Harry Goldie

Radioactive (tritium) ignitors for plasma limiters

Radioactive ignitors using tritium as the active material are shown to be a reliable electron priming source for the RF discharge gap in plasma limiters when cascaded with a diode limiter. This result is based on ion-chamber studies of priming current strength, electron distributions, and thermodynamic and chemical stability of titanium-tritide electron sources immersed in low-pressure gases. The results of X -band measurements of the statistical distribution of output spike leakage amplitudes for overvolted discharge gaps and the threshold of breakdown of the RF gap in tuned plasma limiters containing titanium-tritide ignitors followed by a diode limiter show operating parameters equivalent to keep-alive plasma limiters. Experiments with the tritiated passive priming source substituted for the conventional dc keep-alive discharge show a greatly increased operating life in receiver protectors and gaseous TRs and the improvement of other important electrical parameters such as noise, reliability, and external driving power.

A 26- to 40-GHz fast-acting plasma waveguide switch

A fast-acting broad-band plasma waveguide switch has been developed which provides greater than 60-dB isolation and less than 0.25-dB cold loss over the 26-to 40-GHz frequency range. Switching times are under 200 ns, and the actuating trigger signal is a 150-volt 0.5-µs pulse from a high-impedance source. Geometrical enhancement of plasma density by employing metallic convergence cones is used. This technique provides a moderately ionized plasma from a beam whose strength would normally provide only a weakly ionized plasma in the absence of the convergence cone. A computer program of the transmission equation using a plasma slab model yielded the average plasma density and slab thickness in the waveguide; electric probes were used to detect electron temperatures along the cone axis.

A 2-kW average power X-band receiver protector

A 2-kW average power receiver protector with a 5000-h operating life has been developed. The design is of the gas plasma diode hybrid type which heretofore could provide only one-tenth the power handling for equivalent operating life. Predicted life is based on experimentally obtained molecular sorption coefficients performed at 2-kW average power inXband. The device has been developed for use as a receiver protector in a high-resolution radar to be used at Lincoln Laboratory. This radar will transmit 200-kW average power atXband and consequently requires a high average power receiver protector.

An ac-primed quartz—chlorine stage for X-band receiver protectors

A gas discharge waveguide limiter in X-band with relatively fast recovery characteristics is discussed. The problem of supplying priming electrons at a sufficiently high rate to the microwave gap (to ensure first pulse breakdown at the beginning of the pulse) in a halogen-gas quartz system is overcome by using an ac ignitor. The ac ignitor voltage is coupled through the gas reservoir wall to maintain a weak discharge whose free electrons diffuse toward the microwave gap.

On the measurement of nanosecond recovery time in receiver protectors

The measurement of the recovery period in multistage receiver protectors is analyzed. It is shown that the accepted IEEE definition is unsatisfactory for the recent class of fast-recovery receiver protectors. We consider here the problem encountered when the recovery period is roughly equal to the falltime of the main transmitter pulse. It is found that accurate measurements are possible only when the reference point for the recovery measurement is taken at the singular power point located on the falling edge of the transmitter pulse which is equal to the extinguishing power of the stage which has the longest recovery period. Consequently, an alternate definition is offered which is adequate for all classes of duplexers and receiver protectors.

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 \bar{E} 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 TRs are given.