RF Generator Impedance and Cable Length for Plasma Ignition
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional RF generator devices, particularly class C RF generators, face limitations in applying high enough load-end voltage to initiate and maintain plasma discharge due to self-oscillation and voltage limitations, which restrict the generation of a stable plasma ignition voltage.
Innovation Solution
The RF generator device is configured with a lower internal impedance than the power supply unit, and the electrical length of the power supply unit is adjusted to be within a specific range relative to the fundamental wavelength of the RF AC, allowing the load-end voltage to be doubled or more, thereby overcoming the limitations of conventional systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a class C RF generator is used to amplify power efficiently, then power amplification efficiency is improved, but the load-end voltage is limited and cannot reach the required ignition voltage level
Solution Approach 1:
The patent applies dynamics by making the electrical length of the feed cable variable rather than fixed. The cable length is adjusted dynamically to different electrical lengths (λ/8, λ/4, 3λ/8, etc.) depending on the operating mode - using longer electrical lengths during plasma ignition to achieve high load-end voltage, and shorter electrical lengths during steady-state operation to reduce reflected wave power. This dynamic adjustment resolves the contradiction between voltage amplification and power efficiency.
2Strength
If the cable length of the feed cable is increased to increase load-end voltage, then load-end voltage is improved, but reflected wave power increases causing self-oscillation
Solution Approach 1:
The patent resolves this contradiction by dynamically adjusting the electrical length of the feed cable based on operational requirements. During plasma ignition when high voltage is needed, the cable is set to longer electrical lengths (λ/4, 3λ/8) that provide voltage amplification. During steady-state operation when stability is critical, the cable is adjusted to shorter electrical lengths (λ/8) that minimize reflected wave power and prevent self-oscillation. This time-varying parameter adjustment allows the system to achieve both high voltage and stability at different times.
3Strength
If the electrical length of the feed cable is adjusted to increase load-end voltage, then ignition voltage is improved, but the system becomes more complex to control
Solution Approach 1:
The patent applies parameter changes by systematically varying the electrical length parameter of the feed cable across specific discrete values (λ/8, λ/4, 3λ/8, etc.) to achieve the desired voltage amplification effect. By identifying and utilizing these specific parameter points where the electrical length produces constructive interference and voltage enhancement, the system achieves high ignition voltage through controlled parameter variation rather than through complex circuitry or additional components.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration enables the application of a high enough ignition voltage to the plasma load, ensuring stable plasma generation and preventing self-oscillation, thus improving plasma ignition reliability and stability.
Implementation Method 1
a power supply unit (4) connected between an output end of the RF generator unit (1) and a load end, which is an input end of a load (2), to supply the RF AC to the load (2)
Data Source
Figure 1
Figure 2
Figure 3A~3F
AI summary
An object of the present invention is to increase the load-end voltage and to select an ignition voltage high enough for the load-end voltage of a plasma load to generate a plasma discharge. When RF power is supplied from an RF generator to a load via a power supply unit, (a) the internal impedance of the RF generator is made lower than the characteristic impedance of the power supply unit, and (b) the load-end voltage is increased by selecting the electrical length LE of the power supply unit, which connects between the RF generator and the load to supply RF power, so that the electrical length LE has a predetermined relation with the fundamental wavelength λ of the RF AC. More specifically, the electrical length LE of the power supply unit is selected in such a way that, when the load end, which is the input end of the load, is in an open state, the electrical length LE is (2n-1)·(λ/4)-k·λ≤LE≤(2n-1)·(λ/4)+k·λ (n is an integer, k is {π-2·cos-1(1/K)}/(4π)) with respect to the fundamental wavelength λ of the RF AC.