Accelerator Control System and VME Front End Computer
Yongbin Leng, Guicheng Wang, Yuanji Pei
NSRL, University of Science and Technology of China
P.O. Box 6022, Hefei, Anhui 230029, P. R. China

Abstract
An idea for the new control system of the NSRL 800
MeV storage ring is given. The system, based on the″Standard model″ architecture, consists of the operator
layer, communication layer, I/O control layer and device
interface layer. As the main part of the ring control system,
the main magnet power supply control system is discussedin detail.

OperatorLayer

ManagerLayerOperatorStationFile/PrintServerOperator
StationCalculating
Serverethernet

1 Introduction
The accelerator control system architecture development
has followed the advances in computer technology. The
reduction in price of powerful computers have motivated
new approaches to distributed control system design. As aresult of this new technological support, new designs canbe implemented very quickly. Acceptence of the newstandard is world wide.
A description of the new NSRL control system which
incorporates the universely accepted standards, for
distributed processing is given. The implementation of themain magnet power supply control subsystem and its VMEfront-end computers are discussed in detail.

UNIX HOSTIO Controller
Layer

DeviceInterface
Layer

CAN Bus

Front-end
ComputerDeviceInterface

DeviceInterfaceEquipment

Equipment

Figure 1. New Control System Architecture

2 Control system architecture
2.1 Control system function
The new control system should be a reliable, stable,extensible and fully distributed. It must be capable of: (1)providing a friendly graphical user interface, operating all
the facilities as machines which have separate missions andcontrolling devices in the central control room;(2)controlling and monitoring all equipment of the accelerator
including various magnet power supplies, RF cavities,
vacuum units and beam diagnostic instruments; (3) provide
the tools for analysing the running status of the machineand provide tools for calculating the machine parameters;(4) warning and protecting the equipment when accidents
happen or equipment fails, protecting the people fromradiation.
2.2 Hardware architecture
The control system is based on the ″Standard Model″
architecture of a fully distributed processing system.
Logically the system is composed of four levels from top tobottom, which are: the operator layer, the manager layer,
the I/O controller layer, and the device interface layer asshown in Figure 1.
The operator layer includes a workstation under UNIXrunning display manager routines, and several X terminals

providing a friendly graphical user interface as operator
console. The manager layer includes two powerfulworkstations under UNIX acting as file server andcalculating server. The I/O controller layer includes several
front-end computers based on VME system which consistof CPU boards and a variety of interface cards. Dataacquisition and open or closed loop control functions of theequipment are handled by FECs. The device interface layer
includes a number of single board computers with interface
circuits. Signal conditioning, level matching, and A/D orD/A conversion are completed on this layer.
The operator layer, the manager layer and the I/O
controller layer are connected through ethernet withTCP/IP. Between the I/O controller layer and the device
interface layer, the field bus is adopted as data
communication path.
2.3 Software architecture
The EPICS was adopted as the development tool tocreate the control software. EPICS which is cooperatively
developed by the Los Alamos National Laboratory and theArgonne National Laboratory, provides a wide range offunctionality, rapid application development andmodification, and extensibility at all levels to meet thedemands of experimental physics.

The software architecture is composed of the Operator
Interface layer, the Input/Output controller layer, and thecommunication protocol layer. The OPI layer includes theDisplay Manager, Alarm Handler, Archiver and otherconfiguring tools. UNIX is adopted as the operating system
for this layer. The IOC layer includes a Distributed
Database, Device Drivers and other applications, andVxWorks realtime operation is adopted on this layer. The
communication protocol layer is Channel Access based on
TCP/IP which provides the communication between thevarious subsystems of EPICS.
The main part of the control software can be created
rapidly with EPICS and other application development
tools. So the major software effort was concentrated in thewriting of the I/O device support routines. The
communication routine between I/O controllers and Device
Interfaces, and other special applications, for example theramping routine.
3 M.M.P.S control subsystem
Injection into the ring is at the linac beam energy of 200
MeV. After injection the beam energy in the ring is ramped
up to the operating energy, which is called ramping
operation. In this operation the magnet currents have totrack each other in order to keep the ring lattice unchanged.
The primary function of the main magnet power supply
control system is to assure the synchronization andaccuracy of the magnet currents in the ramping operation.
Because the ramping operation is a realtime process, thissubsystem will be established according to the EPICS
pattern. The Distributed Database loaded into the FEC will
provide supervision and control for all signals of power
supplies. The control current waveforms of power supplies
are generated by software. In order to lower theinterference of external noise, all remote signals must be
converted into digital signals, so AD conversion ofreadback signals and DA conversion of control signals
must be done on the device controller layer.
This subsystem architecture is shown in Figure 2.
3.1 UNIX Host
The UNIX host is a Sun workstation or any otherworkstation under UNIX. Display Manager, AlarmManager, Archiver, Channel Access and other managerial
tools are running here.

(DDB) providing local control, employs the ramping
routine generating the control current waveform data andsending them to power supply interface through CAN BUS
in ramping operation, receives readback data from DCCTinterfaces and status data from power supply interfaces andtransmits them to the OPI in a event driven.
3.4 Power supply interface
The Power Supply Interface is a single board computerwith a CAN interface and A/D, D/A converter. It supports
the D/A conversions of control signals, the A/D
conversions of readback signals, the level conversionbetween TTL and power supply signals, and signals
condition.
3.5 DCCT interface
The DCCT Interface is a single board computer with a
CAN interface and A/D converter. It supports the A/D
conversion of readback data from DCCT, the level
conversion between TTL and DCCT signals, and signal
conditioning.

workstation

UNIX HostCAN BusM. M. P. S.
ConsoleX terminal

M. M. P. S.
FEC

P. S.
Interface

P. S.

DCCT

DCCT
Interface

P. S.
Interface

P. S.

DCCT

DCCTInterface

P. S.
Interface

P. S.

DCCT

DCCT
Interface.
.
.
.
. Architecture
Figure 2. M. M. P.. S. Subsystem

3.2 M.M.P.S. console
The M.M.P.S. Console is an X terminal or an PC with X
terminal server software, which employs the M.M.P.S.
controlling screen, provides the graphical user interface,
accepts commands or parameters input by the operator, anddisplays the status of the power supplies and the readback
data of DCCT, respectively.
3.3 M.M.P.S. FEC
The Front End Computer is a VME based computer with aethernet interface, CAN BUS interface and other function
boards. The M.M.P.S. FEC runs the Distributed Database

4 Key technology
The reformed NSRL control system will adopt mature
innovative technology, and during the process ofdevelopment, we need to master this key technology suchas the distributed database technology, graphical user interface technology, network communication technology, thetransplanting and improvement of EPICS, composition anddevelopment of front-end VME system, development ofdevice interfaces, compilation of I/O device support
routines, compilation of ramping routines and etc. Amongthem, the last four are closely related to the establishment

of the M.M.P.S. control subsystem, so they shall be mainly
dealt with.
5 Outlook
The reform of the control system of our accelerator will
involve the reform of every subsystem, so we chose to startto establish an experimental line controlling the main
magnet power supply, and then spread to the reform of thewhole control system with this model. The control system
will generally realize the integration with international
technology after the reform, the mutual cooperation amonglaboratories will benefit from this. All functional subsystem
realize sharing of data, archiving of working parametersand experimental data. With their open structure, allsubsystems such as linac, transport line and experimentstations will gradually transit into and finally form a
relatively developed computer control system.

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