabricated. The construction of test apparatus for submillimeter wavelengths has begun.

Point contact Josephson junctions operated as microwave mixers at 36 GHz show conversion gain and lower noise than cooled Schottky barrier diodes in the same application. The noise in such junctions with and without rf bias is explored both experimentally and theoretically. The noise power is found to be about a factor 2 above the thermal noise in the resistively shunted junction model. In contrast to previous reports, the inclusion of a shot noise term in the theory for no rf bias overestimates the observed noise substantially. (Author)

This article reviews the present status of Josephson effect detectors of microwave and far-infrared radiation. It includes an elementary exposition of the theory of the Josephson effect and a general discussion of equivalent circuits for real junctions, junction impedance, junction optimization, and junction noise. A detailed description is given of four devices which show promise of competing successfully with non Josephson effect devices. These are the bolometer, the video detector, the heterodyne detector with external local oscillator, and the parametric amplifier. A number of other devices are described in less detail.

It is shown that point contact Josephson junctions can function as millimeter wave heterodyne mixers with conversion gain. The best results achieved thus far show a single sideband conversion gain of 1.3 and a mixer contribution to the system noise temperature of 54K. Both of these results are approximately 5 times better than the best published figures for cooled Schottky barrier diode mixers operated at the same frequency. (Modified author abstract), Presented at the Applied Superconductivity Conference, Oakbrook, Ill, Oct 74.

Heterodyne detection with a point contact Josephson junction was investigated both experimentally and theoretically. The measured performance of the device at 36 GHz is in good agreement with the theory. By operating vanadium point contacts at 1.4K, the authors have achieved a single side band mixer noise temperature of 54K with a conversion gain of 1.35 and a signal bandwidth of the order of 1GHz. From the results one can extrapolate a potentially impressive performance for these devices at submillimeter wavelengths. (Modified author abstract), Presented at the International Conference on Submillimeter Waves and Their Applications (1st), Atlanta, Ga., Jun 74.

A summary is given of work performed during the last year. The chief topics were: Atomic Physics (scattering cross sections; multi-photon transition); Plasma Physics (nonlinear interaction; laser heating; interaction of strong electromagnetic waves); Elementary-Particles Physics (dual models; gauge models; current algebra)., See also report dated 26 Apr 71, AD-725 772.

Negative resistance regions have been observed on the static I sub o-V sub o curves of point contact Josephson junctions when dc biased with a low impedance source. An equivalent circuit model has been developed which successfully explains the experimental results in terms of relaxation oscillations. It is also found that such junctions can be operated either as a one-port amplifier for signals at 5 MHz, or as a 36 GHz heterodyne mixer with large conversion gain.

A review is given in elementary terms of the diffraction of waves from helices, with special reference to the structure of DNA. The essential features of the experimental results are discussed. (Author)

We extend the Monod-Wyman-Changeux of allosteric transitions in enzyme-substrate reactions to a membrane composed of identical units (protomers). It is supposed that each protomer can exist in two states. The interaction between protomers is treated in the molecular field approximation. It appears possible to have a first-order phase transition when the chemical potential of the substrate is varied, holding the temperature constant. The wide range of possible biological implications is discussed. (Author)

The nuclear spin lattice relaxation rate is measured in the temperature range 130 to 300 C, and is found to be expressed by the relation 1/T sub 1 = (1.98 + 0/0082T) x 1000/sec. The two terms are attributable respectively to the quadrupole interaction and the magnetic hyperfine coupling. The latter is expected to be linear in the absolute temperature, and its magnitude a corresponds to the expected Korringa value. A model is constructed on the basis of fluctuations about a quasi-bcc lattice, and values of the rms field gradient (q sub E = 8.5 x 10 to the 24th power/cu cm) are related to the correlation times (tau sub c = 1.6 x 10 to the -13th power sec) for self diffusion and the related step lengths (delta r = 0.38 A) and the breadth of the x-ray diffraction peaks. (Author)

The Knight shift in the superconducting state has been observed in samples containing various sizes of small tin particles. The three main samples were constructed by vacuum evaporation of alternate layers of metal and dielectric (silicon monoxide). The particles are in the form of platelets whose diameter and thickness were measured with an electron microscope. The geometric means of the particle dimensions were 170, 300, and 570 A. The fractions of the normal state shift (referred to alpha tin) remaining at zero temperature were 84, 74, 62 percent respectively. Three other samples produced by a variety of processes gave results consistent with those of the main samples. The data fit well the theory of spin-reversing scattering through spin-orbit coupling which has been proposed to explain the finite Knight shift in superconductors. Two other possible contributions, a shift due to Van Vleck type orbital susceptibility and crystalline field spin-orbit coupling, cannot be ruled out theoretically but do not appear important experimentally. The problem of an extra NMR line width in the small particle samples is discussed. (Author), Doctoral thesis.

The properties of point contact Josephson junctions operated as 36 GHz heterodyne detectors have been extensively studied. The measured performance is in good agreement with the theory developed for microwave coupling, conversion efficiency, and intrinsic noise based on the Resistively Shunted Junction model. A tunable cavity matching structure was designed to obtain good RF coupling to the point contact. By operating vanadium junctions at 1.4 K, a single side band mixer noise temperature of 54 K (referred to the input) with a conversion gain of 1.35 and a signal bandwidth of the order of 1 GHz is achieved. This is significantly better than existing resistive mixers in this frequency range. Harmonic mixing, mixing in the presence of relaxation oscillation, and self local oscillator mixing with Josephson junctions is also tried, but the results are not as promising as fundamental mixing with an external local oscillator. Finally, two additional topics are discussed: a Josephson effect homodyne detector, and a proposed design for superconducting bolometers making use of the recently developed superconducting quantum interference devices. (Author)

The measured performance of Nb-Nb point contact Josephson-junctions used as 36 GHz microwave mixers is in good agreement with the predictions of the resistively shunted junction model. Conversion efficiencies greater than one are attained, with mixer noise temperatures comparable with the best competing devices. (Author)

Fundamental mixing at 36 GHz in non-hysteretic Nb point contacts has been observed with overall conversion efficiencies in the range 0.33 < or = eta < or = 4 and mixer noise temperatures in the neighborhood of ( Taub M) approximately 200K. The observed conversion efficiencies are in good agreement with the Resistively Shunted model. The observed noise can be accounted for by assuming that the Johnson noise in the shunt resistor is the only source of noise driving the junction. Somewhat larger noise is seen from resonantly coupled mixers than is seen when the mixer is driven from an rf current source. Fundamental mixing in hysteretic junctions is limited to a narrow if bandwidth and gives much larger conversion gain but also larger noise. Parametric amplification at the if frequency is seen in hysteretic junctions. Fourth order harmonic mixing with omega sub (LO)/2 pi at 9GHz has been achieved with performance almost comparable to fundamental mixing. Cavity mode mixing appears less promising. (Author)

Different models for the collisional excitation of carbon monoxide (CO) have been investigated by solving the rate equations for the ten lowest energy levels, including stimulated emission and absorption by 3 degrees isotropic radiation, spontaneous emission, and collisions. The results are qualitatively applicable to other linear molecules. They show that a wide range of rotational excitation temperatures, including population inversions, can be produced by the various kinetic temperatures and particle densities which are likely to occur in the interstellar regions containing molecules. (Author)

In the early 1960's two new types of motion in the sun's atmosphere were discovered: the 5-minute oscillations and the supergranulation. The 5-minute oscillations consist of a predominantly vertical hydrodynamic wave motion in the photosphere and chromosphere with amplitudes around 500 meters/sec. The supergranulation consists of a series of convective cells, 30,000 km in diameter, in which material rises at the center, flows horizontally outward, and falls at the boundaries. The horizontal motion in the supergranulation was clearly observed, but its vertical motion was observed only marginally at best. The observations that form the basis of this thesis were made at the Mt. Wilson Observatory 150-foot solar telescope. The observing equipment is described in detail, including the optics, guiding and scanning system, spectrograph, magnetograph, electronics, and data system. The observing procedure used in these observations is carefully described, as is the method of calibrating the doppler, Zeeman, and intensity signals. The initial data reduction is also discussed. Various measurements of the size and lifetime of the 5-minute oscillations are reported. (Author), Sponsored in part by Grant NSF-GA-16765.

Recent investigations into the zenith angle dependence of very high energy (E > 1000 GeV) cosmic ray muons have shown a discrepancy from what would be expected if the muons originate from pions and kaons, as is currently believed to be the case. If this discrepancy is confirmed it could have important implications concerning possibly a new particle or new process. During the past year and a half the author has designed and constructed a large cosmic ray telescope to measure the zenith angle distribution of muons up to 6000 GeV. The apparatus is capable of observing 10 events a day with E > 1000 GeV and should be able to substantiate the above effect with about 9 months of running time. (Author)

The principal works covered are as follows: Further work on cyclotron resonance and electron relaxation times in copper; A new technique for the study of resistivity in metals, using the eddy-current decay method; An automatic electropolisher for copper; New studies of cyclotron resonance in zinc, including the temperature dependence of the effective mass in zinc; An investigation of cyclotron resonance in cadmium; The noise spectrum of flux jumps in Type II superconductors; and, Electron resonance relaxation times in bulk sodium. (Author)

The paper reviews research being conducted on electric discharges in gases. The research includes the following topics: kinetic emission by alkali ions from a clean tungsten or aluminum surface, a technique for amplifying residual ionization in spark and other channels after a time lapse, secondary streamers in lightning, and the breakdown of dielectric oils by streamer pulses.

Studies conducted have investigated computational techniques in many-body systems of several types. These include relativistic two- and three-body equations of the Bethe-Salpeter type; atomic wave functions with correlations; helium fine structure; analyticity in scattering calculations. Several new techniques in numerical analysis, independent of any particular physical problem, have been found. Completed studies also include an analysis of the theory of cascade decays and on the scattering theory of composite particles. Publications covering these researches are referenced. Recent work includes developing techniques for studying atom-atom and ion-atom reactions using the eikonal approximation and evaluation of a recently completed theory of transport of electromagnetic radiation in a plasma. (Author)

One of the major difficulties in calculating transition curves for the melting of DNA is to take into account the fact that all of the base pairs do not have the same stability. Two kinds of base pairs of differing stability corresponding to adenine-thymine and guanine-cytosine are recognized by the model used in this paper. For a periodic arrangement of the two components an exact equation for the partition function is derived. An extension of this result to infinite periods (e.g. random distribution) is given based on perturbation theory. Some new mathemacical methods used to derive these results also prove valuab3e for discussing the simpler problem of the melting of one-component DNA. (Author)

The unrestricted Hartree-Fock theory is used to investigate bond alternation in C(4N+2)H(4N+2) cyclic polyenes. The possible ground states are examined as functions of the parameters in the Pariser-Parr-Pople model hamiltonian. It is shown that charge density wave ground states do not exist for physical values of the input parameters. The normal, or molecular orbital ground state, does give rise to a negligible bond alternation at large N, in agreement with previous workers. Spin density wave ground states exist for most values of the parameters and have lower energy than the normal ground states. These states do not exhibit bond alternation when the sigma bond compression is the same as that used to obtain the normal energy. (Author)

A brief summary and a publications list is presented for research which included atomic physics, plasma physics and statistical mechanics. One of the programs in atomic physics has been aimed at obtaining accurately calculated energy levels for some excited states of Helium. The other program in atomic physics has as its objective the calculation of electronic excitation and charge transfer in ion-atom and atom-atom collisions. In plasma physics a continuing study is being conducted of unstable waves in inhomogeneous plasmas. (Author)

The report reviews work which has been performed in the following areas: Conspiracy theory, the Veneziano model, the Bethe-Salpeter equation, Current algebras, the Multi-peripheral equation, the Quantization of gauge fields, the Structure of local fields.

During the approximate 4-1/2 years of this AFOSR Grant, research activities have been largely confined to the study of conduction electron behavior in metals. These studies included the investigation of effective masses of electrons in cyclotron resonance, some new cyclotron resonance phenomena, the first studies of electron relaxation times by means of cyclotron resonance, the design of an improved eddy current method for measuring the resistivity of metal specimens, and some measurements of flux jumping in type 2 superconductors. (Author)

A summary is given of work performed during the last year. The chief topics were: Atomic Physics (Eikonal approximation, Transport equations, air ionization by laser beams); Plasma Physics (Resonance broadening, quasilinear theory, interaction between particles and normal modes, electromagnetic plasma simulation); Elementary-Particle Physics (Veneziano Model, including unitarization program and models with fermions, multi-peripheral models, current algebra, weak interactions, quantum electrodynamics, field theory). (Author)

The main work accomplished under the contract can be grouped into the following categories: Gapless superconductivity, Quantized vortex rings in superfluid liquid helium, Neutral excitations in superfluid liquid helium, and Far-ultraviolet spectroscopy of liquid helium and other rare-gas substances.

A weak link between two bulk superconductors can exhibit Josephson effects and can be used as a fast, sensitive detector or mixer for electromagnetic radiation. Emphasis in this paper is placed on the millimeter and submillimeter range where such applications are potentially most important, though such devices should also work well at lower frequencies. The peculiar properties of the weak link make possible a variety of modes of operation including one in which it is both local oscillator and mixer. These modes of operation are analyzed and the pivotal experiments are reviewed. Noise and impedance matching are considered and comparison is made with other types of detectors of millimeter and submillimeter waves. (Author)

The study concerns gas-wave-dynamic phenomena during the transient state from combustion initiation to stable detonation. The results should provide basic information on the generation of pressure waves by explosive reactions, important to understanding of combustion instability in rocket chambers and similar devices, as, for instance, supersonic combustion propulsion systems for hypersonic flight vehicles. (Author)