Air cleaning by means of plasmas is a promising technology, says Tom Huiskamp. “The advantage of plasmas is that they enable us to convert many different kinds of harmful molecules into harmless substances. What’s more, in theory this can be done in a highly energy-saving manner.”

However, that does require a plasma reactor with precisely the right properties. An essential component of this is the high-voltage source, as Huiskamp explains. The purifying effect of the plasma comes from so-called radical particles, which are formed by streamers - the gas discharge that acts as the trailblazer for the actual spark.

“As soon as the streamer from the central electrode reaches the reactor wall, a high current starts to run through the plasma. While this current hardly contributes to the purification of the air, it does consume a lot of energy.” Therefore, the trick is to generate the streamers by means of extremely short voltage pulses, in the order of magnitude of nanoseconds, which have died out as soon as the energy-guzzling spark gets started.

In order to find the optimal pulse length and shape, Huiskamp designed a special voltage source, which allows him to manipulate the course of the pulse down to the smallest detail. Such a source is unique in the world, he thinks. “Particularly the rise time of the pulse, i.e. the time it takes the source to rise from zero to maximum voltage, is extraordinary: two hundred picoseconds.”

He illustrates how short this is by means of a comparison. “It takes light about one second to travel from the moon to the earth. In two hundred picoseconds the same light does not travel farther than six centimeters.”

“I’ve even been able to make films of the streamers”

At Electrical Engineering they have been looking into air cleaning with plasmas for twenty years. Meanwhile various practical tests have been carried out, including one conducted in the Dommel tunnel on the TU/e site several years back. “That work was done by my fellow PhD candidate Frank Beckers of Electrical Energy Systems. The reactor he tested is about one cubic meter in size. The research I have conducted was on a much smaller scale and more fundamental.”

To see what his ultra-short voltage pulses bring about exactly in the plasma reactor, Huiskamp made films with a special extremely light-sensitive high-speed camera which his Pulsed Power Technology group can use. “Then you see how the streamers are generated along the electrode, when the voltage pulse moves through it. I’ve even been able to make films of that.”

His new pulse source enabled Huiskamp to achieve unparalleled efficiency for the removal of nitrogen oxide (NO), and his source also functions extremely well for ozone. As a result, his PhD at the end of September was conferred cum laude and in the meantime he has begun a job as a postdoc on an annual contract at Pulsed Power Technology.

If it is up to him, his stay in that group will last much longer than that. “I really like it here and there are still so many things I would like to get to the bottom of. The beauty of this field of expertise is that you need complicated models to design a device, but that you can then knock it together yourself to see whether it actually works.”