Electron beams have established themselves as potential tools both in basic as well as applied sciences. Industry also has been immensely influenced by their vast potential. Beams with varying power and energy are being extensively employed for radiation processing of materials and have totally revolutionized this field. For example electron beams are gradually replacing the old methods of curing of coatings, adhesive and paints. This not only tremendously improves the quality of the products but also gives an everlasting effect. Similarly, the electron beam processing of cables and sheets vastly improves their thermal and mechanical properties. The irradiation of semiconductor devices has brought in a total transformation in the IC and microchip industry. The sterilization of disposable medical products is another area where electron beams have made a big impact. The usage of electron beams for food preservation have revolutionized the concept of food storage. The art of producing exotic colours in gems and stones is also getting monopolized by electron beams. These stones have a big international market. Even the pathogenic germs of the sewage & sludge are being treated by these beams. Now, on a vast scale, the organically contaminated soils are going to be processed by electron beams. The field is growing and expanding at a fast pace.

BARC had long back realized the enormous potential of electron beams and chalked out an elaborate indigenous technological development programme. Depending upon the product and the type of radiation processing, the requirements of energy and power vary vastly. The energy may go anywhere from a few hundred keV to a few MeV and the power from a few hundred watts to a few hundred kilowatts. A single accelerator or one type of accelerator cannot meet such requirements. To cover the diverse areas of applications, it was decided to build a 500 keV, 10 kW DC accelerator, a 3 MeV, 30 kW DC accelerator and a 10 MeV, 10 kW RF Linac.
 

The Electron Beam technology has made inroads in many of the areas. DAE has an ongoing programme for building of industrial accelerators as well as developing their applications. BARC and CAT have taken up programmes to build industrial electron beam machines and related facilities to help Indian industry to keep pace with the technology development.  BARC, that has gathered sufficient experience in the field of electron beam technology, has been setting up an Electron Beam Centre at Navi Mumbai. This centre will be equipped with 3MeV and 10MeV accelerators. The accelerators with such high powers, being designed and built for the first time in the country, are a big technological challenge because of the nonavailability of many of the sophisticated components. This endeavour is described here.

500 keV DC Accelerator
In the year 1995, this accelerator was taken up for development. It is a Cockroft Walton based DC accelerator designed to give 20 mA of electron beam at an energy of 500 keV. The accelerator is housed at BRIT complex, Vashi, Navi Mumbai. Since last year, the accelerator is in regular operation at a power level of about 3.5 kW and energy 350 keV. Its up-gradation to full power level is planned in the near future. In parallel, it is being fully computerized and converted into a single push button machine.
At present, the accelerator is in use for surface modification studies in BARC. Apart from that, industries such as Reliance India Ltd. (RIL) are using it for cross linking of plastic sheets & granules. Hindustan Lever Ltd. (HLL) is planning to irradiate its brand of wheat flour by utilising this facility. Accelerator & Pulse Power Division, BARC and IIT-Madras, Chenai are pursuing radiation damage studies of materials including electrical & electronics circuits.

This is the only indigenously developed accelerator in the country which is operating at such a high power level. A view of this facility is shown in fig. 1.
 

Fig.1 : 500 keV DC Industrial Electron Accelerator

3 MeV, 30 kW DC Accelerator
This accelerator is designed to deliver 30 kW of beam at an energy of 3 MeV. A schematic of this machine is shown in fig. 2. The 5 keV beam from the electron gun is accelerated to 3 MeV in the acceleration tube. The beam, after passing through the scan magnet chamber is let out in the air through the scan horn and is used for processing of the materials. The high voltage system comprising corona guard rings is connected through rectifier chains, each of which generates an effective voltage of about 50 kV. In all, there are 70 such chains giving rise to a voltage of more than 3 MV. The accelerator tank having a diameter of 2 m and a length of 7 m, is pressurized with sulphur hexa fluoride (SF6) at a pressure of 6 atmosphere. SF6 helps in holding the high voltage without any serious breakdown.
 

This machine is full of technological challenges. The 45 kW, 120 kHz oscillator is being designed and built for the first time in the country. The corona guard, RF electrodes and HV dome, that have highly complicated configurations, are being addressed for the first time. All these subassemblies have to be maintained with a mirror finish. The fabrication of the accelerator tank encapsulating the cooling of SF6 gas, is another major task.

10 MeV, 10 kW RF Electron Linac
It is a coupled cavity Linac, capable of giving 10 MeV beam with a power of 10 kW. In fig. 3 is shown a view of this accelerator. The 50 keV electron beam from the gun is accelerated to 10 MeV in the Linac cavity having a length of about 1 m. After the energy analysis, the beam is passed to the scan horn through the sweep scanner. The cavity is powered through a wave guide plumbing line consisting of a circulator, directional coupler, power divider, ceramic window etc. The line is fed by a klystron based microwave source which can deliver a peak power of about 6 MW at a microwave frequency of 2856 MHz. This source is being designed and built by SAMEER, Mumbai. The rest of the systems are similar to the 3 MeV machine.
 

Fig.3 : 10 MeV Industrial Accelerator

The Linac technology is the most sophisticated one. Primarily, the cavity and the microwave source are one of the most intricate subsystems. The cavity should exhibit highest possible Q, the field uniformity and proper dispersion at the operating frequency. The geometrical deviations have to be confined within a few tens of microns. Similarly the microwave source ought to show highest possible stability at the maximum power level. All the microwave components of this accelerator will be handling very high average power, a task being attempted for the first time in the country.

Electron Beam Centre
To exploit the benefits of electron beam technology fully, BARC is setting up an Electron Beam Centre (EBC) at Kharghar, Navi Mumbai. The place is located at a distance of about 25 km from BARC. The land for the same is given by SAMEER, which is also a participant in this programme.

EBC house both, 3 MeV and 10 MeV machines. Apart from housing the two accelerators, the centre is being equipped with labs which will cater to the future developments and advancements to be carried out in the subsystems such as electron guns, cavities, microwave sources, beam handling devices, computer controls, chemical processing, quality controls etc. For taking care of the high voltage components, a clean room is being set up. Apart from that, a small workshop, a library and a seminar hall is also being planned. With the incorporation of all these features, EBC will be a novel & unique facility in the country, for carrying out R & D in the area of industrial accelerators and their applications.
 

Building of Electron Beam Centre at Kharghar A view of the EBC building depicting the 3 MeV & 10 MeV cells is shown below. The building is functional along with all its utilities and the labs. On the accelerators front, quite a few sub-systems such as electron guns, gun modulator, prototype Linac cavity, vacuum pumps, control consoles, power supplies, microwave power source, are being assembled and tested in their respective labs., at the EBC site. These are going through the usual phase of debugging and perfection.

Conclusions
The accelerators with such high powers are being designed and built for the first time in the country. They are a big technological challenge, more so, because of the nonavailability of many of the components such as klystrons, thyratrons, circulators, ceramic windows, acceleration tubes etc., in the country. To put this technology on a strong footing, these will also have to be developed within the country. Here, DAE-BRNS is playing a laudable role. It is roping in many institutions like CEERI Pilani, SAMEER and others, to develop such devices. BARC is going ahead with full force in this endeavour. Within a few years, it should be possible to attain perfection in this intricate technology.The remaining subsystems are in the advanced stages of fabrication at BARC and outside. The accelerators will be available for utilization in the year 2003.