IT’S a fittingly bright California morning when Félicie Albert meets me. We’re outside the National Ignition Facility (NIF), the building that houses the world’s most powerful laser. The intimidating force of armed guards is just part of the scenery when you’re using such potent devices to study the extreme states of matter found in the molten hearts of planets and the nuclear furnaces of stars. “It’s a hot, dense matter – which is a very tricky state,” says Albert. “It’s not condensed and cold, it’s not quite a plasma… it’s really hard to describe.”
Inside, she shows me the . NIF’s cavernous interior, the size of three football fields, is an organised tangle of amplifiers, optics and tubes that shape, smooth and focus 192 beams of light onto a peppercorn-sized fuel capsule. The laser, which switched on in 2009, can generate and release a 500-trillion-watt pulse in just 20 billionths of a second, creating temperatures of more than 100 million °C and pressures exceeding 100 billion atmospheres.
The capsule, containing hydrogen isotopes, sits in a spherical target chamber (pictured, below). Its science-fiction looks bagged it the role of the warp core of the USS Enterprise in Star Trek: Into Darkness. When the laser fires, Albert tells me, the building reverberates with a loud, rumbling hum. And its collision with the fuel capsule generates so much radiation – mostly X-rays – that anyone standing near the target chamber would be in trouble. “You wouldn’t vaporise, but you’d have some serious health problems,” she says.
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The laser is always fired in the presence of a supervising physicist who diagnoses problems and aborts the shot if necessary – a role Albert has played many times. NIF has yet to achieve the “ignition” of its name by sparking a fusion reaction that releases so much nuclear energy it becomes self-sustaining. If it does, it would be a key step to developing clean, sustainable nuclear energy.
When Albert is not at NIF, she is often at the , which, like NIF, is on the campus of Lawrence Livermore National Laboratory. We head over there to see a laser called . After stepping through an automatic shoe-duster – laser optics don’t like dirt – we enter the Titan War Room, where scientists sit near tables strewn with “brain food” like gummy bears, Cheez-Its and Mountain Dew, planning a calibration shot.
Albert’s speciality is harnessing high-energy radiation to take pictures of what’s going on at the atomic level in extreme states of matter, and she’s busy getting Titan up to the task. Unlike the NIF laser, which needs almost 24 hours to reset after a single shot, Titan can fire multiple pulses in a day, including tandem shots fired in quick succession.
Albert is using a technique called laser wakefield acceleration to coax Titan into generating betatron X-rays. For this, you fire a laser pulse into a jet of helium gas to create a plasma in which electrons are accelerated over very short distances to near light-speed. At this speed, they emit a super-short burst of X-rays. But Titan’s fastest pulse, despite taking just 1 trillionth of a second, is still too sluggish: the ideal duration for creating betatron X-rays is less than a twentieth of that. “I’m trying to find out if I can make Titan produce betatron X-ray emissions with slightly longer laser pulses,” Albert says.
Achieving this would allow her to carry out “pump-probe” experiments. In these, the first of a pair of laser pulses make those special X-rays, which are in turn used to take snapshots of the high-energy exotic matter created by the second pulse. Think of it as the ultimate in high-speed photography. “This is the timescale of phenomena that happen at the atomic level,” Albert says. Laser wakefield acceleration also holds the promise of shrinking particle accelerators from mammoth machines to desktop devices.
As we talk, an automated voice comes over the tannoy. “Charging for laser shot in Titan target area. Leave the laser bay and the Titan target area. Firing Titan shot in 3… 2… 1.” We wait a bit, then cover ourselves in clean-room garb and I finally get to meet Titan. Unlike NIF, it fits inside a normal-sized room, and the scientists working on it can configure it themselves, rather than relying on a team of mechanics. “Physically, it can be tough, but I prefer hands-on work,” Albert says. And to make the most of her allotted time with the lasers, she often works 18-hour days for weeks at a time, regularly crawling around inside or underneath them. But then, when you’re dealing with some of the most powerful lasers in the world, intense focus is essential.
This article appeared in print under the headline “I illuminate the insides of stars”
