Ultra-high Speed Monte Carlo Computing Techniques Using Field Programmable Gate Arrays

Advancements in parallel and cluster computing have made many complex Monte Carlo simulations possible in the past several years. Unfortunately, cluster computers are large, expensive, and still not fast enough to make Monte Carlo useful for calculations requiring a near real time evaluation period. For Monte Carlo simulations, a small computational unit called a Field Programmable Gate Array (FPGA) is capable of bringing the power of a large cluster computer into any desktop PC. Because an FPGA is capable of executing Monte Carlo simulations with a high degree of parallelism, a simulation run on a large FPGA can be executed at a much higher rate than an equivalent simulation on a modern single processor desktop PC. In this paper we discuss a simple radiation transport problem involving moderate energy photons incident on a 3 dimensional target. By comparing the evaluation speed of this transport problem on an FPGA to the evaluation speed of the same transport problem using standard computing techniques, we show that it is possible to accelerate Monte Carlo computations significantly using field programmable gate arrays. In fact, we have found that our simple photon transport test case can be evaluated about 650 times faster on a large FPGA than it can on a 3.2 Ghz Pentium-4 desktop PC running MCNP5—an acceleration factor that we predict will be largely preserved for many Monte Carlo simulations.