The development of a new, very small coaxial plasma source based on the microwave plasma torch (MPT) is described. It generates a plasma jet up to 4 mm long and can be operated with a argon gas flow rate less than 70 ml per min at down to 2 W microwave power (2.45 GHz) at atmospheric pressure. It also works well with helium and does not show any wear during a test period of 30 h of operation with argon. It is, in particular, thought to be a source for the atomic spectroscopy of gaseous species. The excitation temperature is found to be ~4700 K for this device operating with helium and 17 W microwave power. A detection limit for an example application in which Cl is detected from HCCl₃ is found to be below 66 ppb.

For the first time, to our knowledge, microstrip circuits are used to match the small MPT to the generator's 50 Ω impedance. The design considerations for the microstrip circuits are discussed and an approximated calculation for the layout is presented. With the introduced procedure it is possible to design even smaller MPTs for special applications.