Data-Taking Network for COMET Phase-I

An experiment to search for a μ-e conversion named COMET is being constructed at J-PARC. The experiment will be carried out using a two-stage approach comprising of Phase-I and Phase-II. The data-taking system of Phase-I was developed based on common network technology. The data-taking system consisted of two types of networks. One is a front-end network. This network bundles around 15 front-end devices that have a 1-Gb optical network port. A front-end computer collects the data from the devices via its network. The other is a back-end network that collects all event fragments from the front-end computers using a 10-Gb connection. We used a low-cost 1-Gb/10-Gb optical network switch for the front-end network. We did not use network switches for the back-end network. The event-building PC has ten 10-Gb network ports, and the front-end PCs are directly connected to the event-building PC with 10-Gb optical network devices. We evaluated the data-taking performance with an event-building using this configuration. The event-building throughput of the front-end network achieved 337 MiB/s. The event-building throughput of the back-end networks achieved 1.2 GiB/s. This means that we can reduce the cost of the data-taking network by using this structure without deteriorating the performance. Moreover, we evaluated the writing speed of the local storage RAID disk system connected to a back-end PC using an SAS interface and a long-distance network copy from the experiment location to permanent storage.