Multifrequency channel microwave reflectometer with frequency hopping operation for density fluctuation measurements in Large Helical Device

Tokuzawa, T.; Ejiri, A.; Kawahata, K.

doi:10.1063/1.3478747

Cited by 9 publications

(6 citation statements)

References 14 publications

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“…Several frequency hopping reflectometer systems have been developed and applied to density fluctuation measurements in many devices [10][11][12]. In these systems, a synthesizer with a frequency of 8-18 GHz is used as a microwave source, and the output of the synthesizer is multiplied by an active multiplier to obtain the required frequency for the measurement.…”

Section: Frequency Hopping Reflectometermentioning

confidence: 99%

Density Fluctuation Measurements Using a Frequency Hopping Reflectometer in JT-60U

Oyama

Takenaga

Suzuki

et al. 2011

Plasma and Fusion Research

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In JT-60U, a frequency hopping reflectometer has been developed to evaluate the poloidal rotation velocity as a Doppler reflectometer and the radial correlation of density fluctuations in plasmas. The system can measure the radial profile of density fluctuations or the radial correlation profile at two spatial points within 250 ms by combining with the other fixed frequency reflectometer. The radial profiles of the poloidal rotation velocity evaluated from the Doppler-shifted frequency spectrum of density fluctuations show a positive radial electric field in co-rotating plasmas and a negative radial electric field in counter-rotating plasmas. Density fluctuation measurement at the internal transport barrier (ITB) using a correlation reflectometer revealed that long-range correlation increased when ITB was degraded owing to the central heating by electron cyclotron waves.

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Section: Frequency Hopping Reflectometermentioning

confidence: 99%

Density Fluctuation Measurements Using a Frequency Hopping Reflectometer in JT-60U

Oyama

Takenaga

Suzuki

et al. 2011

Plasma and Fusion Research

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“…Doppler reflectometry (or Doppler back-scattering) is widely used to measure turbulent flow velocity and amplitude in fusion plasmas. [3][4][5] Two types of Doppler reflectometers have been installed in LHD: a frequency-hopping system 23 and a multi-channel frequency comb system. 24 The frequency-hopping system is installed at the 9-O toroidal port (referred to as the "9-O" reflectometer) and typically set to 30.0 GHz, while the comb system is installed at the 3-O port (referred to as the "comb" reflectometer) and operates with frequencies of 27.7, 29.0, 30.5, 32.0, 33.3, 34.8, 37.0, and 38.3 GHz.…”

Section: Methodsmentioning

confidence: 99%

“…The fluctuation frequencies shown are not adjusted for the Doppler shift and are calculated as in Ref. 23. This figure shows that the fluctuations are strongly peaked near the edge in all frequency ranges, though the lowest frequency range may contain signals from MHD activity, which is not the primary focus of this study.…”

Section: A Separation Of Fluctuation Changes Due To Pellet and Due Tmentioning

confidence: 99%

Novel analysis technique for measuring edge density fluctuation profiles with reflectometry in the Large Helical Device

Creely

Ida

Yoshinuma

et al. 2017

Review of Scientific Instruments

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A new method for measuring density fluctuation profiles near the edge of plasmas in the Large Helical Device (LHD) has been developed utilizing reflectometry combined with pellet-induced fast density scans. Reflectometer cutoff location was calculated by proportionally scaling the cutoff location calculated with fast far infrared laser interferometer (FIR) density profiles to match the slower time resolution results of the ray-tracing code LHD-GAUSS. Plasma velocity profile peaks generated with this reflectometer mapping were checked against velocity measurements made with charge exchange spectroscopy (CXS) and were found to agree within experimental uncertainty once diagnostic differences were accounted for. Measured density fluctuation profiles were found to peak strongly near the edge of the plasma, as is the case in most tokamaks. These measurements can be used in the future to inform inversion methods of phase contrast imaging (PCI) measurements. This result was confirmed with both a fixed frequency reflectometer and calibrated data from a multi-frequency comb reflectometer, and this method was applied successfully to a series of discharges. The full width at half maximum of the turbulence layer near the edge of the plasma was found to be only 1.5-3 cm on a series of LHD discharges, less than 5% of the normalized minor radius.

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“…The Large Helical Device (LHD) is a Heliotron-type device equipped with three tangential neutral beams with a beam energy of 160 -180 keV and two perpendicular beams with a beam energy of 40 -50 keV. The frequency-hopping Doppler reflectometers have been installed in LHD and the frequency is set to 30 GHz in this experiment [15,16]. The analysis technique of the radial scan of reflection point of the Doppler reflectometer using the density ramp up/down in time has been applied in LHD experiment.…”

Section: Density Fluctuations During the Tongue Shaped Deformationmentioning

confidence: 99%

Exhaust of turbulence cloud at the tongue shaped deformation event

et al. 2018

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Exhaust of turbulence cloud at the tongue-shaped deformation which triggers MHD bursts is observed in Large Helical Device (LHD) in the low density plasma with significant contribution of trapped particles injected by perpendicular neutral beam injection. The exhaust of turbulence cloud is characterized by the abrupt large increase of turbulence amplitude in the frequency range of 150 -500 kHz measured with Doppler reflectometer at the edge region of the plasma (r eff /a99=0.98). The increase of turbulence amplitude is significantly large and is by one order of magnitude. This abrupt increase of turbulence level is transient and disappears within one milli-second (typically ∼ 600µs). In contrast, the turbulence level slightly inside the plasma edge (r eff /a99=0.94) decreases by a factor of 2 after the MHD bursts.

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Multifrequency channel microwave reflectometer with frequency hopping operation for density fluctuation measurements in Large Helical Device

Cited by 9 publications

References 14 publications

Density Fluctuation Measurements Using a Frequency Hopping Reflectometer in JT-60U

Density Fluctuation Measurements Using a Frequency Hopping Reflectometer in JT-60U

Novel analysis technique for measuring edge density fluctuation profiles with reflectometry in the Large Helical Device

Exhaust of turbulence cloud at the tongue shaped deformation event

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