Particle accelerators have already become useful, and in many cases an indispensable tool in many applications, such as medical treatments (radiotherapy, production of isotopes for PET), industry (material irradiation and sterilisation, industrial radiography) and safety control (cargo inspection).
More than 90% of accelerators in operation nowadays are machines, producing beams of electrons, protons or ions of low and medium energy (up to 50 MeV). The accelerated particle beams are used either directly or for the generation of the bremsstrahlung radiation, namely soft or hard X-rays.
The new growing trend in accelerator technologies is the design and construction of compact electron accelerators, with low power consumption and relatively low costs, whose output beams meet tight requirements determined by the specific application. In addition they must fulfil very stringent limits on the level of the scattered radiation. The most appropriate types of machines are electron linear accelerators (linacs), or electron machines with beam recirculation, like a race-track microtron (RTM).
An example of a compact RTM is a 12 MeV electron accelerator the Microtron laboratory of the Institute of Energy Technologies (INTE) of the Technical University of Catalonia (Barcelona), in collaboration with the Skobeltsyn Institute of Nuclear Physics (SINP, Moscow) and CIEMAT research centre (Madrid). Its main envisaged application is cancer treatment by means of Intraoperative Radiation Therapy. Due to its principle of operation, the RTM can produce a beam with low energy dispersion and good control of the current and dose. The output beam energies are 6, 8, 10 and 12 MeV, and the change of energy is achieved by simply extracting the beam from a corresponding orbit. In the bending, focusing and extraction magnets of this machine, permanent magnet material as a source of the magnetic field is used. This innovation makes it possible to place the magnets inside the vacuum chamber thus reducing the dimensions of the accelerator head and dispense with the need for magnet power. However, the magnets must be manufactured and initially tuned with quite high precision. The required technology and tuning methods have been already developed and tested at the SINP.
Another example is a linac for industrial radiography and cargo inspection, designed and built at the SINP in collaboration with industrial partners. It allows for continuous regulation of the beam energy (from 3 MeV to 8 MeV) and dose and includes a local shielding with the attenuation coefficient 104. Another feature is a vacuum-sealed design, which means vacuum pumps are not necessary. These and other novel technical solutions make this linac a reliable machine already ordered by a few industrial companies.
In this article, a collaboration of Dr V. Shvedunov (SINP) and A. Sánchez (INTE) are highly appreciated.
Institute of Energy Technologies
Universitat Politècnica de Catalunya