Laser fusion, with a difference

Laser Megajoule (LMJ), a €3 billion research facility completed late last year near France9s Atlantic coast, is a dead ringer for the world9s leading laser fusion lab, the National Ignition Facility (NIF) in California. The similarities are no coincidence. Both sites were designed for the same purpose—to train scores of powerful laser beams on a single target, subjecting it, for an instant, to outlandish extremes of temperature and pressure. The two labs collaborated extensively and, like NIF9s, LMJ9s primary purpose is military: replicating nuclear explosions in miniature so that weapons scientists can ensure their bombs will detonate if needed without having to test them. The French facility, like its U.S. counterpart, will also pursue a sideline in inertial fusion energy research: crushing capsules of hydrogen isotopes with laser pulses so that the isotopes fuse into helium, releasing vast stores of energy that might one day be harnessed in a power plant. But some key design differences may give LMJ a better chance of achieving fusion energy than NIF has.