New frequency translation technique for FM-CW reflectometry (original) (raw)

Coherent Signal Generation and Detection for Millimeter Wave Reflectometry Systems

In view of the more demanding measurements to be performed on next fusion devices a new generation of reflectometer systems must be developed for both density profile and turbulence studies. The new generation reflectometry systems should be able to integrate sweeping and hopping capabilities and should also cope with complex broadband transmission lines and bistatic antenna arrangements. Signal purity and stability becomes a very important issue when the use of compensation networks such as delay lines become impossible. This is the scenario for reflectometry on ITER using ultra broadband frequency operation, bistatic antenna arrangements and long corrugated waveguide lines. The present paper describes a novel system for signal generation and detection (of both main plasma signal and local oscillator signals) capable of fast sweeping, frequency hopping as well as fixed frequency operation. It is based on a single synthesized source and utilizes several oscillators which are locked ...

Microwave Reflectometry Diagnostics: Present Day Systems and Challenges for Future Devices

Plasma and Fusion Research, 2012

Microwave reflectometry technique has experienced significant advances in the last two decades becoming a very attractive diagnostic presently used in almost all fusion devices. This technique allows measuring electron density profiles, plasma instabilities, turbulence and radial electric fields with excellent spatial and temporal resolution. Although it is not straightforward, the extension of reflectometry to future devices is possible partially due to the limited access needed to accommodate the antennas inside the vacuum vessel keeping the sensitive elements as microwave sources and detectors outside the radiation area. However, in order to achieve a good diagnostic performance, limitations related to relativistic effects, intense neutron-and γ-radiation and long pulse operation have to be considered in the reflectometer design phase.

New reflectometer design for density profile measurements on JET

Review of Scientific Instruments, 2006

New transmission lines and antennas recently installed at JET under the EFDA enhancement project "Millimeter Wave Access (MWA)" meet the performance requirements of broadband reflectometry for density profile measurements. Using the new access a fast swept Frequency Modulation Continuous Wave (FMCW) [1, 2, 3, 4] using coherent detection of the reflected signal, was developed to probe the mid-plane plasma in the X-mode polarization in the 50-75GHz frequency range, aiming at measuring the edge density profile in the JET advanced scenarios with axis magnetic field of 2.4T. This paper describes the operating principles of the new system and presents some preliminary results obtained with it. Special attention is given to the fact that this swept reflectometer is capable of operating on bistatic antenna arrangements over long waveguides, by using a local generated reference, as these will be the operating conditions considered adequate for ITER reflectometer.

Microwave imaging reflectometer for TEXTOR (invited)

Review of Scientific Instruments, 2003

Understanding the behavior of fluctuations in magnetically confined plasmas is essential to the advancement of turbulence-based transport physics. Though microwave reflectometry has proven to be an extremely useful and sensitive tool for measuring small density fluctuations in some circumstances, this technique has been shown to have limited viability for large amplitude, high kθ fluctuations and/or core measurements. To this end, a new instrument based on 2-D imaging reflectometry has been developed to measure density fluctuations over an extended plasma region in the TEXTOR tokamak. This technique is made possible by collecting an extended spectrum of reflected waves with large-aperture imaging optics. Details of the imaging reflectometry concept, as well as technical details of the TEXTOR instrument will be presented. Data from proof-of-principle experiments on TEXTOR using a prototype system is presented, as well as results from a systematic off-line study of the advantages and limitations of the imaging reflectometer.

Microwave Imaging Reflectometer for TEXTOR

2002

Understanding the behavior of fluctuations in magnetically confined plasmas is essential to the advancement of turbulence-based transport physics. Though microwave reflectometry has proven to be an extremely useful and sensitive tool for measuring small density fluctuations in some circumstances, this technique has been shown to have limited viability for large amplitude, high kθ fluctuations and/or core measurements. To this end, a new instrument based on 2-D imaging reflectometry has been developed to measure density fluctuations over an extended plasma region in the TEXTOR tokamak. This technique is made possible by collecting an extended spectrum of reflected waves with large-aperture imaging optics. Details of the imaging reflectometry concept, as well as technical details of the TEXTOR instrument will be presented. Data from proof-of-principle experiments on TEXTOR using a prototype system is presented, as well as results from a systematic off-line study of the advantages and limitations of the imaging reflectometer.

Microwave FM-CW Doppler radar for boundary layer probing

Geophysical Research Letters, 1976

A microwave FM-CW radar can obtain be measured. The transmitted signal for microthe complete spectrum of radial velocities of wave FM-CW radars, obtained from YIG-tuned tranboth precipitation particles and refractive-index sistor oscillators, is not phase coherent from fluctuations in the optically clear air. Hereto-sweep-to-sweep. However, the time delay (range) fore the extraction of the Doppler spectrum from this type of radar was believed to be a formidable, if not impossible, task. We have implemented a Doppler processing technique that uses a data acquisition system developed for pulsed Doppler radar. We present Doppler spectra obtained with a zenith-pointing FM-CW radar that demonstrate this new capability. In addition to the strong refractive-index layers observed by the FM-CW radar in the optically clear air, there is evidence that scattering from a background continuum of Cn 2 can be detected when a Doppler operating mode is employed. between transmitted and received signals is only a few tens of microseconds for boundary layer probing, so, the signal phase at the output of the homodyne detection system is •ufficiently coherent from sweep-to-sweep. Therefore, the same processing technique used for the HF radar dat a can be used for microwave FM-CW radars [Strauch, et al., 1975].

Microwave reflectometry diagnostic for density profile and fluctuation measurements on ASDEX Upgrade

Review of Scientific Instruments, 1999

The broadband microwave reflectometry system on ASDEX Upgrade has been recently upgraded with new channels. It has now 12 channels that probe simultaneously the high and low fields plasma, with ultrafast sweeping (20-100 μs). X mode (33-75 GHz) is used for the scrape off layer, and the O mode (16-110 GHz) is reflected from densities between 0.3×1019 and 1.5×1019 m-3. A fast sweeping heterodyne system was developed for the highest frequency channels (50-110 GHz) to cope with higher losses and lower incident power. Fixed frequency operation is employed for fluctuation measurements. A dedicated channel (33-55 GHz) operating in fixed frequency provides a signal to continuously monitor the level of density fluctuations (e.g., L-H transition), during the whole discharge. The diagnostic is fully operated by remote control. The acquisition system is based on specially developed VME boards with up to 1 Gsamp/s sampling rates. Automatic profile inversion was recently implemented using data validation and rejection algorithms. Experimental results are presented to illustrate the profile measurements with O mode and with O and X mode combined operation. We present density profiles measured in a wide range of plasma regimes. Profile modifications due to rotating magnetic islands illustrates the potentialities of the reflectometry to estimate the location of the rational q surfaces.