Improved accuracy and robustness of electron density profiles from JET’s X-mode frequency-modulated continuous-wave reflectometers
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- United Kingdom Atomic Energy Authority (UKAEA), Abingdon (United Kingdom)
- VTT Technical Research Centre, Espoo (Finland)
- Inst. of Superior Tecnico (IST), Lisbon (Portugal). Instituto de Plasmas e Fusão Nuclear (IPFN)
- Universidade Tecnológica Federal do Paraná (UTFPR), Cornélio Procópio (Brazil)
- KTH Royal Inst. of Technology, Stockholm (Sweden)
- CEA, IRFM, Saint Paul Lez Durance (France)
- Institut Jean Lamour (IJL), Champenoux (France); Universite de Lorraine, Champenoux (France); Centre National de la Recherche Scientifique (CNRS), Champenoux (France)
- ITER Organization, St. Paul Lez Durance (France)
- Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
- Consorzio RFX, Padova (Italy); Istituto per la Scienza e Tecnologia dei Plasmi (ISTP-CNR), Padova (Italy)
JET’s frequency-modulated continuous wave (FMCW) reflectometers have been operating well with the current design since 2005, and density profiles have been automatically calculated intershot since then. However, the calculated profiles had long suffered from several shortcomings: poor agreement with other diagnostics, sometimes inappropriately moving radially by several centimeters, elevated levels of radial jitter, and persistent wriggles (strong unphysical oscillations). Here, in this research, several techniques are applied to the reflectometry data analysis, and the shortcomings are significantly improved. Starting with improving the equilibrium reconstruction that estimates the background magnetic field, adding a ripple correction in the reconstructed magnetic field profile, and adding new inner-wall reflection positions estimated through ray-tracing, these changes not only improve the agreement of reconstructed profiles to other diagnostics but also solve density profile wriggles that were present during band transitions. Other smaller but also persistent wriggles were also suppressed by applying a localized correction to the measured beat frequency where persistent oscillations are present. Finally, the burst analysis method, as introduced by Varela et al., has been implemented to extract the beat frequency from stacked spectrograms. Due to the strong suppression of spurious reflections, the radial jitter that sometimes would span several centimeters has been strongly reduced. The stacking of spectrograms has also been shown to be very useful for stacking recurring events, like small gas puff modulations, and extracting transport coefficients that would otherwise be below the noise level.
- Research Organization:
- Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC)
- Grant/Contract Number:
- AC05-00OR22725
- OSTI ID:
- 2438903
- Journal Information:
- Review of Scientific Instruments, Journal Name: Review of Scientific Instruments Journal Issue: 4 Vol. 95; ISSN 0034-6748
- Publisher:
- American Institute of Physics (AIP)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
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