Measured Performance of the LHC Collimators Low Level Control System
A.Masi*, R.Losito, S.Redaelli (CERN)
The LHC will be protected against uncontrolled beam losses by the collimation system, which is made of more than 100 collimators each equipped with two moveable jaws of different materials. The nominal LHC stored beam energy is 362 MJ, therefore a great care has been taken in optimizing the performance of the low level control system. This controls the position and angle of the jaws with an accuracy of a few microns, and monitors the actual position against errors with respect to the desired position at a rate of up to 100 Hz, triggering a fast beam dump in case of problems. We have chosen stepping motors to have an accurate open loop positioning, while LVDTs and resolvers monitor the axes. The National Instruments PXI platform has been adopted as real-time low level hardware. In this paper we describe the control architecture, the low level custom solution implemented on the FPGA and we provide a detailed performance review of the entire system. In particular we present the excellent synchronization of several hundred motors over a profile of about 30 minutes simulating the nominal energy ramp of the LHC and show that the position error is well below the specified 20 microns.