Motion control design of a PMSM and FPGA implementation for the Beam Wire Scanner at CERN

The Large Hadron Collider (LHC) is the world’s largest and most powerful particle collider, and the largest single machine in the world. It is designed to collide proton beams with a collision energy of 14 TeV in the center of mass and an unprecedented luminosity of 1034cm􀀀2s􀀀1. The strong dependency of the interaction rate on the beam sizes motivates the requirement of an accurate measurement of the beam profiles. The Beam Wire Scanner (BWS) belongs to the category of interceptive beam transverse profile measurement instruments. It consists in an electro-mechanical device which measures the transversal beam density profile by moving a thin wire through the beam intermittently. The growing focus on this instrument and the resulting increase in its use during routine accelerator operation has initiated an upgrade of the existing designs. In order to enable the device to scan particle bunches in the LCH at collision energy, a crossing speed of 20 m=s was included in the specifications for the new design. To provide the necessary torque to the system, a frameless Permanent Magnet Synchronous Motor (PMSM) was selected. Several constraints and specifications, including the variable length of the power cable and the necessary minimisation of the vibrations in the wire, make the control of the BWS actuator a challenging task in terms of robustness and performance. This thesis work concerns the design and the implementation of a digital motion controller for this new improved generation of beam wire scanners. The design process starts with the creation of a dynamic model for the hardware, including the mechanical devices, the various installed sensors and the power supply. Then, a Field Oriented Control architecture is proposed and dimensioned to match the design requirements. Several improvements, such as variable structure regulators, Kalman filtering and feedforward actions are included to increase the efficiency and the robustness of the system. After a preliminary testing phase performed on a prototyping platform in order to validate the design, the firmware for the motion controller was finally implemented on a FPGA board in VHDL language. The application of the proposed control methods during the experimental sessions allowed the new generation of the beam wire scanner to work in nominal conditions for the first time.