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The Beam Envelope Limit System (BELS) is designed to ensure the CEBAF accelerator does not exceed its operations and safety envelopes of 800kW and 1MW combined beam power.  This is done by measuring the beam energy and current for each endstation and the Beam Switchyard (BSY), combining the results, and taking  appropriate steps to alert the operator well in advance of any shutdown action.  If necessary however, the BELS has the ability to shut off beam.

The risk reduction required of the BELS is more than a machine protection system but less than a full personnel safety system.  As such, the design architecture is specific to the application.  The BELS is also designed as a "install and forget" system whereby it can operate for years without human intervention.  Features such as self-test, triplicated voting sensors, hot standby power supplies, and data integrity checks add to this ability.  

BELS Main Overview Screen

BELS Description Presentation
 

BELS PLCs

CPU

ACO

AVI

DDI

DDO

BEL to EPICS