Inside the planet’s biggest laser
At California’s National Ignition Facility (NIF), 192 lasers are poised and ready to unleash four million joules of energy on their target: a pea-sized pellet of frozen hydrogen. Making up the world’s highest energy laser system, their goal is to create the intense pressures needed to initiate nuclear fusion – the reaction that powers the Sun. On Earth, fusion could one day provide an almost limitless source of carbon-free energy.
To spark a fusion reaction, hydrogen isotopes deuterium and tritium must be forced together. This means mimicking the temperatures and pressures at the Sun’s core. NIF’s ultraviolet laser beams travel through a system of amplifiers 1,500 metres (4,920 feet) long, ramping up their energy by a factor of a quadrillion. The beams are focused on the tiny gold casing surrounding the fuel pellet. The hot metal releases a pulse of X-rays, which in turn compress the fuel, sending its temperature soaring to 100 million degrees Celsius (180 million degrees Fahrenheit) while the pressure skyrockets to 100 billion times that of Earth’s atmosphere. As the deuterium and tritium are forced together they fuse, releasing the energy locked away in their atomic nuclei.
Currently, powering NIF’s lasers takes up far more energy than the fusion reaction they produce releases. NIF’s goal is to break even – a milestone known as ignition – which will pave the way for the first commercial reactors.