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Results for “MICROWAVE INTERFEROMETER”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Assessment of the beam path deflection for a vertically installed microwave interferometer in SUNIST

Microwave interferometry has been widely employed to provide reliable line averaged electron density measurement on plasma devices. For a vertically installed interferometer on a tokamak, the refraction problem, which distorts the beam path and aggravates power loss at the receiving antenna, may become significant if taking the cross section shape into account. Increasing the frequency of the probing microwave can alleviate the distortion, but at the expense of losing the density resolution. To seek for an optimized frequency, previous calculations are mainly based on the cylindrical column geometry which grossly underestimates the deflection of the beam path induced by the plasma shape, and empirical suggestions indicating n{sub e0}/n{sub c} = 1/2 ∼ 1/3 may not always be the appropriate option. Here a single ray tracing method is applied to estimate the final horizontal deviation at the receiving antenna, which is supposed to represent the level of power loss. The calculation is carried out under the real tokamak geometry in Sino-UNIted Spherical Tokamak (SUNIST) with the cross section parameters obtained from the equilibrium reconstruction, and the result indicates that for a target density of 1.2 × 10{sup 19} m{sup −3}, a frequency of at least 100 GHz is desirable to reduce the power loss to an acceptable level. This would be helpful for the design of a vertically installed interferometer on SUNIST.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS1969

Microwave interferometer controls cutting depth of plastics

Microwave interferometer system controls the cutting of plastic materials to a prescribed depth. The interferometer is mounted on a carriage with a spindle and cutting tool. A cross slide, mounted on the carriage, allows the interferometer and cutter to move toward or away from the plastic workpiece.

Heisman, R. M.↗
DOE OSTI2013

A microwave interferometer for small and tenuous plasma density measurements

The non-intrusive density measurement of the thin plasma produced by a mini-helicon space thruster (HPH.com project) is a challenge, due to the broad density range (between 10{sup 16} m{sup -3} and 10{sup 19} m{sup -3}) and the small size of the plasma source (2 cm of diameter). A microwave interferometer has been developed for this purpose. Due to the small size of plasma, the probing beam wavelength must be small ({lambda}= 4 mm), thus a very high sensitivity interferometer is required in order to observe the lower density values. A low noise digital phase detector with a phase noise of 0.02 Degree-Sign has been used, corresponding to a density of 0.5 Multiplication-Sign 10{sup 16} m{sup -3}.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Multichannel microwave interferometer with an antenna switching system for electron density measurement in a laboratory plasma experiment

This study presents a simple and powerful technique for multichannel measurements of the density profile in laboratory plasmas by microwave interferometry. This technique uses electromechanical microwave switches to temporally switch the connection between multiple receiver antennas and one phase-detection circuit. Using this method, the phase information detected at different positions is rearranged into a time series that can be acquired from a minimum number of data acquisition channels (e.g., two channels in the case of quadrature detection). Our successfully developed multichannel microwave interferometer that uses the antenna switching method was applied to measure the radial electron density profiles in a magnetized plasma experiment. The advantage of the proposed method is its compactness and scalability to multidimensional measurement systems at low cost.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

A high speed compact microwave interferometer for density fluctuation measurements in Sino-UNIted Spherical Tokamak

A single-channel 3 mm interferometer has been developed for plasma density diagnostics in the Sino-UNIted Spherical Tokamak (SUNIST). The extremely compact microwave interferometer utilizes one corrugated feed horn antenna for both emitting and receiving the microwave. The beam path lies on the equatorial plane so the system would not suffer from beam path deflection problems due to the symmetry of the cross section. A focusing lens group and an oblique vacuum window are carefully designed to boost the signal to noise ratio, which allows this system to show good performance even with the small-diameter central column itself as a reflector, without a concave mirror. The whole system discards the reference leg for maximum compactness, which is particularly suitable for the small-sized tokamak. An auto-correcting algorithm is developed to calculate the phase evolution, and the result displays good phase stability of the whole system. The intermediate frequency is adjustable and can reach its full potential of 2 MHz for best temporal resolution. Multiple measurements during ohmic discharges proved the interferometer’s capability to track typical density fluctuations in SUNIST, which enables this system to be utilized in the study of MHD activities.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS1989

The space microwave interferometer and the search for cosmic background gravitational wave radiation

Present and planned investigations which use interplanetary spacecraft for gravitational wave searches are severely limited in their detection capability. This limitation has to do both with the Earth-based tracking procedures used and with the configuration of the experiments themselves. It is suggested that a much improved experiment can now be made using a multiarm interferometer designed with current operating elements. An important source of gravitational wave radiation, the cosmic background, may well be within reach of detection with these procedures. It is proposed to make a number of experimental steps that can now be carried out using TDRSS spacecraft and would conclude in the establishment of an operating multiarm microwave interferometer. This interferometer is projected to have a sensitivity to cosmic background gravitational wave radiation with an energy of less than 10(exp -4) cosmic closure density and to periodic waves generating spatial strain approaching 10(exp -19) in the range 0.1 to 0.001 Hz.

Anderson, Allen Joel↗
DOE OSTI2017

A metal-ceramic coaxial cable Fabry-Pérot microwave interferometer for monitoring fluid dielectric constant

We report a metal-ceramic coaxial cable Fabry-Pérot interferometer (MCCC-FPI) has been developed as a new microwave sensor and demonstrated for fast and reliably measuring and continuously monitoring dielectric constants for pure and mixed liquids. The sensor only requires a simple reference scan of the interferogram for the FPI with its sensing chamber filled with air or under vacuum to determine the actual inter-reflector length. The sensor is validated by measuring room temperature dielectric constant (εr) at high frequencies around 1.4–4.7 GHz for three vegetable oils (corn, sesame, and olive), the synthetic Mobil ® -1 engine oil, and mixtures containing sesame oil and water. The sensor has been also successfully demonstrated for determining εr values for the Mobil-1 oil at various temperatures and for the well-dispersed sesame oil-water mixtures of different compositions. The Bottcher’s model of effective medium theory is shown to be better suited for predicting the ε r of the sesame oil-water mixture than the Maxwell-Garnett and Bruggeman equations of spherical solutions.

47 OTHER INSTRUMENTATION↗
NASA NTRS2004

A Polarimetric Extension of the van Cittert-Zernike Theorem for Use with Microwave Interferometers

The van Cittert-Zernike theorem describes the Fourier-transform relationship between an extended source and its visibility function. Developments in classical optics texts use scalar field formulations for the theorem. Here, we develop a polarimetric extension to the van Cittert-Zernike theorem with applications to passive microwave Earth remote sensing. The development provides insight into the mechanics of two-dimensional interferometric imaging, particularly the effects of polarization basis differences between the scene and the observer.

Piepmeier, J. R.↗
DOE OSTI2021

Design and characterization of a single-channel microwave interferometer for the Helicon Physics Prototype eXperiment

A heterodyne interferometer for measuring the plasma electron density in Helicon Physics Prototype eXperiment (HPPX) has been developed and characterized in the laboratory. The heterodyne-type interferometer uses a probing beam of 85 GHz and a reference beam of 85.7 GHz by using two Gunn oscillators for facilitating frequency modulation. The cutoff density for this frequency is 8.96 x 10 19 m –3 that is much higher than the nominal electron density of the HPPX plasmas. The maximum deflection angle due to the refraction effect is estimated to be 0.63° assuming a parabolic electron density profile, and the impact on the measurement is negligible for the plasmas with a size of 100 mm. Two identical HDPE lenses act as the vacuum windows, and the lenses working together with the transmitter and receiver horns, form a beam with the beam waist of about 20 mm located at the plasma center. The characterization results of the lens and the critical microwave components show good performance. The plasma electron density measurement results are in line with the expectation. Furthermore, the Signal to Noise Ratio (SNR) of the measurement is defined as SNR = 20lg($\bar{n}_{e}$/S), where $\bar{n}_{e}$ and S are respectively the average electron density and the standard deviation of the signal, and the SNR is 80 dB. Finally, this demonstrates the system's capability of providing a clear and detailed density resolution.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS2003

Instrument Reflections and Scene Amplitude Modulation in a Polychromatic Microwave Quadrature Interferometer

A polychromatic microwave quadrature interferometer has been characterized using several laboratory plasmas. Reflections between the transmitter and the receiver have been observed, and the effects of including reflection terms in the data reduction equation have been examined. An error analysis which includes the reflections, modulation of the scene beam amplitude by the plasma, and simultaneous measurements at two frequencies has been applied to the empirical database, and the results are summarized. For reflection amplitudes around 1096, the reflection terms were found to reduce the calculated error bars for electron density measurements by about a factor of 2. The impact of amplitude modulation is also quantified. In the complete analysis, the mean error bar for high- density measurements is 7.596, and the mean phase shift error for low-density measurements is 1.2". .

Dobson, Chris C.↗
NASA NTRS1988

Low-noise interferometer for microwave radiometry

An interferometer for precision measurements in microwave radiometry is proposed which uses two low-noise heterodyne receivers based on SIS tunnel junction mixers in the 40-50-GHz band. The antenna interference pattern has lobes which lead to positive output signals and lobes which give negative output, and the radiometer measures the difference in the power from these lobes without beam switching or instrument motion. The present system cancels instrumental signals, has a very low 1/f noise in the output, and has a zero outpus signal when viewing a uniform source. It is noted that application of the interferometer may be limited to radiometry with relatively large beams.

Timbie, P. T.↗
DOE OSTI2021

Study of detached plasma profile in the divertor simulation experimental module of tandem mirror GAMMA 10/PDX

A divertor simulation experimental module (D-module) in the tandem mirror GAMMA 10/PDX was used for the study of plasma detachment. In previous studies, it was difficult to measure far-upstream plasma parameters in the D-module, and only electrostatic probes on the target plate were used to perform electron temperature and density measurements. Furthermore, to study the detached plasma structure, a Thomson scattering (TS) system and a microwave interferometer system have been installed to measure the inside plasma parameters of the D-module, and a movable electrostatic probe has been placed at the inlet of the D-module to measure the inlet plasma density and temperature. The TS system in the central cell observed the electron temperature and density of the core plasma simultaneously. These measurements revealed the entire density and temperature structure from the core plasma to the divertor plate. The line average electron density measured by the microwave interferometer showed a rollover behavior during detachment. The results indicated that the ionization region was located around the center of the D-module, and it appears to move upstream along the axis.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Reactive flow modeling of small scale detonation failure experiments for a baseline non-ideal explosive

Small scale characterization experiments using only 1–5 g of a baseline ammonium nitrate plus fuel oil (ANFO) explosive are discussed and simulated using an ignition and growth reactive flow model. There exists a strong need for the small scale characterization of non-ideal explosives in order to adequately survey the wide parameter space in sample composition, density, and microstructure of these materials. However, it is largely unknown in the scientific community whether any useful or meaningful result may be obtained from detonation failure, and whether a minimum sample size or level of confinement exists for the experiments. In this work, it is shown that the parameters of an ignition and growth rate law may be calibrated using the small scale data, which is obtained from a 35 GHz microwave interferometer. Calibration is feasible when the samples are heavily confined and overdriven; this conclusion is supported with detailed simulation output, including pressure and reaction contours inside the ANFO samples. The resulting shock wave velocity is most likely a combined chemical-mechanical response, and simulations of these experiments require an accurate unreacted equation of state (EOS) in addition to the calibrated reaction rate. Other experiments are proposed to gain further insight into the detonation failure data, as well as to help discriminate between the role of the EOS and reaction rate in predicting the measured outcome.

42 ENGINEERING↗