Low temperature atmospheric pressure plasmas are a unique form of plasma where the heavy particles (like ions, atoms, molecules, and dust) remain at or near room temperature, despite the electrons being much hotter. This distinctive characteristic allows for diverse applications without causing significant thermal damage to sensitive materials.
Understanding the Key Characteristics
These plasmas combine two critical features: "low temperature" and "atmospheric pressure," which together define their unique properties and utility.
- Low Temperature: The defining feature of these plasmas is that the gas temperature—the temperature of the heavy particles (ions, atoms, molecules, dust)—is kept at approximately room temperature. This is in contrast to "thermal" or "hot" plasmas where all particles, including heavy ones, are at very high temperatures. This characteristic is crucial for applications involving heat-sensitive materials.
- Atmospheric Pressure: Unlike many industrial plasmas that require a vacuum environment, these plasmas operate at ambient atmospheric pressure. This eliminates the need for expensive vacuum equipment, simplifying their setup and operation for various applications.
Physical Dimensions and Energy Considerations
Low temperature atmospheric pressure plasmas can exist in very compact forms:
- Dimensions: They can be generated in very small volumes, ranging from a few millimeters down to and below 100 μm in size. This compact nature allows for precise localized treatment.
For efficient operation and to maintain the low temperature of the heavy particles, especially at atmospheric pressure, specific energy delivery methods are often employed:
- Transient (Pulsed) Plasmas: To avoid significant gas heating at atmospheric pressure, where many collisions occur, these plasmas are often operated in a transient or pulsed mode. In atmospheric plasmas, at least 100-1000 collisions are necessary for efficient gas heating. By using pulsed power, the plasma can be generated and then quickly extinguished, limiting the time available for energy transfer to the heavy particles, thereby keeping their temperature low.
| Feature | Description |
|---|---|
| Gas Temperature | Heavy particles (ions, atoms, molecules, dust) are limited to room temperature. Electrons are typically much hotter. |
| Operating Pressure | Operates at atmospheric pressure, eliminating the need for vacuum systems. |
| Typical Dimensions | Can range from a few millimeters down to and below 100 μm. |
| Heating Mechanism | Often generated as transient (pulsed) plasmas to avoid extensive gas heating. This is important because 100-1000 collisions are needed for efficient gas heating in atmospheric plasmas, and pulsed operation minimizes this energy transfer. |
This unique combination of low gas temperature and atmospheric pressure operation makes these plasmas highly versatile for applications that require reactive species without high heat, such as in medicine, environmental remediation, and surface treatment of delicate materials.
For further reading, refer to the Overview of Tutorial – Low Temperature Plasmas (LTP) from PPPL.
