Millimeter-wave Interferometer Research Articles

Millimeter-Wave Interferometric Angular Velocity Detection

A new method of detecting the angular velocity of moving objects using correlation interferometry is presented. As an object passes through the interferometer beam pattern, the frequency of the signal response is directly proportional to the angular velocity of the object. Only a simple frequency analysis is required to measure the velocity, whereas typical techniques require angle estimation and multiple looks to calculate the rate of angular change over time. The general response of the interferometer is derived, as well as the fringe frequency. The method is verified by detecting the angular velocity of a walking human with a millimeter-wave correlation interferometer, and experimental results of a walking human are presented.

Characterization of a linear device developed for research on advanced plasma imaging and dynamics

Within the scope of long term research on imaging diagnostics for steady-state plasmas and understanding of edge plasma physics through diagnostics with conventional spectroscopic methods, we have constructed a linear electron cyclotron resonance (ECR) plasma device named Research on Advanced Plasma Imaging and Dynamics (RAPID). It has a variety of axial magnetic field profiles provided by eight water-cooled magnetic coils and two dc power supplies. The positions of the magnetic coils are freely adjustable along the axial direction and the power supplies can be operated with many combinations of electrical wiring to the coils. Here, a 6 kW 2.45 GHz magnetron is used to produce steady-state hydrogen, helium, and argon plasmas with central magnetic fields of 875 and/or 437.5 G (second harmonic). In order to achieve the highest possible plasma performance within the limited input parameters, wall conditioning experiments were carried out. Chamber bake-out was achieved with heating coils that were wound covering the vessel, and long-pulse electron cyclotron heating discharge cleaning was also followed after 4 days of bake-out. A uniform bake-out temperature (150 °C) was achieved by wrapping the vessel in high temperature thermal insulation textile and by controlling the heating coil current using a digital control system. The partial pressure changes were observed using a residual gas analyzer, and a total system pressure of 5×10(-8) Torr was finally reached. Diagnostic systems including a millimeter-wave interferometer, a high resolution survey spectrometer, a Langmuir probe, and an ultrasoft x-ray detector were used to provide the evidence that the plasma performance was improved as we desired. In this work, we present characterization of the RAPID device for various system conditions and configurations.

Analysis of line integrated electron density using plasma position data on Korea Superconducting Tokamak Advanced Research

A 280 GHz single-channel horizontal millimeter-wave interferometer system has been installed for plasma electron density measurements on the Korea Superconducting Tokamak Advanced Research (KSTAR) device. This system has a triangular beam path that does not pass through the plasma axis due to geometrical constraints in the superconducting tokamak. The term line density on KSTAR has a different meaning from the line density of other tokamaks. To estimate the peak density and the mean density from the measured line density, information on the position of the plasma is needed. The information has been calculated from tangentially viewed visible images using the toroidal symmetry of the plasma. Interface definition language routines have been developed for this purpose. The calculated plasma position data correspond well to calculation results from magnetic analysis. With the position data and an estimated plasma profile, the peak density and the mean density have been obtained from the line density. From these results, changes of plasma density themselves can be separated from effects of the plasma movements, so they can give valuable information on the plasma status.

Interferometer Systems on LHD

This paper describes the interferometer systems on the Large Helical Device (LHD). LHD is equipped with five interferometer systems, each of which has a different operational purpose and measurable electron density range. A single-channel millimeter-wave interferometer is mainly used for low-density plasmas along a horizontal line of sight on the equatorial plane. Wavelengths of 1 and 2 mm are used for vibration compensation based on two-color interferometry, which has been used since the first operation of LHD. A 13-channel CH3OH laser interferometer (wavelength of 119 μm) covers almost the whole poloidal cross sections of LHD plasmas with a chord separation of 90 mm. It routinely provides temporal behavior and profiles of the electron density. The laser has been developed as a collaboration between the National Institute for Fusion Science (NIFS) and Chubu University. An 80-channel CO2 laser interferometer (10.6 μm) is employed for high-density plasmas such as superdense core plasmas. It adopts an imaging technique with three slablike beams and array detectors to measure the density profile precisely. A phase contrast imaging interferometer, which measures density fluctuations, is combined with the CO2 laser interferometer. Since LHD has strong magnetic shear, a distribution of the density fluctuations is evaluated by using shear technique. A conventional millimeter-wave (4 mm) interferometer is also installed at a divertor region to measure dynamic density responses in a divertor leg. The phase counter used on these interferometers was originally developed at NIFS. The phase resolution of a typical phase counter is 1/100 fringe with a temporal response of 10 μs.

Diagnostics for first plasma and development plan on KSTAR

The first plasma with target values of the plasma current and the pulse duration was finally achieved on June 13, 2008 in the Korea Superconducting Tokamak Advanced Research (KSTAR). The diagnostic systems played an important role in achieving successful first plasma operation for the KSTAR tokamak. The employed plasma diagnostic systems for the KSTAR first plasma including the magnetic diagnostics, millimeter-wave interferometer, inspection illuminator, H(alpha), visible spectrometer, filterscope, and electron cyclotron emission (ECE) radiometer have provided the main plasma parameters, which are essential for the plasma generation, control, and physics understanding. Improvements to the first diagnostic systems and additional diagnostics including an x-ray imaging crystal spectrometer, reflectometer, ECE radiometer, resistive bolometer, and soft x-ray array are scheduled to be added for the next KSTAR experimental campaign in 2009.

Data acquisition system implemented with various platforms for KSTAR diagnostic systems

For the 1st plasma operation of the Korea Superconducting Tokamak Advanced Research (KSTAR) in 2008, 11 diagnostic systems had been developed such as five types of magnetic diagnostics, millimeter-wave interferometer, ECE radiometer, visible survey spectrometer, H_alpha monitor, filter scope and visible/H-alpha TVs to measure basic physics data; plasma current, electron density, temperature, plasma image, impurity, and so on. Data acquisition (DAQ) systems for those diagnostics performed signal conditioning, conversion from analog signal to digital signal with specific bit resolution, and data transmission in synchronized manner. A feature of the KSTAR diagnostic DAQ systems is that the systems have been implemented with various platforms for maximum hardware efficiency, future extendibility and adaptability to diagnostic systems. Another feature is that all diagnostic DAQ systems have been integrated into KSTAR central control system with EPICS (Experimental Physics and Industrial Control System) to configure and monitor them. In addition, all diagnostic DAQ systems operate in a synchronized manner by using local timing units (LTU) which are connected to a central timing unit (CTU) in the KSTAR time & synchronization system (TSS) via a dedicated timing network. Finally, diagnostic data generated during a shot are transferred to a centralized storage system using MDSplus (Model Driven System plus) which is an open source tool to be used widely in fusion environment. This paper will present the implementation of heterogeneous KSTAR diagnostic DAQ systems and their operation results.

Multi-Fringe Counting Technique of Millimeter-Wave Interferometer System for KSTAR

A 280 GHz single-channel horizontal millimeter-wave interferometer system has been installed for plasma electron density measurements on the Korea Superconducting Tokamak Advanced Research (KSTAR). An electron density of plasma is measured on double-path horizontal line with triangular geometry. A cassette system contains two vacuum windows was installed on median port for these purpose. Maximum line-integrated electron density of first plasma is set to 1019 m-2 in this geometry. Since a line density of single-fringe in 280 GHz is 2 × 1018 m-2, a multi-fringe counting circuit has been adopted for a fringe-jump compensation. Measured IF signals are divided into 4 channels which has fringe counting capability of 1, 2, 4 and 8 fringes, respectively. A phase difference between IF signals is converted to DC voltage in each channel according to its fringe coverage. A fringe-jump analysis algorism has been developed for a discrimination of real fringe-jump from noise signal. An electron density of the KSTAR first plasma has been measured and analyzed using this system. Upon these results, an advanced fringe counting scheme will be proposed in this paper.

A 280GHz single-channel millimeter-wave interferometer system for KSTAR

A 280 GHz single-channel horizontal millimeter-wave interferometer system has been fabricated and installed for plasma electron density measurements on the Korea Superconducting Tokamak Advanced Research (KSTAR). A retractable cassette system has been adopted for deep positioning of the interferometer system on large cryostat. The cassette system contains a pneumatic vacuum window shutter and a beam focusing module. The focusing module consists of antennas and aluminum concave mirrors, where an incident beam is reflected on a specially designed carbon inner-wall tile. The module enhances receiving beam power and reduces phase errors due to unexpected beam reflections on a vacuum vessel. Microwave components such as oscillators and mixers are located 2 m away from cryostat with a shielding box. Intermediate frequency signals generated by mixers are transmitted to a diagnostics room, and the phase difference between these signals is measured using a multifringe counting phase comparator. A beam path analysis has been performed for a triangular beam path geometry. An effective line-integrated density can be deduced from measured line-integrated density with these results. A beam path length error due to plasma refraction effect has been determined with various plasma conditions.

Electronically swept millimeter-wave interferometer for spatially resolved measurement of plasma electron density

We report the development and initial implementation of what we believe to be a new rapid- spatial-scan millimeter-wave interferometer for plasma density measurements. The fast scan is effected by electronic frequency sweeping of a wideband (180-280 GHz) backward-wave oscillator whose output is focused onto a fixed blazed diffraction grating. The system, which augments the rotating-grating scanned multiview H-1 heliac interferometer, can sweep the plasma cross section in a period of less than 1 ms with a beam diameter in the plasma of 20 mm and phase noise of the order of 0.01 rad.

Three view electronically scanned interferometer for plasma electron density measurements on the H-1 heliac

We report the development of a three view electronically scanned millimeter-wave interferometer for plasma electron density profile measurement on the H-1 heliac. The system utilizes an electronically tunable backward-wave oscillator whose output is incident on a fixed blazed diffraction grating such that sweeping the source frequency effects a spatial scan of the plasma cross section. Two diagonal views essentially span most of the plasma cross section, while the horizontal arm views the lower half of the plasma. The diffracted beams traverse the plasma in <1ms with a spatial resolution ∼20mm. A study of the density projection dependence on magnetic configuration shows that the presence of low-order rational surfaces in the plasma gives rise to sharp density gradients in the vicinity of the surface.

An interferometric CO survey of luminous submillimetre galaxies

In this paper, we present results from an Institut de Radio Astronomie Millimetrique (IRAM) Plateau de Bure millimetre-wave Interferometer (PdBI) survey for carbon monoxide (CO) emission towards radio-detected submillimetre galaxies (SMGs) with known optical and near-infrared spectroscopic redshifts. Five sources in the redshift range z ∼ 1-3.5 were detected, nearly doubling the number of SMGs detected in CO. We summarize the properties of all 12 CO-detected SMGs, as well as six sources not detected in CO by our survey, and use this sample to explore the bulk physical properties of the submillimetre galaxy (SMG) population as a whole. The median CO line luminosity of the SMGs is = (3.8 ± 2.0) × 10 10 K km s -1 pc 2 . Using a CO-to-H 2 conversion factor appropriate for starburst galaxies, this corresponds to a molecular gas mass = (3.0 ± 1.6) x 10 10 M ○. within an ∼ 2 kpc radius, approximately 4 times greater than the most luminous local ultraluminous infrared galaxies (ULIRGs) but comparable to that of the most extreme high-redshift radio galaxies (HzRGs) and quasi-sellar objects (QSOs). The median CO FWHM linewidth is broad, (FWHM) = 780 ± 320 km s -1 , and the SMGs often have double-peaked line profiles, indicative of either a merger or a disc. From their median gas reservoirs (∼ 3 x 10 10 M ○. ) and star formation rates (≥ 700 M ○. yr -1 ), we estimate a lower limit on the typical gas-depletion time-scale of ≥ 40 Myr in SMGs. This is marginally below the typical age expected for the starbursts in SMGs and suggests that negative feedback processes may play an important role in prolonging the gas consumption time-scale. We find a statistically significant correlation between the far-infrared and CO luminosities of the SMGs, which extends the observed correlation for local ULIRGs to higher luminosities and higher redshifts. The non-linear nature of the correlation implies that SMGs have higher far-infrared to CO luminosity ratios and possibly higher star formation efficiencies (SFEs), than local ULIRGs. Assuming a typical CO source diameter of θ ∼ 0.5 arcsec (D ∼ 4kpc), we estimate a median dynamical mass of ≃ (1.2 ± 1.5) x 10 11 M ○. for the SMG sample. Both the total gas and stellar masses imply that SMGs are very massive systems, dominated by baryons in their central regions. The baryonic and dynamical properties of these systems mirror those of local giant ellipticals and are consistent with numerical simulations of the formation of the most massive galaxies. We have been able to impose a lower limit of ≥ 5 x 10 -6 Mpc -3 to the comoving number density of massive galaxies in the redshift range z ∼ 2-3.5, which is in agreement with results from recent spectroscopic surveys and the most recent model predictions.

Cosmic Microwave Background Observations with a Compact Heterogeneous 150 GHz Interferometer in Chile

We report on the design, first observing season, and analysis of data from a new prototype millimeter-wave interferometer, MINT. MINT consists of four 145 GHz SIS mixers operating in double-sideband mode in a compact heterogeneous configuration. The signal band is subdivided by a monolithic channelizer, after which the correlations between antennas are performed digitally. The typical receiver sensitivity in a 2 GHz band is 1.4 mK s1/2. The primary beams are 045 and 030 FWHM, with fringe spacing as small as 01. MINT observed the cosmic microwave background (CMB) from Cerro Toco, in the Chilean Altiplano. The site quality at 145 GHz is good, with median nighttime atmospheric temperature of 9 K at zenith (exclusive of the CMB). Repeated observations of Mars, Jupiter, and a telescope-mounted calibration source establish the phase and magnitude stability of the system. MINT is the first interferometer dedicated to CMB studies to operate above 50 GHz. The same type of system can be used to probe the Sunyaev-Zel'dovich effect in galaxy clusters near the SZ null at 217 GHz. We give the essential features of MINT and present an analysis of sideband-separated, digitally sampled data recorded by the array. Based on 215 hours of data taken in late 2001, we set an upper limit on the CMB anisotropy in a band of width ?? = 700 around ? = 1540 of ?T < 105??K (95% confidence). Increased sensitivity can be achieved with more integration time, greater bandwidth, and more elements.

Plasma electron density measurement by a digital signal processor based millimetre-wave interferometer

This paper addresses the measurement of the average plasma electron density based on the measurement of a phase, using a 2 mm wavelength single-channel digital millimetre-wave interferometer in the Damavand tokamak. Damavand tokamak discharges have plasma currents up to 40 kA with discharge duration greater than 15 ms and toroidal magnetic fields up to 1.2 T. Phase analysis is done using a digital signal processor which is capable of registering phase variations at a rate of 10π × 104 rad s−1, which corresponds to a change in electron density of 1.5 × 1017 cm−3 s−1. In this paper, the details of the millimetre wave interferometer system along with the implementation of a phase measurement routine based on a TMS320c25 digital signal processor are presented.

Electron Density Profile Measurements on LHD

Several kinds of density diagnostics have been developed and routinely operated to provide density profile information on the Large Helical Device. A 13-channel far-infrared laser interferometer and a two-color millimeter-wave interferometer are used for monitoring the density profile. A CO/sub 2/ laser imaging interferometer has been developed for detailed profiled measurements of density and density fluctuations. A CO/sub 2/ laser densitometer measuring the Faraday rotation was developed for the long-pulse operations of large helical device. Details of each diagnostics and sample results are presented.

Bolometric interferometry: the millimeter-wave bolometric interferometer

Bolometric interferometry is not a new idea, but this technique has not been demonstrated at millimeter wavelengths. The millimeter-wave bolometric interferometer combines the advantages of two well-developed technologies – interferometers and bolometric detectors – and will open a new region of sensitivity and angular resolution not previously accessible to other instruments.

Two‐dimensional synthetic aperture millimeter‐wave radiometric interferometer for measuring full‐component Stokes vector of emission from hydrometeors

Calculations of attainable values for space resolution and radiometric sensibility of a spaceborne two‐dimensional synthetic aperture microwave polarimetric interferometer are carried out. It is shown that for the most preferable Y‐shaped interferometer configuration, it is possible to achieve (within the transparency windows of waveband 3–22.5 mm) a space resolution of 0.5–1 km and a radiometric resolution close to 1 K at the receiver bandwidth of 100 MHz. For cross‐ and T‐shaped resolutions, values close to the above can be reached.

Design of a single-channel millimeter-wave interferometer system for Korea Superconducting Tokamak Advanced Research

A simple single-channel horizontal millimeter-wave interferometer has been designed for plasma electron density measurements on the Korea Superconducting Tokamak Advanced Research (KSTAR). To measure line integrated plasma densities of 2×1019 m−2 in the initial phase of the KSTAR, Gunn oscillator frequency of 280 GHz has been chosen to optimize errors due to both vibration on the beam path and refraction in the plasma. To reduce the free propagation length of the probing beam and to obtain small beam width on the vacuum windows, a retractable cassette system for deep positioning of the diagnostic system has been designed, where microwave parts are located as close as possible to the tokamak with a shielding box. A beam focusing system with concave reflecting mirrors has been designed on the cassette and on the inner wall of the tokamak to reduce beam losses and to minimize beam width in the plasma. The estimated total transmission loss is about 25 dB, and beam widths are reduced significantly in the range of 20–50 mm.

Raman calibration of the LHD YAG Thomson scattering for electron-density measurements

We have calibrated the LHD yttrium aluminum garnet (YAG) Thomson scattering system by using anti-Stokes rotational Raman scattering from air for the measurements of absolute electron-density profiles of LHD plasmas. The air Raman calibration was carried out at near atmospheric pressure and room temperature. Total uncertainty in measured electron densities is estimated to be ±15% or less. Electron densities obtained with the calibrated YAG Thomson scattering show good agreements with those measured by the LHD millimeter-wave interferometer.

Millimeter-wave two-dimensional imaging optical system for interferometer of the GAMMA 10 tandem mirror

A millimeter-wave optical system for plasma diagnostics for measuring the two-dimensional distribution of electron density in the Tsukuba GAMMA 10 tandem mirror has been developed. Two-dimensional images of plasma density of a cross-sectional area of 83 mm×67 mm in the machine axis direction were successfully measured with the optical system. The position at which the present imaging system is installed corresponds to the plug region, and the plasma radius is relatively narrow (less than 100 mm). Information about the density in the area is valuable in the study of confining-potential formation. This optical system was developed for a millimeter-wave phase-imaging interferometer and was designed with the ray tracing method to reduce aberration. It was evaluated experimentally by measuring images of point sources and phase images of dielectric targets. The receiving optical system from the plasma to detector array was designed with a spatial resolution of 28.7 mm and a magnification of 0.30. Ray tracing indicated that the transverse spherical aberration was 78% of the sampling interval of 5.0 mm on an image plane and that even for the worst image point the distortion was 10% of the sampling interval. In the design of the optical system for plasma diagnostics, the off-focus effect due to plasma size (plasma diameter: 200 mm) with electron density profile is proposed and considered.

Ultra–High-Density Molecular Core and Warped Nuclear Disk in the Deep Potential of Radio Lobe Galaxy NGC 3079

We have performed high-resolution synthesis observations of the 12CO (J = 1-0) line emission from the radio lobe edge-on spiral galaxy NGC 3079 using a seven-element millimeter-wave interferometer at the Nobeyama Radio Observatory, which consisted of the 45 m telescope and six-element array. The nuclear molecular disk (NMD) of 750 pc radius is found to be inclined by 20° from the optical disk, and the NMD has spiral arms. An ultra-high-density core (UHC) of molecular gas was found at the nucleus. The gaseous mass of the UHC within 125 pc radius is as large as ~3 × 108 M☉, an order of magnitude more massive than that in the same area of the Galactic center, and the mean density is as high as ~3 × 103H2 cm-3. A position-velocity diagram along the major axis indicates that the rotation curve already starts at a finite velocity exceeding 300 km s-1 from the nucleus. The surface mass density in the central region is estimated to be as high as ~105 M☉ pc-2, producing a very deep gravitational potential. We argue that the very large differential rotation in such a deep potential will keep the UHC gravitationally stable during the current star formation.