Production and Collection of Pion and Muon beams
B. Autin†, J.M. Maugain, P. Sievers, A. Verdier (CERN)
François Méot (CEA-DAPNIA)
26 November 2002
CEA-CERN
Possible
associate laboratories or institutes
IN2P3-Orsay,
RAL, Jülich, PSI, University of Cracow, MAFF ( Munich Accelerator for
Fission Fragments)
.
General
introduction
The
history of neutrino physics follows the traditional line of particle physics
starting with cosmic rays and continuing with accelerator beams. Three
generation of beams can be distinguished:
1.
present
or already decided experiments: K2K, MiniBOONE, MINOS and CNGS,
2.
“super
beams” using higher power proton accelerators (JHF) below 1MW and the off-axis
pion beams,
3.
“ultimate beams” using multi MW proton beams
and combining muon and electron neutrinos or anti-neutrinos.
The
neutrino factory based on muon decay belongs to the third category and time for
decision about such a project is between 2010 and 2015. The project proposed
here concerns the target systems of a neutrino factory including target
technology, transverse collection of pions and muons, beam dump and radiation
shielding. It could be tested, at least in part, on the super-beams before
being applied to the neutrino factory. If pions are the relevant particles for
muon and neutrino physics, neutrons are also produced in abundance. Tests and
applications can thus be envisaged for neutron spallation sources and
accelerator driven systems (ADS) considered for nuclear waste incineration and
energy generation.
Objectives
of the proposed project
The
target systems of ultimate neutrino beams which have been most studied up to
now concern mercury jets emitted in high solenoidal fields. Their technology
has a lot in common with advanced nuclear fusion projects such as ITER. Their
cost is evaluated in the 100 M$ range. Reducing the cost of a neutrino factory
is mandatory to make it acceptable by the particle physics community especially
if a very high energy lepton collider is also wanted. What we propose is a
drastic simplification of the present design by replacing the solenoid by a
magnetic horn, the mercury jet by a solid target and possibly the solenoidal
decay channel by quadrupoles.
In the
scheme presently developed at CERN, the proton driver is a proton linac of 2.2
GeV kinetic energy and its repetition frequency is 50 Hz. All the pulsed
systems acting on the pions or muons must have the same repetition frequency.
Among them, the most critical element is the magnetic horn which focuses the
pions with a current of 300 kA.
The
target takes advantage of this high repetition rate because the instantaneous
temperature rise is such that it can work in a regime where thermal shock waves
are harmless. However, the heat deposited by the proton beam must be quickly
eliminated. It is anticipated that horn and targets will work under extreme
conditions if a single system is exposed to the full charge of the proton beam.
A multiple target and horn scheme is thus under study to improve the
reliability.
The
project has thus five medium and long term objectives.
1.
Reduce
the cost of the presently designed critical elements of the target systems of a
neutrino factory by an order of magnitude yet maintaining acceptable performances.
2.
Build
a high current (300 kA) and high repetition rate (up to 50 Hz) power supply to
test the various pulsed components (horn and magnets). This power supply could
serve as a general test facility for a large range of pulsed devices and not
only within the context of neutrino beams.
3.
Build
a granular target with its cooling circuit and test it in the Oakridge neutron
spallation source.
4.
Test
of the integrated target and horn system in the JHF neutrino beam.
5.
Design
of a multiple channel target system and construction of prototype magnets.
Program
of the project
The system of production and collection of pions and muons has to achieve as high a collection rate as possible in the adverse environment of multi MW beams. The lifetime of the components is a major concern. To address this problem, multiple targets and horns are foreseen so that each subsystem works at a repetition frequency and is exposed to a beam power divided by the number of sub-systems. Typically four channels are considered. Downstream of the horns, the beams are recombined into a single beam line using large aperture magnets that encompass all the beams.
The critical components are the target, the windows traversed by the primary proton beam, the horn and the first magnets. An iterative process between beam dynamics and engineering aspects is to be conducted to converge towards a satisfactory design.
Theory
In all cases, the properties of a tertiary beam have to be optimized. The chain of reactions is indeed p → π → ν for super-beams and p → π → μ for ultimate beams. The various tasks to be accomplished can be listed as follows:
· Proton switchyard.
· Shape and current of the magnetic horn for pions of average energy near 4 GeV and 300 MeV in the case of super and ultimate beams respectively.
· 6D pion distribution at the end of the horn.
· Recombination scheme and magnet characteristics.
· Trajectories of primary and secondary particles downstream of the horn.
·
6D muon distribution at the end of the decay channel.
·
Option of a longitudinal capture of the pions in the
decay channel and characteristics of the RF cavity.
Manpower: 10 man-years.
Cost : 400 k€.
The target design is sufficiently advanced to plan development work.
· Validation of the cooling system (water, air, helium), construction of components 25 k€, spent in 2003.
· Setting up of test at CERN (or in another laboratory where 600 A and de-mineralized water and/or compressed air is available in sufficient quantity) in 2003/4. Manpower for setting up and tests: 6 man-months in 2003/4. Cost: 30 k€.
·
Design, construction and test of prototype target in
single shot mode in a p-beam. Cost: 80 k€ for design and hardware in 2003/4.
Manpower: 6 man-months.
Horn
A prototype horn for a neutrino factory has already been built at CERN.
The unknown is its lifetime that is supposed to be limited by fatigue due to
the combination of electro-mechanical and radiation effects. Technological
study of the horn:
·
Determination of the mechanical characteristics of a sample of alloy
used for the horn as a function of the radiation dose. Calculation of the
mechanical response of a horn to electrical pulses using the characteristics of
an irradiated material.
Cost: 100 k€.
Manpower: 2 man-years.
·
Test of a non-irradiated horn at 300 kA and 50 Hz.
Manpower: 0.5 man-year. Cost: 30 k€.
Power supply, electrical connections and
controls
The power supply, electrical connections and controls should be built with the present state of the art without special development.
· Design and development cost: 350 k€.
·
Construction of charging unit, capacitor bank,
discharge switches, connections and controls: 700 k€.
Test of integrated target and horn
Design of a target system including its full cooling
system to be integrated into a horn for test in the laboratory in 2004/5.
Cost: 380 k€.
Manpower: 2 man-years.
Magnets
In the present design, the first magnets have an aperture larger than 1
m exceeding their length, they are pulsed and are under the fire of secondary
particles. Their study requires:
·
Basic design with choice between magnetic poles or distributed currents
in a circular aperture.
·
Determination of the integrated dipolar and quadrupolar fields on the
reference orbits.
·
3D field map in the presence of adjacent magnets.
·
Correction of undesired multipolar components.
·
Possible need for end magnetic mirrors.
·
Resistance to radiation of insulation between coils and electrical
insulators.
·
Construction of a prototype and test with the general purpose pulsed
power supply.
Cost: 360 k€.
Manpower: 2 man-years.
Beam dumping and target zone
This
subject is not treated yet and might be discussed with the experts of the muon
collaboration.
Summary
Requested
funding from EU? 2455 k€.
The next questions will be addressed in the second draft.
What fraction of the overall cost of the
project is it?
How do you intend to spend the requested
funding?
Funding breakdown, In particular was fraction
is required for manpower (engineers, post-docs, students…), for durable
equipments, for travel and subsistence, for organization of meetings/workshops…
What is the anticipated funding sharing between
participating institutes/lab/industry?