To make the light sources compact and energy efficient an energy recovery Superconducting RF LINAC can be used. However introduction of the energy recovery stage may lead to appearance of beam break-up instabilities. We suggest using a dual-axis, asymmetric cavity insuring full overlapping of operating partial modes only. In this case start currents of HOMs are higher, allowing high average currents to be driven without loss.
One of the solutions to generate high-power beam of electromagnetic radiation either in THz or X-ray ranges, is to use high average current electron beam. Such beams can be generated by a Superconducting RF LINAC and to make the whole system compact, energy efficient it is attractive to add the energy recovery. However, such an addition may lead to appearance of the beam break-up instabilities if high current electron beam is generated and driven through the system. Here we suggest using a dual-axis, asymmetric superconducting cavity for a single turn ERL (arXiv:1509.03675v1). Both, accelerating and decelerating, sections of this ERL consist of the same number of cells and tuned insuring overlap of operating partial modes only, forming the cavity operating eigenmode.
In this work we discuss a single turn SCRF ERL system in which the electron beam transported through the system once. The electrons are accelerated inside the acceleration section, while in the deceleration section most of the electrons energy is extracted and guided through a resonant coupler back into the acceleration section. Both section consist of a same number of individual cells, which are slightly detuned insuring that only the operating partial modes of both sections are fully overlapping (in frequency domain) creating a single operating mode of the cavity. The tuning of the cells is achieved by slight variation of cells’ parameters leading to partial modes’ transverse structure conservation (on a specific axis) and separation of the high order partial modes in the frequency domain leading to increase of the cavity high order eigenmodes start currents. The two sections are linked by a resonant coupler and there is still field leakage from one section to another but as it will be shown, the effect is relatively small. As a result, the possibility for the multi-pass-regenerative BBU feedback mechanism to be established is reduced, HOMs start currents are increased and high (above 1A) average currents can be driven through the system without loss. The theoretical predictions will be compared with the preliminary experimental data and results will be discussed.
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