New Power Supplies Will Keep NIF on Target

The team that keeps the power flowing to NIF’s lasers is taking steps to insure that the facility will have the energy it needs for target shots well into the future.

To keep firing its lasers at a rate of more than a shot per day, NIF must have a robust and reliable power conditioning system, or PCS. The PCS provides nearly 400 million joules (MJ) of electrical energy to energize the giant flashlamps that power the large glass amplifiers that boost NIF’s laser beams to a total infrared energy of more than four MJ.

The NIF PCS is the world’s most energetic capacitor bank. Each of its 192 modules stores two MJ of energy over a period of about 60 seconds in banks of high-voltage capacitors before releasing it to the flashlamps in a 400-microsecond burst (see Power Conditioning System).

Each capacitor module is charged by two power supplies known as cap chargers, each of which sends electricity to the capacitors at a rate of about 15 kilojoules per second. "We have basically 400 power supplies that have to work during a shot," said Pulsed Power Group Leader and PCS Systems Manager Bruno Le Galloudec. "No power supplies, there’s no shot, because we can’t charge the capacitors."

The system’s original power supplies, however, are nearing obsolescence and often require time-consuming and costly repairs—only some of which can be done in the facility. The original vendor is no longer in the power-supply business; a few years ago the PCS Team was able to locate a boutique power-supply repair company, but the owner plans to retire in a few years.

"And so we had a problem on our hands," Le Galloudec said; "400 power supplies that need to be working and no one to take care of them."

In search of a long-term solution, Le Galloudec’s team identified an experienced commercial supplier of high-voltage capacitor charging power supplies to provide replacement units for NIF’s main energy storage modules.

"We identified one big power supply, a 30-kilojoule (per second), 50-kilowatt power supply, and this will be a drop-in replacement" for the existing power supplies as they need to be replaced, Le Galloudec said. Pulsed-power engineer Glen James worked with an industry partner to modify an off-the-shelf design to fit NIF’s needs.

Each new power supply will replace two of the original units, which run in parallel in master-to-slave mode. Usually only one of the two supplies fails, so when the pair is replaced with a new supply the remaining original unit can be retained as a spare.

Le Galloudec said the replacements ultimately could cut the system’s maintenance time in half. "Instead of having to take care of two power supplies we take care of one," he said, "and that will also improve the reliability of the system because you have fewer parts" to maintain, as well as fewer cable connections.

The team worked with the industry partner and NIF software engineer Nattee (Nat) Chotinun to ensure that the new power supply would work with NIF’s Integrated Computer Control System, which governs every aspect of a NIF shot from start to finish. "When we install a power supply like this in the facility we’re going to have to do a database change," Le Galloudec said. "The power supply has to be seen by the system as if it’s a normal power supply. Nat is developing the patch which will allow us to use this new type of supply and this particular model."

"Bruno’s whole operating team has been really helpful in test-driving these units," James added. "Almost everyone participated at one time or another." Le Galloudec said the PCS operators—Dave Schwedler, Allen Harkey, Mike Mcintosh, Daisy Acosta-Lech, Davis Taylor, Miguel Munguia, Joe Foley, Norris Lao, and Huy Nghiem—have been coming to the PCS lab between NIF system shots to run shots with the new prototypes and prepare them for installation.

"We now have the latest drop-in replacement that we’re ready to evaluate," said James."We have just begun testing the second revision of the prototype. So far the prototype is doing quite well."