Operation of Multiple Accelerating Structures in an X-Band High-Gradient Test Stand

Millar, Lee and Burt, Graeme and Wuensch, Walter (2021) Operation of Multiple Accelerating Structures in an X-Band High-Gradient Test Stand. PhD thesis, Lancaster University.

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Abstract

This thesis describes the operation of two high-gradient accelerating structures in a high-power klystron based X-band test stand simultaneously and the phenomena observed in such an arrangement. The LLRF (Low Level Radio Frequency), interlock, and control systems of the test stand are modified to accommodate a dual structure arrangement and the designs are presented. Following this, numerical methods and CST Microwave Studio’s PIC solver are used to model the interactions which may manifest in a multi-structure high-gradient arrangement, namely the signal propagation during breakdown and the behaviour of field emitted current in high-gradient structures. Several implications for modern high-gradient facilities are then provided. In the upgraded test stand the high-gradient accelerating structures were conditioned simultaneously to gradients of approximately 90MV/m and 45MV/m respectively and the aforementioned simulations were validated experimentally. Finally, the development of a Monte Carlo model of high-gradient conditioning and operation is presented and compared with existing test stand data. The model is then used to investigate the effects of modifying the conditioning algorithm currently in use in CERN’s X-band test stands.