Contains reports on six research projects.Office of Scientific Research and Development (OSRD) OEMsr-26

Eisenstein, A. S.

Fineman, A.

Henry, J. H.

Hung, C. S.

Malham, G. W.

Martin, S. T.

Moats, R. R.

Mutter, W. E.

Nottingham, W. B.

Parke, N. G.

Zuckerbraun, J.

Contains reports on five research projects.Office of Scientific Research and Development (OSRD) OEMsr-26

Brown, F. C.

Harrison, G. I.

Dillinger, J. R.

DSpace@MIT

Microwave and Physical Electronics

Contains reports on five research projects

I MICROWAVE AND PHYSICAL EIZCTRONICSA CONSTRUCTION OF 5 MM OXFORD TYPE TUBEStaff N G ParkeDescription of Pro.ect As part of the Research Laboratory program to investigateelectromagnetic phenomena in the frequency region above 30,000 Mc, attempts havebeen made to construct a scaled-down version of the 2K33 reflex klystror It ishoped that the tubes currently being designed will produce oscillations in the5 mm regionStatus The first tubes nroduced did not oscillate probably due to the fact thatit was impossible to get sufficient beam current It is believed that the troublewas caused by poor electron gun alignment As a result of exoerience gained ex-perimenting with the first tube, it has now been redesigned Drawings of theredesigned tube are completed small parts hove been manufactured, and assemblyhas been begun The new tube involves the use of more accurate cavity parts andthe use of kovar at several points to elimirate graded glass seals and some brazingoperations The output waveguide is now made in one piece instead of in three bythe use of a hobbing processB HIGH POWER S-BAND MAGNETROStaff Professor S T MartinJ H HenryR R MoatsDescription of Project As indicated in the June 30 Report, a scaled-up versionof the one megawatt 3 cm rising sun magnetron developed at Columbia RadiationLaboratory is being built for operation at 10 cmStatus The fabrication problems referred to in the previous report are still asource of difficulties Radio freouency brazing in a hydrogen atmosphere has beenadopted as the method for assembling the larger parts of the tubeConsiderable effort has gone into getting adeouate design data forchanging the shape of tne smaller resonator crvities of the AX-9 to simplifymanufacture and assembly of subseouent tubes in which it is desired to experimentwith the shapeThe work on thoria cathodes which has been done at the Bartol Foundationindicates that such cathodes may be more satisfactory than previously availablepulsed cathodes for high power magnetrons In order that such cathodes may bestudied as part of the high power mqgnetron development program a furnace fortheir fabrication has been startedC CATHODE RESEARCH1 Oxide Cathode ResearchStaff Professor W B NottinghamDr A S EisensteinG W MahlmanDescription of ProJect. The use of oxide coated cathodes in magnetrons and similarsulsed devices at the Radiation Laboratory has pointed out the importance of preparingcathodes which "spark" only under the influence of extremely high external fields-5-(09'WAVEGUIDE OUT-r AII TDsAlC~_rUTI 41NI N WINDOWIN I-FORMER. WINDOWCONNECTORHK-7Since the choice of cathode base metal and coating are known to influence the"sparking" properties, studies were undertaken to determine the fundamentalmanner in which each of these affects the "sparking" and emission propertiesof cathodesStatus (a) Interface It is suspected that the influence of tne base metalis that of controlling chemic 1 reactions which occur at the interface betweenthe base metal and coiting X-ray diffraction natterns show that cathodes preparedof a (BaSr)O coating on a 551 Si-"i base metal always contain a BaSi03 interfacelayer betueen the oxide and the base metal This layer may have a thickness asgreat as 10-3 cm Exoeriments are underway to measure the relttive electricalconductivities of (BaSr)O and BaSi03 in bulk so that the role of the interfacein limiting the thermionic emission can be better understood(b) Coating Previous work in the Radiation laboratory indicated thatthe sparking properties of Ba0 were considerably better than those of SrO ormixtures of the two This investigation is intended to either verify or disprovethis contention, and further, to observe how the sparking potential varies withtemperature and work function (as measured over the range 900-1300eK) as the tubeis "aged" by drawing direct current from itAn investigation is being made of the sparking properties of oxide-coated cathodes as a function of (1) type of coating, (2) operating temperature,(3) work function, and (4) operating life Sixteen tubes have been processedFour were coated with pure BaC03 (before orocessing), four with pure SrCO3, fourwith a coating of nure BaC003 on top of a coating of pure SrC03, and four with acoating of pure SrCO03 on top of a coating of pure BaCO3 The sixteen tubes wereprocessed by the methods found to be successful during tne war This consistsof binder removal, conversion of the carbonate to the oxide, and activation bydrawing d-c current up to about 1/2 amp/cm2 and pulse current up to about 20 amp/cma2The tubes are then sealed off, and tested by applying a 1 micro-second pulse ofknown peak voltage and measuring the peak current from the oxide cathode Thepulse voltage is raised until "sparking" occurs This is done for about fourdifferent temperatures in the range 900-1300 0K At this date, insufficient progresshas been made to draw any definite conclusions2 Emissivity of TungstenStaff Professor' 7 NottinghamW E MutterDescription of Project Although tungsten is Drobably the most important emitterof light for illumination purposes, the spectral emissivity has not been determined asa function of the temperature in a manner that is satisfactory for the computetionof data applicable to tungsten fillamentsStatus An erperiment has been started to measure the emissivity of tungstenas a function of wavelength and temperature Existing literature data at two-7-wavelengths are in disagreement and it is expected that the present measurementswill throw some light on this as well as extend the range studied to cover theentire visible and near ultra-violetThe method to be used offers some marked advantages over the normalpyrometric technique in that the wavelength is accurately known and the measure-ment has no subjective aspects The image of a tubular tungsten source containinga small radial hole is focused on the entrance slit of a monochromator At theexit end, a horizontal slit of width smaller than the diameter of the hole in thesource travels up and down along the regultr vertical slit of the instrumentThe emergent flux is detected with a photocell and electrometer for various Dositionsof the traveling slit The ratio of the energy (current) from the surface of thesource to the energy from the hole (block-body) gives the emissivity directly ata given wavelengthThe source for this work has been completed, but measurements have beendelayed pending the installation of a high current d-c generator required for itsoperation3 Electron Emission StudiesStaff Professor W B NottinghamA FinemanC TungThis research has been in anticipation of studies of oxide-cathode materialto determine the energy distribution of the emitted electron at various temoeraturesof operation and to determine the emission as a function of the applied voltageMost previous studies on the question of enission as a function of applied voltagehave yielded curious results because of the deactivation often encountered in suchexperiments It is not certain that we shall be able to avoid this deactivationbut a design in which it will be minimized has been usedD IONIZATION GAUGE RESEARCHStaff Professor N B NottinghamAs a result of an investigation carried on early in 1946 it seemeddesirable to make studies of the ionization gauge as a device for determining thepresence of residual atoms in a vacuum system The conventional ionization gaugesare likely to give faulty results because of the emission of electrons from theion collector due to the absorption of soft x-rays generated at the surface of theelectron collector A second difficulty with the conventional ionization gaugeis that it is prone to oscillate if the vacuum becomes narticularly good Althoughthe studies of a new gauge have been under way daring the past few weeks, resultsare not of sufficient importance to report in detail at present-8-I E HIGH VOLTAGE SPARK GAP TUBESStaff J ZuckerbraunThe development of higher voltage spark gap tubes was initiated becauseof the possibility of their use in providing up to 100 kv pulses for SynchrotroninjectionSeveral of the experimental tubes were built in the Electronics Laboratorytube shop They differed essentially from previous available tubes in that thedistance between the cathode pool and the anode could be variedTwo types of tests were performed with these tubes(1) Tests under static conditions of voltage and current&(2) Tests under pulse conditions where the applied voltage was either of rectangularwave form or where the current was allowed to decay exponentially with timeThe results of the tests indicated the following(1) Tubes having a breakdown strength of 25 kr or higher can be built&(2) A current of 1 ampere through these tubes forms a high voltage glow dischargerather than a low voltage arcs(3) The time in which the glow is established depends largely on the rise time andmagnitude of the trigger voltage and can be made to be less than 1 microsecond,(4) The time-jitter of breakdown also is largely influenced by the trigger pulse andcan be made less than 0 3 microseconds for trigger voltages of about 35 kv with risetimes of about 60 kv per microseconde(5) The amplitude-jitter of the tube drop is small and depends on the gap spacing,At the electrode separation needed for 25 kv tubes this jitter is about 200 volts pergapIt appears feasible to use perhaps four of these tubes in series for 100 kvpulse Pulse width and amplitude can be controlled satisfactorily-9-

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Microwave and Physical Electronics

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