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Two optical detection systems were used to obtain Raman spectra from impregnant samples, tungsten pellets, and cathode surfaces. The advantages of each system are described and their use for cathode diagnostics are explored. The Raman spectra from various impregnant samples are given and preliminary data from tungsten pellets and cathodes at low pressure and at temperatures as high as 860 C are presented. Keywords: Thermionic cathodes, Raman spectroscopy., Sponsored in part by Contract N00014-86-K-0710.

A Pierce-type approach to the analysis of a travelling wave gyroton which utilizes an impedance formulation much like that used for O-type travelling wave tubes has been previously discussed (Grow and Shrivastava 1980 a, 1981, 1982, Grow 1980). The theory is based on a determinental equation that is obtained from the simultaneous solution of a relativistic, cyclotron-rotating electronic equation and a waveguide circuit equation. Expressions for the interaction impedance are presented as a basis for considering the magnetron circuit operating in the 2 pi mode. The cutoff constants are determined for values of the ratio of vane radius to the outer waveguide radius from 0.15 to 1.00. The normalized interaction impedance and the stream voltage are than calculated for each of these magnetron circuit configurations. The results can be used to design a gyrotron travelling wave tube with magnetron-type circuits. (Author).

Impedance calculations have previously been made on a gyrotron operating with a magnetron circuit in the 2pi-mode and cutoff constants were determined and impedance calculations were made for values of the ratio of vane radius to the outer waveguide radius from 0.15 to 1.00. The normalized interaction impedance and the stream voltage was then calculated for each of these magnetron circuit configurations. In this paper, calculations have been made of interaction impedance and stream voltage to achieve operation in the pi-mode. The pi-mode has the advantage of having higher impedance values than the 2pi-mode. This advantage is offset by the necessity of strapping the vanes of the magnetron. These results for the pi-mode are compared with the 2pi-mode and also with a smooth waveguide operating in a Te sub n1 mode. The advantages and disadvantages of all three configurations are discussed. (Author)

With the development of the laser and its enormous bandwidth capabilities, the simultaneous development of the photosensing devices has proceeded. A photodiode is one of these devices and shows great promise due to its inherent sensitivity, ruggedness, and the ability to obtain large internal gain. Because of this, many photodiodes have been built with responses into the microwave region. These devices have extremely small active areas and low quantum efficiencies, as with a point contact photodiode. This paper discusses the problems of building a large area high frequency photodiode and how they were overcome. The theoretical considerations for using a free-running inhomogeneously broadened laser to obtain a millifrequency signal to test the photodiodes are discussed in some detail. These results have been used to obtain the frequency response of the photodiodes.

Raman scattering spectra of a KH2PO4 single crystal were measured at various crystal orientations relative to the incident and scattered light propogation directions. It has been found that the contribution of the long-range electrostatic interaction is less than 10% of the total scattering efficiency of the E(x) and B2(z) modes in KDP. A low frequency mode, previously predicted by group theory, was also observed for the first time.

The feasibility of using the optical technique of Raman scattering to determine the chemical composition of cathode surfaces has been investigated. Reference Raman spectra have been obtained for many of the chemical compounds expected to be present at the surface of dispenser cathodes. In addition, spectra obtained from 5-3-2 impregnant and several cathode surfaces are presented. The potential advantages of the approach are discussed., Sponsored in part by Contract N00014-86-K-0710.

The objective of the project was to conduct a feasibility study on a device to convert millimeter wave images into visible pictures. The planar Fabry-Perot interferometer (FPI) was studied theoretically and experimentally for the passage of millimeter wave beams through it. Experiments showed that millimeter wave images pass through the FPI with little alteration of the intensity profile. The field enhancing effects of the FPI are needed to increase upconversion efficiency of millimeter wave images to visible pictures. Theoretically the passage of an arbitrary field distribution (image) through an FPI can be understood in terms of the transverse modes of the FPI. The diffraction effects were properly included for the various modes in order to obtain the intensity profile at the output. The property of an FPI to act as a spatial band pass filter was pointed out. Experiments were performed to demonstrate spatial filtering characteristics.

Research concerns the evaluation of the high-efficiency capabilities of the cyclotron-synchronous wave amplifier. An experimental evaluation of a one-watt amplifier was made at S-band. A small-signal coupled-mode analysis is being carried out for this device and a large-signal computer study is underway to examine the efficiency capabilities and to provide design data. The S-band amplifier was tested. The gun failed to provide sufficient current due to a faulty gun electrode. The cavity tuning slugs were found to operate satisfactorily. The filamentary stream coupled-mode analysis was modified to account for space-charge and beam focusing effects. (Author)

The analysis of a plane wave propagating through a homogeneous plasma region of dimensions large compared to the signal wavelength has shown that the wave attenuation can be related to physical parameters of the plasma such as electron density, temperature, and pressure. In this report, the plasma in the combustion chamber of a small solid propellant rocket motor is used to investigate the feasibility of determining the temperature of the plasma by using microwave attenuation data. Potassium perchlorate is substituted for some of the ammonium perchlorate in the propellant to give an electron density that produces an easily measurable attenuation. The theoretical results show that for a known propellant composition and potassium perchlorate concentration, both the plasma temperature and chamber pressure at equilibrium may be found from one attenuation measurement. Also, for a known thermodynamic state of the plasma, the electron density may be found from the attenuation data. The method of microwave analysis is shown to be very useful in the study of transient phenomena in that no transducers are required; hence, the time response of the measurement is limited only by the microwave detection circuitry. This technique may be used to study localized disturbances within the plasma region., Report on Project THEMIS.

Steel spheres having a diameter of 3/16 inch (0.476 cm) were accelerated with a 220 or 243 caliber smooth-bore gun up to velocities of 2.5 kilometers per second. The area, volume, and depth of the resulting craters were measured and plotted as a function of either the initial impact energy or momentum of the projectile. The crater volume was a linear function of the projectile energy. A relationship existed between the volume per unit energy and the static shear and compressive yield strengths. A plot of crater area versus projectile momentum had two linear segments. A region of negative slope for penetration versus projectile momentum was found for aluminum, lead, and magnesium targets. The other targets did not have this region. Partridge, VanFleet, and Whited (PB-128 423; 'Crater formation in metallic targets'. Journal of Applied Physics, 29:1332-1336 (1958)) presented data for many of the same targets impacted with spheres of the same material as the target. Comparisons were made between their data and the data obtained using steel spheres for the projectile. Correlation between the data was excellent in most cases.

The basic problem is to investigate the coupling processes between rotating electron beam modes and circuit modes. The problem is to determine analytically and experimentally these coupling processes, and to evaluate them for device application. An experimental device has been constructed and tested which exhibits backward-wave oscillations and forward-wave gain. Power output of 720 watts has been obtained in one experiment. Analytical results in the form of a general wave guide coupled-mode theory are available for guidance and understanding of the experimental results. (Author)

The broad purpose of the research activity reported herein is to extend the useful frequency spectrum into the range from microwave frequencies to optical frequencies and to improve existing devices and techniques in the microwave spectrum. At present this objective is being pursued by studies of electron beam devices, quantum electronic devices, plasmas, and solid-state devices. (Author)

The purpose of this project is to analytically and experimentally evaluate the interaction of waves in a wave guide with waves on a rotating electron beam. The methods of analysis include use of a general coupled-mode theory, a ballistic computer program, and an experimental evaluation. A new tube is being constructed in which the interaction current can be measured, and the reflection of power in the interaction will be reduced. Space-charge effects have been found to split the longitudinal modes so that they are no longer degenerate. Their effect on the coupling coefficients is small, and can be neglected in the first-order perturbation theory. The multiple-beam interaction has been analyzed, and it has been found that the single-beam analysis can be used if the d-c beam current of the multiple beam is replaced by an effective d-c beam current. Boundary conditions are imposed upon the five interacting modes, and it is found that only three waves are excited in the system. Two of these waves travel at beta sub e and are not excited. This allows the start-oscillations conditions to be found as a function of the device parameters for the backward-wave interactions. The problem of power saturation of the backward-wave oscillations has been initiated. Small-signal theory is used to determine an expression for the efficiency. The axial bunching in the O-type backward-wave oscillator is examined to determine how it is related to the a-c current for power saturation so that criteria for determining power saturation may be established for our device. (Author)

The purpose of this project is to evaluate analytically and experimentally the interaction of waves in a wave guide with waves on a rotating electron beam. The methods of analysis include use of a general coupled-mode theory, a ballistic computer program, and an experimental evaluation. It has been found that the previous power saturation criteria are invalid because they were based on a one- and two-dimensional model. A possible criterion is presented based on a three-dimensional model. The power output of the tube is still low, but it is expected that magnetic field shaping will increase it. Also, the tube has been observed to oscillate in two different modes separated in frequency by about 50 MHz. (Author)

Experimental results are reported for a four coupledladder backward-wave oscillator designed for the frequency band from 36-40 kMc. The voltage ranged from 14,000 to 20,000 volts and the power output was in excess of 20 watts at 40 kMc. The slow wave circuit consisted of four 0.005 in. think molybdenum planes separated by 0.010 in. with slots 0.142 in. wide having a pitch of 0.058 in. The electron beam was obtained by a convergent confined-flow cylindrical electron gun to eliminate beam rotation. The solid electron beam 0.116 in. in diameter flooded the ladder circuit with a measure current density of about 8 amps/sq cm. The output terminal was constructed with the individual ladders becoming ridges of a ridge waveguide. This technique was utilized to phase lock the waves on each ladder to obtain output only from the longitudinal mode. Good agreement was obtained between the theoretical and experimental starting current, tuning curve, and power output. The good agreement thus obtained indicates that coupled ladder backward-wave oscillators can be built utilizing the available theoretical results and the serious problem of producing a pure longitudinal mode in a coupled ladders can be solved. (Author)

To satisfy needs for a superior hypervelocity gun, a study was made of the possibility of converting the electrical energy in a capacitor bank to kinetic energy of a projectile through the use of an electric arc discharge in a gun chamber. An arc gun was developed consisting of a chamber with a pair of electrodes and an accelerating barrel. To operate the gun, the chamber is packed with lithium hydride and the barrel is fitted with a nylon pellet. The capacitor bank is discharged into the chamber, causing conversion of the lithium hydride into a low-molecular gas. The expansion of the light gas accelerates the pellet. With a 30 microfarad capacitor bank charged to 17 kilovolts, a 3.7 milligram nylon projectile was accelerated to 5.0 kilometers per second. The efficiency of the energy conversion from the capacitor to the arc was 58.2 per cent, and the efficiency of the energy conversion from the arc to the projectile was 1.82 per cent. The total efficiency of the energy conversion from the capacitor to the projectile was 1.1 per cent. (Author)

Experiments with a rotating electron beam waveguide device have been performed. The device used in this investigation has been found to exhibit a strong transverse wave interaction. The interaction takes place at a frequency which is close to the cyclotron frequency of the electron beam. Frequency measurements indicate that the interaction frequency is slightly less than the cyclotron frequency and that the interaction frequency varies inversely with beam voltage. Both gain and oscillation have been observed. The interaction appears to be of a backwardwave nature. The transverse-wave interaction theory indicates that backward-wave but not forward-wave active coupling may occur. The observed values of gain are less than the calculated values but are within an order of magnitude. The interaction is found to be strong at the cutoff frequencies. This is in agreement with the transverse-wave theory. The interaction appears to be greatly influenced by the reflections in the waveguide circuit. The results of this investigation indicate that strong transverse interactions can occur in fast-wave circuits. Succeeding experimental work will require a circuit which has better transmission over a broad frequency range. This could be easily accomplished with a broadband vacuum window. An improved beam launching system is still needed if beam parameter effects are to be more carefully observed. (Author)