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\section{FACILITY OPERATION MODES}
Many failure modes of a
given facility depend on the
specific operation mode.
A The nominal beam current in single bunch operation
for instance would be considered insufficient for
any useful multi-bunch
filling operation at the same facility.
Therefore we'll We therefore discuss the different operation modes
of our facilities before we
get to are addressing the actual failure modes.
\subsection{ALBA Operation Modes} \subsection{ALBA}
The ALBA light source~\cite{Garc_a_2014}
presently runs
basically with one operation mode: 100$\,$mA multibunch.
The
filling fill pattern consists of 10
bunch trains each with 32
buckets bunches and a 24$\,$ns gap in between.
Since September 2014 ALBA
is running operates in
top-up mode, top-up, before that it was decay mode.
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In top-up the beam decays down to 98.5$\,$mA and is then reinjected to 100$\,$mA.
In the decay mode ALBA injects 120$\,$mA twice per day and let the beam decay to \~80$\,$mA.
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In top-up mode the beam decays down to 98.5$\,$mA and is then accumulated up to 100$\,$mA again.
In the decay mode we were accumulating to 120$\,$mA with 2 injections per day and let the beam decay.
\subsection{BESSY
II Operation Modes} II}
The annual beamtime calendar at BESSY II~\cite{Bakker_1999} is organized in weeks of user
operation, machine development and beamline commissioning, and
shutdown. A standard week of scheduled user beam time starts Tuesday
7:00 a.m. and ends Sunday 23:00 providing three basic user operation
modes. Every other Sunday two
eight hour eight-hour shifts are given to the PTB
(4$^{th}$ mode).
\begin{description}
\item[Multi bunch hybrid mode] comprises 299$\,$mA total
current, kept constant by
permanent top-up injections. top-up.
General bunch pattern is an even filling of 300--350 bunches and a gap of about 100--50 bunches (550$\,$MHz, harmonic number 400).
In addition to this multi bunch current, up to five specific bunches are serving
dedicated experiments.
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\item A higher current (4$\,$mA) camshaft bunch can be inserted in the middle of the (purity controlled) gap for pump-probe experiments
\item Three higher current (4$\,$mA) bunches can be located opposite of the gap, sequentially sliced with
6$\,$kHz repetition, 20$\,$fs laser pulses, generating 100$\,$fs x-ray pulses.
\item One horizontally excited bunch, typically three buckets away from the end of the gap, can be resonantly excited for pseudo-single bunch
experiments by a specific set-up. experiments.
\end{itemize}
In this standard mode two emergency modes of degraded beam conditions are
at disposal: possible:
\begin{itemize}
\item
At problems Problems with the LINAC-booster injector chain BESSY still
can easily switch from LINAC to microtron injector: then multi bunch
top-up is feasible, occasional refilling of the custom bunches require a
preparing decay phase and a closure of the beam shutters.
\item If the top-up lifetime constraint
$>$5h $>$5 hours cannot be met
(e.g. vacuum problems) lowering the nominal current from
299mA 299$,$mA to
some 250$\,$mA \~250$\,$mA allows to stay operational.
\end{itemize}
\item[Single bunch mode] consists of 14$\,$mA in a (purity controlled) single bunch, refilled with top-up, used for time resolved experiments (2--3 weeks/y).
This mode specifically depends on the LINAC. The microtron can inject single bunches only with
insufficient low efficiency, thus a lasting LINAC failure results in a decaying beam degraded mode.
\item[Low Alpha mode] even filling of 100$\,$mA (short pulse mode) or 15$\,$mA (THz mode, non- bursting coherent synchrotron radiation) in an alternating, 12 hour period decaying beam sequence (2--3 weeks/y).
\item[National Bureaux of Standards (PTB)] main user mode, beam conditions according to their experimental requirements.
\end{description}
{\em %{\em Top-up constraints} are imposed by the radiation protection prescriptions and are implemented in the top-up interlock at BESSY II, generating a number of enforced combinations of decay mode, closure of the beam shutters, and several refilling modes.
{\em %{\em Decay only}: Enforced by insufficient lifetime ($t<$5$\,$h) or insufficient injection efficiency (four hour average of injection efficiency Eff$_{\mathrm{avg}}<$90\% enforce
$T=4\,\mathrm{h}*(90\%-\mathrm{Eff}_{\mathrm{avg}})/(100\%-90\%)$ %$T=4\,\mathrm{h}*(90\%-\mathrm{Eff}_{\mathrm{avg}})/(100\%-90\%)$ injection free time). W.r.t. accounting
begin %begin and end of this failure condition is handled according to the 'low-beam-current' criterion.
{\em %{\em Beam shutter closure enforced}: triggered by a single shot with efficiency $ <60\%$, beam current $ <200\,$mA in MB mode or $ <10\,$mA in SB, or an unclear/inconsistent status of the top- up interlock, an enforced decay starts.
Any %Any re-injection shot requires to close the beam shutters first. Then a single shot fulfilling the top up requirements reenables the opening of the beam shutters.
Beam %Beam shutter closure can be shifted within negotiated time limits, but the failure begins at the moment, the interrupting condition has been met.
The %The event stops when top up conditions and the nominal beam current is reached again
\subsection{Elettra Operation Modes} \subsection{Elettra}
Elettra~\cite{Bocchetta_1995} operates for about 75\% of user dedicated time at 2$\,$GeV while for the remaining 25\% at 2.4$\,$GeV; being the only facility to operate at two energies in top-up.
The main operating modes are multibunch with a dark gap of 42$\,$ns and hybrid
(at 20\% of the total user beam time) with a single bunch in the middle of the dark gap.
The operating intensities are 310$\,$mA at 2$\,$GeV and 160$\,$mA at 2.4$\,$GeV with a 5$\,$mA single bunch added when in hybrid mode.
Also the single bunch is automatically refilled by the top-up routine with a delta of 0.5$\,$mA.
For radiation protection
reason, reasons, the booster current must be lower than 0.5$\,$mA.
To be able to maintain the machine in top-up mode some radiation protection constraints must be met.
These are the following:
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%{\em Top-up constraints}
%The integral of the electron charge losses during top-up injection, measured on a relatively long interval time (one hour), must not exceed a prefixed threshold.
%This value is obtained computing the so-called top-up-lost-charge which is the difference between the injected charge, measured through a toroid installed at the end of the BTS TL and the relative current increment, measured through the ring DCCT.
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%(through the inhibition of the Linac gun) if large beam losses occur along the ring.
%Another safety interlock is based on the beam lines gamma monitors.
%If any exceeds a prefixed alarm threshold, the safety system will not interrupt the top-up injection but will {\em close the beam stopper of the affected beam line}.
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{\em Top-up constraints}
The integral of the electron charge losses during top-up injection, measured on a relatively long interval time (one hour), must not exceed a prefixed threshold.
This value is obtained computing the so-called top-up-lost-charge which is the difference between the injected charge, measured through a toroid installed at the end of the BTS TL and the relative current increment, measured through the ring DCCT.
If the integral of the top-up-lost-charge per hour exceeds the prefixed threshold, the {\em top-up process is inhibited for the following hour}.
The integral of the electron charge losses during top-up injection, measured on a relatively brief interval time (about 3 to 5$\,$s) is not within a prefixed threshold.
This interlock will permit the {\em safety system to interrupt quickly the operations}
(through the inhibition of the Linac gun) if large beam losses occur along the ring.
Another safety interlock will be based on the beam lines gamma monitors.
If one of them exceeds a prefixed alarm threshold, the safety system will not interrupt the top-up injection but will {\em close the beam stopper of the affected beam line}.
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\subsection{LNLS-UVX Operation Modes} \subsection{LNLS-UVX}
The UVX at LNLS~\cite{Rodrigues_1998} operates in two modes: 100\% filling (148
buckets) buckets), and single bunch.
It LNLS-UVX operates with low energy injection and the beam is delivered in the decay mode.
In a typical run the initial current is 250$\,$mA, injected at 500$\,$MeV and ramped up to 1.37$\,$GeV, the nominal operation
energy of the machine. energy.
Injection takes place twice a day and is scheduled to last 30 minutes at most.
By the end of the run, after about 11 hours, the current is down to 130$\,$mA.
Single bunch shifts are available since 2003, but the provision of shifts depends on the demand by the users.
Operation in hybrid mode is
impracticable impractical due to the low energy injection and to the characteristics
of the UVX injection system. In the single bunch mode the initial current is typically of
the
order
of 9$\,$mA and is not interesting for
the high flux multibunch users.
\subsection{PETRA
III Operation Modes} III}
PETRA III~\cite{Weckert_2005}, with a circumference of 2.3$\,$km and an RF frequency of 500$\,$MHz, has a harmonic number of 3840.
For about 50\% of the user time PETRA III is operated in a continuous filling mode; the rest of the user time is used for timing modes. All modes are in top-up operation at 100$\,$mA.
In the continuous filling modes either every fourth bucket (960 bunches), or every eighth (480 bunches) is filled;
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The four modes are called "Continuous 960", "Continuous 480", "Timing 40" and "Timing 60".
\subsection{SPring-8 Operation Modes} \subsection{SPring-8}
SPring-8~\cite{Tanaka_2006} runs in 9 operation modes, one of which is multi-bunch mode of twelve 160 bunch-trains, and the others are several bunch modes.
The several bunch modes are grouped
to the simple into several bunch modes and the hybrid ones.
The
simple several bunch modes consist of equally spaced bunches (or bunch-trains), i.e. 203 bunches, 84 trains of 4 bunches, and 29 trains of 11 bunches.
On the other hand, the hybrid modes are composed of partially filled multi-bunch train and isolated single bunches, i.e. 11/29-filling + 1 bunch, 1/7-filling + 5 bunches, 1/14-filling + 12 bunches, 2/29-filling + 26 bunches, and 4/58-filling + 53 bunches.
The impurity of an isolated bunch
are is maintained under $10^{-8}$ in top-up operation.
\subsection{SLS Operation Modes} \subsection{SLS}
The Swiss Light Source (SLS)~\cite{Aiba_2013} runs basically only in one operation mode: 80\% filling (390 out of 480 buckets), 400$\,$mA top-up.
We can add on demand a single bunch in the gap with a higher charge - that is the so called "camshaft mode".
Typically the single bunch is filled to 4 times the charge of the other buckets.
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Switching between the modes does not effect users of the 80\% filling, since the beam current is kept constant at 400$\,$mA in both.
\begin{table}\centering
...
SLS & 1 & ???\\
\end{tabular}
\end{ruledtabular}
\end{table}
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Switching between the modes does not effect users of the 80\% filling, since the beam current is kept constant at 400$\,$mA in both.
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