A system for measuring the local spectrum of a plasma at 4.6 ghz low noise

Abstract

This invention discloses a system for measuring the local spectrum of 4.6 GHz low-clutter waves in plasma, used to measure the local low-clutter power and spectral broadening information in a scraped layer. A 30 GHz microwave source generates a backscattered signal at a specific location in the scraped layer. This backscattered signal is transmitted into the tokamak plasma via a horn antenna in ordinary mode. The new microwave signal, with a frequency of 34.6 GHz, is generated by backscattering at a second horn antenna. This 34.6 GHz microwave signal is then frequency-differentiated by a mixer to 3.5 GHz, and further frequency-differiated by a second 4.6 GHz local oscillator signal to 1.1 GHz. The signal is finally fed into a spectrum analyzer. Unlike conventional copper loop antenna measurements, this system can reflect the local low-clutter power and spectral information, thus enabling more accurate analysis of the parasitic effects of low-clutter waves in the scraped layer.

Description

Technical Field

[0001] This invention belongs to the field of microwave technology, specifically relating to a system for measuring the 4.6 GHz low-hybridity local spectrum of plasma. Background Technology

[0002] Low-hybrid wave current drive (LHCD) is a highly efficient non-inductive current drive method for tokamak plasmas. The EAST tokamak achieved plasma discharges on the order of 1000 s using LHCD heating and current drive. However, under high-density conditions, the dissipation and spectral broadening of LHCD at the boundary become severe, leading to a sharp drop in drive efficiency—the so-called "density limit." This anomalous decrease in LHCD drive efficiency at high densities is a bottleneck limiting its future application in ITER and other reactors. Improving LHCD drive efficiency under high-density conditions is a pressing issue in the field of LHCD research.

[0003] Previous low-clutter experiments have used copper loop antennas to measure the power and spectral information of low-clutter waves. However, this measurement technique has a drawback: it cannot pinpoint the source of the signal being measured. In other words, whether the low-clutter wave is reflected back from the plasma or propagates directly from the antenna port, it will be measured as long as it passes through the copper loop antenna. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a system for measuring the local spectrum of 4.6 GHz low-hybrid waves in plasma. This system can be used to measure the local power and spectral broadening of low-hybrid waves in a scraped layer, thus providing data support for studying low-hybrid boundary parasitic effects, such as wave scattering and parametric decay. A 30 GHz microwave generated by a microwave source is transmitted into the tokamak plasma in ordinary mode (O mode) via a horn antenna. At a certain location in the scraped layer, it backscatters with the 4.6 GHz low-hybrid wave due to the resonance condition, generating a new microwave with a frequency of 34.6 GHz. A second horn antenna receives this 34.6 GHz microwave generated by backscattering. After frequency difference by a mixer, its frequency is reduced to 3.5 GHz. Then, it is further reduced to 1.1 GHz by a second frequency difference with the 4.6 GHz local oscillator. The signal is finally fed into a spectrum analyzer, which measures the wave power and spectral broadening after the second frequency reduction.

[0005] This invention utilizes a horn antenna to radiate microwaves at a specific frequency of 30 GHz into a tokamak plasma. When these microwaves propagate into the turbulent layer, the microwaves, satisfying the resonance condition, resonate with a 4.6 GHz low-level clutter wave, generating a new microwave at a frequency of 34.6 GHz. Here, the resonance condition is... ω SC =ω IN +ω LHHere, k and ω represent the wave vector and frequency, respectively, and the subscripts SC, IN, and LH represent the backscattered microwave, the 30 GHz incident wave, and the 4.6 GHz low-clutter wave, respectively. The newly generated microwave was down-converted twice, and its power and spectral information were measured by a spectrum analyzer. This measurement result reflects the power and spectral broadening information of the low-clutter wave in the turbulent layer, thus enabling a more accurate analysis of the parasitic effects of the low-clutter wave in the turbulent layer.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A system for measuring the 4.6 GHz low-hybrid local spectrum of plasma includes a 30 GHz microwave source, a 31.1 GHz microwave source, a first horn antenna, a second horn antenna, a spectrum analyzer, an amplifier, an isolator, a DC blocker, a 35 GHz low-pass filter, a 3.5 GHz band-pass filter, a 4.6 GHz local oscillator, and a 1.1 GHz band-pass filter. The 30 GHz microwave, after exiting the 30 GHz microwave source, is amplified to 10 dBm, passes through the isolator and DC blocker, and is then radiated into the plasma in O-mode by the first horn antenna. The backscattered microwaves are then received by the second horn antenna and coupled. The coupled microwaves pass through a DC blocker and a 35GHz low-pass filter. After being mixed with the 31.1GHz microwaves by a mixer, a 3.5GHz microwave is generated. This microwave is then fed into a 3.5GHz bandpass filter with a center frequency of 3.5GHz and a bandwidth of 60MHz. It is then subjected to a local oscillator frequency difference with a 4.6GHz local oscillator, resulting in a final frequency drop to 1.1GHz. Finally, it passes through a 1.1GHz bandpass filter with a bandwidth of 60MHz and is sent to a spectrum analyzer, which measures its spectrum.

[0008] Furthermore, the spectrum analyzer has a scan time of ≤20ms and an operating frequency of greater than 1.2GHz.

[0009] Furthermore, the isolator is used to prevent waves reflected from the plasma from entering the 30 GHz microwave source; the DC blocker is used to prevent DC voltage from damaging the 30 GHz microwave source and the 31.1 GHz microwave source.

[0010] Furthermore, when 30 GHz microwaves propagate in the plasma, the following resonance condition is satisfied. ω SC =ω IN +ω LH At that time, the microwave resonates with the 4.6 GHz low clutter wave, generating a new scattered wave with a frequency of 34.6 GHz; where k and ω represent the wave vector and frequency, respectively, and the subscripts SC, IN, and LH represent the backscattered microwave, the 30 GHz incident wave, and the 4.6 GHz low clutter wave, respectively.

[0011] Furthermore, the spectral width Δf of the scattered wave SC The following relationship exists between the incident wave at 30 GHz and the low-clutter spectral width at 4.6 GHz:

[0012]

[0013] Due to the incident wave's spectral width Δf IN The spectral width Δf relative to low clutter LH It is much smaller, therefore, the spectral width of the scattered wave can be approximated as the spectral width of the low clutter wave; the spectral width is defined as the full width when the wave power is reduced to half.

[0014] Beneficial effects:

[0015] Unlike the spectrum measured by conventional copper loop antennas, the measurement results of this invention can reflect the local low-clutter power and spectral information, thereby enabling a more accurate analysis of the parasitic effects of low-clutter in the scraped layer. This provides crucial data support for the experimental analysis of low-clutter current-driven and heating physics under high-density conditions. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the main structure of a system for measuring the 4.6 GHz low-hybrid local spectrum of plasma according to the present invention.

[0017] Figure 2a This is the incident microwave spectrum at a frequency of 30 GHz.

[0018] Figure 2b The spectrum diagrams are for low-clutter waves with two different spectral widths (Δf).

[0019] Figure 2c This is the spectrum of the scattered wave obtained from theoretical calculations. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0021] like Figure 1As shown, a system for measuring the local spectrum of low-hybrid waves in plasma at 4.6 GHz according to the present invention includes a 30 GHz microwave source, a 31.1 GHz microwave source, a first horn antenna, a second horn antenna, a spectrum analyzer, an amplifier, an isolator, a DC blocker, a mixer, a 35 GHz low-pass filter, a 3.5 GHz band-pass filter, a 4.6 GHz local oscillator, and a 1.1 GHz band-pass filter.

[0022] After the 30GHz microwave source is amplified, the power of the microwave becomes 10dBm. After passing through an isolator and a DC blocker, it is radiated into the plasma by a horn antenna in O mode (i.e., the electric field is parallel to the longitudinal field of the tokamak). Then, the backscattered microwave is received by another horn antenna. After being down-frequencyd by two stages of frequency reduction circuits, its spectrum is finally measured by a spectrum analyzer.

[0023] The two-stage frequency reduction circuit consists of a 31.1 GHz microwave source and a 4.6 GHz local oscillator. The microwave signal received by the second horn antenna is first subjected to local frequency difference with the 31.1 GHz microwave source, then passed to a 3.5 GHz bandpass filter with a center frequency of 3.5 GHz and a bandwidth of 60 MHz, and then subjected to local frequency difference with the 4.6 GHz local oscillator, finally reducing the frequency to 1.1 GHz.

[0024] The spectrum analyzer should have a scan time of ≤20ms and an operating frequency greater than 1.2GHz.

[0025] The isolator is used to prevent waves reflected from the plasma from entering the 30 GHz microwave source. The DC blocker is used to prevent DC voltage from damaging the 30 GHz and 31.1 GHz microwave sources.

[0026] When 30 GHz microwaves propagate in plasma, the following resonance condition is met. ω SC =ω IN +ω LH When this occurs, the microwave will resonate with the 4.6 GHz low clutter wave, generating a new scattered wave with a frequency of 34.6 GHz. Here, k and ω represent the wave vector and frequency, respectively, and the subscripts SC, IN, and LH represent the backscattered microwave, the 30 GHz incident wave, and the 4.6 GHz low clutter wave, respectively.

[0027] Theoretically, the spectral width Δf of this scattered wave SC The following relationship exists between the incident wave at 30 GHz and the low-clutter spectral width at 4.6 GHz:

[0028]

[0029] Due to the incident wave's spectral width Δf INThe spectral width Δf relative to low clutter LH The spectral width is much smaller; therefore, the spectral width of the scattered wave can be approximated as the spectral width of the low-clutter wave. Here, the spectral width is defined as the full width when the wave power is reduced to half.

[0030] After the scattered wave propagates from the plasma, it is coupled by a second horn antenna, passes through a DC blocker and a 35GHz low-pass filter, and is then mixed with a 31.1GHz microwave to generate a 3.5GHz microwave. This microwave then passes through a 3.5GHz bandpass filter with a center frequency of 3.5GHz and a bandwidth of 60MHz, is amplified, and then mixed again with a 4.6GHz local oscillator, reducing the frequency to 1.1GHz. Finally, it passes through a 1.1GHz bandpass filter with a bandwidth of 60MHz before being fed into a spectrum analyzer, which measures its power and spectral width.

[0031] Figure 2a The incident wave spectrum has a power of 10 dBm and a bandwidth of 0.2 MHz. Figure 2b The spectrum is assumed to have a power of 25 dBm and spectral widths of 0.5 MHz and 1.0 MHz, respectively, representing low clutter. Figure 2c The scattered wave spectrum obtained from theoretical calculations after two frequency reductions shows that the spectral widths of the scattered wave are 0.54MHz and 1.02MHz, respectively, which are very close to the spectral width of the low clutter wave.

[0032] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A system for measuring the 4.6 GHz low-hybrid wave local spectrum of plasma, characterized in that, The system includes a 30 GHz microwave source, a 31.1 GHz microwave source, a first horn antenna, a second horn antenna, a spectrum analyzer, an amplifier, an isolator, a DC blocker, a 35 GHz low-pass filter, a 3.5 GHz band-pass filter, a 4.6 GHz local oscillator, and a 1.1 GHz band-pass filter. The 30 GHz microwave, after exiting the 30 GHz microwave source, is amplified to 10 dBm. After passing through the isolator and DC blocker, it is radiated into the plasma in O-mode by the first horn antenna. The second horn antenna then receives and couples the backscattered microwave. The coupled microwave then passes through the DC blocker and the 35 GHz low-pass filter. After mixing with the 31.1 GHz microwave in a mixer, a 3.5 GHz microwave is generated. This 3.5 GHz microwave is then fed into a 3.5 GHz band-pass filter with a center frequency of 3.5 GHz and a bandwidth of 60 MHz. It then undergoes a local frequency difference with the 4.6 GHz local oscillator, resulting in a final frequency reduction to 1.1 GHz. Finally, it passes through a 1.1 GHz band-pass filter with a bandwidth of 60 MHz. After being filtered by a GHz bandpass filter, the signal is fed into a spectrum analyzer, which ultimately measures its spectrum. When 30 GHz microwaves propagate in plasma, the following resonance condition is met. , ω SC = ω IN + ω LH At that time, this microwave will resonate with the low clutter wave of 4.6 GHz, generating a new scattered wave with a frequency of 34.6 GHz, where k and ω The subscripts SC, IN, and LH represent the wave vector and frequency, respectively, and represent the backscattered microwave, the 30 GHz incident wave, and the 4.6 GHz low clutter wave. The spectral width Δf of the scattered wave SC The following relationship exists between the incident wave at 30 GHz and the low-clutter spectral width at 4.6 GHz: （1） Due to the incident wave's spectral width Δf IN The spectral width Δf relative to low clutter LH It is much smaller, therefore, the spectral width of the scattered wave is approximately the spectral width of the low clutter wave; the spectral width is defined as the full width when the wave power is reduced to half.

2. The system for measuring the 4.6 GHz low-hybrid local spectrum of plasma according to claim 1, characterized in that, The spectrum analyzer has a scan time of ≤ 20 ms and an operating frequency of greater than 1.2 GHz.

3. The system for measuring the 4.6 GHz low-hybrid local spectrum of plasma according to claim 1, characterized in that, The isolator is used to prevent waves reflected from the plasma from entering the 30 GHz microwave source; the DC blocker is used to prevent DC voltage from damaging the 30 GHz microwave source and the 31.1 GHz microwave source.

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