TR Tube Research Articles

Diffusion Coefficients for Binary, Ternary, and Polydisperse Solutions from Peak-Width Analysis of Taylor Dispersion Profiles

Binary mutual diffusion coefficients D can be estimated from the width at half height W 1/2 of Taylor dispersion profiles using D=(ln 2)r 2 t R/(3W 2 h) and values of the retention time t R and dispersion tube radius r. The generalized expression D h=−(ln h)r 2 t R/(3W 2 h ) is derived to evaluate diffusion coefficients from peak widths W h measured at other fractional heights (e.g., (h = 0.1, 0.2,…,0.9). Tests show that averaging the D h values from binary profiles gives mutual diffusion coefficients that are as accurate and precise as those obtained by more elaborate nonlinear least-squares analysis. Dispersion profiles for ternary solutions usually consist of two superimposed pseudo-binary profiles. Consequently, D h values for ternary profiles generally vary with the fractional peak height h. Ternary profiles with constant D h values can however be constructed by taking appropriate linear combinations of profiles generated using different initial concentration differences. The invariant D h values and corresponding initial concentration differences give the eigenvalues and eigenvectors for the evaluation of the ternary diffusion coefficient matrix. Dispersion profiles for polymer samples of N i-mers consist of N superimposed pseudo-binary profiles. The edges of these profiles are enriched in the heavier polymers owing to the decrease in polymer diffusion coefficients with increasing polymer molecular weight. The resulting drop in D h with decreasing fractional peak height provides a signature of the polymer molecular weight distribution. These features are illustrated by measuring the dispersion of mixed polyethylene glycols.

Gas—Semiconductor Duplexer for Reduced Spike Leakage

Modern radars use ferrite-phaseshift circulator duplexer with TR tube in the receiver arm as a receiver protector. To reduce the spike leakage, diode limiter is needed after the TR tube. This paper gives guideline for selecting diode for low spike leakage and discusses the design consideration of gas-semiconductor duplexer. The constructed duplexer gave spike leakage of 0.004 ergs and flat leakage of 7 mW in the frequency range of 2.7 to 2.9 GHz at 800 kW (peak), 1 μs pulse width.

Comparison of degradations in radar system sensitivities due to TR tube and TR limiter

The degradation of radar system sensitivities due to the TR tube and the TR limiter are calculated. A general expression relating to the various parameters of the TR tube and the TR limiter and noise figure of the receiver is derived from the condition that the TR limiter will be more sensitive than the TR tube with keep-alive, KA. In particular, the TR limiter may be less sensitive than the TR tube with KA due to the higher insertion loss of the TR limiter. The much longer life of the TR limiter, however, may be the deciding factor for its use in a radar receiver.

Physical processes in duplexer discharges in chlorine and oxygen

The high-power properties of the input-window discharge of a TR tube are analyzed in terms of the transmission and reflection coefficients of a thin plasma slab terminated by a low-intensity secondary gap discharge. Computer solutions were obtained for equations expressing the TR properties of arc loss, leakage power, recovery time, and phase shift as functions of collision frequency and electron density. Measurements of arc loss and leakage power in a chlorine discharge yielded values of electron density of 1 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sup> to 6 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13</sup> electrons/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> over a 0.5- to 80-torr pressure range. The recovery period at <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</tex> -band corresponds to a decaying plasma in which electron density decays from 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sup> to 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> electrons/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . This decay occurs in less than 0.5 µs for chlorine discharges. An analysis of the physical mechanisms controlling fast recovery times in electronegative gases shows that the two most important physical mechanisms are recombination of electrons and ions in the early recovery period and electron attachment in the late recovery period. Experimental data is presented for the recovery of chlorine and oxygen over a pressure range of 0.5 to 80 torr. An analysis of measured values of attachment frequency in oxygen indicates that the electron temperature in the recovery period, which is early in the afterglow, was in the 1.4- to 1.2-eV range.

Microwave-excited ionized argon laser

A spectroscopic study of a microwave-excited argon discharge showed that the emission spectrum is rich in Ar <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> lines, suggesting a possibility of attaining laser action in microwave discharges. Laser action was observed in a modified TR tube configuration in a discharge tube of relatively large diameter. The average RF power absorbed in the plasma was less than 20 W.

On noise generated in ignitors of TR tubes

The noise generated by a dc glow discharge inside a coaxial ignitor embedded in a standard X-band TR stage has been studied experimentally and the results analyzed. The noise variation due to changes in physical dimensions, notably the dc and RF gap length, have been experimentally measured and a physical explanation presented to account for the phenomenon. Dependence on dc current, pressure, and gas type was also measured in controlled experiments. It is shown that the generated noise and the coupling of this noise to the microwave transmission line is a critical function of the tip shape and insertion depth of the solid cone into the coaxial ignitor cone. This effect is due to the interception of the charge carriers by the apex of the solid cone. This interception creates a noise current whose axis makes an angle with the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\bar{E}</tex> vector of a propagating mode(s). When this angle is small and the discharge current large, the noise energy in the transmission line becomes large. Data showing a linear dependence of generated noise with ignitor current provides strong evidence that this is shot noise. Calculations of the available thermal power per cycle and the shot noise power per cycle are summed and compared with each other and with experimental values. These calculations further indicate the dominance of shot noise power under experimental conditions simulating a practical TR tube. Conclusions regarding techniques for the development of ultralow noise TR's are given.

A new concept in microwave gas switching elements

A gas switching tube commonly known as a TR tube is an RF energy switch, the operation of which is a function of incident power level. Switch operation is achieved by gaseous ionization. The major problem in the design of gas switching devices has been that of achieving simultaneously a short recovery time and a low arc loss. This problem has been eliminated by the development of the device described in this paper. The design objective was to produce a self-contained TR window for operation at very high powers. The arc loss developed by conventional tube design at these high power levels would be sufficient to melt any known window material. The design of this device is such that the ionizable gas blanket takes the form of a thin-walled cylinder suspended in the iris in a dielectric cylinder. This configuration presents a smaller volume of gas with a reduced cross section and a much shorter diffusion length. These changes result in lower leakage power, faster recovery time, and reduced arc loss. As finally developed, the window does not involve glass-to-metal or ceramic-to-metal seals. The problem of metal sputtering or outgassing is therefore eliminated. By a unique spring pressure support, the problem of strain developed by differences of thermal coefficients of expansion is eliminated. The open-ended design of the cylinder provides excellent facilities for cooling the window. Prototype units have been successfully operated in "L" Band at power levels considerably in excess of 15 mw peak power and 30 kw average power. These units exhibited recovery times of 5 to 20 µsec with high-level attenuation of 26 to 35 db and arc loss below the level of present measuring techniques, i.e., < 0.02 db. A practical window for these high powers with a loaded Q of less than 1.5 has been fabricated.

A new concept in microwave gas switching elements

A gas switching tube commonly known as a tr tube is an rf energy switch, the operation of which is a function of incident power level. Switch operation is achieved by gaseous ionization.

The spike in the transmit-receiver (TR) tubes

The spike leakage signal from high-Q and band-pass tr tubes was recorded as a function of time by using high-speed oscillographic techniques. Transients as short as 0.5 millimicro-seconds (0.5 × 10-9seconds) were resolved. The variation of the 1B24 high-Q tr spike was determined as a function of time for several experimental parameters including the gas type and pressure, initial number of electrons in the tr gap, and peak incident power supplied by the transmitter. Oscillographic recordings show the tr spike leakage power from a commercial gas-filled 1B24 tr tube rises to a peak of 0.3w in a time interval of 6 mµsec. The spike leakage power from a 5863 three-gap band-pass tr tube rises to a peak of 3.6w in 7.5 mµsec. Threshold of microwave gas discharge breakdown measurements in helium gas are used to determine the electric field intensity in the 1B24 tr gap as a function of the waveguide power. From this, the electron motion during the spike interval is calculated. The results indicate that production of electrons in the gap can occur through ionization of the gas by the electrons' radio frequency energies, and by secondary emission at the gap surfaces, as well as through ionization of the gas by the electrons' energies of random motion.

"Developing a combined T-R shutter tube duplexer"

The tube to be described was developed to fill the need in microwave systems for a single light weight unit which would assure complete crystal protection. The design objectives were standard TR functions with a 40db insertion loss at standby condition with low power requirements and a minimum of weight and volume increase over the values of a normal TR tube. An entirely new principle was conceived which permits installation of the shutter within a normal TR tube body. This new shutter has an insertion loss of 40 to 60db in single tubes and up to 90db when incorporated into a dual tube with matching hybrids to form a TR shutter duplexer. By new magnet design techniques, the total weight increase was held to about 2 ounces for a three element X-band tube, and power consumption to about 3.9 watts. The design is such that, in case of power failure, the shutter automatically closes to present the high shutter insertion loss in front of the crystal, which makes it an inherently failsafe device.

A GAS DISCHARGE SWITCH:——II. FOR CONTROLLING LOW LEVEL 10 CM-BAND MICROWAVE SIGNALS

Based on the interaction between r-f field and the electrons furnished from an auxiliary d-c discharge, a gas discharge switch has been developed for controlling low level 10 cm-band signals by modifying the keep-alive electrode of a cell type 1827 TR tube. It has been found that the attenuation was considerably increased when the top of the keep-alive electrode was off-center and close to the side of the lower hollow cylindrical post. Nitrogen or argon at a pressure of about 4 mm Hg was found to be appropriate as a gas filling for such a switch. An attenuation of more than 30 db was obtained from a tube having a keep-alive depth of 0.0 mm and a distance of 0.7 mm from the keep-alive to lowcr-hollow-cone. The gas filling was nitrogen at 4 mm Hg, and the keep-alive current was 1 ma with a d-e gap voltage of about 450 volts. Such a switch has a very long life, as there was no appreciable change in the tube behavior alter operating continuously for several hundred hours.

A GAS DISCHARGE SWITCH:——I.FOR CONTROLLING LOW LEVEL 3 CM-BAND MICROWAVE SIGNALS

A gas discharge switch for controlling low level 3 cm-band signals was developed by modifying a iB24 TR tube. The keep-alive electrode in the tube was placed nearer to the r-f gap, and the aperture of the lower cone was made larger than that in the standard tube. It was observed that a keep-alive depth (distance from r-f gap) of 0.4 mm gave the highest attenuation. Among the various gas fillings tried, nitrogen was found to be most suitable. It gave a high attenuation and a reasonably long tube life. About 44 db attenuation was obtained at a keep-alive current of 0.4 ma with a gas rilling of 12 mm Hg of nitrogen. No detectable r-f noisc was introduced by the keep-alive discharge. A qualitative discussion is presented to account for the attenuation in terms of the motion of the electron furnished by the keep-alive discharge under an r-f field.

Fabrication of a High Power Resonant Wave-Guide Window

The inability of present wave-guide pre-TR and TR tube windows to withstand high transmitter power necessitates improved window design if 3000-megacycle radar systems are to continue using the conventional band pass TR protective device. The fabrication of a glass window with a loaded Q of four is described and operational tests at high line power are discussed. This construction permits the TR tube parts to be brazed in a hydrogen furnace and a more rigorous pumping schedule to be followed. A flow chart of the window processing operations and pictures of the window and pre-TR tube are included.