研究目的
To design, develop, and operate a seven-channel 100-GHz microwave interferometer for measuring the radial profile of plasma density in the Aditya tokamak, with high spatial and time resolutions, and to validate the measurements against Thomson scattering diagnostics.
研究成果
The seven-channel 100-GHz interferometer successfully measures plasma density profiles in the Aditya tokamak with spatial resolution of 7 cm and time resolution of 10 μs. Measurements are validated against Thomson scattering, showing good agreement. The system is effective for real-time density monitoring and control in tokamak operations.
研究不足
The shift counting method for fringes cannot identify decreases or increases in density, assuming density climbs steadily and then decreases with plasma current. Total experimental error is about 10%, and refraction effects must be minimized to avoid crosstalk between channels.
1：Experimental Design and Method Selection:
The interferometer uses microwave interferometry based on phase shift measurements due to plasma density. It employs Gunn oscillators at 100 GHz, directional couplers, magic tees, and detectors. Planoconvex lenses focus the microwave beams to avoid crosstalk. Abel inversion is used to derive radial density profiles from chord-averaged data.
2：Sample Selection and Data Sources:
Plasma discharges from the Aditya tokamak are used, with measurements taken at seven radial positions (r = -21 cm, -14 cm, -7 cm, 0 cm, +7 cm, +14 cm, +21 cm).
3：List of Experimental Equipment and Materials:
Gunn oscillators (100 GHz), isolators, directional couplers (10 dB), variable attenuators, phase shifters (0°–360°), magic tees, detectors, planoconvex lenses (machinable ceramic), horn antennas, WR-10 and WR-42 waveguides, low noise amplifiers, CAMAC digitizers, and optocouplers.
4：Experimental Procedures and Operational Workflow:
Microwave beams are generated and split into reference and plasma paths. Beams pass through plasma, and phase shifts are measured. Signals are amplified, digitized at 100 kHz, and processed to compute density and phase shift. Abel inversion is applied to obtain radial profiles.
5：Data Analysis Methods:
Phase shift is calculated using equations (1) and (2), density from (2), and Abel inversion from (4) and (5). Data is digitized and analyzed for radial profiles and comparison with Thomson scattering.
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Gunn oscillator
100 GHz
Generate microwave signals at 100 GHz for interferometry
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Directional coupler
10 dB
Split microwave power into reference and plasma paths
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Magic tee
Combine signals from reference and plasma paths for detection
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Detector
Detect microwave power and output voltage signal
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Planoconvex lens
Focus microwave beams to control diameter and avoid crosstalk
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Horn antenna
Transmit and receive microwave beams
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Waveguide
WR-10
Carry microwave signals in W-band
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Waveguide
WR-42
Carry microwave signals as oversized waveguide to reduce losses
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Low noise amplifier
Amplify detector output signals
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CAMAC digitizer
Digitize amplified signals for data acquisition
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Optocoupler
Isolate signals during digitization
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Variable attenuator
Adjust power levels in reference path
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Phase shifter
0°–360°
Adjust phase difference between paths
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