Microwave frequency comb Doppler reflectometer applying fast digital data acquisition system in LHD

Tokuzawa, T.; Takahashi, Hayato; Tsujimura, Toru Ii; Emoto, M.; Nakanishi, Hiroyuki; Inagaki, S.; Ida, K.; Yamada, H.; Ejiri, A.; Watanabe, K. Y.; Oguri, K.; Akiyama, Tsuyoshi; Tanaka, K.; Yamada, I.

doi:10.1063/1.5035118

Cited by 19 publications

(19 citation statements)

References 31 publications

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“…Several methods exist for the generation of a comb of frequencies, of which the most common one is probably the usage of a so-called nonlinear transmission line (NLTL) [5,7,9,11]. For the methods presented below, the nonlinear behavior of frequency multipliers is exploited.…”

Section: Hardware Conceptsmentioning

confidence: 99%

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Design of a variable frequency comb reflectometer system for the ASDEX Upgrade tokamak

Happel¹,

Kasparek²,

Hennequin³

et al. 2020

Plasma Sci. Technol.

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Comb reflectometers offer the advantage of measuring at several radial positions in the plasma simultaneously. This allows the investigation of fast timescales during L-H transitions, I-phases, I-mode bursts, transients during heat wave propagation, etc. A drawback of many present-day systems is that they use a fixed frequency difference between the probing frequencies. Hence, although the central probing frequency can be varied, usually the probing frequency difference is fixed. The new design presented in this work uses an advanced microwave generation and detection scheme, which allows for arbitrary probing frequencies and probing frequency separations.

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Section: Hardware Conceptsmentioning

confidence: 99%

“…Two emitter concepts are proposed, one is based on two-tone input into the frequency multiplier, while the other is based on three-tone input. While these concepts will probably yield somewhat less signal-to-noise ratios than the systems based on non-linear transmission lines [5,7,9,11], they are expected to be significantly more flexible.…”

Section: Introductionmentioning

confidence: 99%

Design of a variable frequency comb reflectometer system for the ASDEX Upgrade tokamak

Happel¹,

Kasparek²,

Hennequin³

et al. 2020

Plasma Sci. Technol.

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“…14 We have developed and installed this electron scale turbulence diagnostic to the Large Helical Device (LHD 15 ) plasma, and this is the first report for the application to the helical device to the author's knowledge. In addition, LHD has several ion-scale turbulence diagnostics, such as CO 2 laser used phase constant imaging (PCI), 16 a microwave Doppler reflectometer, 17 and beam emission spectroscopy (BES). 18 The ion scale turbulence observations have been compared with the gyrokinetic simulation (GKV 19,20 ) results.…”

Section: Introductionmentioning

confidence: 99%

W-band millimeter-wave back-scattering system for high wavenumber turbulence measurements in LHD

Tokuzawa

Tanaka

Tsujimura

et al. 2021

Review of Scientific Instruments

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A 90 GHz W-band millimeter-wave back-scattering system is designed and installed for measuring electron scale turbulence (k ρs ∼ 40). A metal lens relay antenna is used for in-vessel beam focusing, and a beam diameter of less than 40 mm is achieved in the plasma core region. This antenna can be steered at an angle of 159 ○ ± 6 ○ , which almost covers the plasma radius. The estimated size of the scattering volume is ∼105 mm at the edge and 135 mm at the core, respectively. A 60 m corrugated waveguide is used to achieve a low transmission loss of ∼8 dB. A heterodyne detection system for millimeter-wave circuits with probing power modulation can distinguish the scattered signal from background noise.

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“…The first results show that the perpendicular rotational velocities obtained with DBS are consistent with the estimates of the poloidal rotation obtained from the charge exchange recombination spectroscopy diagnostics. A radial profile of perpendicular velocity was successfully obtained on the LHD tokamak using a Doppler reflectometer system [13]. The radial electric field was extracted from measurements of perpendicular velocity.…”

Section: Introductionmentioning

confidence: 99%

Review of Advanced Implementation of Doppler Backscattering Method in Globus-M

et al. 2021

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Doppler backscattering (DBS) is a microwave diagnostics method typically used to study the plasma rotation velocity. Apart from conventional techniques, more advanced forms of DBS implementation were suggested on Globus-M. More specifically the study of a variety of oscillating processes was performed using DBS. In this review we present a detailed description of all of the methods and techniques employed in Globus-M alongside results obtained using DBS in all the years up until the shutdown of the tokamak. These include research similar to that done on other devices into the properties of such phenomena like geodesic acoustic modes or limit cycle oscillations, along with innovative works regarding the detection and investigation of Alfven eigenmodes and filaments that were the first of their kind and that provided important and novel results. Apart from that, the specific aspects of DBS application on a spherical tokamak are discussed. An in-depth look into the gradual change and improvement of the DBS diagnostics on Globus-M is also presented in this paper.

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Microwave frequency comb Doppler reflectometer applying fast digital data acquisition system in LHD

Cited by 19 publications

References 31 publications

Design of a variable frequency comb reflectometer system for the ASDEX Upgrade tokamak

Design of a variable frequency comb reflectometer system for the ASDEX Upgrade tokamak

W-band millimeter-wave back-scattering system for high wavenumber turbulence measurements in LHD

Review of Advanced Implementation of Doppler Backscattering Method in Globus-M

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