World’s largest neutrino detector gets a Fujitsu-powered supercomputer upgrade

By Jessica Hall

Top image credit: Kamioka Observatory, ICRR(Institute for Cosmic Ray Research), The University of Tokyo

Fujitsu is a company most associated with cameras and low-cost electronics in the United States, but this is a misperception. The company is a significant manufacturer of semiconductors, with its own SPARC processors, supercomputer designs, and cloud services. Last month, we discussed how Fujitsu had partnered with ARM to add support for ARM’s new vector processing SIMD to upcoming supercomputer architectures. But that’s not the only big iron the Japanese firm has in the proverbial fire. The company announced this week that it’s been hired to build an experiment-analysis system for the Kamioka Observatory’s Super-Kamiokande facility in Tokyo, Japan.

Super-Kamiokande is the world’s largest neutrino detector. Like the LUX dark matter experiment, it’s sunk a kilometer underground in a former mine. While neutrinos interact only weakly with matter, basically all other radiation is barred from passing through the detector by matter: specifically, the thousands and thousands of tons of dense matter surrounding the water tank. That includes cosmic rays, whose spallations could mimic neutrinos.

Neutrinos themselves, however, pass through just fine. When one of them hits the water, they’re capable of traveling faster than the speed of light through that medium (which is slower than the speed of light in a vacuum, so don’t worry). The resultant shockwave acts just like a sonic boom in our atmosphere — right down to the fact that the shape of the cone is related to the speed of the neutrino. It’s called Cherenkov radiation. Most of us think of radioactive things as glowing green, and this might well be because of green radium paint. Cherenkov radiation, however, glows a gentle, terrifying blue.

Cherenkov radiation at the Advanced Test Reactor. By Argonne National Laboratory, via Wikipedia

It’s only even visible as a blue halo because it’s such a high-energy phenomenon. Our blue-sensing cones are less sensitive than the green or red ones. That’s what the photodetectors in the tank at Super-Kamiokande are meant to find: the blue. They form a grid so that they can look for the Cherenkov radiation’s characteristic rings in the pattern of photodetector activation.

In 1987, the Super-K detector caught 19 neutrinos from the nearest supernova blast we’d ever seen — 19 of the billion trillion trillion trillion trillion neutrinos we expect were emitted. It’s since been used to directly confirm the production of solar neutrinos, which it did in almost real time because neutrinos don’t get trapped beneath the surface of the sun for thousands of years like photons. Neutrinos take only the usual eight or so light-minute travel time to get here. The new supercomputer should make it much easier to model the behavior of neutrinos when we do catch them. The system lets the facility exploit much greater processing power for event reconstructions and simulations.

According to Fujitsu, the new cluster will consist of 85 Primergy RX2530 M2 servers, backed up by a high-speed distributed file system and data processing system. The RX2530 M2 isn’t the heaviest hitter on the proverbial block, but these are two-socket systems with support for the latest Intel Xeon E5v4 processors. The cluster will have 2,380 cores total, which works out to 28 cores per server and 14 cores per socket. Fujitsu is promising a SPECint_rate2006 benchmark score of 107,100, or roughly triple that of the existing system. Maximum storage capacity of the system, at least for now, is 9PB. But I’m pretty sure that the best thing about this entire system is that it’s apparently all backed up on tape drives.