\input mini:defs.eoi_epsfig %\input defs.eoi %\def\tensor#1{\vbox{\ialign##\crcr % \leftrightarrowfill\crcr\noalign{kern-1pt\nointerlineskip} % $\hfil\displaystyle{#1}\hfil$\crcr}}} \begin{document} \renewcommand{\arraystretch}{1.5} %\begin{titlepage} \pagestyle{empty} \begin{center} {\LARGE\bf An R\&D Program for Targetry and Capture \\ \vspace{0.2in} at a Muon-Collider Source} \\ \vspace{0.25in} {\LARGE\sc A Proposal to the BNL AGS Division} \\ \vspace{0.25in} \input targetprop.author \vspace{0.2in} (September 28, 1998) %{\Large\bf Abstract} \end{center} \newpage \pagestyle{plain} \pagenumbering{roman} \begin{center} {\Large\bf Executive Summary} \end{center} Present designs for a muon collider call for a copious source of muons: $5 \times 10^{14}\ \mu$/s distributed over 15 pulses/s, each only a few ns long. These muons arise from the decay of low-energy pions that are produced by the interaction of a beam of $1.5 \times 10^{15}$, 16-24-GeV protons/s with a high-$Z$ target. The proton beam power is 4~MW, of which 10\% is deposited in the target at a density of about 30~J/g per pulse. The target is surrounded by a 20-T solenoid magnet that captures pions of transverse momentum up to 225~MeV/$c$ into a decay channel. To avoid absorption of the spiraling pions near the target, the latter cannot be cooled by contact with a local thermal bath. Rather, the material of the target must move out of the interaction region to be cooled elsewhere. The baseline design is for a target in the form of a pulsed jet of liquid metal such as Ga, Hg or molten Bi/Pb. A backup design is a nickel target in the form of a band that moves through the interaction region somewhat like the blade of a bandsaw. The decay channel includes a series of low-frequency rf cavities inside a 1.25-T solenoid. The cavities are phased so as to compress the energy spread of the decay muons, for better injection into the subsequent muon-cooling channel. This process of ``phase rotation'' is more effective when the first rf cavity is located as close as possible downstream of the target. The targetry scenario leads to several critical technical questions, which are to be addressed in the proposed R\&D program: \begin{itemize} \item What is the effect of the pressure wave induced in the target by the proton pulse? If the liquid target is dispersed by the beam, do the droplets damage the containment vessel? \item What is the effect of the magnetic field of the capture solenoid on the motion of the liquid-jet target? Is the jet badly distorted by Lorentz forces on the eddy currents induced as the jet enters the field? Does the magnetic field damp the effects of the beam-induced pressure wave? \item Can the first rf cavity of the phase-rotation channel operate viably in close proximity to the target? \item What is the yield of low-energy pions from 16-24-GeV protons incident on the target of the muon-collider source? \item Can numerical simulations of target behavior be developed that permit reliable extrapolation of the data we obtain? \end{itemize} The proposed R\&D program into these targetry issues for a muon-collider source consists of eight parts: \begin{enumerate} \item Initial studies of liquid (and solid) target materials with a proton beam at the AGS. \item Studies of a liquid-metal jet entering a 20-T magnet at the National High Magnetic Field Laboratory (NHMFL) in Florida. \item Studies of a full-scale liquid-metal jet in a beam of $10^{14}$ protons per pulse, but without magnetic field. \item Studies of a liquid-metal jet + proton beam + 20-T pulsed solenoid magnet. \item Studies of a 70-MHz rf cavity downstream of the target in the proton beam, but without a magnet around the cavity. \item Continuation of topic 5, with the addition of a 1.25-T, 1.25-m-radius solenoid surrounding the rf cavity. \item Characterization of the pion yield downstream of the target + rf cavity. \item Simulation of the performance of liquid-metal targets: thermal shock, eddy currents. Validation of the simulation by exploding-wire studies. \end{enumerate} The first two topics in the program should establish reasonably quickly whether there are any first-order difficulties in the use of a free liquid jet as a proton target in a strong magnetic field. Should this be the case, the solid-band option then would be emphasized. Topics 3-7 explore the next level of technical difficulties in constructing a target that meets the parameters of a muon-collider source. Not covered in this program are the serious issues of operation of a moving target in a high-repetition-rate beam and in the consequent intense radiation environment. Topics 1 and 3-7 are to be pursued in the FEB U-line of the AGS. In no case do we require more than a few beam pulses per hour. However, there are several other beam requirements that are very aggressive: \begin{itemize} \item RMS beam-spot size $\sigma_r = 1$ mm for a single extracted bunch of $10^{13}$, 24-GeV protons at the target station for topic 1. \item Six-bunch extraction of $10^{14}$, 24-GeV protons for topics 3 and 4. \item Pulses of length $\sigma_t = 2$ ns for topics 5 and 6. These pulses could be at 7 GeV, and could involve only single-bunch extraction. \item Slow beam of only $10^6$ protons/s at 16-24 GeV for topic 7. For this, the U-line could be operated as a secondary beamline. \end{itemize} Topics 4-7 involve apparatus of substantial size and likely will require development of a new target station along the U-line. The 20-T pulsed magnet of topic 4 also serves as the dump for the proton beam. If the U-line is to continue to be used by others for occasional studies with large integrated proton dose, the new target station must be located downstream of a removable beam dump, to avoid excessive activation of our apparatus. Considerable magnet power is required: \begin{itemize} \item The 20-T pulsed magnet of topic 4 requires 4 MW. It is designed to be energized by the MPS power supply, which would be relocated to the U-line. \item The 1.25-T solenoid magnet that surrounds the rf cavity of topic 6 will require 1.2 MW, if its coil is resistive. \item The 2-T bent solenoid magnet of the spectrometer of topic 7 will require 1.4 MW, if its coil is resistive. \end{itemize} A scenario is presented for accomplishing this R\&D program over a four-year period, with funding estimated at approximately \$1, \$2, \$3, and \$1M for the four years, respectively. \newpage \tableofcontents \newpage \pagenumbering{arabic} %\medskip \section{Introduction} \input targetprop.intro \clearpage \section{Critical Targetry Issues} \input targetprop.issues \clearpage \section{The R\&D Program} \input targetprop.program \input targetprop.appendix \clearpage \section{Appendix C: Personnel, Schedule, Budget} \input targetprop.budget \clearpage \begin{thebibliography}{99} \input targetprop.bib % \end{document} -- this is contained inside targetprop.bib