Intermediate frequency band digitized high dynamic range radiometer system for plasma diagnostics and real-time Tokamak control

Abstract

Document VersionPublisher's PDF, also known as Version of Record (includes final page, issue and volume numbers) Please check the document version of this publication:• A submitted manuscript is the author's version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher's website.• The final author version and the galley proof are versions of the publication after peer review.• The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. An intermediate frequency (IF) band digitizing radiometer system in the 100-200 GHz frequency range has been developed for Tokamak diagnostics and control, and other fields of research which require a high flexibility in frequency resolution combined with a large bandwidth and the retrieval of the full wave information of the mm-wave signals under investigation. The system is based on directly digitizing the IF band after down conversion. The enabling technology consists of a fast multi-giga sample analog to digital converter that has recently become available. Field programmable gate arrays (FPGA) are implemented to accomplish versatile real-time data analysis. A prototype system has been developed and tested and its performance has been compared with conventional electron cyclotron emission (ECE) spectrometer systems. On the TEXTOR Tokamak a proof of principle shows that ECE, together with high power injected and scattered radiation, becomes amenable to measurement by this device. In particular, its capability to measure the phase of coherent signals in the spectrum offers important advantages in diagnostics and control. One case developed in detail employs the FPGA in real-time fast Fourier transform (FFT) and additional signal processing. The major benefit of such a FFT-based system is the real-time trade-off that can be made between frequency and time resolution. For ECE diagnostics this corresponds to a flexible spatial resolution in the plasma, with potential application...

Modification of the collective Thomson scattering radiometer in the search for parametric decay on TEXTOR

“…An additional spectrometer, sharing the transmission line with the gyrotron, measures the back-scattered radiation. 9,10 This in-line receiver samples a down-converted signal directly with a fast digitizer, and spectra are generated by Fourier analysis. The in-line receiver has a high frequency resolution (0.5 MHz) compared with the CTS receiver whereas time resolution of the CTS receiver is higher than that of the in-line system.…”

“…Additionally, a new spectrometer was connected to the inline system antenna through a 3 dB splitter. 9,10 By combining these two radiometers, a detailed study of the anomalous signal was undertaken. 11 The observations have been suggested to originate from the parametric decay instability and has motivated a re-evaluation of the parametric decay instability power threshold.…”

Resolving the bulk ion region of millimeter-wave collective Thomson scattering spectra at ASDEX Upgrade

“…This increase in acquisition time can be used to improve the signal-to-noise ratio for individual measurements by lengthening the acquisition time per gyrotron pulse, or it can be used to cover a larger part of each plasma discharge. In the long term, real-time FFT processing and averaging of the data using fieldprogrammable gate arrays 54 will enable near-continuous coverage and may allow real-time analysis of the spectra to infer plasma parameters such as the ion temperature and rotation velocity. Work is now underway to implement such a system in one of the CTS receivers on AUG.…”

Temporally resolved plasma composition measurements by collective Thomson scattering in TEXTOR (invited)

“…We also note that a similar technique has been used to study strong scattering phenomena in plasmas with tearing modes using the inline ECE receiver at TEXTOR. [16][17][18][19] The acquisition technique described here easily meets the requirements on frequency resolution, but the high sample rate and limited memory on the oscilloscope constrains the total measurement time to 50 ms. Measurements over long time spans therefore requires careful management of the available memory. However, in initial experiments with this acquisition technique the overriding concern was not the temporal resolution.…”