Results from evaluation of a long pulse pilot data acquisition system on MAST

The limited memory and data rate of CAMAC data acquisition systems is unable to accommodate proposed increases in the MAST plasma duration of up to an order of magnitude. Therefore, some recent pilot exercises have evaluated new technology to replace CAMAC. One of the pilot systems explored the use of modern CompactPCI “intelligent” data acquisition devices. These can operate stand-alone, using an onboard Linux operating system and Ethernet connection without the need for a host computer.The approach to data capture and management was simplified to minimise development time. A simple Linux shell script running on each device was found sufficient to automate the whole acquisition cycle, and this was successfully commissioned in one day. This approach avoided the need for compiled programs but prevented use of the in-house standard shot file archiving library. Instead, each channel's data was written to a separate file as a simple array of samples. This work around was found to offer advantages in terms of flexibility, simplicity and scalability.The experience of handling much higher volumes of acquired data than was practicable with CAMAC has also raised important issues about the scalability of existing data management and analysis systems when each data item contains many mega-samples. The experience and lessons learned will help guide the future direction of data acquisition strategy on MAST.