6/9 MeV S-BAND STANDING WAVE ACCELERATING STRUCTURE FOR CONTAINER X-RAY INSPECTION SYSTEM AT RTX P. Buaphad ∗ , Radiation Technology eXcellence, Daejeon, 34025, Korea Advanced Radiation Technology Institute, KAERI, Jeongeup-si, Jeollobuk-do, 56212, Korea also at University of Science and Technology, Daejeon, 34113, Korea Y. J. Kim † , S. S. Cha, B. C. Lee, H. K. Cha, J. H. Ha, Advanced Radiation Technology Institute, KAERI, Jeongeup-si, Jeollobuk-do, 56212, Korea K. B. Song, H. D. Park, S. Y. Yoo. Radiation Technology eXcellence, Daejeon, 34025, Korea Abstract Recently, there is needs of the X-ray inspection systems around the world to combat terrorism, drug and weapons smuggling, illegal immigration, and trade fraud. A compact standing wave (SW) linear accelerator (linac) for container X- ray inspection system has been produced at Radiation Tech- nology eXcellence (RTX) to meet this growing need. The RF accelerating structure uses SW side-coupled structure fed by a 5 MW e2v magnetron with frequency of 2856 MHz. The electrons are accelerated from DC gun with energy of 25 keV to the final energy of 6 or 9 MeV at the X-ray tar- get and generate X-ray with the dose rate of 8 Gy/min and 30 Gy/min at 1 m after target for electron energy of 6 MeV and 9 MeV respectively. In this paper, we describe the design and optimization of side-coupled RF structure with an oper- ating mode of π/2. The beam dynamic of particle along the RF structure is also included in this paper by using ASTRA code. INTRODUCTION Nowadays, there are more than half a billion container shipments around the world annually [1]. In order to conduct inspections effectively and efficiently, X-ray scanner is used to inspect cargo for nuclear materials, weapons, drugs or trade fraud, and to prevent contraband from entering their countries [2, 3]. Cargo scanning system consists of an elec- tron accelerator, a target of bremsstrahlung radiation gen- eration, and an array of detectors. X-rays reveal the basic shape of the cargo inside a container and recognize materials inside it [3]. The electron accelerators are required for self shielded systems and reasonably compact that can be design as a mobile systems [4]. Recently, RTX develops the compact S-band linac for in- spection of containers [5]. It is primarily aimed to accelerate the electron beam to the prescribed energy and dose rate with the compact structure. With the 25 keV DC electron gun and 5 MW input RF power, we design the compact S-band SW linac using side-coupled structure operating in π/2 mode. This accelerator can accelerate electrons to 9 and/or 6 MeV. This electron energy can give a sufficiently high yield of the X-ray providing an effective depth of up to 30 cm steel penetration [4]. This paper describes the de- ∗ buappika@kaeri.re.kr † yjkim@kaeri.re.kr sign of electron linac with side-coupled structure, and the interaction between electrons and RF fields along the linac. ELECTRON GUN AND MAGNETRON The compact S-band linac consists of a DC electron gun, an accelerating structure based on side-coupled structure, and an RF magnetron. The ALTAIR A102414 electron gun is used and can be applied a gap voltage to 25 kV [6]. It is connected directly to the accelerating structure, so that the first cell wall acts as the anode. The magnetron that we have chosen for the container inspection systems is a MG 6028 fast tuned magnetron made by e2v technologies [7]. It can generate RF power at an RF frequency of 2856 MHz, and it is also tunable over the range of 10 MHz with a speci- fied 0.11 % duty factor. The magnetic field is provided by MG 6030 electromagnet. The RF output power is coupled to the rectangular-shaped waveguide with internal dimensions of 72.14 × 34.04 mm. DESIGN PARAMETERS The compact electron linac as the X-ray source in cargo inspection system usually works in a pulsed mode and needs very stable dose rate X-ray pulses [9]. The X-ray beam is produced by bremsstrahlung radiation when electron beam hits a tungsten target at the end of linac. Normally, the dose rate is in proportion to the duty factor, beam current, and electron energy as given by [8,9] J x = C · η · D · I p · V n acc . (1) Where C is the beam capturing coefficient, η is photon con- version efficiency, n is the electron energy factor, D · I p is the average beam current at gun in unit µA, V acc is the electron energy in MeV, and J x is the dose rate in cGy/min at 1 m after the X-ray target. Our compact S-band linac is designed to be operated in two modes: high-energy mode, HE-mode (9 MeV) and low- energy mode, LE-mode (6 MeV). The desired dose rates at 1 m after tungsten target for LE-mode is 8 Gy/min while the HE-mode requires the output dose rate of 30 Gy/min. To achieve this requirement, the beam current produced by electron gun needs to be calculated first. The parameters for the dose rate calculation of two operating modes are listed in Table 1. If the beam capturing coefficient is 50%, the peak current at the electron gun can be obtained as shown in Fig. 1. TUPOY010 Proceedings of IPAC2016, Busan, Korea ISBN 978-3-95450-147-2 1924 Copyright © 2016 CC-BY-3.0 and by the respective authors 02 Photon Sources and Electron Accelerators A08 Linear Accelerators