Designing and Developing Components for Accelerator Control Systems with NI Based Tools

Author(s):
Fausto Distante - SIDEA

Industry:
Research

Products:
Data Acquisition, Modular Instruments, PXI/CompactPCI, Reconfigurable I/O, LabVIEW, Digital I/O

The Challenge:
About 90% of the successes in tumour treatments are due to the efficacy of loco-regional treatments: surgery and radiotherapy. The use of accelerated particle beams (hadrontherapy) is a step forward in the historical development of more targeted and effective cancer treatments which better spare healthy tissues. Relying on the above mentioned rationale, hadrontherapy has been practiced in many centres since the early 1950’s. These centres were located at the beginning in research facilities built for fundamental physics and since the 1990’s also in hospital-based facilities conceived with the objectives of treating patients. The accelerating machine is either a cyclotron or a synchrotron and the dimensions of such machines may reach a diameter of about 25 meters. In this paper we will present and discuss the overall architecture and the most interesting components of the control system of one of these machines (CNAO) which is currently in advanced construction in Italy. Our company, which has a long time through expertise in the area of the control and data acquisition systems for physics experiments, has been assigned in 2005 the international tender for the development of the whole control system of the facility. We have chosen for the most relevant parts of the control system National Instruments and LabVIEW based platforms as the basic building blocks along with our design expertise.

The Solution:
The Italian National Center for Oncological Hadrontherapy (CNAO) is a new centre under construction in Pavia, about 30 kilometres South-West of Milan. It will be devoted to the treatment of deep seated tumours with light ion beams (proton, carbon ions and others) and to clinical and radiobiological research. The centre is manly financed by the Italian Ministry of Health. The founders of CNAO were five major hospitals, seated in Milan and Pavia, and the TERA Foundation. Since 2003, INFN (the Italian National Institute of Nuclear Physics) is Institutional Participant of CNAO, together with the Universities of Milan and Pavia, the Polytechnic of Milan and the Town of Pavia. The realisation of CNAO started in September 2002 and at present it is foreseen to start the operation of the machine and to begin the preparation to treatments in fall 2007. CNAO is a plant that supplies particle beams for medical treatments of tumours. To adapt the cure to the particular conformation of the tumour during each treatment the physical conditions of the beam changes many times. A cycle is the period of time the machine takes to produce a beam having a planned energy, deliver the dose to the tumour and go back to the initial condition. Thus, depending on the physical characteristics of the beam, the equipments that constitutes the accelerator complex has to be set into different running conditions. A running condition lasts, in general terms, the length of a single cycle.

The main task of the control system of CNAO is to load each equipment of the facility with the relevant settings depending on the planned cycles to be executed and to monitor the achievement of the planned results. The operators can supervise the behaviour of the plant by selecting relevant information that are displayed on the operator consoles.
Due to the fact that many settings have to be assigned in a very strict time window, depending on the cycle evolution, the control system will also supply different time depending signals needed to the plant for triggering activities.

The conceptual architecture of the control system foresees that it is divided into subsystems. Subsystems contain parts that are logically or physically linked or belong to a single part of the facility. Each subsystem is further decomposed into equipment components. They are entities that represent the type of a recognisable logical or physical part of the accelerator such as a power supply, a beam source, a diagnostic measurement system. Equipment components contain instances that are actually the recognisable logical or physical part of the accelerator. Thus the equipment component named Power Supply shall represent the behaviour of all the power supplies present in the plant, whereas an instance of the equipment component Power Supply shall describe a particular power supply installed in a well defined place and having specific characteristics. The characteristics of equipment components instances are described and accessed through properties and operations. Each single equipment component can be accessed by the external world through a HMI called Virtual Instrument that presents to the user all the related properties and operations. Subsystems as a whole can supply general services to perform operations or set or acquire information belonging to the specific subsystem as a single entity. Process and procedures are built to achieve the goals the control system as a whole is intended for.

The architecture of the control system may be represented as a concentric layer model. The main layers are:

• The Presentation & Operation Layer;
• The Concentrator & Data Manager Layer;
• The Equipment Server Layer (ESL);
• The Equipment Electronics Layer (EEL).

During the 2006 our work has been mainly focused on the last two layers. The main features of these layers may be summarized as follows.

The Equipment Server Layer is composed of two processes families. The first comprises the RT processes to transfer to and from the field the relevant data synchronised with predefined time dependent signals distributed by a central unit (Master Timing). The second family includes the processes allowing direct transfer of data between the field and the Concentrator & Data Manager Layer.

The Equipment Electronics Layer deals with the specific interfaces of the field devices. Particular crates, with incorporated microprocessor, handle all the related processes while the relevant data are downloaded in the cards or in ancillary mass storage during offline sessions depending on the level of security and quality assurance requested for the specific device. The real time processes executing in this layer shall be normally triggered by timing events generated and distributed by the Master Timing.

Actually the EEL is foreseen to include nearly 300 RT CPUs whose operations must be synchronized by a distributed digital timing facility with a resolution ranging from 10 µs (fast system) to 100 µs (slow system).

The RT CPUs are mainly National Instruments NI PXI based systems (with NI data acquisition and instrument boards) while the remaining part are NI CompactRIO systems. The Real-Time operating system used for all the systems is NI LabVIEW Real-Time.
Nearly 100 NI PXI-7811 FPGA boards have been used to develop custom designed digital pattern generators to drive the different equipments in the different running conditions.

The digital timing facility with the 100 µs resolution has been developed as a specialized message passing Ethernet application running under NI LabVIEW Real-Time. The fastest timing has been developed as a custom designed optical network with specialized boards in cPCI format. The software that drives the whole timing subsystem has been developed under NI LabVIEW Real-Time.

The first prototype of the control system is in use since January 2007 to allow the tests on the first components of the CNAO accelerator facility.

Author Information:
For more information on this Case Study, contact:
Fausto Distante
SIDEA
eng@sidea.it

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