Dispersion Interferometer Using a Modulation Amplitude on LHD

Since a dispersion interferometer is insensitive to mechanical vibrations, a vibration compensation system is not necessary. The CO2 laser dispersion interferometer with phase modulations on the Large Helical Device utilizes the new phase extraction method which uses modulation amplitudes and can improve a disadvantage of the original dispersion interferometer: measurement errors caused by variations of detected intensities. The phase variation within ±2 × 1017 m?3 is obtained without vibration compensation system. The measured line averaged electron density with the dispersion interferometer shows good agreement with that with the existing far infrared laser interferometer. Fringe jump errors in high density ranging up to 1.5 × 1020 m?3 can be overcome by a sufficient sampling rate of about 100 kHz

Infrared Dispersion Interferometer for Plasma Diagnostics

Interferometry is used in plasma physics experiments and in particular in nuclear fusion experiments to measure the time evolution of electron density with high time resolution and low measurement error. Since the plasma refractive index depends upon the electronic density, a measure of the interferometric phase shift between an electromagnetic wave traveling through the plasma and one traveling outside plasma allows assessing the electron density. In the frame of the diagnostic development for the Divertor Tokamak Test facility (DTT), a new Italian tokamak device, a master thesis is proposed to study a specific interferometer concept knows as “dispersion interferometer― which does not need the wave traveling outside plasma. With respect to other interferometric optical schemes adopted in nuclear fusion experiments (e.g. the two color interferometers), a dispersion interferometer has the double advantage of simplicity and insensitivity to vibrations, which are the main source of error in the electron density measurement with interferometry. The thesis work can have both design/modelling and experimental activities. The design/modelling task will consist in: determining a suitable dispersion interferometer optical scheme/set-up that fits the DTT mechanical structure; dimensioning and modelling the critical elements of the system, such as the nonlinear crystal (by considering thermal and walk-off effects), detectors and electronics; studying an appropriate technique of phase modulation for heterodyne detection and of signal extraction. The experimental work will concern tests on solutions previously designed as described above and the realization of a prototype dispersion interferometer to be built by considering the mentioned modelling and experimental test.Interferometry is used in plasma physics experiments and in particular in nuclear fusion experiments to measure the time evolution of electron density with high time resolution and low measurement error. Since the plasma refractive index depends upon the electronic density, a measure of the interferometric phase shift between an electromagnetic wave traveling through the plasma and one traveling outside plasma allows assessing the electron density. In the frame of the diagnostic development for the Divertor Tokamak Test facility (DTT), a new Italian tokamak device, a master thesis is proposed to study a specific interferometer concept knows as “dispersion interferometer― which does not need the wave traveling outside plasma. With respect to other interferometric optical schemes adopted in nuclear fusion experiments (e.g. the two color interferometers), a dispersion interferometer has the double advantage of simplicity and insensitivity to vibrations, which are the main source of error in the electron density measurement with interferometry. The thesis work can have both design/modelling and experimental activities. The design/modelling task will consist in: determining a suitable dispersion interferometer optical scheme/set-up that fits the DTT mechanical structure; dimensioning and modelling the critical elements of the system, such as the nonlinear crystal (by considering thermal and walk-off effects), detectors and electronics; studying an appropriate technique of phase modulation for heterodyne detection and of signal extraction. The experimental work will concern tests on solutions previously designed as described above and the realization of a prototype dispersion interferometer to be built by considering the mentioned modelling and experimental test

Conceptual Design of Electron Density Measurement System for DEMO-Relevant Helical Plasmas

Electron density measurement remains indispensable to control fueling on a DEMO reactor. For steady-state operation of the DEMO reactor, density measurement should be highly reliable and accurate. A dispersion interferometer and a Faraday polarimeter are free from measurement errors caused by mechanical vibrations. Hence combination of the two diagnostics yields a suitable system for density measurement on future steady-state fusion reactors. A wavelength around 1 ?m is one of the desirable candidates in terms of the fringe shift and the Faraday rotation angle, the variety of optical components, and the efficiency of frequency doubling for the dispersion interferometer. This paper presents a conceptual design for the dispersion interferometer and Faraday polarimeter with a 1 ?m light source

Compact interrogation system of fiber Bragg grating sensors based on multiheterodyne dispersion interferometry for dynamic strain measurements

Dual-comb multiheterodyne spectroscopy is a well-established technology for the highly sensitive real-time detection and measurement of the optical spectra of samples, including gases and fiber sensors. However, a common drawback of dual-comb spectroscopy is the need for a broadband amplitude-resolved absorption or reflection measurement, which increases the complexity of the dual comb and requires the precise calibration of the optical detection. In the present study, we present an alternative dispersion-based approach applied to fiber Bragg grating sensors in which the dual comb is compacted by a single dual-drive-unit optical modulator, and the fiber sensor is part of a dispersion interferometer. The incident dual comb samples a few points in the spectrum that are sensitive to Bragg wavelength changes through the optical phase. The spectra reading is improved due to the external interferometer and is desensitized to changes in the amplitude of the comb tones. The narrow-band detection of the fiber sensor dispersion changes that we demonstrate enables the compact, cost-effective, high-resolution multiheterodyne interrogation of high-throughput interferometric fiber sensors. These characteristics open its application both to the detection of fast phenomena, such as ultrasound, and to the precise measurement at high speed of chemical-/biological-sensing samples. The results with a low-reflectivity fiber Bragg grating show the detection of dynamic strain in the range of 215 nepsilon with a 30 dB signal to noise ratio and up to 130 kHz (ultrasonic range).This research was funded by the Spanish Education, Culture and Sports ministry, grant number FPU16/03695 (FPU program 2016 SIA: 998758) and by the Spanish Ministry of Economy and Competitiveness, grant number TEC2017-86271-R (PARAQUA project). This work was supported by the Madrid Government (Comunidad de Madrid-Spain) under the Multiannual Agreement with UC3M in the line of Excellence of University Professors (EPUC3M26), and in the context of the V PRICIT (Regional Programme of Research and Technological Innovation)

Acceleration of Bayesian model based data analysis

Inverse problems for parameter estimation often face a choice between the use of a real-time scheme with strong approximations or rigorous post-processing with explicit uncertainty handling. Plasma physics experiments set a particularly high demand of both and a solution that meets all of these requirements is missing. Standard Bayesian analysis is an excellent tool for the case at hand, with the disadvantage of extensive processing times. This work therefore presents a solution that satisfies the scientific requirements while reducing the need for a speed vs. rigorosity trade-off.Die Bestimmung von Parametern bei inversen Problemen beinhaltet eine Abwägung zwischen vereinfachenden Annahmen für Echtzeitverfahren und rigoroser Datenanalyse mit Fehlerbetrachtung. Experimente in der Plasmaphysik stellen besonders hohe Anforderungen an beide, und eine Lösung, die diese Anforderungen erfüllt, fehlt. Die Bayessche Analyse ist ein exzellentes Werkzeug für diese Problemstellung, mit dem Nachteil langer Laufzeiten. Diese Arbeit stellt eine Lösung dar, die den Anforderungen entspricht und die Notwendigkeit der Abwägung zwischen Geschwindigkeit und Rigorosität reduziert