The Proton LINAC Control
as Part of the DESY Accelerator Chains Control SystemA. Labudda, DESY, Hamburg, Germany

The control system of the DESY 50 MeV Proton
LINAC has been replaced by a PC-based distributed
system. Applications of radio frequency control for theAlvarez structure and the quadrupoles, inside as well as
the beam transport and monitoring system, are reported.
The DESY accelerator chains control system [1] – mainly
written in Visual Basic – is composed of small andflexible modules which can be linked into one of the threelevels for servers, services and operation. Most of theLINAC control applications were taken from thesemodules with no or slight modifications.

1 INTRODUCTION
The first step in accelerating protons for the 920 GeV
superconducting storage ring HERA is done in a linear
accelerator called LINAC III. The protons, in the form ofH¯ ions, are generated in a magnetron source and areaccelerated by several RF cavities (radio frequency
quadrupol RFQ and Alvarez structure). The beam is
focused by quadrupol magnets most of which are runningin a pulsed mode and bent by permanently powered dipol
magnets. Intensity and position of the beam are controlled
at different positions down the beam line. The momentum
for a small amount of the particles is measured after−stripping the two electrons of the H -ions. Thus turned
into protons these particles are counterbended by a dipol
magnet and turned towards a multiwire monitor (harp).
All this equipment – complemented by controls for
vacuum, temperature and beam burst triggering – ishandled by a LAN linked PC system, which is inaccordance with the DESY standard of distributed PC
control for particle accelerators.
The basic features of this PC based system are• Employ one PC for each group of devices as aserver for one line of a „Serial Data Acquisition
and Control bus“ (SEDAC [2]) dealing with several
crates of device control units.
• All server and console PCs needed for one
accelerator are gathered in one LAN segment.
Broadcast messages play an important part in data
communication and are send to all PCs in thesegment.
• The server PCs regularly send the equipment statusof their devices into the LAN-Segment bybroadcast (”Updating”).
• The server PCs listen to the LAN for equipment

control commands (”Operating”, ”File Handling”).
Client applications are running on consol PCs.
The consol programs listen to the LAN and display
the actual status and recent monitoring.
• The consol programs also accept commands
entered by an operator and communicate them tothe respective server (operating).
• Program coding is done in Visual Basic supported
by C based functions for Visual Basic extension.
Except HERA-P all of DESYs current particle
accelerators are controlled or will be controlled by an
instance of this control system for particle accelerators.
The LINAC III instance of the DESY accelerators
control system has been designed and implemented since
fall 1997. The project is almost done for all the components.
The magnetron source is still under control of a Norsk
Data mini computer.
••

Magnetron Source
andhigh frequency source
RebuncherRadio frequency
quadrupol(RFQ)
Radio frequency
cavities
Alvarez structure

Abstract

Debuncher
Dipol

Measure thebeam position
by a multiwire
monitor.

Dipol
Strip the electrons of the
H ions and inject theprotons into the proton
synchrotron DESY III.

Figure 1: Schematic picture of the LINAC III

2 TOPICS OF LINAC III DEVICEGROUPS.
2.1 Radio
The radio [3] application is the control systems heartbeat. With a frequency of 1 Hz the application sends adata packet, called the „Cycle Message“, into the LAN.
The Cycle Message contains the primary description of
the accelerators state, like energy, current and the unique
number of the particular Cycle Message.. By receiving theCycle Message, every device server is doing the „update
job“, i.e. read out of all of its devices present data andbroadcast this data into the LAN.

2.2 File Operator
The file operator [4] is used to store and reload
satisfactory device settings for a group of devices or all
devices of an accelerator. The file operator is separated in
two parts, the client and server. The client is the operators
user interface. By the client the operator is able to manage
the file list and send synchronised commands to the server.
The LINAC III file operator is the same for any of
DESYs accelerators, except HERA.

2.3 Multiwire Monitor
The harps consist of 32 wires for each monitor. Beamparticles hitting the wires are discharged. The charges
were gathered and amplified to create digital profiles ofthe beams x- and y-axis. The beam profiles are used tocalculate the LINACs emmitance and energy. Thesoftware’s job is to read beam profile by the harps analog
digital converter. Another job of the software is to readand set the harps position inside the beamline.

2.4 Monitoring
The LINAC III has got some groups of monitors to
inspect the LINAC’s state. The different monitors observe
the device temperature, magnetic fields, the beam current
and the beam position. Every device server has to read out
the monitors, triggered by the radio software. Additionallythe beam position monitor has to move the monitors foil
into or out of the beamline.

2.5 Correction Magnet
The correction magnets [5] of the LINAC III are
situated between the Alvarez structure and DESY III tocontrol the beam. The software was taken from the former
developed instances of magnet control. Because of thisreason the magnets device manager [5] and the connection
to file operating is the same as any of DESYs accelerators.

2.6 Pulsed Magnets
There are 84 magnets to focus and steer the beam in theMedium Energy Beam Transportline and in the Alvarez

tanks. The magnets are running in a pulsed mode becauseof the limited cooling capacity inside the Alvarez tanks.
The programs by which they are operated are developed
from those used for the main magnets. As most functionsof the pulsed magnets are the same as of the othermagnets, there is no difference in the program structure.
Slight alterations had to be done considering different
functionality (e.g. delays) and different modules
controlling the power supplies.

2.7 Main Magnets in the High Energy BeamTransportline
In the High Energy Beam Transportline there are 18
quadrupoles and dipoles for focusing and beam steering.
They are used by direct current power supplies. As themodels controlling them are the same as in other DESY
accelerators, the programs used there could be used here
without alteration, with a different setup data only. The
program set consists of a standard device manager [6] (aconsole program, by which each single magnet can beoperated), a device server program which performs theseoperations, a device server program triggered by the radio
which collects all magnet data and sends them into theLAN by broadcast and another device server program
which serves the file operator.

2.8 RF and Cavity Tuning Control
There are now six cavities in LINAC III. The most important ones are the RFQ and three Alvarez tanks. They
do the work of accelerating and partly focusing the beam.
A rebuncher cavity between RFQ and the first tank aswell as a debuncher between the last tank and DESY III
only optimises the beam with respect to the input
requirements of the next accelerator. The cavities aretuned to a RF frequency f0 = 202.56 MHz. They are reso–3
nating at a duty cycle of typically 0.25*10 . Radio
frequency fine tuning of the cavities is done by motor
driven piston tuners.
On the consoles there are service programs forswitching the RF transmitters, phase and amplitude modulations and cavity tuning. Control items for theseprocedures are placed on a block-diagram-like background picture relating status and error flags, setting andmonitoring values to their respective hardware in a simpleway.

2.9 Oscilloscope
Every accelerator has between one and four oscilloscopes for signal diagnostics by the operator. There is one
oscilloscope in LINAC III. Signalmultiplexers are used tosee different signals on the scopes display. The whole setup of multiplexers and scopes can be saved and loaded byoperator commands. The scopes curve data is read out
every second for further signal diagnostics by the software.
The same software is also used for other accelerator

controls. Oscilloscopes have not been supported by theformer “Norsk Data mini computer control system”.

2.10 Vacuum
The LINAC III vacuum is separated in 6 sections.
Between two sections a valve is installed. Every vacuum
section has got vacuum measuring devices and vacuumpumps. Because of the huge area from normal air pressure
to vacuum two different types of vacuum measuring
devices and vacuum pumps are used.
Three device server, used for getter pumps, turbo
pumps and valves, get all vacuum data. The server
triggered by the radio to read the present data of thedevices. The data is send into the LAN by broadcast. They
can be displayed by the servers dedicated console
applications. The console applications display the devices
data with an optional history of one hour.
A more detailed description of Vacuum Control Systems Upgrade and Analysis Features is presented in theseproceedings [7].

2.11 Beam Chopper
The beam chopper is used to cut the roundish signal ofthe beam source. The result is a pulse of the beam withsharp edges and well defined timings. Another job of thebeam chopper is to optimise the beam length with respect
to the input requirements of the next accelerator DESY III.
The beam chopper is controlled by the PC. All of theadjustments are taken every second and can be set by theoperator using the beam choppers device manager or theFile operator. The beam chopper software will be used tocontrol the electron LINAC too.

3 CONCLUSION
The new LINAC III control system was built to replace
the previous Norsk Data mini computer system. Becauseof the small and flexible application modules the upgrade
was done in a short time. Applications with no device
access like the radio could be copied directly from otheracclerators control systems. If the same devices had beenused at an upgraded acelerator control system, the source
could be copied directly, too. Only the setup data had tobe created new. Finaly the expenditure of porting anapplication from one accelerator control system to anotherdepends on the compatibility of the devices. The range of
spended time is from hours up to 6 months, e.g. thesoftware of the scopes was copied from PETRA, the database was created in one hour. The LINACs RF is a uniquedevice. It took six months to rewrite the software.

4 REFERENCES[1] R. Schmitz , “ A Control System for the DESY
Accelerator Chains ”, these proceedings[2] H. Frese and G. Hochweller, “The Serial Data
Acquisition System at PETRA”, IEEE Nucl. Sci. 26,1979, pp. 3384.
[3] U. Glöer, “Multiprogram-Synchronization via LAN”,
Proceedings PCaPAC’96, DESY, 1997[4] J. Wilgen, “File Driven Machine Operation atPETRA”, Proceedings PCaPAC’96, DESY, 1997[5] J. Maas, “Orbit Correction at PETRA and HERA e”,
Proceedings PCaPAC’96, DESY, 1997
[6] W. Gerhardt, “Vacuum Control Systems Upgrade andAnalysis Features at DESY”, these proceedings[7] J. Wilgen, “The Standardized Device-Manager”,
Proceedings PCaPAC’96, DESY, 1997