Storing EPICS process variables in HDF5 files for ITER

Abstract

EPICS (Experimental Physics and Industrial Control System) is the main technology used by ITER for distributed

control of all its systems. EPICS uses an architecture based on a distributed protocol that allows the exchange of

control data (process variables) between different elements and subsystems. In its previous versions, EPICS used

“Channel Access” as the communication protocol, and its control variables had a simple structure that allowed

the exchange of a very limited set of primitive data types. From its version 7, EPICS uses a new “pvAccess”

protocol, and its process variables allow for nested data types that can form very complex data structures which

can contain thousands of fields. From the perspective of data storage, these pvAccess variables and their nested

data types include important challenges both at a functional level and at a performance level.

In this paper, the EPICS storage system that has been implemented for ITER is presented. This system stores the

EPICS process variables in standard HDF5 files that ensure not only the accessibility and maintainability of the

data, but also its full compatibility with the rest of the ITER data storage system.