New 15 MeV electron accelerator for non-destructive testing

Abstract

A 15 MeV accelerator with the dose rate from 80 to 120 Gy/min at 1m from the target has been designed and manufactured in NPK LUTS, the D.V.Efremov Institute, NIIEFA. The accelerator is intended for nondestructive testing (radiography, introscopy, tomography) of large scale products. Under tests an X-ray beam with the boundary energy of 15-16 MeV and dose rate of 100 Gy/min has been produced. When operating with longer pulse lengths of the accelerated electron current, the beam power was up to 140 Gy/min; with lower currents the 18 MeV energy was attained at a dose rate of 40-50 Gy/min. Biperiodic accelerating structure with axial coupling cells is applied in the accelerator. The accelerating structure buncher provides RF-focusing of the electron beam, therefore there is no need for focusing the solenoid. The focus spot diameter is no more than 2mm. To provide the electron beam stability, the accelerator is equipped with a system for automatic frequency tuning (AFT). The AFT system ensures both coarse tuning of the driver frequency against the temperature of the accelerating structure and fine tuning - against the minimum reflected power. The anode voltage of the klystron amplifier is stabilized by using a de-Q-ing system. A charging choke and pulse forming network (PFN) are located inside the irradiator unit to increase the distance between the modulator and irradiator up to 100m and to reduce losses when high-voltage high-current pulses are transmitted. The low-voltage klystron (anode voltage up to 55 kV) applied in the accelerator allows reducing the machine weight and dimensions (1100 kg and 2040x880x920mm). The accelerator is equipped with a PC-based automatic control system. In the accelerator intended for the radiographic inspection there is an external collimator with movable diaphragm jaws for testing small fragments of an inspected product.