GASEOUS IMPURITIES AND THE PERFORMANCE OF VR-TUBES J. E. Drennan and F. C, Todd (Battelle Memorial I n s t i t u t e )

The charac te r i s t ios of-VR-tubes were improved and new types were developed from a study of the phenomena i n t h e glow discharge. A smooth voltage-current characterist ic without hysteresis i s obtained wi th noble gases of smaller atomic weight when the gaseous impurity content i s less than one part per million (Penning, F. M., and Moubis, J., Phil ips Research Reports, vol. 1, p.119;' 1946). Under many conditions, the mean energy per electron freed from a hollow cathode. is l ess than from a plain cathode, but the problem of cleaning the metal of d i e solved gases i s increased. Techniques to obtain high purity and , to shorten the l i f e of v i r tua l l eaks from the glass and the electrode materials will be presented. In adckltion, the Loss of energy from the discharge through the' d i f fusion of metas- tablera wi l l be discussed, and some of t he e f f ec t s on the charac te r i s t ics w i l l be i l l u e r a t e d with performance curves.

DEPENDENCE OF MICROWAVE CAVITY CHARACTERISTICS ON PROPERTIES OF ENCUSED REGIONS OF A DC DISCHARGE

Burton J. Udelson and John E. Creedon (National Bureau of Standards) The use.of cold cathode dc discharges i n a transmission type microwave cavity

t o control the incident rf power h a s been invest igated as a function of the gas pressure, discharge current, and the region of the discharge exposed to t he rf f i e l d . This was accomplished by introducing a small longitudinal element of a dc discharge i n the high f ie ld gap of a re-entrant S-band cavity. The percentage of power transmitted, reflected, and absorbed by the cavity may be easily obtained by standard microwave techniques. These measurements may be related to the complex conduqtivity, electron density, and collision frequency, 3 c, of the discharge which'are determined from microwave measurements of t he sh i f t of resonant frequency and change of voltage ,standing wave r a t i o a t resonance of the cairity caused by the discharge .

Discharges i n the gases argon and hydrogen i n t h e millimeter pressure range and milliampere current range have been studied. Experiments in the posi t ive column of the discharge show as expected that attenuation is a maximum in the pressure range a t which '2) c = W where W is the radian microwave frequency, It was found f o r a given discharge that the negative glow region produces the maximum microwave attenuation, indicating the use of this region i n attenuator and modu- la tor tubes and .related devices when maxjmum control of microwave energy a t mini- mum discharge parer is desired.

MAGNETRON HEATER DESIGN TO AVOID UNDESIRABU MAGNETIC EFFECTS R. L. Vance and C. Maggs (Bell Telephone Laboratories, Ino.)

The hea ters .of magnetrons are usual ly powered with ac, since do heater supplies represent unwelcome complications. In some magnetrons the resultant field from the ac power, i n connection wi th the magnetic f i e l d of the pole-pieces, superimposes a frequency modulation on the magnetron output power which i s undes i rab le in cer ta in radar applications. This i s par t icu lar ly so with s ingle hel ix wound heaters. An accompamng deleterious mechanical effect, which increases with temperature, i s t h e cycl io s t ress ing of the heater w i r e a s the coi ls cont inual ly move back and for th . A so lu t ion for some magnetron designs i s t o provide a heater which creates very l i t t l e ac f ie ld , thus minimizing the modulation and s t ress ing e f fec ts . A design o f a double he l ix hea te r used in 4552 magnetrons and r e s u l t s of life t e s t s and performanoe in equipment are described. 9 This work was sponsored by the.Air Force 4nd the 8ignal Corps.

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