Availability and Reliability Issues for ILC Page: 1 of 4
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AVAILABILITY AND RELIABILITY ISSUES FOR ILC*
T. Himelo, J. Nelson, N. Phinney, SLAC, Menlo Park, CA 94025, USA
M. Ross, FNAL, Batavia, IL 60510, U.S.A.
The International Linear Collider (ILC) will be the
largest most complicated accelerator ever built. For this
reason extensive work is being done early in the design
phase to ensure that it will be reliable enough. This
includes gathering failure mode data from existing
accelerators and simulating the failures and repair times
of the ILC. This simulation has been written in a general
fashion using MATLAB and could be used for other
accelerators. Results from the simulation tool have been
used in making some of the major ILC design decisions
and an unavailability budget has been developed.
The International Linear Collider as presently planned
will have over 20 km of superconducting linear
accelerator, two 6 km circumference damping rings (DR),
a complex Beam Delivery System to focus beams down
to 5 nm, a polarized electron source and an undulator
based positron source. Taken altogether, this will be one
of the most complex machines ever built. It has over an
order of magnitude more parts than most accelerators.
A typical high energy physics (HEP) accelerator
currently has an availability of 75-85%. With so many
more components that could potentially fail, the ILC
availability would be unacceptably low unless significant
attention is paid to component reliability.
Because of this concern, high availability design work
started at an early stage of the ILC project. Much of this
work depends on an availability simulation developed for
the purpose. Results from this simulation have been used
to make major design decisions for the ILC and also to
develop an unavailability budget for the components and
Many accelerators have estimated their availabilities
during the design phase with a spreadsheet. SNS and APT
are among the examples examined before embarking on
the simulation. These spreadsheets used formulas to
combine the availabilities of components to get the
availability of the whole. There are also commercially
available reliability software packages to perform such
calculations. The approach taken here was to write a
simulation which could allow several complexities to be
handled that would have been nearly impossible in a
spreadsheet and quite difficult in the commercial software
packages. These complexities include the recovery and
tuning time needed after a downtime, the complex
redundancies built into the ILC design, the way in which
accelerator physics experiments (Machine Development
or MD) can be done when only part of the accelerator is
*Work supported by the U.S. Department of Energy under contract
#email: thimel at slac.stanford.edu
available, and the way in which many devices are
typically repaired during an access by a limited number of
people. By writing a simulation tailored to the task, it was
possible to incorporate knowledge derived from the
authors' accumulated decades of experience in running
The simulation, named availSim, takes as input a list of
components, their quantities, mean time between failure
(MTBF), mean time to repair (MTTR), and the effect of
their failure. It then simulates the failure and repair of
components while tracking the integrated luminosity. The
components include items identified as potential sources
of failure from experience with existing facilities, such as
klystrons, modulators, magnets, magnet power supplies,
power supply controllers, vacuum pumps, pump power
supplies, movers, diagnostics, water pumps, etc.
The rest of this paper covers the features of the
simulation, some quantitative information mined from
previous accelerators and used as input to the simulation,
some implementation details, results, and conclusions,
FEATURES INCLUDED IN AVAILSIM
Many features are included in the simulation to make it
as realistic as possible.
Each component fails at a random time with an
exponential distribution determined by its MTBF. When a
component fails, the accelerator is degraded in some
fashion. A klystron failure in the main linac simply
reduces the energy overhead. The accelerator keeps
running until this overhead is reduced to zero. Similarly
there are 21 DR kickers where only 20 are needed so only
the second failure causes downtime. Some components
such as most magnet power supplies cause an immediate
downtime for their repair.
Each component can be specified as hot swappable
(meaning it can be replaced without further degrading the
accelerator); repairable without accessing the accelerator
tunnel, or repairable with an access to the accelerator
tunnel. A klystron that is not in the accelerator tunnel is
an example of a hot swappable device. If a BPM
electronics module is housed in a crate that does not have
to be turned off when the module is replaced, then it is hot
swappable. These repairs are simulated to occur in a time
MTTR after the failure. Devices which are not hot
swappable, such as magnets and individual channels of
multi-channel modules, are only repaired when the
accelerator is down.
Without doubt the downtime planning is the most
complicated part of the simulation. This should come as
no surprise to anyone who has participated in the planning
of a repair day. It is even harder in the simulation because
computers don't get a gestalt of the situation like humans
do. Briefly, the simulation determines which parameter
Invited talk presented at Particle Accelerator Conference (PAC 07), 6/25/2007-6/29/2007, Albuquerque, NM, USA
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Himel, T.; Nelson, J.; Phinney, N.; /SLAC; Ross, M. & /Fermilab. Availability and Reliability Issues for ILC, article, June 27, 2007; [Menlo Park, California]. (digital.library.unt.edu/ark:/67531/metadc878283/m1/1/: accessed November 21, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.