Reconstruction of Edge Density Profiles Using Ultrashort-Pulse Reflectometry in LHD

Yokota, Yoshiyuki; Mase, A.; Kogi, Y.; Tokuzawa, T.; Kawahata, K.

doi:10.1585/pfr.1.040

Cited by 10 publications

(7 citation statements)

References 4 publications

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“…In this case, we assume a profile shape of 1 − ρ 4 , where ρ is a normalized radius. Such an assumption for the edge density profile is necessary for reflectometry using O-mode polarization [12,13]. The density increase resulting from the rf heating seems related to the degree of the absorption of the wave.…”

Section: Profile Measurementsmentioning

confidence: 99%

Relative Frequency Calibration for Fast Frequency Sweep Microwave Reflectometry

Ejiri

Shimada

Yamada

et al. 2007

Plasma and Fusion Research

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A frequency-modulated reflectometer with a frequency band of 26.5 to 40 GHz has been constructed and installed in the TST-2 spherical tokamak to measure fast density profile evolution. In order to calibrate the instantaneous frequency for various frequency sweep rates, a waveform matching method has been proposed and applied to the reflectometer. This method compares the interference patterns (i.e., waveforms) of a fixed target reflection, which do not depend on the sweep rate, and obtains the instantaneous frequency by fitting the target waveform time to the time for a reference sweep waveform. This allows evaluation of output frequency stability. The overall frequency error, including reproducibility, is around 0.1 GHz. Sweep rates up to 20 µs were used to measure the density profile evolution during rf heating.

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Section: Profile Measurementsmentioning

confidence: 99%

Relative Frequency Calibration for Fast Frequency Sweep Microwave Reflectometry

Ejiri

Shimada

Yamada

et al. 2007

Plasma and Fusion Research

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“…There are two cut-off frequencies for the extraordinary mode, known as left-hand cut-off frequencies w is the plasma frequency [9,10]. Based on the observed relation between frequencies and the corresponding time delays (or phase changes), the plasma density profile or magnetic field profile can be inferred [11,12].…”

Section: Introductionmentioning

confidence: 99%

Numerical simulation of ultrashort-pulse reflectometry (USPR) on EAST

Chen

et al. 2023

Plasma Sci. Technol.

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Microwave reflectometer is a popular non-intrusive plasma density diagnostic instrument on tokamaks, which provides centimeter and millisecond level resolution. The ultra-short pulse reflectometer (USPR) achieves plasma density measurement by emitting a chirped wave containing a broadband signal and measuring the time of flight from different frequency components. An USPR system is currently being built on EAST (Experimental Advanced Superconducting Tokamak) to meet the needs of diagnostic of the pedestal density evolution, such as high-frequency small ELMs (Edge Localized Modes). In order to predict the density reconstruction of EAST USPR system, this work presents a numerical simulation study of the beam propagation of the chirped wave of extraordinary waves (X-mode) in the plasma based on Python. The electron density profile has been successfully reconstructed by the reflection signal interpretation. The small gap between right-hand cut-off layer and electron cyclotron resonance layer, due to the low plasma density on the plasma edge, brings unexpected leakage from transmitting microwave beam to pedestal and core region. This kind of "tunneling" effect will cause the reflected signal to have energy loss in the low frequency band. The study also discusses the influence of the poloidal magnetic field on the reflected signal. The spatial variation of the poloidal magnetic field will lead to the conversion between extraordinary (X) waves and ordinary (O) waves, which leads to the energy loss in the reflected signals. The simulation results show that the "tunneling" effect and the O-X mode conversion effect have little effect on EAST USPR system, so the currently designed transmit power meets the working requirements.

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“…We have applied ultrashort-pulse reflectometry ͑USPR͒ to Large Helical Device ͑LHD͒ at the National Institute for Fusion Science ͑NIFS͒. 5,6 An impulse with a pulse width less than 30 ps is used as a source. Since the bandwidth of an impulse is proportional to the inverse of the pulse width, we can cover the frequency range of micro-to millimeter waves as a single source.…”

Section: Introductionmentioning

confidence: 99%

Reconstruction of edge density profiles on Large Helical Device using ultrashort-pulse reflectometry

Yokota

Mase

Kogi

et al. 2008

Review of Scientific Instruments

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Reflectometry has been expected to be one of the key diagnostics to measure density profiles. We have applied an ultrashort-pulse reflectometry (USPR) system to Large Helical Device in the National Institute for Fusion Science. Wide frequency band system is required to obtain wide density profile since an incident wave is reflected at the density layer corresponding to its cutoff frequency. The reflectometry utilizes an impulse with less than 30 ps pulse width as a source. Since the bandwidth of an impulse has an inverse relation to the pulse width, we can cover the frequency range of micro- to millimeter waves (18-40 GHz) with a single source. The density profiles can be reconstructed by collecting time-of-flight (TOF) signals for each frequency component of an impulse reflected from the corresponding cutoff layer. We utilize the signal record analysis (SRA) method to reconstruct the density profiles from the TOF signal. The effectiveness of the SRA method for the profile reconstruction is confirmed by a simulation study of the USPR using a finite-difference time domain method.

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Reconstruction of Edge Density Profiles Using Ultrashort-Pulse Reflectometry in LHD

Cited by 10 publications

References 4 publications

Relative Frequency Calibration for Fast Frequency Sweep Microwave Reflectometry

Relative Frequency Calibration for Fast Frequency Sweep Microwave Reflectometry

Numerical simulation of ultrashort-pulse reflectometry (USPR) on EAST

Reconstruction of edge density profiles on Large Helical Device using ultrashort-pulse reflectometry

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