Safeguards for the World’s Most Powerful Laser

BELLA_laser

Designing the world’s most powerful lasers is no mean feat. But researchers at Lawrence Berkeley National Laboratory are equally proud of a complementary system they’ve created, one that protects humans from the powerful beams.

The Berkeley Lab Laser Accelerator (BELLA) system set the record when it delivered a petawatt of power in a pulse just 40 femtoseconds long at a pulse rate of one hertz in July. If delivering 1015th watts of power in a quadrillionth of a second isn’t impressive enough, BELLA’s size may be.

The system fits into four moderately-sized rooms. Making big strides is not new at LBNL. Researchers there often push state of the art technology, discovering many atomic elements from plutonium in 1940 though seaborgium in 1974.

Generating that level of light makes personal protection extremely important. Laser light exposure could obviously be extremely dangerous. Radiation created by the system, which was developed with help from the French manufacturer Thales, is equally dangerous.

Berkeley Lab experts also turned to outside experts for safety. BELLA’s personnel protection system (PPS) was designed and implemented by Deterministic Systems (DSi) of Walnut Creek, California.

Not surprisingly, that was a safe selection. DSi has a proven track record at the facility in Berkeley, California. DSi implemented a Siemens S7-319F-based radiation personnel protection system in what’s known as Cave A.

That system prevented access to the room when harmful radiation could be generated. It also disabled the source of radiation when the room had not been checked for the absence of people or some failure of the system allowed it to be accessed.

Building upon proven safety technology provides many benefits. One important factor is that personnel already know how to operate and maintain the system. Another is that it’s fairly straightforward to implement.

Bella_automation equipment“The ability to send safety information and control from one room to another using only Ethernet and a set of power wires made the design clean and easily modifiable during the design phase,” says David Di Giorgio, DSi’s lead engineer on the Cave A and BELLA projects. “In the future, this will also allow LBNL to modify the system to continue to fulfill their needs as the needs of the experiments change.”

Control and monitoring of BELLA’s safety system is achieved with a single Siemens S7-319F safety PLC and four remote safety IO racks located in panels residing in the four rooms that comprise BELLA.

Four Siemens touchscreen HMIs are located in the rooms to allow staff to control and monitor the system. One HMI is used for radiation control, functions similarly to the one HMI used for Cave A’s radiation control. The remaining three HMIs are located in the three rooms that comprise BELLA’s three laser safety zones.

Each HMI allows a user to monitor the entire system but, for safety’s sake, only allows the user to control devices located in the laser safety zone the HMI is located in. Indicators on the HMI show the status of all the safety devices in the system. They show not only if the device is on or off, but if it has failed electrically. Separate local and global active alarm lists of both custom safety alarms and automatically generated alarms indicate where the problem is in the system. Global and local alarm logs allow users to not only view the history of alarms but allow notes about major mode changes in the system to be recorded for evaluation.

Although all 4 HMIs function differently, many features are the same on all of them. All four were all coded with a single program that simply requires a different integer to be set before downloading the program to identify which HMI it is and have all the buttons respond accordingly.

The Cave A system was greatly revamped to accommodate the great increase in the number of devices controlled for BELLA as well as a wider variety of devices. BELLA has 14 access doors used to keep people out of areas that they can’t safely enter. Thirteen of these doors are used for laser safety.

Based on the access privileges of a user trying to enter a door, the system allows door with magnetic locks to be unlocked when other doors in the system are closed, producing a man trap so laser light can’t exit from any BELLA Laser Zones enabled for laser light production.

Other doors without mag locks are only monitored. If they are detected open when the Laser Zone they manage is enabled, the PPS will safety shut the laser system down. Shutting the lasers down is achieved through control of 18 laser shutters, three laser beam dumps, and 17 laser power supply enable circuits.

Two large window shutters also block two large picture windows which allow viewing the main laser bay while the laser is not active. If the system detects that either of these is not closed, it safely shuts the lasers down.

One access door leads to the Experimental Cave. This is the only zone where radiations should be produced. The PPS lets personnel into BELLA’s Experimental Cave to investigate the room before allowing a combination of radiation-generating devices to be enabled. Once the PPS ensures that the area has been fully checked, the door to the Experimental Cave is locked and multiple flashing lights and buzzers warn people that the system will soon be enabled for High Energy Mode. After a period of time, High Energy mode is enabled.

Whether High Energy mode is enabled or not, two radiation monitors located outside of the Experimental Cave will shut down the main laser shutter if radiation above a certain level is detected outside the cave.

Lasers always need some protection for safety, and that requirement soars when you’ve got the world’s most powerful laser. The personnel protection system ensures that BELLA can help researchers push science without endangering themselves or others. DSi has a proven track record for safety, based on Siemens automation solutions. The highly specialized safety system for BELLA will help scientists focus on research without worying about safety.

Photo Credit: Lawrence Berkeley Nat’l Lab – Ro

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