Design of the High Luminosity Large Hadron Collider Crab Cavity Support System

Jones, Thomas and Burt, Graeme (2020) Design of the High Luminosity Large Hadron Collider Crab Cavity Support System. Masters thesis, Lancaster University.

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Abstract

This thesis describes the development of the High Luminosity Large Hadron Collider (HL-LHC) Crab Cavity Support System, including a preliminary options study, conceptual design and analysis, leading to the detailed design, testing and operation of the complete system. Superconducting Crab Cavities are an essential part of the High Luminosity upgrade of the Large Hadron Collider at CERN. The cavities are used to rotate bunches of hadrons (Protons or Lead ions) prior to collision in order to reduce their crossing angle. This provides a higher probability of individual hadron-hadron interaction which leads to increased scientific output of the machine. The cavities function at 2 Kelvin, and therefore require a controlled cryogenic environment in which to operate. The cavities are powered by radio waves (RF), and the operating RF frequency is controlled by a mechanical tuner. The complete suite of components required for operational cavities is known as a Cryomodule. A critical aspect of cavity performance is how they are supported within the cryomodule. Correct design of these support structures ensures the cavities are aligned to the rest of the machine and that they operate at the RF frequency expected. The structures are required to be as stiff as possible whilst minimising ‘heat leak’ from the outside world at 300 Kelvin to the cavities operating at 2 Kelvin. The support system also needs to allow the cavities to contract as they cool, such that stress is minimised to acceptable levels within each sub-system of the cryomodule. The unique form of the Crab Cavities for LHC together with constraints from the RF input coupler required a novel cavity support system to be developed. The new concept of a cavity ‘Blade’ support produced by the author, in addition to the author’s work on design optimisation of the cavity tuning device, contributed significantly to the success of the Prototype DQW Cryomodule. This was tested with beam on the Super Proton Synchrotron, achieving the world’s first crabbing of a proton bunch.