Millimeter-wave Beam Research Articles

Operational characteristics of a 14-W 140-GHz gyrotron for dynamic nuclear polarization

The operating characteristics of a 140-GHz 14-W long pulse gyrotron are presented. The device is being used in dynamic nuclear polarization enhanced nuclear magnetic resonance (DNP/NMR) spectroscopy experiments. The gyrotron yields 14 W peak power at 139.65 GHz from the TE(0,3) operating mode using a 12.3-kV 25-mA electron beam. Additionally, up to 12 W peak has been observed in the TE(2,3) mode at 136.90 GHz. A series of mode converters transform the TE(0,3) operating mode to the TE(1,1) mode. Experimental results are compared with nonlinear simulations and show reasonable agreement. The millimeter-wave output beam was imaged in a single shot using a pyroelectric camera. The mode patterns matched reasonably well to theory for both the TE(0,1) mode and the TE(1,1) mode. Repeatable mode patterns were obtained at intervals ranging from 0.8 s apart to 11 min apart at the output of the final mode converter.

Compact antenna for two-dimensional beam scan in the JT-60U electron cyclotron heating/current drive system

A compact antenna system was designed and fabricated to enable millimeter-wave beam scanning in the toroidal and poloidal directions of the JT-60U tokamak for electron cyclotron heating (ECH) and electron cyclotron current drive (ECCD) experiments. The antenna consists of a fast movable flat mirror mounted on the tokamak vacuum vessel and a rotary focusing mirror attached at the end of the waveguide that is supported from outside the vacuum vessel. This separate support concept enables a compact structure inside a shallow port (0.68×0.54×0.2m) that is shared with a subport for an independent diagnostic system. During a plasma shot, the flat mirror is driven by a servomotor with a 3-m-long drive shaft to reduce the influence of the high magnetic field on the motor. The focusing mirror is rotated by a simple mechanism utilizing a push rod and an air cylinder. The antenna has been operated reliably for 3 years after a small improvement to the rotary drive mechanism. It has made significant contributions to ECH and ECCD experiments, especially the current profile control in JT-60U.

Development of CW and short-pulse calorimetric loads for high power millimeter-wave beams

An increased power handling of rf-beam loads is required by the development of high power gyrotrons for fusion research, as well as the achievement of full capability to work under vacuum conditions, which is imposed by the use of evacuated transmission lines. New techniques were developed at IFP/CNR, leading to two prototypes. One is capable of 1 MW CW operation, while the second one is designed for precise measurements at short-pulses (0.1 s) at higher peak power (2 MW). Preliminary tests at 140 GHz, high power and long pulse (500 kW, 10 s) were performed.

Joining of ceramic tubes using a high-power 83-GHz Millimeter-wave beam

Summary form only given. The high power beams that can be generated by CW gyrotrons represent a promising energy source for high-temperature processing of materials. An experimental facility based on an 83-GHz, 15 kW CW industrial gyrotron has been set up at the Naval Research Laboratory to investigate novel mm-wave-beam-based approaches to processing ceramic materials including sintering, coating, and joining applications. Current experimental and theoretical studies are investigating the formation of strong bonds between ceramics and between ceramics and metals using controlled, selective heating of the joint area. In this paper, the results of current joining experiments were described. In particular, the results from the joining of ceramic tubes for a dielectric-loaded accelerator was presented. Additionally, novel methods for temperature sensing as well as monitoring of the ongoing process was given.

Millimeter-wave beam former using liquid crystal

By using liquid crystal, a beam former is fabricated and evaluated that can electrically steer the beam direction at millimeter wave frequencies. The beam former is constructed by alternately stacking liquid crystal and copper foil layers. By using a membrane impregnated with liquid crystal as the liquid crystal layer, a simple configuration is realized that does not require a solid substrate or spacer. In the experiment, it is found that the maximum phase shift is about −420° at 60 GHz and the beam steering angle is about ±13°. The structure works in a broad bandwidth from 50 to 75 GHz. The structure is also used as a dielectric lens to correct the phase distribution of electromagnetic waves fed from a pyramidal horn antenna. It is therefore demonstrated that various beam forming functions can be obtained. On the other hand, the insertion loss is 5 to 8 dB. To reduce the loss, it may be necessary to reduce the dielectric loss of the liquid crystal at millimeter wave frequencies. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 88(8): 10–18, 2005; Published online in Wiley InterScience (www. interscience.wiley.com). DOI 10.1002/ecjb.20173

Alignment Method of ECH Transmission Lines Based on the Moment and Phase Retrieval Method Using IR Images

New alignment methods of millimeter-wave transmission lines for Electron Cyclotron resonance Heating are proposed and evaluated on a high power level. These methods are based on the measured data of infrared images on the target, which is irradiated by the high power millimeter-waves at several positions. The first and second moments and retrieved phase obtained from these data are used to determine the propagation direction of the millimeter-wave beam along the waveguide axis. It is demonstrated that these methods have sufficient resolution to discriminate 0.1 deg., which is required to restrict the transmission loss below 1% over the 100 GHz range.

Conductor loss reduction for liquid crystal millimeter-wave beam former

Means of reducing the conductor loss of a liquid crystal millimeter-wave beam former were studied. The conductor loss is caused by surface currents flowing on electrodes of the beam former for applying control voltages to the liquid crystal layers. By making the electrode thickness comparable to or thinner than the skin depth, the surface currents that flow on both sides of the electrode in opposite directions cancel each other; consequently, the conductor loss can be reduced. Simulation results proved that doing so can effectively reduce the conductor loss.

Free and pulsed jet rotational spectra and van der Waals motions of ethanol⋯argon

The rotational spectrum of the ethanol⋯argon van der Waals complex has been investigated by free-jet absorption millimeter-wave and molecular beams Fourier transform microwave spectroscopy. The spectra of normal and OD isotopomers have been assigned, but only for the complex with trans-ethanol. Ar motions produce vibrational splittings of 1.6662(7) and 1.70(2) MHz for the two isotopic species, respectively. The barrier hindering the tunnelling motion has been evaluated to be about 55 cm −1. The van der Waals structural parameters are: r 0(Ar–O) = 3.56(1) Å, α 0(∠ArOC) = 94°(1) and τ 0(∠ArOCC) = 71°(1). The dissociation energy, as obtained from centrifugal distortion effects, is 2.1 kJ mol −1.

Joining of materials with millimetre-wave beam source

An 83 GHz gyrotron-based, millimetre-wave beam system is being used for a range of material processing. One very promising application of this technology is in joining of ceramic and ceramic composite materials and has unique advantages over competitive techniques. The significant advantage is localisation of heating, with the millimetre-wave beam controlled by reflective optics, permitting inexpensive fixturing and instrumentation and minimising thermal damage to components. Another is the possibility of depositing energy specifically in a narrow joint region, through a guided wave effect. A corollary advantage of the process is the possibility of very rapid thermal cycling during joining, minimising thermal degradation of materials being joined.

Circular-Polarized Reconfigurable Grating Antenna for Low-Cost Millimeter-Wave Beam-Steering

This communication presents a circular-polarized (CP) reconfigurable grating antenna for low-cost millimeter-wave beam steering. A CP grating array is introduced. Using an inertialess mechanical movement, the grating design can be reconfigured along the surface of a dielectric image line, allowing a directive CP beam to steer across a wide range of angles. Over 43/spl deg/ of beam steering is achieved at 32.5 GHz with axial ratio less than 1 dB across the entire scan range. Measured performance agrees well with theory. These results are inherently scalable to higher millimeter-wave frequencies and should have numerous uses in emerging millimeter-wave satellite communications applications and other related systems for mobile communications and radar.

Vernon Ellsworth Derr

Vernon Ellsworth Derr, a pioneer and leader in optical remote sensing of the atmosphere, died on 24 July 2003 in Boulder, Colorado, of complications of Parkinson’s disease.Born on 21 November 1921 in Baltimore, Maryland, Vernon served in the US Army Signal Corps with the rank of captain. He then entered St. John’s College in Annapolis, Maryland, and graduated with an AB in 1948. He was awarded a PhD in physics by Johns Hopkins University in 1959. His thesis work, conducted under the guidance of Richard Cox, was on the irreversibility of quantum mechanical systems perturbed by random forces; it led to a Physics Review paper in 1960.Vernon then joined the Martin Co in Orlando, Florida, as principal scientist in charge of the quantum electronics group, which used wavelengths spanning the range from millimeter waves to UV to study molecular structures. For spectroscopic studies, the group developed instruments, including lasers, masers, and a millimeter-wave molecular beam machine, for applications such as nuclear pumping of lasers and atomic frequency standards. In 1967, Vernon joined the newly formed Wave Propagation Laboratory of the Environmental Science Services Administration (now the National Oceanic and Atmospheric Administration, NOAA). This remote-sensing laboratory, a descendant of the Central Radio Propagation Laboratory of the National Bureau of Standards, already had expertise at radio frequencies ranging up to 100 GHz. The inclusion of Vernon (and three other members of his Martin team) added critically needed competence in millimeter, IR, and optical frequencies. As head of the submillimeter section, Vernon pioneered the development of an extraordinarily wide range of active (radarlike), passive (radio-metric), and line-of-sight (attenuation) studies of the atmosphere and its constituents.During the early 1970s, his research group developed one of the first transportable light detection and ranging systems for the study of air pollution. The scannable LIDAR system transmitted IR, visible, or UV radiation, which enabled multi-wavelength studies of the scattering and transmission characteristics of atmospheric aerosols. That system was deployed in several experiments, including some of the earliest studies of air pollution—the Denver Brown Cloud—in the Denver, Colorado, basin. In keeping with Vernon’s insatiable scientific curiosity and broad range of interests, he also used LIDAR to study ice characteristics in cirrus clouds and to investigate the feasibility of Raman LIDAR measurements of profiles of temperature and water vapor. Working with Ron Schwiesow of the submillimeter section, Vernon also developed one of the earliest carbon dioxide Doppler LIDAR systems to measure atmospheric winds. Mounted initially in a small camper and later deployed in a light aircraft, the continuous-wave instrument obtained some of the earliest measurements of airflow in desert dust devils and waterspouts. That research set the stage for many later applications of Doppler LIDAR to study a wide variety of atmospheric phenomena, including canyon and valley flows, sea breezes, low-level jets, wake vortices, thunderstorm outflows, and forest fires. A unique contribution was Vernon’s organization and editing of the 30-chapter, 650-page text Remote Sensing of the Troposphere (NOAA, 1972). The book is a landmark overview of the physics of the lower atmosphere and the application of remote-sensing techniques to atmospheric problems.In 1981, George Ludwig selected Vernon as deputy director of the Environmental Research Laboratories, the 1300-person, 10-laboratory research arm of NOAA. From 1983 to 1988, he served as director of NOAA-ERL and then, until his retirement in 1991, as senior scientist in NOAA’s Office of Oceanic and Atmospheric Research. From 1991 to 1994, he was a senior scientist in the jointly sponsored NOAA-University of Colorado Cooperative Institute for Research in Environmental Science at CU Boulder.Vernon was an excellent scientist and science administrator. A stimulating communicator, teacher, and mentor, he taught an optical remote-sensing course at Colorado for many years as an adjunct professor. His awards included a US Presidential Distinguished Rank Award in 1988 and the Department of Commerce’s highest award, the Gold Medal, in 1991.Until afflicted with Parkinson’s disease, Vernon enjoyed sports, especially tennis. He was active in music circles and sang in community choruses, including Gilbert and Sullivan operettas. Vernon was blessed with 60 years of happy marriage and a close family of two daughters, a son, and a grandson.Vernon Ellsworth DerrPPT|High resolution© 2004 American Institute of Physics.

Design and Analysis of a Reconfigurable Dual-Beam Grating Antenna for Low-Cost Millimeter-Wave Beam-Steering

This paper presents a reconfigurable dual-beam grating antenna for low-cost millimeter-wave beam steering. Experimental results indicate that this multibeam approach provides over /spl plusmn/50/spl deg/ beam steering at fixed frequencies across the entire 35 to 40 GHz band, with excellent radiation patterns maintained across the scans. An approximate analysis developed for the reconfigurable antenna closely predicts the observed scan angles and main beam radiation patterns across the complete range of scan states. These results should have numerous applications in millimeter-wave beam-steering technology.

Processing of Advanced Materials with a High Frequency, Millimeter-Wave Beam Source and other Microwave Systems

Materials Science and Component Technology Directorate, Naval Research Laboratory,4555 Overlook Avenue S.W., Washington DC 20375-5343, U. S. A.'E-mail: imam@anvil.nr.navy.milKeywords: microwave processing, millimeter-wave processing, ceramics, materials, joining,coating, coating removal, rapid sinteringAbstract. An 83 GHz gyrotron-based, millimeter-wave beam system is being used in materialprocessing: in rapid sintering of oxides, ferrites, and metal-ceramic composites to retain very finegrain structure in the product for improved mechanical and electromagnetic properties; in joining ofceramic and ceramic composite materials (with unique advantages- localization of heating, permit-ting inexpensive fixturing and instrumentation and minimizing thermal damage to components; de-positing energy specifically in a narrow joint region through a guided wave effect), and in coatingdensification and coating removal where the high frequency and short wavelength permit significantenergy deposition in relatively thin coatings. In a related effort, we are using a low frequency mi-crowave system for low cost continuous production of nanophase metals. This process should pro-duce a range of nanophase metals, metal oxides and mixtures of these, in sizeable quantities and atlow cost. The results of various experiments in these areas will be discussed, as will the potential oflow and high frequency microwave processing of advanced materials.IntroductionThe authors have been investigating the use of microwave and millimeter-wave systems inmaterial processing. Such systems can have unique advantages or capabilities vs. conventionalmaterial processing. We have investigated the use of 2.45 GHz and 35 GHz cavity systems in rapidthermal processing of ceramics [1-6]. We are currently using two particular systems: an S-Band,2.45 GHz system for continuous production of nanophase oxides and metals, and an 83 GHz, mil-limeter-wave beam system for sintering, joining, coating and coating removal [7-13]. Presently, theS-Band system uses a waveguide or a resonant cavity, while the millimeter-wave system operates ina quasi-optical mode, with the millimeter-wave beam controlled by reflective optics.Typically, microwave processing is promoted on the basis of thermal efficiency or rapidheating via in-depth energy deposition. We have been exploring the use of the millimeter-wavesystem in very rapid sintering of nanophase materials, particularly ferrites. Here, the in-depthheating permits very rapid processing (<10 minute cycles) intended to preserve very fine grainstructure in the product. For small components, cycle times of less than 1 minute are possible.Theory suggests that the nature of the magnetic behavior of these ferrite materials is expected tochange dramatically at grain sizes comparable to the magnetic domain. In the case of other materi-als, the fine grain size obtained leads to excellent mechanical properties and the possibility of su-perplastic net shape forming- a possible processing route for ceramics is rapid sintering of powdercompacts to nanophase green parts, then consolidation to full density and simultaneous shaping viausing superplastic forming.We are also investigating the use of the millimeter-wave beam system in joining of ceram-ics, applying coatings to ceramics and metals, and removal of coatings from metals and composites.Here, the millimeter-wave beam system provides unique advantages. The heating effects can beconfined to an area as small as a square centimeter, permitting very localized thermal processing.

Radiation characteristics and performance of millimeter-wave horn-fed gaussian beam antennas

Radiation characteristics and performance of Gaussian beam antennas (GBAs) are studied theoretically and experimentally in the 60 GHz band. A GBA consists of a plano-convex half-wavelength Fabry-Perot (FP) resonator excited by a guided source with a metal flange. Two reflecting metal mesh mirrors are formed on both faces of the cavity. After a review of the principles and quasi-optical performance of plano-convex FP resonators illuminated by a plane wave, a new formulation is proposed to compute the radiation patterns of GBAs: the usual expression of the waist radius inside open resonators is modified to account for the horn aperture and for the grid parameters of the plane mirror. Standard closed-form relations of vector Gaussian beams are then used to compute the radiated copolar components. In particular, it is shown that the plane mirror is not an equiphase surface, due to the metal flange of the horn. The true phase distribution is approximated by a spherical wavefront. As a result, the directivity of the antenna becomes lower than its quasi-optical value. Experimental data obtained at 60 GHz with several pyramidal horns and various cavities agree very well with the theory. Sidelobes are lower than -25 dB, and the cross-polarization level is the same as that of the primary radiator. Universal curves showing the variations of resonant frequency, -3 dB bandwidth, gain, and radiation efficiency as a function of mirror reflectivity are very useful for the design of GBAs.

Material Processing with a High Frequency Millimeter-Wave Source

A millimeter-wave beam based on a 15-kW, continuous-wave, 83-GHz gyrotron with superconducting magnets system is being investigated for use in material processing. The millimeter-wave beam can be focused to a few millimeters and manipulated quasi-optically and has been used in the following experiments: joining of ceramics (both similar and dissimilar materials), brazing of poled piezoelectric ceramics without significant heating and depoling, and coating of metals and polymers. Joining has been done directly and with reactive brazes. In coating, the beam's short wavelength and absorption depth permit effective ceramic-coating deposition on lower temperature materials, e.g., polymers and metals, without significant substrate heating, and localized deposition of coatings as well. Finally, the millimeter-wave source has been used in the efficient production of nanophase metal and ceramic powders, via a greatly accelerated modified polyol process producing smaller powders of greater uniformity. The results and implications of the various experiments will be discussed with some theoretical calculations and modeling.

Mirror-Trapped Plasma Heated by High-Power Millimeter-Wave Radiation as an Electron-Cyclotron-Resonanse Source of Soft X-Rays

Soft X-ray line emission of pulse electron-cyclotron-resonance (ECR) discharge in Argon sustained by a powerful beam of millimeter waves in a mirror magnetic trap was investigated. An X-ray spectrum in the range of 6–17 nm has been obtained, and the absolute spectral intensity of radiation in this range has been determined. It was shown that such a discharge is an effective source of soft X-ray radiation with an approximately 10% conversion efficiency of microwaves into X-rays and a spectral power maximum of 7.3 kW/nm at a wavelength of 9 nm.

Interference and Guiding Effects in the Heating of Ceramic Slabs and Joints with Millimeter-Wave Radiation

This paper presents an analysis of some of the electromagnetic wave effects that occur when millimeter-wave beams are used for processing ceramic slabs and joints. These include interference effects on the couplings of the beam into a dielectric slab, guiding of the millimeter-wave beam through a ceramic joint, and standing-wave effects on the uniformity of energy deposition within the slab or joint. It also calculates the extent of the mitigation of the nonuniform energy deposition by thermal smoothing via heat conduction.

Remote millimeter-wave beam control by the illumination of a semiconductor

The aim of this paper is to use diffraction gratings, produced by projecting a grating pattern onto a semiconductor wafer from a remote location, to control the direction of a reflected beam. We find the conditions for which diffraction at the specular angle is small so that most of the radiation goes into adjacent interference maxima whose directions may be controlled by changing the period of the projected pattern. Some preliminary experiments are reported.

Numerical analysis of quasi-optical mode converters Part 2: Analysis of azimuthal waveguide deformations using the boundary element method

Advanced launchers of quasi-optical mode converters fed by rotating high-order gyrotron modes employ wall deformations to pre-shape the rf field in order to avoid diffraction losses. The in-waveguide mirror concept separates transverse and axial millimetre-wave beam shaping, the mirrors having azimuthal or axial deformations only. A numerical technique based on the boundary element method will be presented to analyse the transverse field evolution due to azimuthal wall deformations. The transverse beam properties can be evaluated by this method.

Millimeter-wave beams with phase singularities

Beams of millimeter-wave radiation carrying phase singularities have been generated using specially configured plane and blazed gratings. The blazed grating converts a plane wave into such a beam with very high efficiency. All of the properties of these beams that have been seen at optical wavelengths, such as the hollow profiles of the beams and the way a beam already carrying a singularity is subsequently diffracted, are shown to appear at millimeter wavelengths.