Cold atmospheric plasma: Its time-dependent effects on the elimination of bacterial colony on periodontal manual scalers.

Background: This in vitro study investigated the time-dependent bactericidal effects of cold atmospheric argon plasma treatment of periodontal hand scalers as well as the scanning electron microscopic view of the scaler tip surfaces before and after plasma treatment. Materials and Methods: The study used 34 periodontal hand scalers which were divided into test and control groups. The scaler tips were inoculated with Escherichia coli and Staphylococcus aureus bacteria, following which the scalers in the control and test groups were subjected to conventional sterilization and argon plasma sterilization, respectively. Varying exposure times of plasma treatment were done on the test group samples to evaluate the minimum time required for complete sterilization. Subsequently, streaks were made on plate count agar using each of these instruments. The agar plates were then kept in an incubator for 24 h, following which bacterial colony count was assessed (colony-forming units/mL). Furthermore, the scanning electron microscopic (SEM) view of the scaler tip was studied before and after plasma treatment. Results: A complete elimination of bacterial load (Gram-positive as well as Gram-negative) from the instrument surface was achieved by the plasma exposure time of 15-20 s. SEM analysis did not show a significant difference before and after plasma treatment as not many organic residues were present on the scaler tip. Conclusion: Cold atmospheric pressure plasma is an efficient and time-saving method of sterilization, capable of destroying both Gram-positive and Gram-negative bacteria.

Cold Plasma: Clean Technology to Destroy Pathogenic Micro-organisms.

Atmospheric pressure cold plasma is a promising technology in fighting pathogenic micro-organisms. In times of Covid-19 pandemic, it was decided to modify two types of cold plasma devices to study their effectiveness in the killing of pathogenic micro-organisms. These studies have shown that both the devices are efficient in this purpose. While pencil like microwave based device can destroy Aeromonas bacteria and its bacteriophage from 6 cm distance in 2 min, the larger (~ 40 cm2) RF plasma based device could do the similar killing ability for the larger possible area in 4 min. Optical Emission Spectroscopy (OES) studies revealed that both these devices produce OH radicals which helped in the destruction of both bacteria and its bacteriophage. With suitable modifications, these devices, especially the larger area device may even be implemented for the elimination of Covid-19 affected wards of hospital without using any sensitive chemical process.

Note: design and development of improved indirectly heated cathode based strip electron gun.

An improved design of indirectly heated solid cathode based electron gun (200 kW, 45 kV, 270° bent strip type electron gun) has been presented. The solid cathode is made of thoriated tungsten, which acts as an improved source of electron at lower temperature. So, high power operation is possible without affecting structural integrity of the electron gun. The design issues are addressed based on the uniformity of temperature on the solid cathode and the single long filament based design. The design approach consists of simulation followed by extensive experimentation. In the design, the effort has been put to tailor the non-uniformity of the heat flux from the filament to the solid cathode to obtain better uniformity of temperature on the solid cathode. Trial beam experiments have been carried out and it is seen that the modified design achieves one to one correspondence of the solid cathode length and the electron beam length.

A new design of indirectly heated cathode based strip type electron gun.

A new design of indirectly heated solid cathode based electron gun (200 kW, 45 kV, 270° bent strip type electron gun) has been presented. The design issue addressed is the uniformity of temperature on the solid cathode using (a) a multi-segmented filament with variable height as the primary heat source and (b) trapezoidal shaped single long filament as the primary heat source. The proposed design in this paper is based on computer simulation and validated by extensive experimentations. The design emphasis is on maintaining uniform temperature on the solid cathode. The designed multi-segment filament and the single long filament provide a temperature uniformity on the solid cathode of about 250 K and 110 K, respectively. The better temperature uniformity inspite of the thermal expansion, in case of a single long filament tightly clamped at two ends, has been possible due to shaping of the single filament with a number of constituent sections such that the thermal expansion of different sections forming the actual filament takes care of not only the mechanical stability but also does not affect the emitting surface of the filament. Experiments show that the modified design achieves a one to one correspondence of the solid cathode length and the electron beam length emitted from the solid cathode.

Note: Design of transverse electron gun for electron beam based reactive evaporation system.

In this paper design of a 10 kV, 10 kW transverse electron gun, suitable for reactive evaporation, supported by simulation and modeling, is presented. Simulation of the electron beam trajectory helps in locating the emergence aperture after 90° bend and also in designing the crucible on which the beam is finally incident after 270° bend. The dimension of emergence aperture plays a vital role in designing the differential pumping system between the gun chamber and the substrate chamber. Experimental validation is done for beam trajectory by piercing a stainless steel plate at 90° position which is kept above the crucible.

Design and development of indirectly heated solid cathode for strip type electron gun.

Design analysis of a high power indirectly heated solid cathode (for a 200 kW, 45 kV, and 270 degrees bent strip type electron gun) has been presented. The design approach consists of simulation followed by extensive experimentation with different cathode configurations. The preferred cathode is of trapezoidal section (8 x 4 x 2 mm(3)) with an emitting area of 110 x 4 mm(2) made up of tantalum operating at about 2500 K. The solid cathode at the operating temperature of 2500 K generated a well defined electron beam. Electromagnetic and thermomechanical simulation is used to optimize the shape of the beam. Thermal modeling has also been used to analyze the temperature and stress distribution on the electrodes. The simulation results are validated by experimental measurement.