• T. Mastorides, J.D. Fox, C.H. Rivetta, D. Van Winkle
  SLAC, Menlo Park, California
• P. Baudrenghien, A.C. Butterworth, J.C. Molendijk
  CERN, Geneva

Radio Frequency (RF) accelerating system noise and non-idealities can have detrimental impact on the LHC performance through longitudinal motion and longitudinal emittance growth. A theoretical formalism has been developed to relate the beam and RF loop dynamics with the bunch length growth [1]. Measurements were conducted at LHC to validate the formalism, determine the performance limiting RF components, and provide the foundation for beam diffusion estimates for higher energies and intensities. A brief summary of these results is presented in this work.

[1] T. Mastorides et. al., "RF system models for the LHC with Application to
Longitudinal Dynamics", prepared for submission to Physical Review ST-AB.

• D. Van Winkle, J.D. Fox, T. Mastorides, C.H. Rivetta
  SLAC, Menlo Park, California
• P. Baudrenghien, A.C. Butterworth, J.C. Molendijk
  CERN, Geneva

The LHC Low Level RF system (LLRF) is a complex multi-loop system used to regulate the superconductive cavity gap voltage as well as to reduce the impedance presented by RF stations to the beam. The RF system can have a profound impact on the stability of the beam; a mis-configured RF system has the potential of causing longitudinal instabilities, beam diffusion and beam loss. To configure the RF station for operation, a set of parameters in the LLRF multi-loop system have to be defined. Initial system commissioning as well as ongoing operation requires a consistent method of computer based remote measurement and model-based design of each RF station feedback system. This paper describes the suite of Matlab tools used for configuring the LHC RF system during the start up in Nov2009-Feb2010. We present a brief overview of the tool, examples of commissioning results, and basics of the model-based design algorithms. This work complements our previous presentation [1], where the algorithms and methodology followed in the tools were described.

[1] D. Van Winkle et. al. 'Feedback Configuration Tools for LHC Low Level RF System,' PAC'09, Vancouver, Canada, May 2009, THZCH03, p. 249 (2009); http://www. JACoW.org.

• L. Arnaudon, P. Baudrenghien, O. Brunner, A.C. Butterworth
  CERN, Geneva

The LHC ACS RF system is composed of 16 superconducting cavities, eight per ring, housed in a total of four cryomodules each containing four cavities. Each cavity is powered by a 300 kW klystron. The ACS RF power control system is based on industrial Programmable Logic Controllers (PLCs), but with additional fast RF interlock protection systems. Operational performance and reliability are described. A full set of user interfaces, both for experts and operators has been developed, with user feedback and maintenance issues as key points. Operational experience with the full RF chain, including the low level system, the beam control, the synchronisation system and optical fibres distribution is presented. Last but not least overall performance and reliability based on experience with beam are reviewed and perspectives for future improvement outlined.