
\chapter{R\&D Program}

\label{r_and_d}

\section{Introduction}

Successful construction of a muon storage ring to provide a copious source
of neutrinos requires many novel approaches to be developed and
demonstrated. To construct a high-luminosity Muon Collider is an even
greater extrapolation of the present state of accelerator design. The
breadth of R\&D issues to be dealt with is beyond the resources available at
any single national laboratory or university.

For this reason, in 1995, interested members of the high-energy physics and
accelerator physics communities formed the Neutrino Factory and Muon
Collider Collaboration (MC) to coordinate the required R\&D efforts
nationally. The MC comprises three sponsoring national laboratories (BNL,
FNAL, LBNL) along with groups from other U.S. national laboratories and
universities and individual members from non-U.S. institutions. Its task is
to define and carry out R\&D required to assess the technical feasibility of
constructing initially a muon storage ring that will provide intense
neutrino beams aimed at detectors located many thousands of kilometers from
the accelerator site, and ultimately a $\mu ^{+}\mu ^{-}$ collider that will
carry out fundamental experiments at the energy frontier in high-energy
physics. The MC also serves to coordinate muon-related R\&D activities of
the NSF-sponsored University Consortium (UC) and the state-sponsored
Illinois Consortium for Accelerator Research (ICAR), and is the focal point
for defining the needs of muon-related R\&D to the managements of the
sponsoring national laboratories and to the funding agencies (both DOE and
NSF). Though the MC was formed initially to carry out R\&D that might lead
eventually to the construction of a Muon Collider, more recently its focus
has shifted mainly, but not exclusively, to a Neutrino Factory.

The MC maintains close contact with parallel efforts under way in Europe
(centered at CERN) and in Japan (centered at KEK). Through its international
members, the MC also fosters coordination of the international muon-beam
R\&D effort. Two major initiatives, a Targetry Experiment (E951) in
operation at BNL and a Muon Cooling R\&D program (MUCOOL), have been
launched by the MC. In addition, the Collaboration, working in conjunction
with the UC and ICAR in some areas, coordinates substantial efforts in
accelerator physics and component R\&D to define and assess parameters for
feasible designs of muon-beam facilities.

\section{R\&D\ Goals}

The approach taken by the MC to define the overall R\&D program was to
decide what we wished to accomplish in a five-year time span in each area
and then determine what is needed to reach that goal. For this exercise, we
assume a technology-limited schedule, that is, we assume that the required
financial resources and personnel are available. With this approach, we
expect that a five-year technology-limited plan will result in:

\begin{itemize}
\item  all optics designs being completed and self-consistent

\item  validation experiments being completed or well along

\item  all required hardware being defined

\item  prototypes of the most challenging and costly components being
completed or well along, i.e., we know how to build the ``hard parts''

\item  being ready to begin the design of, and provide cost estimates for,
most of the remaining components
\end{itemize}

At the end of the five-year period, the above goals would put the MC in
position to request permission to begin a formal Conceptual Design Report
(CDR) for a Neutrino Factory. It is expected that this CDR stage would take
1--2 years to complete. The CDR would document a complete and fully
engineered design for the facility, including a detailed bottom-up cost
estimate for all components. This document would form the basis for a full
technical, cost, and schedule review of the construction proposal,
subsequent to which construction could commence after obtaining government
approval.

As an ``intermediate milestone'' we envision preparing a Zeroth-order Design
Report (ZDR) after three years. The ZDR will examine the complete systems of
a Neutrino Factory, making sure that nothing is forgotten, and will show how
the parts merge into a coherent whole. While it will not present a fully
engineered design with a detailed cost estimate, enough detail will be
presented to ensure that the critical items are technically feasible and
that the proposed facility could be successfully constructed and operated at
its design specifications.

\section{R\&D Program Issues}

A Neutrino Factory comprises the following major systems: Proton Driver,
Target and (Pion) Capture Section, (Pion-to-Muon) Decay and Phase Rotation
Section, Bunching and Matching Section, Cooling Section, Acceleration
Section, and Storage Ring. These same categories exist for a Muon Collider,
with the exception that the Storage Ring is replaced by a Collider Ring
having a low-beta interaction point and a local detector. Parameters and
requirements for these systems are generally more severe in the case of the
Muon Collider, so a Neutrino Factory can properly be viewed as a
scientifically productive first step toward the eventual goal of a collider.
As noted earlier, the R\&D program we envision is designed to answer the key
questions needed to embark upon a ZDR after three years. After completion of
the full five-year program, it is expected that a formal Conceptual Design
Report could begin. Longer-term activities, related primarily to the Muon
Collider, are also supported and encouraged.

Each of the major systems has significant issues that must be addressed by
R\&D activities, including a mix of theoretical, simulation, modeling, and
experimental studies, as appropriate. A brief summary of the key physics and
technology issues for each major system is given below.

\bigskip \textbf{Proton Driver}

\begin{itemize}
\item  Production of intense, short proton bunches, e.g., with space-charge
compensation and/or high-gradient, low frequency rf systems
\end{itemize}

\textbf{Target and Capture Section}

\begin{itemize}
\item  Optimization of target material (low-\textit{Z} or high-\textit{Z})
and form (solid, moving band, liquid-metal jet)

\item  Design and performance of a high-field solenoid ($\approx $20 T) in a
very high radiation environment
\end{itemize}

\textbf{Decay and Phase Rotation Section}

\begin{itemize}
\item  Development of high-gradient induction linac modules having an
internal superconducting solenoid channel
\end{itemize}

\textbf{Bunching and Matching Section}

\begin{itemize}
\item  Design of efficient bunching system
\end{itemize}

\textbf{Cooling Section}

\begin{itemize}
\item  Development and testing of high-gradient normal conducting rf (NCRF)
cavities at a frequency near 200 MHz

\item  Development and testing of efficient high-power rf sources at a
frequency near 200 MHz

\item  Development and testing of LH$_{2}$ absorbers for muon cooling

\item  Development and testing of candidate diagnostics to measure emittance
and optimize cooling channel performance

\item  Design of beamline and test setup (e.g., diagnostics) needed for
demonstration of transverse emittance cooling

\item  Development of six-dimensional analytical theory to guide the design
of the cooling section
\end{itemize}

\textbf{Acceleration Section}

\begin{itemize}
\item  Optimization of acceleration techniques to increase the energy of a
muon beam (with a large momentum spread) from a few GeV to a few tens of GeV
(e.g., recirculating linacs, rapid cycling synchrotrons, FFAG rings) for a
Neutrino Factory, or even higher for a Muon Collider

\item  Development of high-gradient superconducting rf (SCRF) cavities at
frequencies near 200 MHz, along with efficient power sources (about 10 MW
peak) to drive them

\item  Design and testing of components (rf cavities, magnets, diagnostics)
that will operate in the muon-decay radiation environment
\end{itemize}

\textbf{Storage Ring}

\begin{itemize}
\item  Design of large-aperture, well-shielded superconducting magnets that
will operate in the muon-decay radiation environment
\end{itemize}

\textbf{Collider}

\begin{itemize}
\item  Cooling of 6D emittance (\textit{x}, \textit{p}$_{x}$, \textit{y}, 
\textit{p}$_{y}$, \textit{t}, \textit{E}) by up to a factor of $10^{5}-10^{6}
$

\item  Design of a collider ring with very low beta (a few mm) at the
interaction point having sufficient dynamic aperture to maintain luminosity
for about 500 turns

\item  Study of muon beam dynamics at large longitudinal space-charge
parameter and at high beam-beam tune shifts
\end{itemize}

\textbf{Detector}

\begin{itemize}
\item  Simulation studies to define acceptable approaches for both near and
far detectors at a Neutrino Factory and for a collider detector operating in
a high-background environment

\item  Develop ability to measure the sign of electrons in the Neutrino
Factory detectors
\end{itemize}

\section{FY 2001 R\&D Plans}

\subsection{Targetry}

This year, a primary effort of the Targetry experiment E951 was to carry out
initial beam tests of both a solid carbon target and a mercury target. Both
of these goals were accomplished at a beam intensity of about 4 $\times $\ 10%
$^{12}$ ppp, with encouraging results. Measurements of the velocity of
droplets emanating from the jet as it is hit with the proton beam pulse from
the AGS compare favorably with simulation estimates. High-speed photographs
indicate that the beam disruption at the present intensity does not appear
to propagate back upstream toward the jet nozzle, which will ease mechanical
design issues for this component.

\subsection{MUCOOL}

The primary efforts this year were to complete the Lab G rf test area and
begin high-power tests of the 805 MHz cavities that were completed earlier
this year. A test solenoid for the facility, capable of operating either in
solenoid mode (its two independent coils powered in the same polarity) or
gradient mode (with the two coils opposed), was tested up to its design
field of 5 T. An open-cell cavity has been installed and conditioning at
high-power is under way to explore gradient limitations we will face in a
cooling channel. A second cavity, having Be foils to close the beam iris, is
now being tuned to final frequency. This cavity will permit an assessment of
the behavior of the foils under rf heating and give indications about
multipactor effects.

Development of a prototype LH$_{2}$ absorber is in progress. A large
diameter, thin (125 $\mu $m) aluminum window has been successfully
fabricated by machining from a solid disk. A new area is being developed at
FNAL for testing the absorbers. This area, located at the end of the proton
linac, will be designed to permit beam tests of components and detectors
with 400 MeV protons. It will also have access to 201-MHz high-power rf
amplifiers for cavity testing.

Initial plans for a cooling demonstration will be firmed up this year. This
topic will be covered separately in Section \ref{Demo}.

\subsection{Feasibility Study-II}

This year the MC participated heavily in a second Feasibility Study for a
Neutrino Factory, sponsored by BNL. The results of the study were quite
encouraging (see Chapter 4 of this report), indicating that a neutrino
intensity of $1\times 10^{20}$ per Snowmass year can be sent to a detector
located 3000 km from the muon storage ring. It was clearly demonstrated by
means of these two studies that a Neutrino Factory could be sited at either
FNAL or BNL. Component R\&D needed for such a facility was identified, and
is included in the program outlined here.

\subsection{Simulation and Theory}

In addition to Study-II, this year the effort has focused on longitudinal
dynamics. We are developing theoretical tools for managing the longitudinal
aspects of cooling, with the goal of developing approaches to 6D cooling,
i.e., ``emittance exchange.'' This is a crucial aspect for the eventual
development of a Muon Collider, and would benefit a Neutrino Factory as
well. In particular, work has begun on studies of the ring cooler~\cite
{BalbekovRing} which has the potential to cool in 6D space, if the beam can
be injected and extracted from it. Avenues are being explored to see if it
can also function as a cooling demonstration where pions are produced in an
internal target.

\subsection{Component Development}

The main effort in this area is aimed at development of a high-gradient
201-MHz SCRF cavity. This year a test area of suitable dimensions is being
fabricated at Cornell. In addition, a prototype cavity is being fabricated
for the Cornell group by our CERN colleagues. Mechanical engineering studies
of microphonics and Lorentz detuning issues are being carried out. These
will lead to plans to stiffen the cavity sufficiently to avoid serious
vibration problems in these large structures.

\subsection{Collider R\&D}

Studies of possible hardware configurations to perform emittance exchange,
such as the compact ring proposed by Balbekov~\cite{BalbekovRing}, are now
getting under way. An emittance exchange workshop was held at BNL in the
fall of 2000, and a second workshop is being planned for October, 2001. In
addition to the efforts on emittance exchange, a workshop on an entry-level
Muon Collier to serve as a Higgs Factory was hosted this year by UCLA and
Indiana University. The focus of this meeting was to begin exploring the
path to get from a Neutrino Factory to a Higgs Factory. Even beyond the
cooling issues, the bunch structure required for the two facilities is very
different (the Collider demands only a single bunch), so the migration path
is not straightforward.

\section{FY2002 R\&D plans}

\subsection{Targetry}

For the targetry experiment, design of a pulsed 20-T solenoid and its 5-MW
power supply will begin. One or more selected targets will be tested with
beam this year. Simulations in support of this activity will continue.
Improvements in the AGS extraction system will be investigated, with the
goal of approaching the design single-bunch intensity of 1.7 $\times $ 10$%
^{13}$ ppp on target. An upgrade of the AGS extraction kicker to permit fast
extraction of the entire beam will be studied.

Radiation tests on selected coil materials will begin this year, to verify
behavior prior to actual magnet fabrication. As part of this work, we will
measure neutron yields from the target, to compare with predictions of the
MARS code. Systems studies of the target facility will continue to identify
and test key issues related to handling and remote maintenance, with special
attention paid to mercury-handling issues.

The next level of engineering concepts for a band target will be developed.
If its engineering aspects can be mastered, this approach might be a good
technical backup to the mercury jet .

\subsection{MUCOOL}

Testing work remaining for the 805 MHz components will continue this year in
Lab G. Completion of the linac test area at FNAL, initially to accommodate
the absorber tests and ultimately to house the 201-MHz cavity test, will
occur this year. Thermal tests of a prototype absorber will commence there.
Design and fabrication of cooling channel components required for the
initial phase of testing will begin, including a high-power 201 MHz NCRF
cavity and diagnostics that could be used for the experiment. Provisions
will be made to test both Be windows and grids for the cavity.

\subsection{Simulations and Theory}

Simulations this year will focus on iterating the front-end channel design
to be compatible with realizable component specifications. Studies of the
acceleration system and the storage ring will include errors and
fringe-field effects. From these studies will come component specifications
for the acceleration system and storage ring components. Simulation efforts
in support of a cooling demonstration program, and work on emittance
exchange, will both continue.

\subsection{Component Development}

A prototype induction linac cell, designed to operate at $\approx $1.5 MV/m
and including an internal superconducting solenoid with suitable dimensions
and field strength, will be designed. A prototype 201-MHz SCRF cavity will
be tested at low power. An initial input power coupler design will be tested
and validated. Detuning issues associated with the pulsed rf system will
also be evaluated. Finally, because of the large stored energy in a 201 MHz
SCRF cavity, a reliable quench protection system must be designed and
tested. Design of a prototype high-power rf source will begin, in
collaboration with industry.

\section{FY2003 R\&D plans}

\subsection{Targetry}

For the targetry experiment, AGS extraction kicker modifications to permit
high intensity beam tests ($\approx $1 $\times $ 10$^{14}$ protons per
pulse) will begin. The 20-T target solenoid for E951 will be fabricated this
year. Measurements of particle yield in this target geometry, but without a
solenoid will be made. These will use a much lower beam intensity (1 $\times 
$ 10$^{6}$ protons per pulse), for 6 weeks of parasitic beam time. Tests of
radiation-hard materials will be completed and selected candidate materials
will be used to begin manufacture of an actual (warm) solenoid coil for
testing in a high-radiation environment. The target simulation effort this
year will focus on understanding experimental results from the targetry
experiment.

\subsection{MUCOOL}

High-power tests of the 201-MHz NCRF cavity will begin in the linac test
area. Beam tests will be carried out with a prototype LH$_{2}$ absorber.
Fabrication of all remaining components, such as the solenoids, will
commence.

\subsection{Simulations and Theory}

Additional effort will be given to beam dynamics studies in the RLAs and
storage ring, including realistic errors. Work on finalizing the optics
design for the arcs will be done. Assessment of field-error effects on the
beam transport will be made to define acceptance criteria for the magnets.
This will require use of sophisticated tracking codes like COSY that permit
rigorous treatment of field errors and fringe-field effects. Because the
beam circulates in each RLA for only a few turns, the sensitivity to magnet
errors should not be extreme, though the large energy spread will tend to
enhance it. In many ways, the storage ring is one of the most
straightforward portions of a Neutrino Factory complex. However, beam
dynamics is an issue here as the muon beam must circulate for many hundreds
of turns. Use of a tracking code such as COSY is required to assess fringe
field and large aperture effects. As with the RLAs, the relatively large
emittance and large energy spread enhance the sensitivity to magnetic field
and magnet placement errors. Suitable magnet designs are needed, with the
main technical issue being the relatively high radiation environment.
Another lattice issue that must be studied is polarization measurement. In
the initial implementation of a Neutrino Factory it is expected that
polarization will not be considered, but its residual value may be important
in analyzing the experiment.

\subsection{Component Development}

Magnet designs suitable for the arcs of the recirculating linacs (RLAs) and
the muon storage ring will be examined this year. Both conventional and
superconducting designs will be compared where either is possible. With SC
magnets, radiation heating becomes an issue and must be assessed and dealt
with. Designs for the splitter and recombiner magnets will be developed
and---depending on how nonstandard they are---prototypes will be built.
Tests of a 201 MHz SCRF cavity will continue this year, including
demonstration of the ability to shield nearby magnetic fields in a realistic
lattice configuration. Fabrication of a prototype induction linac module and
its pulser system will begin this year.

\section{FY2004 R\&D plans}

\subsection{Targetry}

For the targetry experiment, the work this year will focus on completing
systems studies of the final target station, including issues of radiation
handling and safety. Target facility studies will progress to prototypes or
full-size models of key components, as needed, to verify the design
concepts. A (normal conducting) test solenoid coil based on the materials
tests in prior years will be completed and tested in a radiation environment.

\subsection{MUCOOL}

A full cooling cell will be assembled and bench tested. After testing, it is
anticipated that these components will be installed in a beam line and
tested with protons. The goal here is not to demonstrate cooling, but to
demonstrate operation of the components in a radiation environment. Upon
completion of the integration tests, these components will be available for
testing in a muon beam as part of the cooling demonstration experiment.

\subsection{Theory and Simulation}

Work on the Zeroth-order Design Report will commence this year. This
activity will require about two years of significant effort, leading to a
document that presents a description of all aspects of a Neutrino Factory,
in sufficient detail to demonstrate technical feasibility of the full
facility.

\subsection{Component Development}

High-power tests of the 201-MHz SCRF cavity will be carried out at FNAL. The
induction linac prototype module will be completed and tests will begin.

\section{FY 2005 R\&D plans}

This year should see the completion of the ZDR followed by a community
review of its contents. Thereafter, we will be ready to seek permission to
begin a formal CDR. Work on the Cooling Demonstration Experiment (see
Section \ref{Demo}) will be a primary activity this year.

\section{Required Budget}

Table \ref{tab:budget} summarizes the projected budget requirements for the
activities described above. The numbers represent our estimate of the
required resources \textit{from all sources}, including direct DOE funding
for the MC, DOE base program support from the sponsoring Laboratories, NSF
support to the UC, state support for the ICAR, and possible contributions by
foreign collaborators. The scale of R\&D is consistent with the experience
of other large accelerator projects, both past and present, and in that
sense is ``realistic.'' The funding profile in Table \ref{tab:budget}
corresponds to the technology-limited schedule we are considering. If this
level of funds is not available, the R\&D work would proceed more slowly.
Indeed, the amount of support available in FY2001, and that projected for
FY2002, already fall short of what is required, with the result that the
schedule shown here has begun to slip. It is worth noting that the increase
in FY2004 and FY2005 is associated mainly with the cooling demonstration
experiment. If we were to assume equal sharing among the U.S., Europe, and
Japan in this endeavor, as seems reasonable, then about \$8M of the
tabulated costs in each of these years would be borne by non-U.S. funds. In
that case, a program with roughly flat funding (from all U.S. sources) in
the \$15M range would permit us to complete the R\&D program in a timely way.

\bigskip

\begin{table}[tbh]
\caption[R\&D budget to reach a CDR]{MC\ R\&D budget to reach a CDR in a
technology-limited schedule.}
\label{tab:budget}
\begin{center}
\begin{tabular}{lllllll}
\hline
\textbf{R\&D area} & \textbf{FY01} & \textbf{FY02} & \textbf{FY03} & \textbf{%
FY04} & \textbf{FY05} & \textbf{Sum} \\ 
& \textbf{(\$M)} & \textbf{(\$M)} & \textbf{(\$M)} & \textbf{(\$M)} & 
\textbf{(\$M)} & \textbf{(\$M)} \\ \cline{2-7}
MUCOOL & 4.9 & 3.8 & 4.3 & 11.3 & 11.2 & 35.4 \\ 
Targetry & 4.7 & 3.8 & 4.1 & 3.5 & 2.1 & 18.2 \\ 
Beam Simul. & 2.3 & 2.0 & 2.0 & 2.0 & 2.0 & 10.3 \\ 
Accel./SR & 1.0 & 0.7 & 0.7 & 0.7 & 0.7 & 3.6 \\ 
Components & 1.9 & 4.5 & 7.5 & 4.3 & 4.0 & 22.2 \\ 
ZDR Prep. &  &  &  & 4.0 & 6.0 & 10.0 \\ \cline{2-7}
TOTAL & 15 & 15 & 19 & 26 & 26 & 100 \\ \hline
\end{tabular}
\end{center}
\end{table}

\section{Cooling Demonstration Experiment}

One of the more important R\&D tasks that is needed to validate the design
of a Neutrino Factory is to measure the cooling effects of the hardware we
propose. At the recent NUFACT'01 Workshop in Japan, a volunteer
organization, to be chaired initially by Alain Blondel from Geneva
University, was created to organize a cooling demonstration experiment that
would begin in 2004. See Chapter on International activities on further
details on this committee. Present membership in this group (with
representatives from the U.S., Europe, and Japan), the ``Muon Cooling
Demonstration Experiment Steering Committee'' (MCDESC), is listed in the
chapter on International Activities. The Steering Committee is responsible
for choosing a technical team to develop the proposal details, suggest a
beamline, and propose components to be tested, including absorbers, rf
cavities and power supplies, magnets, and diagnostics. This technical team
will likewise be assembled from experts from the three geographical regions.

The aim of the proposed experiment is twofold:

\begin{enumerate}
\item  To show that we can design, engineer, and build a section of cooling
channel capable of giving the desired performance for a Neutrino Factory

\item  To place it in a muon beam and measure its performance, i.e., to
validate that it performs as predicted by simulations
\end{enumerate}

\noindent It is clear that the experience gained from this experiment will
be invaluable for the design of an actual cooling channel.

The present concept is to carry out a single-particle measurement of cooling
effects, starting from a single cell of cooling hardware. We believe that
the measurement of the emittance change can be done with a precision\label%
{Demo} of about 0.5\% with standard single-particle detection techniques.
The main technical uncertainty in this concept is the ability of the
detection equipment to function properly in the large x-ray flux resulting
from very high gradient rf cavity operation. This aspect can be explored
almost immediately in the Lab G test area at FNAL, where high-gradient
cavity testing is just getting under way. (The x-ray intensity from the
cavity is expected to scale with electric field as $E^{10}$. Taking a
positive slant, this means that a small reduction in operating voltage will
lead to a large reduction in x-ray intensity.)

The plan of the Steering Committee is to create a short document ($\approx $%
10 pages) by December 15, 2001 that will define the key technology choices
and the venue for the experiment. Thereafter, a full technical proposal,
including a cost estimate suitable for presentation to the various funding
agencies, would be prepared by June, 2002. Though there obviously is no cost
estimate yet, it is expected that getting a single cooling cell into a muon
beam will require about \$10M. Thereafter, it is expected that more cells
would be added, either identical to that in the first test or perhaps of a
different design. With this in mind, it is reasonable to suppose that the
initial funding commitment needed---shared among the three regions---will be
about \$20M. \ This is consistent with the estimate presented in Table \ref
{tab:budget}. However, the profile in Table \ref{tab:budget} would have to
move forward by one year. The overall U.S. requirement of \$15M per year
would remain unchanged. (Later, it may be of interest to continue this
experimental effort, perhaps including longitudinal cooling techniques,
though that is certainly beyond the initial scope of the proposed
experiment.)

