High speed FPGA-based Phasemeter for the far-infrared laser interferometers on EAST

Yao, Yuan; Liu, H.; Zou, Zhiyong; Li, W.; Lian, H.; Jie, Yinxian

doi:10.1088/1748-0221/12/12/c12043

Cited by 3 publications

(1 citation statement)

References 7 publications

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“…A well-known problem with this method is the fringe jump that arises from the phase comparison technique, due to the arcus-tangent function (when the phase difference reaches π or −π). To obtain a valid and reliable electron density, the phase information with a fringe jump needs to be unwrapped [10][11][12][13][14][15][16]. Accurate and real-time fringe counting method is essential for the plasma control system (PCS), especially for electron density feedback control.…”

Section: Fringe Jump In the Hcn Interferometer On Eastmentioning

confidence: 99%

A fringe jump counting method for the phase measurement in the HCN laser interferometer on EAST and its FPGA-based implementation

YAO 姚,

YANG 杨,

TI 提

et al. 2024

Plasma Sci. Technol.

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The electron density is usually diagnosed by the laser-aided interferometers. The phase difference signal obtained after phase demodulation is wrapped, which is also called fringe jump. A method has been developed to unwrap the phase difference signal in real-time by using FPGA, specifically designed to handle fringe jumps in the Hydrogen Cyanide (HCN) laser interferometer on the EAST superconducting tokamak. The method is designed for phase demodulator using the Fast Fourier Transform (FFT) method at the front end. The method is better adapted for hardware implementation compared to complex mathematical analysis algorithms, like Field Programmable Gate Array (FPGA). The method has been applied to process the phase measurement results of the HCN laser interferometer on EAST in real-time. Electron density results show a good confidence on the fringe jump unwrapping method. Further possible application on other laser interferometers, like the POlarimeter-INTerferometer (POINT) system on EAST is also discussed.

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Section: Fringe Jump In the Hcn Interferometer On Eastmentioning

confidence: 99%

A fringe jump counting method for the phase measurement in the HCN laser interferometer on EAST and its FPGA-based implementation

YAO 姚,

YANG 杨,

TI 提

et al. 2024

Plasma Sci. Technol.

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Design and implementation of plasma electron density measurements based on FPGA with all-phase FFT for tokamak devices

Shu

Lai

Chen

et al. 2021

Review of Scientific Instruments

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Plasma electron density is one of the most fundamental parameters when studying tokamak plasma physics, which is widely used in plasma control systems and plasma physics analyses. A hydrogen cyanide laser interferometer is generally applied to measure the plasma electron density in many tokamak devices. Therein, the plasma electron density is calculated by measuring the phase difference between the reference signal and the detector signal. This work provides a new way to realize real-time measurements of the plasma electron density with a phase comparator and processing system based on a field-programmable gate array chip. The system integrates a signal processing module, an all-phase fast Fourier transform (ap-FFT) module realized via matrix operations and phase comparisons, and a network communication module all in one board. This work concludes that the ap-FFT is robust and accurate for phase calculations compared with a windowing FFT. A data-reuse method and a phase shift method are proposed to improve the time resolution and phase range. The phase error is less than 0.1° and the time resolution is 0.025 ms, which is better than hardware methods and traditional software methods. This system is highly flexible with reduced design costs to meet the requirements of a tokamak, which can provide a valuable reference for other tokamak and phase difference comparisons.

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A phase processor used in terahertz interferometer for tokamak

Shi

Yang

et al. 2022

J. Inst.

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The commonly used phase processing techniques include coherence method, zero-crossing comparison method and FFT method. Due to the influence of noise, amplitude modulation and frequency modulation, these phase processing methods are easy to cause errors, thus affecting the measurement accuracy. In this paper, a phase processor based on all-phase fast Fourier transform is developed. The principle of the phase processing algorithm is analyzed, and the implementation process of the algorithm on FPGA is described. The effectiveness of the method is tested under different conditions. The experimental results show that the standard deviation of phase processing is 0.387° when the signal is sampled simultaneously under 90% AM modulation. When asynchronous sampling and 50% FM, the phase processing error is 0.371°. This phase processer has been used to the terahertz interferometer of the HL-2M device, the phase change of the output signal of the interferometer can be accurately processed when the plasma density changes dramatically, and the loss of phase processing information can be effectively avoided in the plasma diagnosis process. Based on the technical research proposed in this paper, a more accurate phase processing reference scheme is provided for plasma diagnosis of interferometer.

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High speed FPGA-based Phasemeter for the far-infrared laser interferometers on EAST

Abstract: High speed FPGA-based Phasemeter for the far-infrared laser interferometers on EAST

Cited by 3 publications

References 7 publications

A fringe jump counting method for the phase measurement in the HCN laser interferometer on EAST and its FPGA-based implementation

A fringe jump counting method for the phase measurement in the HCN laser interferometer on EAST and its FPGA-based implementation

Design and implementation of plasma electron density measurements based on FPGA with all-phase FFT for tokamak devices

A phase processor used in terahertz interferometer for tokamak

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