Hot spots and flash points

Hot spots and flash points rf technology
Hot spots and flash points rf technology

mono match

We recently got a returned Octiv sensor with the connector melted and this reminded me of hotspots and flashpoints.

In the world of RF engineering transmissions lines are matched and current and voltage are uniform along the cable. In the plasma world transmission lines are used to carry power to the plasma. A matching network is used to match the power supply to the plasma but the connection, effectively a transmission line from the matching network to the plasma electrode is not matched. I am not an RF engineer but even a physicist knows that there is a reflected wave at the end of the unmatched transmission line.

Does this matter? If the transmission line from the Matching Network has resistive loss then it will matter. A standing wave establishes along this line and the current will change from a minimum to a maximum. I call the maximum a "hotspot" because this is where most of the power is lost. The location of the hotspot depends on the impedance of the plasma. Where the minimum in current occurs we have a maximum in the voltage. This is the flashpoint. If you are going to get an arc then it will be here. In designing and maintaining stable and reliable plasma systems knowing exactly where the hotspot and flashpoints are is very useful. You can even chose to avoid either or both depending on the distance from the matching network to the plasma.

The final point to watch is that their locations moves with the plasma impedance.