Fpga-Based High Bandwidth Integral Electron Density Interferometer For Mast-U

Brunner, K. J.; O’Gorman, T.; Naylor, G.; Scannell, R.; Cunningham, G.; Sharples, R. M.; Dipper, N. A.

doi:10.22323/1.240.0138

Cited by 2 publications

(2 citation statements)

References 7 publications

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“…It is therefore necessary to "unwrap" the phase signal, which is done directly after the CORDIC algorithm as indicated in figure 4. The corresponding methods are well established in previous FPGA-based interferometers [8].…”

Section: Unwrapping and Offset Correctionmentioning

confidence: 99%

Real-time dispersion interferometry for density feedback in fusion devices

et al. 2018

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Interferometry as one of the most common core fusion diagnostics has traditionally suffered from incomplete vibration compensation. Dispersion interferometry promises a more complete compensation of vibrations. For this reason it is being employed in an increasing number of experiments. However, thus far none of them have shown reliable real-time low-latency processing of dispersion interferometry data. Nonetheless this is a necessity for most machines when trying to do density feedback control, most notably in long discharges like the ones planned at the W7-X stellarator and ITER. In this paper we report the development of a new phase extraction method specifically developed for real-time evaluation using field programmable gate arrays (FPGA). It has been shown to operate reliably during the operation phase OP1.2a at W7-X and is now routinely being used by the W7-X density feedback system up to very high densities above 1.4×1020 m-2 without showing 2π-wraps and exhibits increased wrap stability by double-data-rate sampling. A rigorous error analysis has been conducted shedding insights into the signal composition of a dispersion interferometer have been gained. This includes the environmental effects, most notably air humidity, on the phase measurement and the correction thereof.

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Section: Unwrapping and Offset Correctionmentioning

confidence: 99%

Real-time dispersion interferometry for density feedback in fusion devices

et al. 2018

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“…These are however unfavorable for high-performance fusion machines, since they result in high levels of refraction. As such, fusion experiments rely on interferometric measurements such as two-color interferometry (2CI) or dispersion interferometry (DI) to remove the Φ ∆L -contribution [10,13].With appropriately calibrated systems Φ ∆L can be neglected. Ignoring errors from the signal evaluation, the measured phase in a fusion setting is therefore :…”

Section: Environmental Phase Modelmentioning

confidence: 99%

Compensation of phase drifts caused by ambient humidity, temperature and pressure changes for continuously operating interferometers

et al. 2019

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A: Fusion experiments rely heavily on the measurement of the line-integrated electron density by interferometry for density feed-back control. In recent years the discharge length has increased dramatically and is continuing to rise, resulting in environmentally induced phase drifts to become an increasingly worrisome subject, since they falsify the interferometer's measurement of the density. Especially in larger Tokamaks the loss of density control due to uncontrolled changes in the optical path length can have a disastrous outcome. The control of environmental parameters in large diagnostic/experimental halls is costly and sometimes infeasible and in some cases cannot be retro-fitted to an existing machine. In this report we present a very cheap (ca. e 100), easily retro-fitted, real-time capable phase compensation scheme for interferometers measuring dispersive media over long time scales. The method is not limited to fusion, but can be applied to any continuously measuring interferometer measuring a dispersive medium. It has been successfully applied to the Wendelstein 7-X density feed-back interferometer. K: Plasma diagnostics -interferometry, Digital signal processing (DSP), Pattern recognition, cluster finding, calibration and fitting methods 1Corresponding author.

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Fpga-Based High Bandwidth Integral Electron Density Interferometer For Mast-U

Cited by 2 publications

References 7 publications

Real-time dispersion interferometry for density feedback in fusion devices

Real-time dispersion interferometry for density feedback in fusion devices

Compensation of phase drifts caused by ambient humidity, temperature and pressure changes for continuously operating interferometers

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