750 kV DC Accelerator
A Direct Current Accelerator for industrial applications is designed and developed at Raja Ramanna Centre for Advanced Technology, Indore. The operating voltage range for the accelerator is 300 to 750 kV with a maximum beam power of 20 kW. The high voltage is generated using balanced Cockroft-Walton voltage multiplier circuit by a chain of diodes and capacitors. The AC Mains is first converted into low voltage DC in the converter. This DC converter drives a high frequency inverter. The accelerator can irradiate small samples to large sheets of 1.2 m width. The effective penetration in unit density material in double sided irradiation with this accelerator is 4 mm.
Accelerator with beam extraction chamber
The electron gun, acceleration column, focusing coil, high voltage multiplier stack etc. are housed in a 1.5 m diameter and 3.2 m high pressure vessel. Using a 50 micron thick titanium foil, the electron beam is extracted into air.
Electron gun and accelerating column
Applications of 750 keV DC Accelerator
- Rubber Tiles Irradiation
Ship Building Centre at Visakhapatnam has a requirement of surface treatment of rubber tiles using electron beam. These tiles are irradiated at their premises using an imported accelerator. Dosimetry study and process evaluation were carried out at their facility. Based on these results, some tiles were irradiated using this accelerator. The photograph shows a sample rubber tile being arranged over the conveyor prior to its radiation treatment. The tiles were to be irradiated in two stages, first with polyester resin and then with a glass cloth over it. The required dose range varies from 100 kGy to 250 kGy during the entire process. Dose non-uniformity was within ±10%. After the radiation treatment and aging, ‘bond pull strength test’ was carried out. In this test, the glass cloth which was spread over rubber tile and treated with electron beam is peeled off using a special machine. The glass cloth should withstand a minimum stress level of 15 kg/cm2 before peeling. These results were achieved.
- Surface Irradiation of Potatoes
Potatoes were irradiated using this accelerator at various dose levels. The potatoes irradiated with a surface dose of 500 Gy and more have not shown any sprouting even after three months when kept at controlled temperature of 20 degree Celcius. Photograph shows the irradiated and un-irradiated potatoes after three months. Successful surface irradiation using low energy electron accelerator is a major milestone in food irradiation technology as it will keep the bulk material unaffected by the irradiation and we can increase the throughput many folds as compared to irradiation by gamma rays.
- Surface Irradiation of seeds
Surface Irradiation of 34 varieties of seeds for disinfection was carried out in collaboration with National Bureau of Plant Genetic Resources, New Delhi. Post irradiation experiments on the seeds have shown marked improvements in the quality of seeds. The photograph shows the seeds on the conveyor system prior to irradiation.
- Irradiation of paper pulp sheets
About 100 kg of pulp was irradiated at a dose level of 5 kGy and handed over to Grasim, Nagda for it's pilot plant evaluation, targeting an irradiated pulp viscosity between 7 - 8 cp. Another lot of 10 kg each were irradiated at different dose levels of 4, 5, 6, 7, 8, 10 and 12. kGy with the aim of generating data on the viscosity drops resulting from different doses. The photograph shows the pulp sheets under irradiation.
- Curing of Coatings on wood
Electron Beam Curing of coating on wood samples were carried out in collaboration with ShriRam Institute for Industrial Research, N. Delhi. 100 to 400 kGy dose was given to a variety of wood samples coated with different polymers and resins. The figure below shows irradiated wood samples.
- Sterilization of Sanitary Napkins
Sterilization of sanitary napkins was carried out using this accelerator at the dose level of 25 to 30 kGy. The Napkins were found sterile by analyzing with direct inoculation techniques.
- Radiation Grafting of PP Sheet
Experiments on grafting of polypropylene sheets were carried out using this accelerator. Total dose of 200kGy was given in multiple passes. The sheets were to be given a predefined dose and after some fixed time they had to be immersed in ACN solution at a fixed temperature. The number of passes and the duration of waiting time were varied to optimize the results. Dose variation was found to be within ±10%.
- Curing of paint on metal sheets
Metallic sheets coated with paints were cured using this accelerator. The figure below shows the EB cured paint coatings on metallic sheets.