The ATLAS detector records proton-proton collisions provided by the Large Hadron Collider (LHC) at CERN. These collisions are recorded every 50 ns (or 20 MHz frequency) leading to data flows of 10 Pb/s (1 Pb is 106 Gb). These data flows are far above the capabilities of today’s conventional computing and network technologies. As a result, a very small fraction of these data (less than 1 in 106 events) can be kept for further analysis in conventional computing farms. In order to achieve this rejection, very fast decisions need to be made on the basis processing of large data volumes in order to decide what data to keep and what data to further transfer. This is accomplished with dedicated devices: high-throughput electronics. The upgraded LHC will provide collisions at rates that will be at least 10 times higher than those of today. This imposes new challenges for which new, more advanced designs are required.
The ATLAS group at Wits is developing a high-throughput electronics laboratory on campus. High-throughput electronics deals with massive transfer of data at very high rates in challenging environments. Very fast decisions need to be exercised in order to select of modify large amounts of data at high rates. These would include environments with high level of radiation, possible event upsets and other factors that may produce data corruption. In these conditions data monitoring, error identification and recovery are tasks that are performed as the data is transferred and formatted for further processing by higher-level units. This laboratory will serve the needs for upgrade of the ATLAS detector and more specifically, the Tile Calorimeter and the Silicon Strip sub-detectors. Both sub-detectors enjoy strong commonalities in the way data is transferred and how the off-detector electronics are designed. Same infrastructure and technical assistance can be used for both sets of projects.
The picture to the right is the current Read out Drivers (ROD) in use.
The pictures below are two views of the proposed layout of the electronics lab. Click here to see more.
A study of Single Event Upsets (SEU) was performed on a commercial pulse-width modulator controller chip for switching power supplies. We performed tests to study the probability of an SEU occurring as a function of incident particle(hadron) energy. A SEU in this context is a radiation induced software error that, due to the nature of the radiation, is random. We discuss the performance of the circuit, and present a solution using external circuitry to effectively eliminate the effect.
After a comprehensive set of radiation tolerance measurements to qualify the new switching power supply for the ATLAS TileCal front-end electronics. We discovered a sensitivity to single event upsets. This was surprising since the previous design had been measured for SEU tolerance and found to be satisfactory, and since we used mostly the same parts in the new design. Our studies over the course of a year identified the cause being a flip flop in the controller chip. Fortunately, we were able to find a fix for this in the design before going into production. We also showed that there is an energy dependence of SEUs in this design. This study underscores the importance of specifying the energy range of interest for SEU tolerance, which will be dependent on the environment.
The full article can be found here.
A poster of the study can be found here.