BIOPLASMAS & PLASMAS WITH LIQUIDS - Joint Conference of COST ACTIONS TD1208 “Electrical discharges with liquids for future
applications” & MP1101 Biomedical Applications of Atmospheric Pressure Plasma Technology, Bertinoro, Italy, 13th-17th September 2015
Microwave plasma torch at water surface
Evgenia Benova1, Mariana Atanasova1, Todor Bogdanov2, Plamena
Marinova2
1
DLTIS, Sofia University, 27 Kosta Loulchev street, Sofia, 1111, Bulgaria
Faculty of Physics, Sofia University, 5 James Bourchier Blvd., Sofia, 1164, Bulgaria
2
Argon plasma torch sustained by 2.45 GHz electromagnetic wave can be in contact with water
surface or penetrate inside the water at big enough wave power. Even if the plasma slightly
touches the water surface there is effect on the particles kinetics both in the gaseous plasma
and in the liquid. The mean power necessary for sustaining an electron-ion pair in the water
discharge is much higher than in the gases. In addition, the propagation of the electromagnetic
wave sustaining the discharge in water is problematic: the water dielectric permittivity strongly
depends on the wave frequency and the temperature and varies between 6 and 86. At wave
frequency of 2.45 GHz and temperature 100 ºC its value is 50 which leads to very fast decay of
the electromagnetic wave. If the water temperature is lower the plasma permittivity is even
higher and can reach 80 at room temperature (20 ºC).
We have studied both theoretically and experimentally the electrodynamics of the wave
propagation when the gas discharge is in contact with water (Fig. 1a) or penetrating inside it, as
well as the kinetics of elementary processes in the gaseous plasma and in liquid. Depending on
the wave power and the gas flow it is possible to produce plasma with low (room) temperature
(Fig. 1b) or with much higher temperature. The plasma is non-equilibrium one with electron
temperature lower than the gas/liquid temperature. Because of this many radicals and
chemically active particles can be produced even at low temperature. It is found out that this
kind of discharges can produce noticeable effects and depending on the regime of operation
can find various applications for surface treatment, sterilization, surface energy change and
others, including thermo-sensitive materials and liquids treatment.
a)
b)
Fig. 1 Plasma torch sustained by travelling wave in contact with water (a) and finger (b)