Beam Dynamics of CBETA and its potential applications to the UK-XFEL

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EMMA (Electron Machine with Many Applications) was the world's first non-scaling FFAG and was built and operated at Daresbury Laboratory. EMMA successfully demonstrated a new type of acceleration as well as a new type of beam transport [1]. EMMA used the ALICE (Accelerators and Lasers In Combined Experiments) as an injector. ALICE was an energy recovery linac (ERL) accelerator.A new project is currently underway at Cornell University in the US, in collaboration with Brookhaven National Laboratory (BNL) [2]. This project combines the non-scaling FFAG concept demonstrated on EMMA together with the idea of energy recovery into one accelerator called CBETA (Cornell and Brookhaven ERL Test Accelerator). CBETA is a prototype for the electron transport part of an electron-ion collider (EIC) and it uses recirculation to increase the electron beam energy by a factor of four in permanent, Halbach-type, high acceptance, quadrupoles and combined function magnets. Because the recirculation uses the same non-scaling FFAG style transport that was used on EMMA, all the energy trajectory fit in the same arc.This novel style of recirculation leads to some extremely interesting options for the next phases that an accelerator like CBETA could have. In particular, if the four different energies can easily be separated and the bunch quality preserved, then it should be possible to run four different energies, and hence output wavelengths, free electron lasers (FELs). Furthermore, the four different FELs would be perfectly synchronised thus facilitating pump-probe experiments with biological samples etc. This may require the addition of elements such as sextupoles or higher order magnets with the purpose of ameliorating the beam quality so as to ensure lasing of the bunch.The PhD student would be expected to explore the various possibilities for improving the output bunch as well as forming a central part, as far as a possible CBETA upgrade is concerned, of the wider collaboration outlined below*. The student would also be expected to have an active role in the commissioning of the first phase of CBETA.