CTTS: The Composite Timing and Trigger System of the JET Machine

Paper: 357
Session: B (poster)
Presenter: Terella, Carlo, JET JOINT UNDERTAKING, Abingdon
Keywords: control systems, networking, data acquisition systems, trigger systems

CTTS: The Composite Timing and Trigger System of the JET machine

Carlo Terella

JET Joint Undertaking
Control and Data Acquisition Systems Division
Abingdon, OX 14 3EA, UK


The Joint European Torus (JET) is the major project in the European nuclear
fusion programme. JET operates the largest tokamak device in the world for
studying the magnetic confinement of plasmas in condition close to those
required by a fusion reactor.

The Control and Data Acquisition Systems (CODAS) Division is responsible for
the fully integrated computer-based control, monitoring and data acquisition
system which is essential for the operation of the tokamak itself, auxiliary
equipment and diagnostic devices. CODAS equipment is scattered over an
experimental area of ~ 300 x 300 metres. There are more than 70000 I/O
points. The data collection taken for a single machine pulse exceeds 300

Within CODAS, the Composite Timing and Trigger System (CTTS) is used for
distributing timing marks, real time triggers and other commands throughout
the JET plant. Development began in 1993 having in mind the requirements for
the VME-based systems that JET was starting to deploy in that period. CTTS
had also to be compatible with the large number of pre-existing CAMAC
instrumentation crates, by allowing a fully synchronised operation of mixed
VME and CAMAC without substantial changes to the installed hardware base.

CTTS operates by broadcasting a 2M bit/sec synchronous signal from a
centralised master encoder. The distribution is mainly over a fibre-optic
network, but electrical RS-485 is also locally supported. A dual-level
multiplexing scheme is employed, with two basic time resolutions of 40
microseconds and 1 millisecond. In addition, there is provision for an
addressing mechanism which allows command transmission to a specified

The deployment of CTTS has required the in-house design of several hardware
modules which are largely based on Field Programmable Gate Arrays (Xilinx
40xx series). The modules for use in VME systems also contain an embedded
processor (Eltec SAC-30). Major CTTS components are: the Advanced CTTS Encoder
(ACE), the VME Service Module (VPLS) and the Universal Timer and Trigger
(UTT1) .

CTTS started to operate in January 1994 and evolved in successive stages. At
present more that 80 modules are used in this site-wide system and all JET
control & data acquisition is synchronised either directly or indirectly
through it.