INTERNATIONAL ELECTRON DEVICES ANNUAL MEETIKG 413

supported meander line anode circuits which combine fundamental forward-wave interac- tion with direct liquid cooling of each circuit vane. Beryllium secondary-emission cold cathodes are ruggedly supported on cooled beryllia insulators, allowing cathode coolant t o remain a t ground potential. Beam cut-off electrodes, with mu's exceeding 3, are mounted in the drift space region of the cathode structure The TWT is ppm fo- cused; the CFA's are packaged with fully shielded permanent magnets. The weight of the entire chain, including circulators, is less than 125 pounds.

The QKS1396 driver CFA operates at 10 kV, 35 kiV peak, 175 watts average with 45 percent efficiency. The QKS1397 final stage CF.4 operates at 30 kV, 1 M W peak, 5000 watts average at approximately 50 percent efficiency. Data to be presented include measured sensitivity of RF output power and phase to changes in dc operating volt- age, R F drive level, and frequency. Beam-on and beam-off noise level measurements are given. The behavior of the tubes during' RF starting and at beam current shut-off is dis- cussed, the cutoff electrode pulse require- ments are specified, and limits on pulse repe- tition rate and pulse duration are predicted for each tube.

6 ) An X-Band Voltage Tunable Magnetron Using a @-Mode Interdigital Structure- E. J. Cook and W. A . Frutiger, Varian Associates, Beverly, Mass. Circuit-coupling considerations make

conventional pi mode VThI operation above C band an increasingly difficult task. This paper reviews a program, sponsored under U. S. Army Electronics Command Contract DA-36-039-AMC-O2199E, in which many of the restraints on higher frequency VTM operation have been relaxed through the use of the N/2+ 1 modes of an interdigital struc- ture. Among the principal advantages of this higher order mode operation are 1) circuit sizes in band comparable to conventional S-band devices; 2 ) the opportunity for heavy coupling, and 3) a reduction in cathode radi- ation. The major complicating factor is that mode separation is not equivalent to the pi mode case and that the two null field pat- terns of t he S /2+1 modes are spatially degenerate. These problems, though, have been overcome by careful choice of vane number and by the use of mode positioners.

Construction of the theta-mode VTMs differs from the lower frequency devices in that internal cavities are used, since the di- electric loading of conventional windows is excessive at X band. Emitter, injector elec- trode, and cold cathode design are quite con- ventional.

The design frequency range of these de- vices was 8.5 to 9.6 GHz, over which several watts of Cit: power has been obtained. Oper- ation at various magnetic field strengths has been obtained. Operation at various mag- netic field strengths has been studied and ex- cellent low-field performance obtained. The efficiency at 2250 gauss, a B I B , of 1.5/1, is 10 percent, and greater than 1 watt of aver- age power can be obtained over the 1100- MHz tuning range.

Higher order mode operation of VTMs has been established as a feasible method of extending their performance range to X band and beyond.

7) Improved Methods for Tuning Micro- wave Devices-13,'. €€. Perkins , Li t ton Industries, T,Villiamsport, P a . -4 new generation of frequency agile air-

borne radars has created a need for magne- trons with fast random tuning and accu- rately monitored output frequencies.

This paper will discuss various means of tuning microwave cavities specifically ap- plied to coaxial magnetrons. A number of different tuning arrangements presently being sold will be briefly discussed with emphasis placed on the new whisper tuner. Advantages and disadvantages of the var- ious designs will be pointed out in light of present system requirements.

The design of a whisper tuner is based on motion obtained from piezoelectric ceramics and is a significant improvement over pre- sent existing tuning arrangements.

Performance to date on a Ku-band co- axial magnetron with whisper tuning in- clude: tuner cycling rates up to 1 MHz; tuning range of 50 MHz with mechanical tuning from 16.0 to 17.0 KMHz; accurate following of a command input within the above limits; accurate voltage read-out proportional to frequency (the tuning ele- ment is the transducer) ; no increase in size or weight.

8) Automatic Measurement of the Probabil- ity Density Functions of Microwave Noise Generators-C. D. Bates, U. S. A r m y Electronics Command, Fort Mon- mouth, N . J., and M. Ettenberg, City College of New York, N. Y. Since the advent of microwave noise

generators, an expeditious method for mea- suring the amplitude statistics (probability density function) of the microwave noise spectrum has not been developed.

This paper describes a new measurement technque in which the probability density function (pdf) of microwave signals is auto- matically obtained. The pdf plot obtained can then be compared with a standard dis- tribution function such as the Gaussian dis- tribution to ascertain the quality of the noise generated by the microwave noise source.

The method discussed furnishes the noise investigator with a new, swift, and accurate measurement tool for the quality analysis of the noise generator under study.

SESSION 5-QUANTUM ELECTRONICS I: LASERS AND MODULATION Chairman: R. A. Paananen Organizer: J . E. Geusic 1) Device Aspects of a Far-Infrared Water-

Vapor Laser-P. D. Coleman, W . Q. Jeffers, C. Johnson, and C. Wi t l ig , Uni- versity of Illinois, LTrbana, Ill. Recent work on output coupling, pulsed

power output, frequency, and mode control of a water vapor laser oscillator are re- ported. Also, the characteristics of a water- vapor laser amplifier will be described.

Using a semi-confocal laser cavity con- sisting of a spherical metal mirror and a flat silicon mirror with the second side a spheri- cal surface, the power from a water-vapor laser can be focused and increased above the hundred-watt level. At this pulsed power level, the l-apid attenuation of the laser sig-

nal in moist air results in a loud acoustical noise This acoustic effect persists even if the laser signal is passed through a monochro- mator. Wavelength measurements using only the ear as a detector can be accurately made.

If the flat mirror in a semi-confocal reso- nator is replaced by a metal reflection grat- ing, single frequency operation of the laser can be obtained on most lines, simply by rotating the grating to the appropriate angle by means of a sine drive. This technique eliminates laser spiking, improves laser stability and mode control. I t also permits new laser lines to appear, having power out- puts comparable to normally strong lines.

bleasurements on a water-vapor laser amplifier will be described. Gains of 3.71, 3.36, and 2.06 dB/m have been measured on the 23.36, 27.97, and 35.84 micron lines under pulsed conditions. Gain curves versup drive current and pressure are presented.

2) Energy Output Degradation of Czo- chralski Ruby Lasers-C. 116. Stickley, H. Wi l ler , E. E. Hoell, C. C. Gallaghel, and R. A . Bradbury , A ir Force Cambridge Resewch Laboratory, Bedford, Mass . Extensive comparisons of Czochralski

and Verneuil ruby lasers have been made; such tests have become important. due to the recent lack of availability of Verneuil ruby. The p~incipal point of this paper is that the energy output of a long-pulse Czochralslci ruby laser gradually drops until after several hundred firings it has decreased to about 20 percent of its initial value. b 7 e have observed this in all Czochralski rods tested but have seen only slight evidence of this in Verneuil ruby. Two batches of Czochralslri ruby were tested, one grown in 1964 and the other ea1 ly in 1966. KO simple explanation (such as a change in threshold or the development of damage in the rod) has been found yet which can explain the decreases seen for the two batches; within each batch, however, the symptoms are approximately uniform from rod to rod. All Czochralski crystals, however, do develop an orange coloration. Some ex- hibit a decrease in R1 line absorQtion, and an increase in absorption at 4800 -4 as seen by Hoskins and Soffer's and Schultz;" they attribute the 4800 A absorption increase to defects created in the crystal. Our data in- terpretation, to date, indicates that these types of changes can only barely explain the decrease in energy observed. Tests will be continued to determine what effect Pyrex has on filtering the pump light.

of Crd+ in a-AlnOs" P i y s . Rev., vol. 133, p. ,4490, 1964. 16 R. H. Hoskins and B. H. Soffer. "Observation

when irradiated by intense light, Phys. Letlevs, "01. 1 7 G. V. Schultz, Colour change of a ruby crystal

9. D. 301, 1964.

3) A Study of Rate-Gas Spectra and Their Effect on Pumping E.fficiencies of Neo- dymium Lasers-F. S. Barnes and J . R. Oliver, University of Colorado, Boulder, Colo. A 25 percent decrease in the threshold

energy necessary to produce lasing action in neodymium can be expected when a change is made from xenon- to krypton-filled flash lamps. In particular, a drop in threshold energy from 22.8 to 17.0 joules was observed by changing to krypton and optimizing the lamp pressure, all other parameters remain- ing constant.