Radiation Processing Facility (RPF) Accelerator Physics Design:

One of the very important applications of electron linear accelerators (linacs) is that they can irradiate food and agricultural products, for enhancing food safety, and also for better food preservation. In addition, electron linacs can also be used for sterilization of medical products. Irradiation can be done directly by the electron beam, or by x-rays generated by the electron beam. Induced radioactivity in the irradiated product is not of much concern, provided the energy of the electron beam is limited to 10 MeV for the electron beam irradiation mode, and 7.5 MeV for the x-ray mode of irradiation. ABPS is responsible for physics design of high average power electron linac for radiation processing facilities.

A 10 MeV, 6 kW electron linac has been built recently at Raja Ramanna Centre for Advanced Technology, Indore for irradiation applications. The section has been contributing in this important project by carrying out the electromagnetic and beam dynamics studies for an optimized design of travelling wave electron accelerator, along with its RF couplers. One such accelerator (Linac-B1) has already been commissioned and achieved a beam power of 5 kW and a nominal beam energy of 9 MeV. The accelerating structure of this linac is of 2π/3 mode traveling wave type, and it is an integrated buncher-cum-accelerator structure. A schematic of the accelerating structure is shown below:


The electromagnetic design of traveling wave accelerating structure has been done using SUPERFISH and CST-MWS. The end to end 3D electromagnetic simulation of the accelerating structure integrated with input and output RF couplers has been performed using the code CST-MWS. Electric field distribution inside the accelerating structure is shown in the following figure.



Numerical studies have been performed to check the efficacy of a method that has been developed for tuning of a traveling wave bunching-cum-accelerating structure in simulation environment. Studies have also been performed on transient beam loading in these structures.

Recently, a 9.5/7 MeV dual energy 10 kW electron linac, with energy filtering system is being developed at RRCAT. Complete layout of the accelerator, starting for electron gun to the final product is shown below. End to end beam dynamics simulations have been performed, starting from the electron gun to the product.


Schematic layout of the accelerator for Radiation Processing Facility (RPF)
In order to enhance the RF to beam power conversion efficiency, a constant gradient (CG) type TW structure has been recently designed.

ABPS is also engaged in studies for design of a 200 MeV injector linac for the proposed High Brilliance Synchrotron Radiation Source (HBSRS). The desired normalized rms beam emittance and rms energy spread of the beam at the output of the linac is 24 mm-mrad and 0.5%. Configuration of the injector linac, which is currently being studied, is shown in the figure, given below. Traveling Wave (TW) accelerating section will consist of 04 nos. of 3.7 m long constant gradient (CG) TW accelerating structures with suitable matching sections in between. Standing Wave (SW) Buncher Section will consist of a 1.13 m long bi-periodic, on-axis coupled structure. Optimization studies to achieve the desired parameters for the high brightness as well as high resolution mode of HBSRS are going on.