Taylan Sipahi

Frequency Domain Simulations of Co-linear X-band Energy Booster (CXEB) RF Cavity Structures and Passive RF Components with ACE3P

Due to their higher intrinsic shunt impedance X-band accelerating structures offer significant gradients with relatively modest input powers, and this can lead to more compact light sources. At the Colorado State University Accelerator Laboratory (CSUAL) [1] we would like to adapt this technology to our 1.3-GHz, L-band accelerator system using a passively driven 11.7 GHz traveling wave X-band configuration that capitalizes on the high shunt impedances achievable in X-band accelerating structures in order to increase our overall beam energy in a manner that does not require investment in an expensive, custom, high-power X-band klystron system. Here we provide the comparisons of the important parameters achieved using SUPERFISH and OMEGA3P for our Co-linear X-band Energy Booster (XCEB) system that will allow us to achieve our goal of reaching the maximum practical net potential across the X-band accelerating structures while driven solely by the beam from the L-band system. GENERAL CONCEPT The CSU Accelerator Facility will initially focus on the generation of long-wavelength, free-electron lasers pulses, as well as the development of electron-beam components and peripherals for free-electron lasers and other light sources. It will also serve as a test bed for particle and laser beam research and development. One of the most important parts of this accelerator is the linac that was constructed by the Los Alamos National Laboratory for the University of Twente TEU-FEL Project. In addition to the capabilities of this linac we would like to further increase the electron beam energy without additional significant investments. Our idea is to utilize the electron beam from the L-Band RF gun as a drive source for a passive X-band linac structure thus allowing us to increase the beam energy by using the Lband power together with the inherent high shunt impedance of the X-band structure [2]. Figure 1 presents the general layout of our proposed CXEB system. We started with the power extraction mechanism using the beam from the L-band linac passing through the power extraction cavity (PEC). This power is then delivered to the X-band main accelerating cavity (MAC) structures. Then, when a bunch periodically passes through the whole system we can achieve significantly higher beam energies. This is done by simple switching of the photocathode drive laser pulses and shifting the phase onto the cathode such that it puts the bunch into the accelerating phase of all accelerator structures. Finally, we described the achievable photon wavelength with our existing high-energy electron beam using an undulator magnet system for a compact FEL system at CSU. The details of our XCEB will be presented in our paper that is to be published in the following weeks. X-BAND POWER EXTRACTION CAVITY (PEC) In our previous studies [3,4] we described the general idea that can provide us some additional electron beam energy via an inexpensive and compact way using our proposed X-band Co-linear energy booster (XCEB) at CSU. We have presented the electromagnetic field mapping studies using SUPERFISH, the Maxwell solver of LANL’s Group code [5]. In this concept we used two different types of X-band traveling wave (TW) RF cavity structures. The first one is designed as a power extraction cavity (PEC) that can provide us the needed power via our L-band system. The second one, the main accelerating cavity (MAC), is designed for lower group velocity for efficient RF power deposition to the electron beam in the cavity. In SUPERFISH, for the specified normalization method and structure length ( ), the average axial electric field E0. stored energy ( ), and the dissipated power ( ) on the metal surfaces with surface resistance ( ), can be calculated. From these quantities, SUPERFISH reports the cavity quality factor ( ) and shunt impedance per meter ( ), that can allow us to calculate the achievable power at the end of the X-band PEC. Figure 1: The case of four accelerating structures for the system under study MOPMW036 Proceedings of IPAC2016, Busan, Korea ISBN 978-3-95450-147-2 480 C op yr ig ht