Conceptual Design of a Dispersion Interferometer Using a Ratio of Modulation Amplitudes

Akiyama, Tsuyoshi; Kawahata, K.; Okajima, S.; Nakayama, Keiichi I.

doi:10.1585/pfr.5.s1041

Cited by 20 publications

(23 citation statements)

References 11 publications

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“…Hence, interpretation of the measured data is straightforward. Because good temporal and density resolution have already been confirmed with CO 2 lasers (wavelength 10.6 µm) [6][7][8][9], the DI is the most promising candidate. …”

Section: Alternative Density Measurement Methodsmentioning

confidence: 99%

“…Figure 2 shows a schematic view of the phasemodulated DI [6][7][8][9]. A mixed beam consisting of the fundamental and second harmonic components, which is generated with a nonlinear component, is used as a probe beam.…”

Section: Wavelength Selection For Demorelevant Helical Plasmasmentioning

confidence: 99%

“…2 Schematic view of the dispersion interferometer using the ratio of the modulation amplitude. modulation and phase extraction method using the ratio of modulation amplitudes [7][8][9] are applied to overcome a disadvantage of the DI: measurement errors caused by variations in the detected intensity. After passing through a plasma, another second harmonic component is generated from the fundamental.…”

Section: Wavelength Selection For Demorelevant Helical Plasmasmentioning

confidence: 99%

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

Akiyama

Yasuhara

Tokuzawa

et al. 2012

Plasma and Fusion Research

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Electron density measurement remains indispensable to control fueling on a DEMO reactor. For steadystate 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 steadystate fusion reactors. A wavelength around 1 µm 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 µm light source.

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Section: Alternative Density Measurement Methodsmentioning

confidence: 99%

Section: Wavelength Selection For Demorelevant Helical Plasmasmentioning

confidence: 99%

Section: Wavelength Selection For Demorelevant Helical Plasmasmentioning

confidence: 99%

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

Akiyama

Yasuhara

Tokuzawa

et al. 2012

Plasma and Fusion Research

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“…In contrast, the DI has no issue even if the plasma term is smaller than 2π owing to its immunity to vibrations. Thus, the DI becomes free from fringe jump errors if an appropriate wavelength is selected.Techniques that improve the resolution of DIs are currently being introduced [2][3][4][5]. This paper reports improved resolution and long-time stability in a DI that adopts phase modulation [2] with a photoelastic modulator (PEM) and a new signal processing method that uses a modulation amplitude ratio [4,5].…”

mentioning

confidence: 99%

“…This paper reports improved resolution and long-time stability in a DI that adopts phase modulation [2] with a photoelastic modulator (PEM) and a new signal processing method that uses a modulation amplitude ratio [4,5]. Figure 1 shows a schematic view of the present optical and electrical systems used for bench testing.…”

mentioning

confidence: 99%

Improved Resolution and Stability in a Dispersion Interferometer Using a Modulation Amplitude Ratio

Akiyama

Kawahata

Okajima

et al. 2010

Plasma and Fusion Research

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A dispersion interferometer is immune to mechanical vibrations, which is a great advantage for application to steady-state fusion reactors. This paper describes the performance of a phase-modulated dispersion interferometer with a new phase extraction method using a modulation amplitude ratio. On steady-state fusion reactors, reliable electron density measurement is required for fueling control. However, the signal-to-noise ratio (S/N) of conventional interferometers is affected by mechanical vibrations. In addition, fringe jump errors are possible at high densities. One possible approach to these problems is the use of a dispersion interferometer (DI) [1]. The DI is immune to mechanical vibrations, and hence does not need a vibration isolator. A two-color system is also not needed even if short-wavelength lasers (a CO 2 laser and a YAG laser, for example) are used. The fringe jump errors are attributed to 2π ambiguity in the phase shift. If short-wavelength laser light with a phase shift smaller than 2π is selected, the interferometer becomes free from fringe jump errors in principle. However, the S/N is significantly degraded because the phase shift due to vibrations (∝ 1/λ, λ: wavelength) increases and that due to a plasma (∝ λ) decreases for conventional interferometers. In contrast, the DI has no issue even if the plasma term is smaller than 2π owing to its immunity to vibrations. Thus, the DI becomes free from fringe jump errors if an appropriate wavelength is selected.Techniques that improve the resolution of DIs are currently being introduced [2][3][4][5]. This paper reports improved resolution and long-time stability in a DI that adopts phase modulation [2] with a photoelastic modulator (PEM) and a new signal processing method that uses a modulation amplitude ratio [4,5]. Figure 1 shows a schematic view of the present optical and electrical systems used for bench testing. The light source is a CO 2 laser with an output power and wavelength of 8 W and 10.6 µm, respectively. The focused laser light is injected into a nonlinear crystal of AgGaSe 2 to generate the frequency-doubled component (FD1). A mixed beam consisting of the fundamental and frequency-doubled components, whose polarizations are orthogonal, passes through a PEM with a drive frequency where c p = e 2 2ε 0 m e c, ω: angular frequency of the laser light, Δd: change of the optical path length due to vibrations, c: light speed, e: charge of the electron, ε 0 : dielectric constant, m e : mass of the electron, n e : line averaged electron density, L: path length in a plasma, and φ 1 , φ 2 : initial phase. The phase of the detected interference signal I is difference between phases above. Because the phase terms resulting from vibrations, 2ωΔd/c, are common, as shown

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Development of the CO2 dispersion interferometer on HL-2M Tokamak

Wang¹,

Li²,

Li³

et al. 2022

Fusion Engineering and Design

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Conceptual Design of a Dispersion Interferometer Using a Ratio of Modulation Amplitudes

Cited by 20 publications

References 11 publications

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

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

Improved Resolution and Stability in a Dispersion Interferometer Using a Modulation Amplitude Ratio

Development of the CO2 dispersion interferometer on HL-2M Tokamak

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