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Problems related to very high power windows at microwave frequencies
84
Abstracts of Communications
m6thodes de mesure insistant particuli~rement sur les conditions de travail g r6aliser pour que les valeurs obtenues soient absolument ind6pendantes de l'appareillage de mesure. (4) Nous donnerons quelques r6sultats d'adsorption, en fonction principalement de la temp6rature du getter, de la pression du gaz au-dessus du getter, de la pression de flash du getter. 33.25. Ion Induced Re-emlssion of Noble Gases from a Nickel Surface* : E. A. TRENDELENBUR6~ and J. H. CARMICHAEL. Westinghouse Research Laboratories, Pittsburgh 35, Pennsylvania, U.S.A. Each of the noble gases, He, Ne, A, and Kr, has been ionically pumped with an energy of about 100 eV into a nickel target and has been subsequently released by a similar bombardment using a different noble gas. As described by Brown and Leck:~ a mass spectrometer permitted the measurement of both the re-emission of the trapped atoms and the trapping of the bombarding particles. The re-emission mechanism is described in terms of a simple model which assumes that the trapped atoms are released by the bombarding particles through a mechanism of sputtering of either the target material or the trapped gas or a combination of both. The experimental results are in agreement with the model. A direct replacement of a trapped atom from its trapping site by a bombarding particle is shown to be a relatively unimportant factor in the re-emission process. Measurements of the re-emission rates of the trapped atoms have yielded information concerning the depth distribution of the trapped atoms in the nickel target. In particular, saturation of the depth distribution has been observed for Ne, A, and Kr, at concentrations below one equivalent monolayer while He showed no such effects at the highest concentrations used, which corresponded to approximately 15 equivalent monolayers. 33.26. Present Stage of the Researches on the Adsorption of Gases by the Getters Evaporated from Barium Alloys: DELLA PORTA. Societe Apparecchi Elettrici e Scientifici, Milan, Italy. The methods and the techniques employed for the study of the adsorption of gases by barium getters are outlined. The development of the researches in this field from the almost empirical measurements of the adsorption capacity and gettering rate up to the present strictly chemical-physical perspective of the problem is emphasized. The method of the Knudsen flow can yield fully informative data on the nature and the course of this process. The value of the method is greatly enhanced when tests are carried out at a constant pressure on the evaporated metallic film : the experimental curve shows directly the variations of the sticking probability and fully demonstrates the evolution of the process particularly in regard to its dependence on the fraction of surface covered. Some results obtained with this method relating to the influence of the pressure, the temperature and the getter evaporation conditions on the adsorption of gases are illustrated as well at the influence of the subesquent treatment of the evaporated film. The case of nitrogen is examined in detail and discussed. 33.31. Problems Related to Very High Power Windows at Microwave Frequencies: J. JASBERG and J. V. LEBACQZ. Stanford University, Stanford, U.S.A. It has been difficult to obtain satisfactory output windows for those microwave tubes which operate in the multi-MW range. Although such high-power tubes may be used for a number of purposes, this paper considers only the experience gained during the past five years with a number of large klystrons which are used to supply rf power to the Stanford Mark III linear electron accelerator. This machine is used for research in nuclear physics, *This work was supported by the U.S. Atomic Energy Commission under Contract AT(I 1-1)570. tPresent A d d r e s s : Gerfitebau-Anstalt Balzers, Principality of Liechtenstein. ~Brit. J. Appl. Phys. 161, 6 (1955).
and it is driven by 20 klystrons operating at approximately 2850 Me, and each delivering a peak power of 15 to 20 MW, and an average power of a few kW watts. The windows in these tubes are used to isolate the klystron vacuum from the poorer vacuum existing in the accelerator. The results obtained with a number of different window designs have been inconsistent, and generally poor. However, in recent years, a high-alumina, ceramic disk window has been used, and a reasonably satisfactory average window life of 2000 hr has been obtained. Toward the end of increasing this life, perhaps to 5000 hr, studies have been made of the mechanism of window failure. This paper presents a discussion of the kind of failure to which such windows are subject, and also a description o f some of the phenomena which are observed at the window, both during and after operation. 33.32. Versuche zur Bestimmung yon C~isiumdampfdruck bei der Herstellung yon Sb-Cs und Ag-O-Cs Photokathoden : E. KANSKYand S. JERIC. Institut za electroniko, Ljubljana, Jugoslavija. Sb-Cs und Ag-O-Cs Photokathoden entstehen bei der Reaktion von dtinnen Antimon und Silberoxydschichten mit C/isiumdampf im Vacuum. FOr das theoretische Studium und eine zweckm/issige Fi~hrung des Herstellungsprozesses ist es sehr wichtig den Dampfdruck tiber der Schicht w/ihrend des Formierens zu kennen. Dieser Druck h~ngt yon der Zustr6mungsgeschwindigkeit des C~tsiumdampfes, der Kinetik der Bildung yon C/isiumverbindungen in der Sehicht und vom Zersetzungsdampfdruck dieser Verbindungen ab. Es wurden Versuche gemacht diesen Druck bei dem Formieren der Sb-Cs und Ag-O-Cs Kathoden zu bestimmen. Die Resultate wurden mit den thermodynamisch gesch~itzten Werten vergliechen. 33.33. Probable Explanation for the Composition of Residual Gases in Electronic Valves: F. H. R. AL~ER, H. J. R. PERDIJK and P. G. VAN ZANTEN. Philips' Gloeilampenfabrieken, Eindhoven, Netherlands. In electronic valves containing a barium getter mirror sometimes a small gas pressure is observed after storing during some weeks. This gas consists mainly of CH4 which gas quickly disappears without having harmful effects when the valve is put into use. The source of this gas is not very well known. Although it might be explained by assuming that the valve had not been properly heated during pumping and that some gassy organic material is still present afterwards, an alternative explanation is thought to be more likely. This explanation is based on experiments made during investigations on efficiencies of barium getter mirrors for CO. It will be shown that barium carbide will be formed. With the aid of a mass-spectrometer the reaction of getter mirrors (partly saturated by CO) and water vapour has been studied and in many cases CH~ has been detected. Afterwards the occurrence of CO and water vapour in commercial valves will be discussed. 33.34. Testing of Minute Oxidation of the Base Metal for Oxide Cathode : Y. TACHIHARA, T. HATA and M. ONIZUKA. Engineering Laboratory, Mitsubishi Electric Mfg. Co., Ltd., Amagasaki, Hyogo, Japan. Electron emission of the oxide-coated cathode is sharply affected by slight oxidation of impurities contained in the nickel core metal. This minute oxidation occurs during ingot melting, rolling, annealing, forming and tube exhausting. A new method was developed for testing of the cathode base metal without using the thermionic emission test through electronic tubes. This new method makes use of the fact that the corrosion rate of metals in acid or alkaline solution is markedly affected by minute oxidation. The extent of oxidation, the depth of oxidation and the oxidation resisting power of the metal for cathode core can be estimated from the curve of time and the weight of metal specimen in an acid solution. Tube exhausting process can also be checked.
Abstracts of Communications
m6thodes de mesure insistant particuli~rement sur les conditions de travail g r6aliser pour que les valeurs obtenues soient absolument ind6pendantes de l'appareillage de mesure. (4) Nous donnerons quelques r6sultats d'adsorption, en fonction principalement de la temp6rature du getter, de la pression du gaz au-dessus du getter, de la pression de flash du getter. 33.25. Ion Induced Re-emlssion of Noble Gases from a Nickel Surface* : E. A. TRENDELENBUR6~ and J. H. CARMICHAEL. Westinghouse Research Laboratories, Pittsburgh 35, Pennsylvania, U.S.A. Each of the noble gases, He, Ne, A, and Kr, has been ionically pumped with an energy of about 100 eV into a nickel target and has been subsequently released by a similar bombardment using a different noble gas. As described by Brown and Leck:~ a mass spectrometer permitted the measurement of both the re-emission of the trapped atoms and the trapping of the bombarding particles. The re-emission mechanism is described in terms of a simple model which assumes that the trapped atoms are released by the bombarding particles through a mechanism of sputtering of either the target material or the trapped gas or a combination of both. The experimental results are in agreement with the model. A direct replacement of a trapped atom from its trapping site by a bombarding particle is shown to be a relatively unimportant factor in the re-emission process. Measurements of the re-emission rates of the trapped atoms have yielded information concerning the depth distribution of the trapped atoms in the nickel target. In particular, saturation of the depth distribution has been observed for Ne, A, and Kr, at concentrations below one equivalent monolayer while He showed no such effects at the highest concentrations used, which corresponded to approximately 15 equivalent monolayers. 33.26. Present Stage of the Researches on the Adsorption of Gases by the Getters Evaporated from Barium Alloys: DELLA PORTA. Societe Apparecchi Elettrici e Scientifici, Milan, Italy. The methods and the techniques employed for the study of the adsorption of gases by barium getters are outlined. The development of the researches in this field from the almost empirical measurements of the adsorption capacity and gettering rate up to the present strictly chemical-physical perspective of the problem is emphasized. The method of the Knudsen flow can yield fully informative data on the nature and the course of this process. The value of the method is greatly enhanced when tests are carried out at a constant pressure on the evaporated metallic film : the experimental curve shows directly the variations of the sticking probability and fully demonstrates the evolution of the process particularly in regard to its dependence on the fraction of surface covered. Some results obtained with this method relating to the influence of the pressure, the temperature and the getter evaporation conditions on the adsorption of gases are illustrated as well at the influence of the subesquent treatment of the evaporated film. The case of nitrogen is examined in detail and discussed. 33.31. Problems Related to Very High Power Windows at Microwave Frequencies: J. JASBERG and J. V. LEBACQZ. Stanford University, Stanford, U.S.A. It has been difficult to obtain satisfactory output windows for those microwave tubes which operate in the multi-MW range. Although such high-power tubes may be used for a number of purposes, this paper considers only the experience gained during the past five years with a number of large klystrons which are used to supply rf power to the Stanford Mark III linear electron accelerator. This machine is used for research in nuclear physics, *This work was supported by the U.S. Atomic Energy Commission under Contract AT(I 1-1)570. tPresent A d d r e s s : Gerfitebau-Anstalt Balzers, Principality of Liechtenstein. ~Brit. J. Appl. Phys. 161, 6 (1955).
and it is driven by 20 klystrons operating at approximately 2850 Me, and each delivering a peak power of 15 to 20 MW, and an average power of a few kW watts. The windows in these tubes are used to isolate the klystron vacuum from the poorer vacuum existing in the accelerator. The results obtained with a number of different window designs have been inconsistent, and generally poor. However, in recent years, a high-alumina, ceramic disk window has been used, and a reasonably satisfactory average window life of 2000 hr has been obtained. Toward the end of increasing this life, perhaps to 5000 hr, studies have been made of the mechanism of window failure. This paper presents a discussion of the kind of failure to which such windows are subject, and also a description o f some of the phenomena which are observed at the window, both during and after operation. 33.32. Versuche zur Bestimmung yon C~isiumdampfdruck bei der Herstellung yon Sb-Cs und Ag-O-Cs Photokathoden : E. KANSKYand S. JERIC. Institut za electroniko, Ljubljana, Jugoslavija. Sb-Cs und Ag-O-Cs Photokathoden entstehen bei der Reaktion von dtinnen Antimon und Silberoxydschichten mit C/isiumdampf im Vacuum. FOr das theoretische Studium und eine zweckm/issige Fi~hrung des Herstellungsprozesses ist es sehr wichtig den Dampfdruck tiber der Schicht w/ihrend des Formierens zu kennen. Dieser Druck h~ngt yon der Zustr6mungsgeschwindigkeit des C~tsiumdampfes, der Kinetik der Bildung yon C/isiumverbindungen in der Sehicht und vom Zersetzungsdampfdruck dieser Verbindungen ab. Es wurden Versuche gemacht diesen Druck bei dem Formieren der Sb-Cs und Ag-O-Cs Kathoden zu bestimmen. Die Resultate wurden mit den thermodynamisch gesch~itzten Werten vergliechen. 33.33. Probable Explanation for the Composition of Residual Gases in Electronic Valves: F. H. R. AL~ER, H. J. R. PERDIJK and P. G. VAN ZANTEN. Philips' Gloeilampenfabrieken, Eindhoven, Netherlands. In electronic valves containing a barium getter mirror sometimes a small gas pressure is observed after storing during some weeks. This gas consists mainly of CH4 which gas quickly disappears without having harmful effects when the valve is put into use. The source of this gas is not very well known. Although it might be explained by assuming that the valve had not been properly heated during pumping and that some gassy organic material is still present afterwards, an alternative explanation is thought to be more likely. This explanation is based on experiments made during investigations on efficiencies of barium getter mirrors for CO. It will be shown that barium carbide will be formed. With the aid of a mass-spectrometer the reaction of getter mirrors (partly saturated by CO) and water vapour has been studied and in many cases CH~ has been detected. Afterwards the occurrence of CO and water vapour in commercial valves will be discussed. 33.34. Testing of Minute Oxidation of the Base Metal for Oxide Cathode : Y. TACHIHARA, T. HATA and M. ONIZUKA. Engineering Laboratory, Mitsubishi Electric Mfg. Co., Ltd., Amagasaki, Hyogo, Japan. Electron emission of the oxide-coated cathode is sharply affected by slight oxidation of impurities contained in the nickel core metal. This minute oxidation occurs during ingot melting, rolling, annealing, forming and tube exhausting. A new method was developed for testing of the cathode base metal without using the thermionic emission test through electronic tubes. This new method makes use of the fact that the corrosion rate of metals in acid or alkaline solution is markedly affected by minute oxidation. The extent of oxidation, the depth of oxidation and the oxidation resisting power of the metal for cathode core can be estimated from the curve of time and the weight of metal specimen in an acid solution. Tube exhausting process can also be checked.