By James Schultz

Jefferson Laboratory's safety-first tradition was enhanced in May with installation of the Lab's first-ever beam-envelope limit devices. The multi-hall system measures beam power at three locations, in Halls A and C and the beam switchyard electron-beam dump. Monitor-managers average a trio of measurements to ensure that JLab doesn't exceed an overall, maximum safety envelope of one million watts, or one megawatt.

"We've been upgrading the accelerator to give us higher and higher energies. For the first time in JLab history, we have the potential to approach one million watts," explains Kelly Mahoney, group leader for safety systems. "In our operating agreement with DOE we have a speed limit of sorts, roughly 800,000 watts. This system will guarantee we stay within those limits."

This latest addition complements the Lab's two other major safety systems: personnel safety and machine protection. In terms of people protection, JLab standards are robust, and include radiation, microwave-energy and electrocution safeguards.

Automatic equipment shutdowns occur whenever a sophisticated network of software and hardware detects a potential hazard. The Lab's cryogenics systems also pose a possible threat to human health: escape of helium gas could replace breathable oxygen in certain areas. Sensors therefore constantly monitor oxygen content at each of the end stations, in the accelerator tunnel and within the Free Electron Laser (FEL) complex.

Machine-protection mechanisms are an integral part of the Labs safety systems and are designed to protect equipment from inadvertent contact with the electron beam. Mis-steered beam can burn a hole through beam-line components within 50 millionths of a second. The Lab's Fast Shutdown system (FSD), is intended to detect mis-steered beam and to enable users to quickly terminate beam when needed.

Bolstering JLab safety is technological innovation in the form of programmable logic controllers, or PLCs. The Lab was the first national laboratory to use PLCs to oversee personnel safety status on a continuous basis. Systemwide, 15 PLCs monitor approximately 2,500 accelerator-related components, ensuring that inputs are consistent with outputs. If not, devices shut down and power is turned off.

"When compared to other laboratories, the safety culture at JLab is noticeably better. It has to do with line management," says Robert May, radiation control group head in the Accelerator Division. "Safety professionals are taken seriously here. There's an opportunity for dialogue regarding productivity and the need for a safe environment."

JLab Expertise In Demand
Putting a relentless emphasis on safety does come with a price. False trips shutdowns due to equipment or operator error occur on average once a week. Improved training, more reliable software and better controls are all in the offing to attempt to reduce such occurrences.

The Safety Systems Group includes Kelly Mahoney, group leader (sitting), and (left to right) Henry Robertson, Jim Coleman, John Jefferson and Roger Housman. They monitor and control the beam-envelope limit system, the machine protection system and the personnel safety system from their console in the Machine Control Center.

Much of the group's safety practices are derived from those used in high risk industries such as chemical processing and medical accelerators. These industries have had to solve some of the same problems faced by the Laboratory. "We use industry experience as a template to ensure that our safety systems follow best-industry practice," says Mahoney. "We also work with national and international standards committees for programmable safety systems to ensure that the needs of the accelerator community are represented."

The Lab's reputation for safety has led to consulting contracts with other facilities in the U.S. and abroad. JLab safety specialists are working with colleagues at the Spallation Neutron Source at Oak Ridge National Laboratory in Tennessee to review safety system designs and make suggestions for system implementation. Other clients include accelerators pending or under construction at a laboratory in Greece, and at Michigan State and Indiana University.

Improvements to the Lab's safety systems are ongoing. By January 2000, safety systems group leader Mahoney expects that each end station will be able to terminate beam without shutting off the beam systemwide, as is now the case. An automated machine-status message system is also under development. Personal computers will dial up the JLab accelerator public address system, which in turn will patch through to the Lab's public address system with news and updates.

Preparations are also underway to ensure that the Lab's protection systems will be equipped to handle the planned CEBAF upgrade to 12 GeV and the scheduled FEL upgrade to 20 kilowatts. Both upgrades will place higher demands on the safety systems' reaction time and reliability.

"In the safety improvement business, every time we turn around it's a new piece of hardware," Mahoney says. "It's a pretty demanding systems integration task: frustrating at first, but satisfying in the end. Its what keeps us on the leading edge of accelerator safety."

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Updated June 27, 2003