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Technique has been developed for attaching and sealing tubes to header plates using a unique roll-forming tool. Technique is useful for attaching small tubes which are difficult to roll into conventional grooves in header plate tube holes, and for attaching when welding, brazing, or soldering is not desirable.
Incident shock-wave velocities were measured in the Langley 6-inch expansion tube, operated as a shock tube, with air, argon, carbon dioxide, and helium as test gases. Unheated helium was used as the driver gas and most data were obtained at pressures of approximately 34 and 54 MN/sq m. A range of pressure ratio across the diaphragm was obtained by varying the quiescent test-gas pressure, for a given driver pressure, from 0.0276 to 34.5 kN/sq m. Single- and double-diaphragm modes of operation were employed and diaphragms of various materials tested. Shock velocity was determined from microwave interferometer measurements, response of pressure transducers positioned along interferometer measurements, response of pressure transducers positioned along the driven section (time-of-arrival gages), and to a lesser extent, measured tube-wall pressure. Velocities obtained from these methods are compared and limitations of the methods discussed. The present results are compared with theory and the effects of diaphragm mode (single or double diaphragm), diaphragm material, heating of the driver gas upon pressurization of the driver section, diaphragm opening time, interface mixing, and two-dimensional (nonplanar) flow are discussed.
Various types of photomultiplier tubes useful for space applications were irradiated with 1- and 2-MeV electrons at Van Allen radiation belt fluxes of 100,000 to 10 millions electrons/sq cm-sec. The increase in the dark current due to electron irradiation was observed at various bias voltages under worst-case conditions (no shielding). Results were presented in the form of dark current plotted against electron flux. All the tubes tested showed extremely large increases in dark current. Tube types 541A, 6217, 6199, and 6903 exhibited the largest increases under irradiation, whereas type 1P22 was affected the least. All the damage observed was transient. The luminescence produced in the optical window probably accounts for a large part of the dark-current increases, but there were some effects possibly due to direct irradiation of the photocathode and dynode chain.
An analytical and experimental program to demonstrate the technical feasibility of a high efficiency coupled cavity traveling wave tube with periodic permanent magnetic focusing operating at 12.06 GHz, with 1 to 2 kilowatts CW power is described. Such a tube would ultimately be used for broadcasting power transmission from a satellite. The electron gun was designed to be demountable with a replaceable cathode, and the tube to be operable in a bakeable vacuum chamber with its collector replaced by a collector. Therefore, the high efficiency design was concerned with the slow wave structure only, utilizing velocity resynchronization. A special adapter was designed which incorporated an electromagnet refocusing section and a collector baseplate to facilitate testing the collector. CW output power of 1000 watts yielding 21.5% electronic efficiency was demonstrated, with a minimum output power of 525 watts across the specified 160 MHz bandwidth.
Motivated by the filamentary structure of solar magnetic fields, this paper considers the propagation of quasi-longitudinal waves along a slender magnetic tube in pressure equilibrium with the ambient medium. The velocity of such waves is expressed in terms of the Alven speed and the sound speed inside the tube. The divergence of a vertical magnetic tube in a stratified atmosphere introduces a critical frequency below which propagation is impossible.
Inspection tool for tubing consists of metal casing housing elastic collar. Collar is clamped around weld site under test. Leakage through weld is contained within chamber and is bled to detector via tubing attached to fitting. Tool, originally designed to detect fluid leakage in tubing, can be used to detect gas leaks.
Infant mortality, useful life, and wearout phase of twt life are considered. The performance of existing developmental tubes, flight experience, and sequential hardware testing are evaluated. The reliability history of twt's in space applications is documented by considering: (1) the generic parts of the tube in light of the manner in which their design and operation affect the ultimate reliability of the device, (2) the flight experience of medium power tubes, and (3) the available life test data for existing space-qualified twt's in addition to those of high power devices.
The Varian cup and slat dynode chain was modified to have a flat cathode. These modifications were incorporated in an all-electrostatic photomultiplier tube having a rise time of 0.25 n sec. The tube delivered under the contract had a flat S-20 opaque cathode with a useful diameter of 5 mm. The design of the tube is such that a III to V cathode support is mounted in place of the existing cathode substrate. This cathode support is designed to accept a transferred III to V cathode and maintain the cathode surface in the same position as the S-20 photocathode.
This final report presents the results of the design, development, and test of experimental and production units of a PPM focused traveling wave tube (L-5394) that produces 225 watts of CW RF power over 85 MHz centered at 12.080 GHz. The tube uses a coupled cavity RF circuit with a velocity taper for greater than 26 percent basic efficiency. Overall efficiency of 50 percent is achieved by the incorporation of a multistage depressed collector designed at NASA Lewis Research Center. The collector is cooled by direct radiation to deep space. The tube was designed to be used for broadcasting power transmission from a satellite.
Several dummy tubes imitating the IUE Camera System design were encapsulated with Solithane 2, Conathane EN-11, Green and Black Hysols and SMRD 432. Various flaws were purposefully placed in some of these. Partial discharge testing in vacuum under direct voltage conditions was carried once a week for 12 weeks, 15 kv dc being applied during normal working hours for 40 hours duration per week. None of the units showed much damage during this time judging by the P.D. energy histograms. A more complete mathematical presentation is given on diffusion and permeation than previously. Measurements of diffusion constants for various silicone rubbers are carried out by the Time-Lag method and compared to other determinations in the literature. Calculations of the time required for diffusion through a thick wall are demonstrated in the long time approximation and for dimensions pertaining to void and wall sizes of a delamination problem in the LANDSAT-C vidicon tubes. An actual delaminated LANDSAT-C tube and some facsimiles are immersed in vacuum for long periods and tested for catastrophic breakdown due to diffusion of gas, by application of high voltage.
A flexible accurate large-signal computer program has been developed for the design of coupled-cavity traveling wave tubes. The program is written for a TSS-360 time sharing system. The beam is described by a disk model and the slow wave structure by a sequence of cavities or cells. The computational approach is arranged so that each cavity may have different geometrical or electrical parameters than its neighbors. This allows the program user to simulate a tube of almost arbitrary complexity. Input and output couplers, severs, complicated velocity tapers, and other features peculiar to one or a few cavities may be modeled by a correct choice of input data. The beam-wave interaction is handled by a new approach in which the RF fields are expanded in solutions to the TM wave equation retaining all significant space harmonics. The program was used to perform a design study of the TWT developed for the CTS satellite. Good agreement was obtained between the predictions of the program and the measured performance of the flight tube. The internal check on power balance was satisfied within plus or minus 0.2 per cent of input beam power.
A numerical program was developed to compute transient laminar flows in two dimensions including multicomponent mixing and chemical reaction. The program can compute both incompressible flows and compressible flows at all speeds, and it is applied to describe transient and steady state solutions for low subsonic, coaxial entry, tue flows. Single component, nonreacting flows comprise most of the solutions, but one steady state solution is presented for trace concentration constituents engaging in a second order reaction. Numerical stability was obtained by adding at each calculation point a correction for numerical diffusion errors caused by truncation of the Taylor series used to finite difference the conservation equations. Transient computations were made for fluids initially at rest, then subjected to step velocity inputs that were uniform across each region of the entry plane and were held constant throughout the computation period. For center tube to annulus velocity ratios of 0.5 and 2.0, the bulk fluid in the tube initially moved in plug flow, but strong radial flows developed near the injection plane which moved the fluid into the high shear region between the jets and away from the tube wall.
The usefulness of vee-trough concentrators in improving the efficiency and reducing the cost of collectors assembled from evacuated tube receivers was studied in the vee-trough/vacuum tube collector (VTVTC) project. The VTVTC was analyzed rigorously and various mathematical models were developed to calculate the optical performance of the vee-trough concentrator and the thermal performance of the evacuated tube receiver. A test bed was constructed to verify the mathematical analyses and compare reflectors made out of glass, Alzak and aluminized FEP Teflon. Tests were run at temperatures ranging from 95 to 180 C. Vee-trough collector efficiencies of 35 to 40% were observed at an operating temperature of about 175 C. Test results compared well with the calculated values. Predicted daily useful heat collection and efficiency values are presented for a year's duration of operation temperatures ranging from 65 to 230 C. Estimated collector costs and resulting thermal energy costs are presented. Analytical and experimental results are discussed along with a complete economic evaluation.
Two methods are investigated for alleviating wall interference effects in a shock tube test section intended for testing two-dimensional transonic airfoils. The first method involves contouring the test section walls to match approximate streamlines in the flow. Contours are matched to each airfoil tested to produce results close to those obtained in a conventional wind tunnel. Data from a previous study and the present study for two different airfoils demonstrate that useful results are obtained in a shock tube using a test section with contoured walls. The second method involves use of a fixed-geometry slotted-wall test section to provide automatic flow compensation for various airfoils. The slotted-wall test section developed exhibited the desired performance characteristics in the approximate Mach number range 0.82 to 0.89, as evidenced by good agreement obtained between shock tube and wind tunnel results for several airfoil flows.
An examination is made of the effect of the turbulent boundary layer on the uniformity of the flow initiated by a nonsteady expansion wave traveling in a long, constant-area tube. Closed-form expressions for the flow perturbations first are obtained from the linearized equations of motion. Measured static pressure histories for both lowand high-tube Mach numbers are used for comparison. Detailed discussions of the limitations of the linearized model and its extension to high-tube Mach numbers are given. Agreement is shown between a modified version of the linearized model and the experimental results. A model of viscous nonsteady pipe flow is used to explain the nonlinear pressure decay observed at very large length-to-diameter ratios.
A test bed for experimental evaluation of a fixed solar collector which combines an evacuated glass tube solar receiver with a flat plate/black chrome plated copper absorber and an asymmetric vee-trough concentrator was designed and constructed. Earlier predictions of thermal performance were compared with test data acquired for a bare vacuum tube receiver; and receiver tubes with Alzak aluminum, aluminized FEP Teflon film laminated sheet metal and second surface ordinary mirror reflectors. Test results and system economics as well as objectives of an ongoing program to obtain long-term performance data are discussed.
NASA research in the area of traveling wave tube technology is reviewed, with emphasis on the basic physics of guns and collectors and a computer model for the interaction between the electron beam and the RF circuit. The design of a multistage depressed collector, capable of multiplying tube efficiency by a factor of two or more, is presented; one such design has been adopted for commercial traveling wave tube production. A three-dimensional model of electron trajectories toward the collector also receives attention, as does the problem of RF circuit losses.
When aluminum tubing having good corrosion resistance and postweld strength is needed, type 5083 alloy should be considered. Chemical composition is carefully controlled and can be drawn into thin-wall tubing with excellent mechanical properties. Uses of tubing are in aircraft, boats, docks, and process equipment.