A CONTROL SYSTEM FOR THE DESY ACCELERATOR CHAINS
Rüdiger Schmitz, DESY, Hamburg, Germany

Abstract
DESY has nine accelerators in operation. The reliableand operator-friendly control of these accelerators isnecessary for the successful operation of HERA, DORISand PETRA in order to provide a good experimental
environment for the four experiments at HERA and thenumerous users of synchrotron light at DORIS andPETRA. As already reported in PCaPAC’96 PETRA wasupgraded to a PC-based control system in spring 1996.
Proven concepts and improved programs have been usedto renew the control system of storage ring DORIS in the
shutdown of 1997. A step by step migration of controls
from the old system to the PC-based one is under way andis carried out during normal machine operation of thelepton and proton preaccelerators. In the following anoverview of the underlying concepts of the homogeneouscontrol system will be given.

1 INTRODUCTION
All of DESY’s nine accelerators are operated by asmall shift crew from one central control room. The preaccelerators (see Table 1) LINAC II, PIA and DESY II
provide the electrons or positrons for the storage ringsDORIS III and PETRA II. LINAC III and DESY III
provide protons for PETRA II. PETRA II acts as a preaccelerator for electrons and positrons for HERA e, ofprotons for HERA p and as a synchrotron radiation source
made up of electrons or positrons.
Table 1: The Preaccelerators
Max.
Accelerator
Type of particle
energyLINAC II
LINAC IIIPIA
DESY IIDESY IIIPETRA II-+e /ep- +e /e (Accumulator)- +e /ep- +e /ep

450 MeV
50 MeV
450 MeV
8 GeV
7.5 GeV
12 GeV40 GeV

Length /circumference
70 m
32 m29 m
293 m
317 m
2304 m

According to the needs of HERA or DORIS III (seeTable 2) the appropriate accelerator chain has to be set upto fill HERA p with protons, HERA e with electrons andDORIS III with positrons. When PETRA II is not needed
as preaccelerator for HERA, it is filled with electrons orpositrons to produce synchrotron radiation.

Four experiments have been set up at HERA: TheZEUS and H1 experiments study the collisions of the 920
GeV protons of HERA p with the 27 GeV electrons ofHERA e in the interaction regions. The HERA-Bexperiment investigates CP-violation with an internal
target in HERA p while the HERMES experiment investigates nucleon spin with polarized electrons of HERA e.
PETRA II supports an undulator beamline when operating
for synchrotron radiation users. DORIS III services 10beamlines from wigglers or undulators and 30 fromdipoles.
Table 2: Parameters of HERA and DORIS IIIAccelerator
Type of particleMax.
Circumenergy
ference- +27 GeV 6336 m
HERA ee /ep
920 GeV 6336 m
HERA pDORIS IIIp
4.5 GeV289 m
Figure 1 below is a schematic summary of the accelerator chains, showing particle flow from their creation inthe LINACs through to their destinations DORIS III,PETRA II, HERA e or HERA p.

e-/e+p

LINAC II

LINAC III50
MeV

PIADESY
III

450
MeV
DESY
II

7.5
GeV
PETRA
II

4.5
GeV

7.0
GeV

DORIS
III

40
GeV

12
GeV

HERA pHERA e920
GeV

27
GeV

Figure 1: Schematic representation of the acceleratorchains.

••

2 CONTROL OF OPERATIONSControlling all the accelerators described above involves a lot of devices differing in number and type. The
following table gives an idea of what we are dealing with:
Table 3: Main Accelerator Devices
Device TypeUnits(approximately)
Main magnet power supplies
600
Correction coils power supplies
1400
RF systems
230
Pulsed magnets power supplies
70
Vacuum3000
Beam position monitors
800
General beam measurement300
instrumentation
Air conditioning, water cooling500
Most of these devices are interfaced to the PCs by
1means of the inhouse field bus SEDAC [1][2]. A bus isconnected to a PC via the standard parallel port using theSEDPC-Controller [3], this assembly is called a SEDACLine. In total there are some 140 lines connecting 1100
crates, each crate housing up to 11 interface modules.
About 300 PCs control these devices. Information ismade available to the operators in the central control room
on about seventy 20" color monitors. Sitting at the PCs in
the control room the operators can actively control theabove-named devices and are therefore at all times able tosupervise the accelerator chains. Software programs areconstantly being (re-)developed in order to ensure optimalfunctioning of the whole process.

3 CONTROL SYSTEM SEGMENTS
Closing all the accelerators down at any one time is unthinkable. This is one reason why it is impossible to build
a single unsegmented control system for all the accelerators. Following good engineering practice the control
system is split into control system segments:••••

between 10 and 50 PCs in one segment
PCs of one segment are connected via 10Mbit/s
thin ethernet technology without a router, building a2LAN .
actual device information available in the LANintersegment network communication available
autonomous operation of a segment
similar configuration and design

HERA p obeys other criteria but can be seen in thiscontext as a segment. There are contributions about its
system TINE [4] in this workshop.

4 DESIGN OF CONTROL SYSTEMSEGMENTS
There are some building blocks which we use in allsegments. The PCs in their different roles are one building
block. With the exception of the File Servers they run MS
Windows 3.11, the programs are written in Visual Basic
3. The File Servers run Novell Netware 4.11. We
distinguish four kinds of PCs:
• Device Servers with access to the interface modules,
mainly SEDAC.
• Console Servers for the operator interface• LAN Servers for common facilities in a LAN• File Servers
Standardized program packages for common tasks in allsegments are another building block. Device access via
SEDAC and the network communication are otherimportant blocks.
The LINAC III control system as an example of how
the building blocks have been used is described in a paperin these proceedings [5].
Figure 2: Schematic view of a Control System Segment

4.1 Device ServerLANs

Name
IpLan
IeLan
DoLan
PeLan
HeLan
TINE

Table 4: Control System Segments
Accelerators controlled
Number of PCs
LINAC III, DESY III
30
LINAC II, PIA, DESY II
35
DORIS III and beam-lines40
PETRA II and beamlines
50
HERA e and beamlines
45HERA p
100

These segments are formed according to the following
criteria:• minimum interference between segments• minimum data exchange
1

Serial Data Acquisition and Control system

ConsolesRouterFileserver

Device PCs
Archive

One Device Server is employed for each device type ofan accelerator. There are normally at least 3 programs
running on a Device Server:• an update program reading the present status of thedevices and sending them as broadcast packets intothe LAN.

2Local Area Network••a command execution program connected to aconsole programa program servicing the File Operator program
running at the console.

4.2 Console Server
Console Server PCs display the status of the devices bysimply ‘tuning’ their packet filter to the identification ofbroadcast packets they are interested in. Additional
display programs add no extra load to the network orDevice Servers.
A lot of devices are controlled by the standard Device
Manager Program [6] which allows the devices to operate
in all their functions. Simultaneous operations on several
devices - spread over many Device Servers - is done withthe File Operator Program [7]. To some extent theconsoles are automatically configured according to theoperation mode of the accelerator. The operator will
always find the same information at the same place.

4.3 LAN Server
The Radio PC generates the ‘cycle message’[8] for theLAN. This broadcast packet contains general accelerator
parameters. It is send every second and there is one foreach accelerator in the segment. The Device Servers listen
to the ‘cycle message’ and start their update programs onreception.
One ALARM Server [9] handles error- and alarmmessages generated by the Device Servers or the ALARM
PC itself.
The Archive Server(s) collect and retrieve selected dataout of the broadcast packets of the Device Servers.

4.4 File Server
The File Servers act as a filestore and as a router. Eachsegment has two File Servers, the Control File Server andan Auxiliary File Server. The Control File Server is therepository of all programs (including the operating systemfor the PCs) as well as all data to operate the accelerators.
The Auxiliary File Server stores files which are notessential for the operation; but they are meant for trouble
shooting, offline analysis of runs etc.
The routing capabilities provide connectivity to othersegments but prohibit broadcasts to be flooded into allother segments.
Although a segment can operate autonomously, i.e.
disconnected from the other segments, the File Servers ofall LANs as well as all other network resources are
3objects of one common NDS Database.

4.5 Standardized Program Packages

For some device types there are programs which arevery similar in all segments. Examples are the vacuum
devices and magnet power supplies. The vacuum example
is presented in these proceedings [10].
The number of programs in one segment to operate theaccelerators is between some 100 and 300.

4.6 Network Communication
Network access is provided by inhouse developmentsof custom controls which add peer to peer datagram- andconnection oriented communication functionality to the
Visual Basic 3 language. These controls allow usage ofNovell’s IPX- as well as the TCP/IP protocol.
IPX broadcasts play an important role. All status
information of all devices is available to all PCs in theLAN with an update rate of 1Hz by this means. Because
all Device Servers start their update cycle triggered by the‘cycle message’ the LAN usage does not vary much fromsecond to second and may be called the ‘fingerprint’ ofthe LAN.
The normal load is slightly less the worst case load.
Average utilisation varies over the LANs from 7% to25%, nearly half of this is contributed by broadcasts.
Some information is useful and desired in other LANs,
Device Servers then send multiple packets with different
destination LAN addresses.

5 GLOBAL TASKS
Some tasks are independent of an accelerator orcommon to all accelerators. PCs serving these tasks arelocated in the LANs connecting the Control File Servers
or the Auxiliary File Servers.
These tasks are:• Synchronize all Radio Servers in the LANs by one
Main Radio.
• Provide Operator Consoles to operate vacuum
devices, magnet power supplies of all accelerators
as well as to control the access of persons into theaccelerators.
• Give access to the DESY Intranet and to TINE
control system segment• Supply the data of the Archive Servers and theAuxiliary File Servers for a Web Server to publish
them for further analysis.

6 TIME SCALE AND STATUS
We started with the PC project in 1994 with a learning
phase. At that days the control system was based on about460 NORD -minicomputers. Today we still have 10
running in mission critical jobs, which we will haveremoved at the end of this year.

The Device Manager and the File Operator programs
have been already mentioned above.
43Netware Directory Services © Novell

Computers of NORSK DATA company, Norway, ceased toexist.

The milestones of our control system project are listed
in the table below:
Table 5: Milestones in Control System ProjectYearMilestone
1994 Development phase
Start of PC project,
1996 Development and installation phase
PETRA upgraded to PC-based Control SystemSegment
Part of HERA e Control System Segment
realized
1997 Development, installation and operation phase
DORIS II upgraded
1998
LINAC III upgradedparts of LINAC II, PIA, DESY II, DESY III
upgraded
HERA e upgrade finished
HERA p (TINE) completed
1999 End of era of NORD-minicomputers..

7 CONCLUSION
In the last five years our experience with the threephases - development, installation and operation - of our
new control system project allows us to draw thefollowing conclusions:• The commercial standard PCs of the 95 vintage orlater are powerful and reliable enough forprofessional use in a larger computer network
designed to control accelerators of different sizes
and complexities.
• Integration of new hardware into a running control
system is possible without major problems.
• The available commercial software tools are spectacularly powerful at an extremely low price• Upgrading inhouse developed applications to thelatest operating system environment was possible
without undue effort.
• Given the wide-spread use of PCs one can assume
knowledge of the basics and only specialist
explanations are required.
• One major disadvantage of the new software tools
arises from their immense variety of possibilities
they offer. The art of writing a suitable program foraccelerator control is to use as little as possible ofwhat is offered by the software - without using toolittle.
• The concept described allowed a smooth upgradingfrom the NORD computer controlled system to thePC based one in a period of approximately six years.
It was not even a replacement, but a redesign adding
a lot of new features we could not even dream about
in the NORD era.

•A great uniformity has been achieved, this eases thejob of the operators when switching from one
accelerator to another and of course the developers
job too.

8 REFERENCES[1] H. Frese and G. Hochweller, “The Serial Data
Acquisition System at PETRA”, IEEE Nucl. Sci. 26,1979, pp. 3384.
[2] M.Werner,“SEDAC (Ein Überblick)”, DESY HERA
96-05 Beschleuniger Betriebsseminar 1996, May
1996,pp 621, in german.
[3] R. Stadtmüller, “SedPc - Interfacing SEDAC andPCs”, Proceedings PCaPAC’96, DESY, 1997[4] P. Duval, “TINE: An Integrated Control System forHERA”, these proceedings.
[5] A. Labudda , “The Proton Linac Control as Part ofthe DESY Accelerator Chains Control System”,
these proceedings[6] J. Wilgen, “The Standardized Device-Manager”,
Proceedings PCaPAC’96, DESY, 1997[7] J. Wilgen, “Filedriven Machine Operation atPETRA”, Proceedings PCaPAC’96, DESY, 1997
[8] U. Glöer, “Multiprogram-Synchronization viaLAN”, Proceedings PCaPAC’96, DESY, 1997
[9] M. Werner, “Administration of Alarms at PETRA”,
Proceedings PCaPAC’96, DESY, 1997[10] W. Gerhardt, “Vacuum Control Systems Upgradeand Analysis Features at DESY”, these proceedings