Discharge Plasma Control via Displacement Current Rate
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Solution Overview
Problem
Existing methods for generating atmospheric pressure glow discharge plasma are unstable and prone to filamentary discharges when impurities are present, leading to loss of plasma uniformity and control, especially at the breakdown and extinction stages.
Innovation Solution
A method and arrangement that control the displacement current rate of change to suppress filamentary plasma development, using an LC matching network and pulse forming circuit to synchronize displacement current variations with plasma breakdown, allowing for stable and uniform glow discharge plasma formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional plasma generation methods are used at atmospheric pressure, then plasma can be generated, but the plasma becomes unstable and develops filamentary discharges when impurities are present
Solution Approach 1:
The patent applies preliminary anti-action by controlling the voltage to have a negative change in time (dV/dt < 0) at the start of the plasma pulse. This preliminary control action suppresses the development of instabilities and filamentary discharges before they can grow into major plasma failures. By anticipating and counteracting the instability development at the breakdown stage, the method prevents the worsening of plasma uniformity while maintaining reliable plasma generation.
2Reliability
If voltage is controlled to suppress instabilities at plasma breakdown, then plasma stability improves, but a too large voltage drop will suppress the plasma altogether
Solution Approach 1:
The patent employs dynamics by using time-varying voltage control with specific dV/dt characteristics at different stages of the plasma pulse. The voltage control is dynamic rather than static, allowing the system to suppress instabilities at breakdown (when needed) while maintaining adequate power delivery during the sustained discharge phase. This dynamic control enables the plasma to receive appropriate voltage suppression at critical moments without suffering from continuous power reduction.
Solution Approach 2:
The method uses periodic AC voltage applied to the electrodes, with each half-cycle representing a plasma pulse. The voltage control parameters (including dV/dt characteristics) are optimized for each periodic cycle, particularly at the breakdown phase. This periodic action allows repeated suppression of instabilities at the start of each pulse while maintaining high power density during the active discharge portion of each cycle, thus resolving the contradiction between stability and power.
3Productivity
If filamentary discharge is used to generate ozone, then large quantities can be produced, but the plasma filaments puncture or treat the surface unevenly
Solution Approach 1:
By applying negative dV/dt control at the plasma breakdown stage, the method prevents the formation of filamentary discharges in the first place. This preliminary anti-action against filamentation ensures that the plasma remains in a uniform glow discharge mode throughout the treatment process, thereby maintaining surface treatment uniformity while still achieving high productivity through sustained stable discharge.
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
The method effectively suppresses instabilities and maintains a uniform glow discharge plasma, even in the presence of impurities, by controlling the dynamic resistance of the plasma, enabling higher power density and improved surface treatment of materials.
Implementation Method 1
The plasma is generated in a gas or a gas mixture by energizing the electrodes from AC power supply means
Implementation Method 2
Atmospheric Pressure Glow (APG) discharge plasma is used in practice
Implementation Method 3
controlling the voltage applied to the electrodes to have a negative change in time (dV/dt) at the start of the plasma pulse
Implementation Method 4
an electronic feedback circuit may be used to implement the feedback voltage control
Implementation Method 5
An inductance in saturation, which is positioned in series with the electrodes, may be used to implement such a control mechanism
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
Method and arrangement for controlling a discharge plasma in a discharge space (11) having at least two spaced electrodes (13, 14). A gas or gas mixture is introduced in the discharge space (11), and a power supply (15) for energizing the electrodes (13, 14) is provided for applying an AC plasma energizing voltage to the electrodes (13, 14). At least one current pulse is generated and causes a plasma current and a displacement current. Means for controlling the plasma are provided and arranged to apply a displacement current rate of change for controlling local current density variations associated with a plasma variety having a low ratio of dynamic to static resistance, such as filamentary discharges. By damping such fast variations using a pulse forming circuit (20), a uniform glow discharge plasma is obtained.