Showing papers by "Varian Associates published in 1980"

Stacked multijunction photovoltaic converters

Abstract: Solar cells with different bandgaps are stacked to form a multijunction photovoltaic converter with a high conversion efficiency. By stacking the cells mechanically rather than by growing them all at one time, the most convenient combination of materials may be selected for the cells. The stacking is completed by means of a glass sealing layer with moats containing inter-cell contacts which are bonded to the cells.

Mixed phase chromatographic compositions

Abstract: The mixed phase packing material of this invention, enables rapid separation of multi-sited biopolymers. This separation is achieved by "tailoring" the distance between organo-silyl groups covalently bonded to the rigid support at the Angstrom distance needed for reversible separation of the biopolymers of interest and "capping" other sterically available active sites on the support with a relatively inert compound.

Bean scanning and method of use for ion implantation

Abstract: In an ion implantation system, departure from uniform ion dosage of a planar workpiece is first compensated by modulating the scan rate of at least one coordinate of scan deflection in accordance with a non-linear waveform. The non-linear waveform is digitally synthesized from a plurality of contiguous linear segments, such segments having equal projection on the time axis. The pattern of two-dimensional scanning is then configured to correspond to an astable Lissajous figure. When the trace of such Lissajous figure returns to the initial origin of the pattern, the origin is then displaced by a fraction 1/n of the interval between parallel traces of the basic Lissajous pattern and the displaced Lissajous pattern is executed and again displaced n times until the interval has been traversed. The number n is chosen with reference to scan amplitude and the lateral extension of the beam at the workpiece; a sufficient noise component is tolerated in the deflection system to dither the beam about the average scan trace in order to remove small pattern in homogeneities.

End point detection method for physical etching process

Abstract: A method for determining the end point for a physical etching process step measures the current at the target being etched and detects changes in the current. Changes in the current measured at the target are indicative of transitions between dissimilar materials or of depth of penetration in a particular material. Momentary changes in the etching flux of the physical etching process are factored out by measuring the current on a mask placed in the vicinity of the target and by subtracting mask current from current measured at the target.

Variable field coupled cavity resonator circuit

Abstract: In a resonant chain of coupled cavities such as used in a standing-wave linear particle accelerator it is often desirable to change the field strength in some cavities relative to some others. For example, if the output particle energy of an accelerator is changed by varying the fields of all cavities, the distribution of energies of output particles is disturbed. This distribution is largely controlled by the fields in the first group of cavities traversed by the particle beam. According to the invention, the fields can remain constant in the first group and be varied in following cavities. This is done by varying the distribution of electromagnetic field in one cavity asymmetrically with respect to the preceding and the following cavity. The asymmetric coupling produces different acceleration fields in one part of acceleration structure relative to another part. In an accelerator whose accelerating cavities are coupled via non-interacting side cavities, the different coupling may be produced by making the standing-wave field in one side-cavity asymmetric with respect to its coupling irises.

The organometallic VPE growth of GaAs1−ySby using trimethylantimony and Ga1−xInxAs using trimethylarsenic

Abstract: The organometallic vapor phase epitaxial growth of Ga1−xInxAs and GaAs1−ySby using trimethylarsenic and trimethylantimony as the Group V sources is reported and the relevant chemistry is discussed. Growth rate and composition variations as a function of temperature are given for GaAs1−ySby. A result of particular importance is that no detrimental room temperature gas phase reaction is observed between triethylindium and trimethylarsenic. Consequently, the growths are performed at one atmosphere pressure without the need for any complicated injection schemes in the reactor design.

Unitary electromagnet for double deflection scanning of charged particle beam

Abstract: A unitary electromagnet having two gaps is provided for the double deflection scanning of a charged particle beam. The unitary electromagnet is configured to permit traverse by said beam through the gaps in a plane defined by the gaps. The depth of the gaps is large as compared to the length to accommodate the scan of the beam. The mode of scanning is determined by the waveform used to energize the windings of the electromagnet and includes axial sweep scanning, off center scanning and split scanning.

Flange sealing joint with removable metal gasket

Abstract: An all-metal joint is provided wherein a metal gasket disposed between mating flanges can readily be removed when the joint is disassembled. Opposing faces of the mating flanges are configured to provide a recess between the flanges in which a soft metal gasket of annular configuration can be received when the flanges are coupled together. Symmetrically disposed ridges on the opposing flange faces penetrate into a peripheral region of the gasket, thereby causing a portion of the gasket material to flow into an annular groove that forms the periphery of the recess between the opposing flange faces. This compressed material in the annular groove provides a gas-tight seal between the mating flanges. The configuration of the opposing flange faces is such that when the joint is dissassembled, the net force tending to retain the gasket in position against either one of the flange faces is minimized. In particular, each flange face is configured so that the residual compressive forces present when the flange coupling mechanism is released, distributed over the surface of the gasket, are in net effect substantially equal to or greater than the frictional and bonding forces that might tend to retain the gasket in contact with either flange. In this way, the gasket tends to break away from the mating flange faces when the joint is disassembled.

Accelerator side cavity coupling adjustment

Abstract: In a standing-wave coupled-cavity linear particle accelerator the energy of the emergent particles can be adjusted by making the accelerating fields in one section of the accelerator different from those in another section into which the rf drive power is introduced. To do this the adjoining end cavities of the two sections are coupled through a "side" cavity which is not traversed by the particle beam. The coupling coefficients of the side cavity to the two accelerating cavities are made unequal to create the difference in accelerating cavity fields. Asymmetrical coupling is realized by varying the extension of center conductor posts into the side cavity by means of a vacuum sealed mechanism for moving the center posts while maintaining microwave current connection between the center posts and the side cavity.

High efficiency 90 GHz InP Gunn oscillators

Abstract: High efficiency InP Gunn devices and oscillators have been developed for the millimetre wave range. At approximately 90 GHz, the highest c.w. efficiency measured was 4.7% and the highest pulsed efficiency was 6.3%. Output powers of 126 mW c.w. and 236 mW pulsed have been achieved.

Sample spinning mechanism for NMR probes

Abstract: An air bearing sample spinner for use in an NMR probe has a first air bearing established between frusto-conical mating surfaces of rotor and stator to provide levitation and rotation. A cylindrical portion projects from the rotor into a similar coaxial cylindrical portion of the stator where a journal bearing is provided for centering of the rotor in the stator housing.

O.M. v.p.e. growth of AlGaSb and AlGaAsSb

Abstract: The epitaxial growth of AlGaSb and AlGaAsSb alloys by o.m. v.p.e. is reported. The growth technique and the dependence of the alloy composition on the input flux of gases are discussed.

Polar mode scattering in ballistic transport GaAs devices

Abstract: Polar optic scattering in a ballistic transport n-GaAs device at 77 K is shown to be significant for voltages above the threshold for polar phonon emission, 0.035 V. Monte Carlo results for electron effective velocities at fields expected in such devices support this conclusion.

Cryostat with external refrigerator for super-conducting NMR spectrometer

Abstract: An improved cryostat for the superconducting magnet of an NMR spectrometer comprises a nested structure of isothermal shells surrounding a thermally conductive central reservoir of substantially spherical shape containing liquid helium in which the superconducting solenoid remains operational when only partially immersed. A radiation shield surrounding the central reservoir is cooled by the boil-off of escaping helium vapor. The radiation shield is enclosed within a isothermal shell maintained at the temperature of liquid nitrogen by thermal contact with a liquid nitrogen reservoir disposed above the region of the central reservoir and shielded therefrom by a wall of the isothermal shell. An outer radiation shield surrounds the liquid nitrogen reservoir and associated isothermal shell and the outer radiation shield is maintained at a temperatures of the order of 180° K. by an external refrigeration facility. A hermitically sealed containment vessel forms the outer wall of the cryostat and provides a port for evacuating to a very low common pressure all the interior spaces between adjacent nested structures. The spacing between adjacent nested surfaces is maintained by a novel internal mechanical bracing system of low thermal conductivity comprising polyester cords disposed under tension between adjacent shells.

Field-assisted semiconductor photoemitters for the 1—2-µm range

Abstract: Photoemission data and model calculations are presented for a field-assisted semiconductor photoemitter which has achieved reflection-mode quantum efficiencies as high as 8.0 percent at 1.55 µm. The cathodes are p-p heterostructures employing lattice-matched InP-InGaAsP alloys. A thin electron semitransparent Schottky barrier provides the biasing contact for field-assisted electron emission. Parameters for optimal photoemission and sources of dark-current emission are discussed.

200 kW pulsed and CW gyrotrons at 28 GHz

Abstract: Pulsed and CW gyrotron oscillators have been designed and constructed for use in electron cyclotron resonance heating in plasma fusion experiments. The tubes are designed for 200 kW output at 28 GHz with beam input of 80 kV and 8 A. The pulsed design has been operated at duty factors of 5% and pulse lengths up to 40 msec. The CW design has produced output of 200 kW CW with an efficiency of 50%. It also operated with 52% efficiency at an output level of 170 kW CW. The tubes are designed for power output in the TE 02 circular electric mode in oversize (2.5 inch diameter) circular waveguide. Some investigations of mode purity of the output will be described. The design and operation of waveguide components such as bends and mode filters for use with the gyrotrons will be discussed.

Use of trimethylantimony and trimethylarsenic for organometallic v.p.e. growth of GAAs1-ySby and Ga1-xInxAs

Abstract: The use of trimethylarsenic and trimethylantimony as group V sources for the organometallic v.p.e. growth of GaAs1-ySby (0 ≤ y ≤ 0.11) and Ga1-xInxAs(x ≈ 0.29) is reported. No room-temperature reaction is observed between triethylindium and trimethylarsenic and the growths are made at ambient pressure with no special reactor modifications.

Sensitivity NMR probe

Abstract: In an NMR probe containing an observe coil and a decoupling coil, the signal-to-noise ratio of the observe channel is improved by inserting a back-to-back parallel combination of diodes in series with the decoupling coil to present an infinite impedance in the decoupling channel in its passive state for induced RF signals from the observe coil.

A C-band gyro-TWT

Abstract: The operating characteristics of a gyrotron travellng wave tube (gyro-TWT) operating at C-band are reported. Detailed testing showed that at higher beam voltage and current and with a magnetic field profile increasing in magnitude toward the rf output window, the output power could be increased from 50 kW at 16.6% efficiency to 128 kW at 24% efficiency. The maximum efficiency measured was 26% at 120 kW. Experimental data on small and large signal gain, bandwidth, output power and efficiency will be presented. The gyro-TWT employs a magnetron injection gun to provide an electron beam with a prescribed perpendicular to parellel velocity ratio. Inherent in this type of electron gun is a finite spread in the two velocity components. An alternate method for producing an electron beam with very low spread in the velocity components is presented. Design data will be presented.

Planar vacuum seal for isolating an air bearing

Abstract: A graded planar seal is provided between opposing planar surfaces (62, 64) for isolating an air bearing in a vacuum environment (16). The air bearing (22, 24, 26, 62, 64) supports a structure (20) such as a semiconductor mask or wafer and functions in a vacuum environment without severely degrading the quality of the vacuum. The air bearing is isolated from the vacuum by the use of the graded planar seal which establishes a pressure gradient from the level of the air which supports the air bearing (22, 24, 26, 62, 64) to the level of the vacuum environment (16). The gradient is established across the seal by evacuating gas through successive orifices (42, 44. 46, 52) in opposing planar members (12, 14).

Shuttleless toroidal core winder

Abstract: Disclosed is an apparatus for simultaneously winding multiple strands of wire into turns about a toroidal core in rapid fashion. The apparatus includes a U-shaped wire receiving channel having a semi-circular portion with a gap and a pair of open-ended legs. The ends of the channel legs are positioned adjacent opposite sides of a rotatably mounted drum which is driven by a resilient endless belt engaging approximately one half of its annular outer surface. A toroidal core is supplied and rigidly supported in the gap by a core feeding mechanism. A grooved gap crosser is thereafter extended through the central opening of the core to bridge the gap and complete the channel. A pair of pinch roller type feed/brake mechanisms propel and guide the leading ends of the wires into the channel, through the core opening, and up one channel leg to the drum. There the wires are frictionally held between the drum and the belt and they are positively driven into the other channel leg, through the core opening, and back to the drum. Continued feeding of the wire results in the formation of a coil having a plurality of vertically stacked, oval-shaped loops which extend through the core opening and are alternately made of different ones of the wires. Thereafter, staggered braking of the trailing ends of the wires causes the loops to be successively peeled radially inwardly from the channel and the drum as the coil is continuously circulated. The loops are tightened into turns about the core as it is slowly rotated about its axis by the core feeding mechanism. First and second shear mechanisms cut off the trailing and leading ends of the wires at the beginning and end of the winding operation, respectively.

Design concepts for a high-impedance narrow-band 42 GHz power TWT using a fundamental/forward ladder-based circuit

Abstract: A low-cost, narrowband, millimeter wave space communications TWT design was studied. Cold test interaction structure scale models were investigated and analyses were undertaken to predict the electrical and thermal response of the hypothetical 200 W TWT at 42 GHz and 21 kV beam voltage. An intentionally narrow instantaneous bandwidth (1%, with the possibility of electronic tuning of the center frequency over several percent) was sought with a highly dispersive, high impedance "forward wave' interaction structure based on a ladder (for economy in fabrication) and nonspace harmonic interaction, for a high gain rate and a short, economically focused tube. The "TunneLadder' interaction structure devised combines ladder properties with accommodation for a pencil beam. Except for the impedance and bandwidth, there is much in common with the millimeter wave helix TWTs which provided the ideal of diamond support rods. The benefits of these are enhanced in the TunneLadder case because of spatial separation of beam interception and RF current heating.

Feedback fifo for cyclic data acquisition and nmr instrument control

Abstract: Cyclic instrument control and data acquisition functions which are critically dependent upon synchrony are directed from a computer based system including a FIFO buffer (30) adapted to feedback the most recently active word from its output register (36) and re-store said word at a corresponding sequential position (34) in the FIFO queue. To accomodate complex and interleaved control and data acquisition cycles, each FIFO word has a state portion for commanding external devices, a persistence portion for specifying the duration of selected state active in the FIFO output buffer for a desired persistence interval, and a repetition portion for specifying the number of consecutive discrete repetitions of the currently active state-persistence datum at the output of the FIFO. Termination of the cyclic sequence is accomplished at the expiration of a preselected number of complete cycles. The FIFO input address is selected automatically in accord with the number of words comprising a single complete sequence of instrument control/data inquisition functions.

Permanent magnet structure for linear-beam electron tubes

Abstract: High-power linear-beam electron tubes require an extended uniform magnetic field to focus their beam in an elongated cylinder. When permanent magnets are used to energize the magnet structure, there is inevitably a leakage field outside the main flux-return path. The leakage field can refocus the beam in the tube's collector, damaging it. When the collector has air-cooling fins, it is not practical to shield it completely with magnetic material. In the invention, the leakage field is reduced by making the energizing magnet at the collector end axially magnetized and the magnet at the cathode end radially magnetized. Also, a shield around the outside of the fins may be added.

Strong anion exchange composition

Abstract: A strong anion exchange composition useful in monophosphate nucleotide isomer separations is comprised of an inert porous particle having a silyl alkyl ammonium compound fixedly attached by a covalent silicon-oxygen-silicon bond to the surface thereof. A process for synthesizing the strong anion exchange composition in an aqueous solvent is disclosed together with methods for separation of monophosphate nucleotide isomers, highly phosphorylated nucleotides and aldopentose carbohydrates using a column packed with this strong anion exchange composition.

Device and method for spinning a sample for NMR probes

Abstract: An air bearing sample spinner for use in an NMR probe has a first air bearing established between frustoconical mating surfaces (34, 36) of rotor (30) and stator (35) to provide levitation and rotation. A cylindrical portion (33) projects from the rotor (30) into a similar coaxial cylindrical portion of the stator (35) where a journal bearing is provided by radial jets (41) for centering of the rotor (30) in the stator housing (35).