\subsection{Accelerator systems}
\subsubsection{R \& D tasks}

In this section, an outline of the the R\&D programme required to
reduce the technical risks that the Neutrino Factory project presents
is given.
Since detailed descriptions of the R\&D programme are available
elsewhere, the R\&D programme will be presented as a concise list of
the tasks that must be accomplished.
In the paragraphs which follow, important design and R\&D topics are
identified, a number of which are printed in boldfaced type to
indicate that their completion is essential to the production of the
RDR. 

\paragraph{Proton driver}

The IDS-NF will not have a specific proton driver in its baseline
design.  
Instead, multiple laboratories will describe how they could
construct a proton driver that meets our specifications. 
R\&D that will be important to the Neutrino Factory project will have
two goals: to demonstrate that the facility in question can meet our
requirements, and to provide an estimate of the cost, over and above
existing or planned facilities, of constructing an proton driver for a
Neutrino Factory.   
Particular challenges of a Neutrino Factory proton driver are the high
power and consequently high currents required, the very short bunches
that must be delivered, and injecting such an intense beam into the
various rings that are needed.

\paragraph{Target}

The principal R\&D tasks that must be carried out to complete the
specification of the Neutrino Factory target are:
\begin{itemize}
  \item \textbf{Re-design of the solenoid capture system and its 
                shielding:}\\
    Two areas of concern necessitate this:
    \begin{itemize}
    \item {\it Cryogenic thermal loads:}\\
      The heat load on the superconducting
      magnets is too high in the current design.  Specifications
      must be defined for the heat load per proton driver pulse (temperature
      rise on each pulse), the local maximum, time-averaged heat load
      (required local cryogen flow rate),
      and the total time-averaged heat load (thermal capacity
      of cryogenic system).  The shielding system must be re-designed to
      meet these requirements.
    \item {\it Mechanical forces:}\\  
      The forces on the solenoids are extremely
      high.  Specifications for acceptable forces need to be defined,
      and the shielding re-design must be constrained to meet these
      specifications.
    \end{itemize}
  \item Coolant flow in the internal shield:\\  
    A system needs to be designed and simulated to ensure adequate
    coolant flow everywhere. 
    It would be prudent to test the coolant flow patterns in a full
    size mockup, for which inexpensive low-\textit{Z} beads will
    suffice.
  \item \textbf{Definition of the full infrastructure for a target
    station}. \\
    This must include the outer shielding and containment, the remote
    handling systems, and the mercury loop.  These need to be defined
    to sufficient detail that a cost estimate can be made and any
    significant technical issues identified.
  \item Nozzle design and tests: \\
    The performance of the 1~cm diameter nozzle for the mercury jet in
    the MERIT experiment was poorer than desired at jet velocities of
    15-20~m/s.  
    A program of simulation and design is under way with the goal of
    developing a better nozzle.  
    This issue should not, however, be left only to design, but should
    be addressed in laboratory tests once a revised design is
    developed, on the time scale of 2~years.
  \item \textbf{The beam dump:}  \\
    A complete design of the beam dump must be
    produced.  This must allow for the possibility of a failure
    of the mercury flow, in which case the entire proton beam would
    be incident on the dump.  Since the beam dump would contain mercury,
    the hydrodynamics of the jet and the beam hitting this pool
    must be understood, and systems to mitigate the effects of the
    splash must be designed and simulated.  It would also be useful
    to conduct a laboratory test of the system in the presence of
    the mercury jet.
  \item Pion yield calculations and measurements: \\
    Different particle production simulation codes have produced
    results that, while in broad agreement, sometimes disagree in
    detail for predicting quantities that are important to the
    design of a Neutrino Factory~\cite{Strait:2009}.
    Studies must continue to compare
    the results from different codes, compare their results with
    experimental data, and assess the uncertainty in our predictions.
    Collecting additional experimental data to
    improve the models in the codes, as proposed in \cite{Sadler:2010}
    would also be desirable.
  \item Beam window designs:\\
    Complete designs of the windows
    must be performed.
\end{itemize}

\paragraph{Muon front-end}

The R\&D tasks required to complete the specification of the muon
front-end are:
\begin{itemize}
  \item RF cavities in magnetic fields: \\
    Our understanding of the limitations on RF gradients caused by
    magnet fields must be be improved through experiments such as
    MuCool.  
    As the limitations are better understood, lattice designs will
    need to be revised accordingly, either by modifying the baseline
    design or switching to one of the alternative designs. 
  \item \textbf{Particle losses:}  \\
    A system for managing particle losses needs to be defined.
    Three items have been identified for investigation: a proton absorber
    to remove low momentum protons; a chicane to remove high momentum
    protons; and transverse collimators to remove high amplitude particles.
    A Wien filter has also been suggested as a method to filter off-momentum
    particles.  Energy deposition in various systems, in particular
    superconducting magnets, must be computed.
    Appropriate shielding
    will need to be designed.
  \item \textbf{A full engineering design:} \\
    Designs for superconducting magnets,
    RF cavities, and their associated services are required.
    Heat deposition in lithium hydride absorbers need to be studied,
    and an active cooling system need to be designed if needed.
  \item Futher optimization of lattice optics:\\  
    In particular, between
    the phase rotation and ionisation cooling sections, there is a
    longitudinal mismatch, and the transverse matching can also
    be improved.
  \item Ionisation cooling experiments:\\  
    In particular, the results from MICE are critical.
\end{itemize}

\paragraph{Linac and RLAs}

To complete the specificaiton of the linac and RLA systems, the
following tasks must be completed:
\begin{itemize}
\item \textbf{Full lattice design:}\\
  While the lattice design is nearly complete, there are a few sections
  (such as matching sections in the arcs and the second injection
  chicane) which still need to be designed.
\item \textbf{Magnet designs:}\\
  First-pass designs of all magnets need to be made.
  \item \textbf{Physical layout:}\\
    In particular this is necessary
    around injection chicanes, 
    separators, and arc crossings, to ensure that the theoretical lattice
    design can be constructed.
  \item \textbf{Full particle tracking:}\\  
    Particles need to be tracked through
    the entire system.  This needs to include realistic magnet
    designs. Matching sections designs need to be adjusted
    to reduce losses.
\end{itemize}

\paragraph{FFAG}

The principal R\&D tasks required to complete the specification of the
muon FFAG are:
\begin{itemize}
  \item \textbf{Determine the optimal amount of, and method for, the
    chromaticity correction;}
  \item \textbf{Compute the matched beam in longitudinal phase space:}\\
    Computing the optimal phase space shape for the longitudinal
    distribution is complex~\cite{Berg:2006ih}.  This needs to be
    done for this design, taking into account the asymmetric
    dependence of time of flight on energy and the dependence of
    time of flight on transverse amplitude;
  \item \textbf{Design matching to other systems:}\\
    In particular for longitudinal phase space.
  \item \textbf{6-D tracking through the system;}
  \item \textbf{Determine error tolerances;}
  \item \textbf{Perform approximate cost comparison of FFAG design for an RLA
      replacement;}
  \item \textbf{Produce single-layer combined-function designs for main ring
      magnets;}
  \item \textbf{Hardware studies of kicker magnets and their power
      supplies.} 
\end{itemize}

\paragraph{Decay ring}

To complete the specification of the decay ring, the following issues
must be addressed:
\begin{itemize}
  \item \textbf{Design injection system;}
  \item \textbf{Decide on inclusion of sextupoles;}
  \item \textbf{Polarimeter design;}
  \item Design of OTR system for angular divergence measurement;
  \item \textbf{Decide on optimal system for measuring or computing
    neutrino flux spectrum going to far the detectors;}
  \item Compute particle spectrum based on storage ring tracking: \\
    An accurate neutrino spectrum is needed to simulate the far
    detectors' performance.
    The spectrum and trajectories of lost muons, electrons, and
    synchrotron radiation photons are needed
    to compute heat loads in the storage
    ring and undesired particles in the near detector.
\end{itemize}

\subsubsection{Plan to produce the RDR}

Our primary goals for the accelerator portion of the RDR are to have:
\begin{itemize}
\item A complete design for a Neutrino Factory accelerator facility that
  we believe is technolically feasible and would have the required
  performance;
\item An estimate of the cost of such a facility.  Ths will require
  designs of the system components at a sufficiently detailed level to
  produced such a cost estimate;
\item A complete end-to-end tracking result for a realistic particle
  distribution through the system to verify that the system works as
  expected. 
\end{itemize}
An approximate timeline for computing these tasks is shown in figure
\ref{fig:acc:rdr}.   
These tasks give the required input for attaining the primary goals
for the RDR.  
The timeline does not include common tasks such as supplying
component designs and making cost estimates, except when they are
emphasized because, for instance,
component designs are more ambiguous than usual.
\begin{figure}
  \includegraphics[width=\linewidth]%
    {04-RandD-plan/RDR-acc-Timeline-110111.eps}
  \caption{
    Approximate timeline for completing important tasks needed
    for the RDR.
  }
  \label{fig:acc:rdr}
\end{figure}
