ECH Power Deposition Study in the Collisionless Plasma of LHD

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.

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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

Creely

Ida

Yoshinuma

et al. 2017

“…Simulations involving both components allow for comparison study to be made. Since it is important to know this wavevector information, scattering position, and beam bending effects, the LHDGauss ray tracing code 26,27 on the AutoAna system 28 is used to analyze the experimental conditions immediately after each LHD plasma discharge.…”

Section: Figmentioning

confidence: 99%

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

Tokuzawa

Tanaka

Tsujimura

et al. 2021

Self Cite

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.

“…The Doppler reflectometer is expected to measure the radial profile of perpendicular velocity v ⊥ . For this aim, the radial observation position and the wavenumber k ⊥ is calculated by the ray tracing code LHDGAUSS 24,25 which uses the radial profile of electron density and temperature measured by the Thomson scattering method. 26 Figure 7 shows the radial profile of v ⊥ in the hyper mode operation as the comb output and batch operation as the data acquisition.…”

Section: B Radial Profile Of V ⊥mentioning

confidence: 99%

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

Tokuzawa

Takahashi

Tsujimura

et al. 2018

We succeeded in increasing the radial observation points of the microwave frequency comb Doppler reflectometer system from 8 to 20 (or especially up to 45) using the high sampling rate of 40 GS/s digital signal processing. For a new acquisition system, the estimation scheme of the Doppler shifted frequency is constructed and compared with the conventional technique. Also, the fine radial profile of perpendicular velocity is obtained, and it is found that the perpendicular velocity profile is consistent with the E × B drift velocity one.