MODELLING OF RADIO-FREQUENCY WALL CONDITIONING IN SHORT PULSES IN A STELLARATOR

Results of numerical modelling of electron cyclotron (EC) short pulse wall conditioning discharge are presented. The analysis carried out with the usage of a self-consistent model that simulates radio-frequency (RF) plasma production in stellarator type machines in the ion cyclotron and EC frequency ranges. The discussion of the results of the calculations is presented.

Magnetic nozzle radiofrequency plasma thruster approaching twenty percent thruster efficiency

Development of a magnetic nozzle radiofrequency (rf) plasma thruster has been one of challenging topics in space electric propulsion technologies. The thruster typically consists of an rf plasma source and a magnetic nozzle, where the plasma produced inside the source is transported along the magnetic field and expands in the magnetic nozzle. An imparted thrust is significantly affected by the rf power coupling for the plasma production, the plasma transport, the plasma loss to the wall, and the plasma acceleration process in the magnetic nozzle. The rf power transfer efficiency and the imparted thrust are assessed for two types of rf antennas exciting azimuthal mode number of $$m=+1$$ m = + 1 and $$m=0$$ m = 0 , where propellant argon gas is introduced from the upstream of the thruster source tube. The rf power transfer efficiency and the density measured at the radial center for the $$m=+1$$ m = + 1 mode antenna are higher than those for the $$m=0$$ m = 0 mode antenna, while a larger thrust is obtained for the $$m=0$$ m = 0 mode antenna. Two-dimensional plume characterization suggests that the lowered performance for the $$m=+1$$ m = + 1 mode case is due to the plasma production at the radial center, where contribution on a thrust exerted to the magnetic nozzle is weak due to the absence of the radial magnetic field. Subsequently, the configuration is modified so as to introduce the propellant gas near the thruster exit for the $$m=0$$ m = 0 mode configuration and the thruster efficiency approaching twenty percent is successfully obtained, being highest to date in the kW-class magnetic nozzle rf plasma thrusters.

Effects of Plasma Treatment on Cooking and Physical Qualities of Pigmented Thai Rice

Plasma surface modification processes account for most of the commercial uses of surface modification because they are fast, efficient methods for improving the adhesion, wettability properties and other surface characteristics of a variety of materials. This research was aimed to investigate of surface modification of pigmented rice by plasma technique. Two rice varieties namely Kum Doi Saket and Hom Nil rice were used. The samples were subjected to plasma treatment with different gas types to determine suitable gas type. The types of gas for plasma treatment were argon, nitrogen and air. The output voltage of the plasma was 0.1428 W at the frequency of 110 Hz and treatment time of 40 min. It was found that plasma treatment with various gas types on the samples caused a reduction in cooking time and increase in water uptake ratio, length expansion ratio and volume expansion ratio, an increase in water absorption, a decrease in contact angles as compared to untreated sample. These results were related to etching of the bran layer of the rice grain which allowed better water transfer into the grain during cooking. It was also found that plasma production using plasma gas had more effect on texture of the rice grains, as compared to without plasma treatment.