Nuclear tests at warp speed

Asci White: Size of two basketball courts

BBC Click Online's David Jamieson is granted special permission to visit the high security US facility which houses one of the world's fastest supercomputers.

The nuclear bomb is the most awesome manmade destructive force there is, but these most powerful of weapons are no longer atmospherically tested.

The testing of the US's nuclear weapons now takes place inside one of the world's fastest computers, IBM's Asci White.

"We have to have the capability to simulate the explosion of a nuclear warhead," said David Novak, deputy associate director of the Asci programme, at the Lawrence Livermore National Laboratory, just outside of San Francisco. "That's very challenging in its own right.

"It's very high temperature, very high density, very short periods of time, strong shocks travelling around - all the things that make a simulation difficult occur here."

Fast simulations

The Asci White is the size of two basketball courts. Over 8,000 processors linked together by a high-speed network give it a peak operating speed of over 12 trillion calculations per second.

Novak: Aims to build world's fastest, most powerful simulation capability

It has six terabytes of memory, and 160 terabytes of disk space, enough to hold six times the entire book collection of the Library of Congress.

"On the hardware side, its goal is to build the fastest, most powerful simulation capability in the world," said Mr Novak.

"On the software side, the idea is to develop large-scale codes that will run as efficiently on 10,000 processors as if they were running on one computer."

Simulations run on Asci White can be visualised on a massive display screen in a nearby conference room.

As well as modelling explosions, the computer is used for studying the way nuclear weapons change composition as the stockpile of warheads ages.

"Not only are they exposed to harsh environments and atmospheres, but they're also radioactive, so the radioactive decay of the material causes the material composition to change," said Mr Novak.

"It also causes interaction between the various elementary particles that are emitted in the decay to interact with other materials, and change the performance."

Security precautions

At all times throughout the site, there are reminders that this is a classified facility.

Even the windows to the vault can, at the flick of a switch, be made opaque when classified operations are under way.

But Asci White is also used for peaceful purposes. Major US universities work on the machine to research the way stars explode, simulate the performance of jet engines and rocket motors, and test how materials react under intense shocks.

As powerful as Asci White is, some of the life science computing challenges on the near horizon will demand even faster machines.

White itself will no doubt be left in the dust, as the race for more computing speed continues.