Control of Total Voltage in the Large Distributed RF System of LEP

Dr. Edmond Ciapala, L. Arnaudon
CERN

The LEP RF system is made up of a large number of independent RF units situated near the interaction points around the ring. These units can have different available RF voltages and they may be inactive or unable to provide full voltage at any given time. The original RF voltage control system was based on local RF unit voltage function generators pre-loaded with individual tables for energy ramping. This was replaced this year by a more flexible global RF voltage control system. A central controller in the main control room has direct access to the units over the LEP TDM system via multiplexers and local serial links. It continuously checks the state of all the units and adjusts their voltages to maintain the desired total voltage under all conditions. This voltage is distributed between the individual unit voltages to reduce the adverse effects of RF voltage asymmetry around the machine as far as possible . The central controller is a VME system with 68040 CPU and real time multitasking operating system. Event driven communication handlers allow fast reliable concurrent data communication with the remote units. The RF unit low level RF G64 equipment controllers use a VME 68030 CPU to achieve the necessary response time and reliability.