Application Cases

Experimental Name: Radio Frequency Discharge Plasma Excitation and Emission Spectroscopy Diagnostic System

Research Direction:
Exploring the active control effect and mechanism of radio frequency discharge plasma excitation on the unsteady behavior of shock wave/boundary layer interaction (SWBLI) in supersonic flow. The study focuses on the application of plasma excitation in flow control, aiming to experimentally reveal the physical characteristics of radio frequency discharge plasma and its regulatory effects on shock oscillation and boundary layer structure. Specifically, the research is divided into two core parts: first, analyzing the spectral characteristics of plasma in a low-pressure static environment to investigate the influence of discharge parameters (power, frequency) on electron temperature, vibrational temperature, and electron density; second, studying the control effect of plasma excitation on the dynamic characteristics of SWBLI in a supersonic wind tunnel, with a focus on changes in shock oscillation frequency and the response of boundary layer flow structures.

Experimental Objective:
To investigate the influence of radio frequency discharge plasma power and frequency on plasma characteristics (such as electron temperature) and their control effects on suppressing low-frequency shock oscillation, enhancing high-frequency energy, and inducing boundary layer vortex structures in supersonic flow fields, providing experimental support for active flow control technologies.

Testing Equipment:
Radio frequency power amplifier ATA-8035, surface discharge actuator, low-pressure chamber, vacuum pump, fiber optic spectrometer, supersonic wind tunnel, compression ramp test model, high-speed camera, xenon light source, concave mirror, knife edge, oscilloscope, digital delay generator, impedance matching circuit.

Experimental Procedure:
In a low-pressure chamber (12 kPa), a fiber optic spectrometer (0.4–1.1 μm) was used to collect emission spectra from radio frequency discharge plasma (0.5–1.1 MHz, 20–50 W). Electron temperature, vibrational temperature, and electron density were derived using the Boltzmann slope method and Stark broadening inversion. Simultaneously, in a Mach 2 supersonic wind tunnel, a compression ramp test model (20° deflection angle) was installed. Plasma thermal perturbations were applied via a surface discharge actuator, and a schlieren imaging system (xenon light source + concave mirror + knife edge) combined with a high-speed camera (100 kHz frame rate) was used to capture shock oscillation and boundary layer separation bubble dynamics. A digital delay generator enabled microsecond-level synchronization between discharge excitation and image acquisition. Spatial Fourier transform was employed to extract the dominant frequency of shock oscillation, and wavelet coherence analysis quantified the phase relationship between separation zone vortex structures and shock motion. Finally, dynamic mode decomposition (DMD) characteristics under different discharge parameters were compared using the MATLAB platform to establish a control model for plasma thermal perturbation and multi-scale coupling of shock wave/boundary layer interactions.

Figure 1: Block Diagram of Radio Frequency Discharge Emission Spectroscopy Diagnostic System

Figure 2: Block Diagram of Experimental System for Unsteady Control of Shock Wave/Boundary Layer Interaction (SWBLI)

Figure 3: Compression Ramp Test Model

Experimental Results:
Spectral tests showed that when the load power increased from 20 W to 100 W (at a fixed frequency of 1 MHz), the nitrogen molecular spectral line ratio (391.4 nm/380.5 nm, indicating electron temperature) increased from 2.1 to 3.3, while the spectral line ratio (371.1 nm/380.5 nm, indicating vibrational temperature) remained stable at 0.82 ± 0.05. The electron density measured by the Stark broadening method remained at (1.2 ± 0.3) × 10¹⁵ cm⁻³. When the frequency increased from 0.5 MHz to 1.5 MHz (at a fixed power of 100 W), the electron temperature spectral line ratio first increased and then decreased, peaking at 3.5 at 1.1 MHz. Flow control experiments indicated that without excitation, the dominant shock frequency was 0.8–2.5 kHz (accounting for 62% of the total energy). After applying 0.7 MHz excitation, low-frequency shock energy decreased by 37%, while high-frequency energy (>10 kHz) increased by 3.2 times, and the standard deviation of shock displacement decreased from 3.2 mm to 2.5 mm. When the excitation frequency increased to 1.0 MHz, the characteristic shock frequency shifted to 5.8 kHz (an increase of 230%), and spatially coherent vortex structures appeared in the reattached boundary layer (energy density increased by 4.5 times). The phase locking error between shock front pulsation and discharge was less than 5 μs, validating the modulation effect of plasma thermal perturbation on multi-scale coupling of shock wave/boundary layer interactions.

Figure 4: Radio Frequency Surface Discharge Images and Corresponding Emission Spectra at 12 kPa

Figure 5: Emission Spectra and Relative Spectral Intensity Changes Under Different Load Powers

Figure 6: Emission Spectra and Relative Spectral Intensity Changes Under Different Frequencies and Powers

Figure 7: Time Series Frequency Spectrum of Shock Position

Product Recommendation: ATA-8000 Series Radio Frequency Power Amplifier

Figure: ATA-8000 Series Radio Frequency Power Amplifier Specifications and Parameters