Distributed Implementation Plan for a Large, Distributed
Accelerator Control System
W. R. DeVan, Oak Ridge National Laboratory, S. A. Lewis, Lawrence Berkeley National Laboratory
D. P. Gurd, Los Alamos National Laboratory, J. Hammonds, Argonne National Laboratory
J. D. Smith, Brookhaven National Laboratory
MS 6338, P.O. Box 2008, Oak Ridge, TN, 37831, USAAbstract•

The proposed Spallation Neutron Source (SNS) is anaccelerator-based 1 – 2 MW pulsed neutron source to bebuilt in Oak Ridge, Tennessee. The facility has five major
sections— a"front end" consisting of a 65 Kev H– ion source
followed by a 2.5 MeV RFQ; a 1 GeV linac; a storage ring;a 1 MW spallation neutron target; and the conventional
facilities to support these machines. These components will
be designed and implemented by five collaborating
institutions: Lawrence Berkeley National Laboratory (frontend); Los Alamos National Laboratory (linac); Brookhaven
National Laboratory (storage ring); Oak Ridge National
Laboratory (neutron source and conventional facilities);and Argonne National Laboratory (instruments). It is
proposed to implement a fully integrated control system for
all aspects of this complex. The integration will be based
upon the widely-used EPICS control system toolkit. This
paper introduces the SNS project, discusses the technicaland organizational issues of planning a large control system
to be developed collaboratively at five different
institutions, and describes approaches being taken toaddress those issues.

•1 Introduction
The Spallation Neutron Source (SNS) will be a 1 MW
(upgradable to 2 MW) accelerator-based facility that
produces pulsed beams of neutrons by bombarding amercury target with intense beams of 1 GeV protons. It isbeing designed primarily to meet the needs of the neutron
scattering community, with operations expected to begin in
2005. Some reference design parameters are given in Table
1.
The SNS is a truly collaborative project, with theparticipating laboratories taking lead roles andresponsibilities for specific sections of the complete
facility. Laboratories were chosen on the basis of theirexpertise in particular technology areas. The leadlaboratory for a given section is responsible for assembling
all necessary resources to accomplish not only the design
but also the fabrication, testing, installation, andcommissioning of its part of the SNS at the Oak Ridge site.
Specific roles and responsibilities are as follows:•ORNL is responsible for overall project management
and coordination; for conventional facilities andconstruction; for maintaining and operating the SNS
once completed; and for managing future upgrades.
•LBNL is responsible for the front end systems,••

including ion source and RFQ.
LANL is responsible for the linac systems and has
coordination responsibility for the controls design.
BNL is responsible for the accumulator ring andassociated transport lines.
ORNL is responsible for the primary target system.
ORNL and ANL are jointly responsible for theexperimental systems (instruments, beamlines,choppers, etc.).
Table 1- Design Parameters

REFERENCE DESIGNPARAMETER
Pulse repetition rate
Peak ion source H- current
Linac length
Linac duty factor
Linac final beam energy
Accumulator ring circumf.
Ring orbit rotation time
Pulse length at ring injection
Kicker gap at ring injection
Ring filling fraction
Number of injected turns
Ring filling time
Protons per pulse on target
Protons per second on target
Time avg. beam current
Beam power on target

INITIAL(1.0 MW)
60 Hz
35 mA493 m
6.2%
1.0 GeV220.7 m841 ns
546 ns295 ns65%1225
1.02 ms
1.04 X1014
6.3 X
1015
1.0 mA
1.0 MWUPGRADE(2.0MW)
70 mA

2.08 X 1014
1.25 X 1016
2.0 mA
2.0 MW

2 Project management″Memoranda of Agreement″ (MOAs) formalize agreements between the SNS Project, represented by ORNL, andeach of the participating laboratories. Each MOA covers
general provisions for laboratory management, cost andoverhead, resource allocations, communication, change
procedures, and reporting requirements. Requirements as tothe technical scope of work are detailed in addenda
specifying how R&D, design, fabrication, installation, andcommissioning activities will be carried out. Control
system tasks, both on a local and global level, will becovered under these MOAs.
The organizational structure of SNS includes a controls

group leader reporting directly to the project director, at thesame level organizationally as the leaders of the othermajor technical areas such as the linac, ring andconventional facilities. This structure recognizes theimportance of the integrated control system to the overall
success of the project. It also places the controls groupleader in position to mediate differences between
laboratories.
Distributed control system tasks have been placed within
the project′s Work Breakdown Structure (WBS) under thetechnical area served. For example, the linac control systemfalls under the the linac’s section of the WBS. However,global control functions have been assigned a WBS sectionof their own. To facilitate management and integration of
the various control subsystems, the control system groupleader will be given authority over the budgets for control
system tasks regardless of where they fall in the WBS.
3 Communication within the collaboration
The heart of communication throughout thecollaboration is the monthly collaboration meeting. Thesemeetings are held at each collaborating laboratory inrotation so that the complete team for each laboratory canattend every few months. Meeting agenda include current
and upcoming activities, action items, project-widedecisions and concurrences, and the status of technicalwork. The control systems working group (see section 4below) frequently meets in conjunction with thesemeetings.
A network server with a file transfer protocol (FTP)
front end was established at the project office at ORNL tocapture electronic data and documents. Personnel at ORNL
can log on directly to the server, and team members atother laboratories can access it via FTP. Direct remote log
in will be available shortly.
An Oracle data base (linked to the SNS Project
Information World Wide Web Page), has been establishedto gather, store, process, and make available project data.
Web page access is password-protected, and the data baseis organized around the project WBS. It is presently being
used to manage accelerator and target physics parameters
and to process project cost estimate information.
Engineering parameters, the project schedule, and a masterequipment data base are near-term expected uses.
Eventually the system will be used for procurement status
reports, work package and earned-value tracking, and otherproject management uses.
The formation of a collaboration to implement SNS is
one of the project’s greatest strengths; it gives the project
access to a wealth of expertise and experience. However, italso presents formidable challenges to the implementationof a facility-wide integrated control system. Traditionally,
the five laboratories have differing approaches.
Geographical separation between laboratories adds anothercomplication. These challenges have been recognized byproject management and efforts are being made to mitigate
them. Specific actions being taken to ensure that SNS will
have a truly integrated control system are discussed in thefollowing sections.

4 SNS control systems working group
The importance of coordinating the controls effort forsuch a widely distributed project was recognized very earlyin the project. A “ Control Systems Working Group” wasappointed with members from each of the collaborating
institutions. This group interacts using telephone
conference calls; and, when appropriate, meets at the sametime as the SNS collaboration meetings described above.
The working group is recognized by SNS management at
the same level as the project leaders for each of the major
sections: front end, linac, ring, neutron source, instruments
and conventional facilities. The working group has two
principle areas of responsibility and activity:• design and implementation of common or ″global″
systems such as network infrastructure, system
software, common applications (e.g. archiving, saveand restore, operator interface), timing andsynchronization subsystem, beam permit and fast
protect systems, control room design, etc; and• establishing standards to be applied to the distributed
control systems which are the responsibility of thevarious sections of the project. These will include
distributed processors, preferred I/O modules,
fieldbuses, interface standards, PLCs, isolation
standards and a uniform device and signal naming
standard.
The working group will not itself design or implement″global″ systems, but instead will specify requirements andcriteria, allocate the work among the collaborators, andoversee its progress. The lead laboratories themselves have
responsibility for implementing the controls required fortheir assigned sections of the facility. This includes I/O
modules and crates, local database development, special
applications and automation, etc.
5 Initial standardization decisions
Integration
One of the first decisions made by the working group wasthat the SNS control system should be completelyintegrated. That is, a single infrastructure and set ofstandards would be applied to all aspects of the facility.
This approach was not entirely obvious. It was certainly
conceivable to have each collaborating team develop asystem of their own, using approaches in use at their homeinstitutions, and then to superimpose an integratingsuperstructure. Moreover, it has not been the usual practicein accelerator laboratories to include either target andexperimental instruments or conventional facilities (powersystems, plant cooling systems, HVAC, etc) in theaccelerator control system infrastructure. Related to thisapproach was agreement on a flat architecture, that is, anarchitecture which minimizes hardware layers. The more
obvious approach of a distributed system, particularly
suited to the SNS situation of distributed development, wasalso agreed. Finally, it was decided that the popular toolkit
approach was appropriate.
EPICS

The inaugural meeting of the contol systems working
group determined that all five of the collaborating
laboratories had operating EPICS1 systems, and that threeof the working group members had themselves direct
experience in the development of EPICS-based systems.
The experience base that this represented, the track recordof EPICS, the recognized need for an open systemstandard, and the general acceptance of EPICS in theaccelerator community quickly lead to a decision to use theEPICS model as the basis for the SNS control system. Thisdecision represents an important first step in the attainmentof an integrated control system. Not only did the project
reach a quick consensus on underlying infrastructure andtoolkit, but that consensus was reached early enough toallow time to prepare standards and examine remaining
integration issues.
Interface
A second important decision was the definition of a
default interface to the control system at the input to a
crate-based system. The transducer or measuring
instrument itself belongs to the system it is in, as does thecabling from the instrument to the I/O module front
panel. Standards will be established for the signals
presented to these modules. Ownership of signal andbreak-out boxes remains to be established.
This approach is consistent with the way in which theinitial SNS cost estimate was developed. The definition
above is only the default interface. It is understood that thisdefinition can be modified on a case-by-case basis.
Probable exceptions are in the beam instrumentation andlow-level RF systems, where sophisticated and custom I/O
modules are likely to be developed and packaged in
specialized form-factors such as VXI. The default interface
is shown in Figure 1.
Controls Network

VXI (RF)
uP

VXIuP

VMEuP

VME
uP

VMEuP

SpecialInterface

Device naming convention
A critical element of the integration strategy is aconsistent, hierarchical, plant-wide naming convention.
From the operational and control system point of view, thenaming convention will provide standard names for devices
and signals. However, these names should also be
integrated with all aspects of the project models, equipment
databases, cable plant databases, etc. The goal is to adopt anaming convention that is unambiguous and clear but at thesame time flexible and easy to use. The names and method
will represent the official names of devices, will be used incontrol system databases, and will appear in archives oflogged data and with error messages. The naming
convention is currently being developed and should beready for use soon.
6 Technical issues
The most interesting technical issue facing the SNS
controls team has to do with timing and synchronization.
The entire accelerator chain, including accelerating
structures, choppers and bunchers, injection and extraction
kickers and data acquisition systems must be synchronizedwith each other and with a large number of independentlyphased neutron choppers. These choppers, a key element inall of the neutron scattering experiments, are large, rapidlyrotating (thousands of rpm) flywheels with slots, which areused to select neutrons of a specific energy from thespectrum emitted by that target. Where there is a singlechopper, protons can be extracted based upon a signal fromthat chopper. Where there are several choppers, thequestion becomes: ″who is the boss?″. The solution to thisissue affects both the rf low-level and power systems, aswell as the timing and synchronization system. A workshop
has been planned to discuss the most appropriate strategy
for SNS.

GPIB
PLC

PLC

Default Interface

RFInstrumentation

Beam
Instrumentation

Precision
ADCs, DACs,
Motor Controllers,
etc...

GPIB
Instruments

Process Control
Instruments(eg Vacuum)

CCDTL System

Linac

Figure 1-Interface to SNS Control System
Notwithstanding the existence of this default interface,
it is the intent of the controls group to develop a seriesof detailed interface definition documents to delineate

1

between subsystem and global functions, and to assure aseamless interface between parts of the control system
executed by different institutions.

Experimental Physics and Industrial Control System. EPICS is
cooperatively developed by many collaborators, primarily at
LANL, ANL and TJNAF. It is now in use at over 80 institutions
worldwide for accelerators, telescopes, detectors, large industrial
plants and a variety of smaller experiments and instruments.

7 Conclusions
A collaboration of five national laboratories is proposing
to construct a 1 MW (upgradable to 2 MW) acceleratorbased pulsed spallation neutron source (SNS) in OakRidge, Tennessee. The control system is being overseen bya working group with members from all participating
institutions, and is recognized organizationally as acomponent equal to each of the accelerators. The control
system design will be integrated over the entire facility, andwill be based upon the commonly used EPICS toolkit.