The UK Neutrino Factory Design

1
The UK Neutrino Factory Design
This diagram shows the main systems that
constitute the neutrino factory. Four areas are
highlighted in which the UK will perform key
technology demonstrations within the next five
years.
Proton Driver Front-End Test Stand (FETS) The
basis of a neutrino factory is a powerful (45MW)
pulsed proton accelerator, known as a proton
driver. It starts with an H- ion source followed
by components for low-energy beam transport and
acceleration (LEBT, RFQ). An important operation
known as beam chopping must also be performed at
low energies it produces clean gaps in the beam
that allow injection into a circular accelerator
without any beam loss, which at these power
levels would produce unacceptable
radioactivity. The LEBT and RFQ are being
designed at Warwick and Imperial College
respectively, while RAL has an active ion source
research programme and chopper development
project. Together, these will make FETS a
full-scale prototype of the initial segment of
the proton driver, soon to begin construction at
RAL. Other Applications The proton driver for a
next-generation neutron spallation source is very
similar to that for the neutrino factory and FETS
meets the specification for both projects. The
technique of beam chopping will find applications
in nearly all high-power proton accelerators,
including those for nuclear waste transmutation,
materials testing (for example IFMIF, which
supports the ITER fusion experiment) and safe
subcritical nuclear power plants known as energy
amplifiers.
The neutrino factory complex could be built up in
stages an outline plan exists to incrementally
upgrade the ISIS accelerator at RAL, supporting
both the neutrino factory and enhancements to the
current neutron and muon science (aligning with
the UK Neutron Strategy technology case). The
neutrino factory itself can be upgraded to a
high-energy machine known as the muon collider,
which would extend capabilities across the whole
of particle physics, surpassing the LHC at CERN
in several areas.
Present 2010s 2020s 2030s
Proton Power 150kW 1MW ? 2.5MW ? 5MW 1MW ? 2.5MW ? 5MW
Neutron Science ISIS ISIS MW Upgrade ESS-class Machine
Neutrino Physics Neutrino Factory
Fundamental Higgs Physics Muon Collider
Left staging scenario leading to a UK muon
collider.
Right plan view of the new accelerators
superimposed on the RAL and Harwell site.
LEBT Low Energy Beam Transport
RFQ Radio Frequency Quadrupole
H- Ion Source
Beam Chopper
180MeV H- Linac
Achromat for removing beam halo

• Two Stacked Proton Synchrotrons (full energy)
• 6GeV
• 78m mean radius
• Each operating at 25Hz, alternating for 50Hz
  total

• Proton bunches compressed to 1ns duration at
  extraction
• Mean power 5MW
• Pulsed power 16TW

Stripping Foil (H- to H/protons)
FFAG Electron Model of Muon Acceleration
(EMMA) An new kind of accelerator called a
non-scaling FFAG has been devised for muon
acceleration before the storage ring. FFAGs, or
Fixed Field Alternating Gradient accelerators,
achieve similar goals to synchrotrons but with
fixed magnetic fields. This removes a major
limitation for the neutrino factory as muons,
which decay in roughly 2.2ms, must be accelerated
quickly and powerful magnets can only be varied
slowly. The term non-scaling here means that
cheaper dipole and quadrupole magnets can be used
instead of the original, custom-shaped scaling
FFAG magnets. Despite these advantages, a
non-scaling FFAG has never been built before. A
scaled-down machine called EMMA, using electrons
instead of muons, could soon demonstrate the
technology at Daresbury Laboratory, where an
existing electron accelerator will be able to
provide its input beam. Other Applications FFAGs
have the potential to lower the cost or increase
the performance of a variety of accelerators.
Proton and ion versions of the machines have been
suggested as compact sources for next-generation
cancer radiotherapy. Larger versions could be
competitive with synchrotrons as proton drivers.

• Two Stacked Proton Synchrotrons (boosters)
• 1.2GeV
• 39m mean radius
• Both operating at 50Hz

Target enclosed in 20Tesla superconducting
solenoid
Solenoidal Decay Channel (in which pions decay to
muons)
RF Phase Rotation
(produces pions from protons)
Proton Beam Dump
FFAG I (3-8GeV)
Muon Cooling Ring
FFAG II (8-20GeV)
FFAG III (20-50GeV)
Solenoidal Muon Linac to 3GeV (other technologies
possible)
Muon Ionisation Cooling Experiment (MICE) The
muon beam must be cooled, or reduced in size,
to fit inside the accelerators downstream. This
can be achieved by a technique known as
ionisation cooling. The principle of ionisation
cooling is to pass muons travelling in a range of
directions through a material or absorber whose
constituent atoms they ionise, losing energy in
the process. Momentum is lost in the direction
of travel, but then replaced only in the forward
direction by the electric field in an
accelerating cavity placed after the absorber.
Thus transverse momentum is consistently removed,
producing a well-collimated beam of muons that
can be focussed to a smaller size
downstream. While muon cooling is theoretically
possible, it has not been tried in practice and
the technical obstacles are considerable for
instance, the best absorber material is liquid
hydrogen, which must be contained and cooled to
cryogenic temperatures. Therefore the MICE
Collaboration will build a short section of an
ionisation cooling channel at RAL, using muons
from the ISIS accelerator to measure the cooling
effect to an accuracy of 0.1, in order to
predict the performance of the full neutrino
factory cooling channel.
9001000 m below ground
Physics Motivation The recent discovery that
neutrinos have mass has invalidated the current
standard model of physics. A new theory is
required, with the potential to explain on a
deeper level why the particles of nature are as
they are, but the only experimental data that can
inform such a theory is data that contradicts the
standard model. Hence neutrino mass measurements
are one of the few windows onto these new laws of
nature. When neutrinos were believed to be
massless, their interaction with other leptons
(via the weak nuclear force) was predicted to
occur in a straightforward manner, where ne
interacted with e, nm with m and nt with t.
However, with the introduction of mass, the
states previously believed to be fundamental
turned out each to be a mixture of new states n1,
n2 and n3. As these parts have different masses,
their quantum wavefunctions will become out of
synchronisation over time, making the mixed
neutrino appear to oscillate so that it interacts
with types of lepton other than the one it was
formed with. This oscillation occurs as a
function of L/E, the distance to the detector
divided by the neutrino energy. As higher-energy
neutrinos are much easier to detect, the neutrino
factory places detectors as far away as practical
from the source to let these oscillate fully.
The oscillation wavelength measured will be a
direct indicator of the neutrino masses.
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THE UK NEUTRINO FACTORY CONCEPTUAL DESIGN AND
DEVELOPMENT S J Brooks, on behalf of the UKNF
Collaboration (E-mail s.j.brooks_at_rl.ac.uk
Tel [phone]) ASTeC Intense Beams Group,
Building R2, Rutherford Appleton Laboratory,
Chilton, Didcot, Oxfordshire OX11 0QX In the last
decade, one of the most surprising discoveries in
particle physics was that neutrinos are not
massless particles, as previously believed, but
instead have very small masses. A powerful and
high-quality source of neutrinos is needed to
make accurate measurements that will provide the
deciding factor between alternative unified
theories of physics, currently indistinguishable
by experiment. The Neutrino Factory is a particle
accelerator complex that would produce neutrinos
beams able to travel through the Earths interior
and be detectable thousands of kilometres away.
The neutrinos in this beam are produced by the
decay of another particle called the muon. Muons
need to be accelerated to high energies in order
to produce neutrinos in sufficiently focussed
beams, which is a significant challenge as the
acceleration must happen before they decay (muons
last on average 2.2 microseconds). Muons also
need to be manufactured with another accelerator
since such unstable particles are not readily
obtainable in nature. This is achieved by
colliding a proton beam of power 4-5MW with a
stationary target, producing muons as reaction
products. This proton accelerator is also
suitable for use as an intense pulsed neutron
source, providing an order of magnitude
improvement over the current record-holding ISIS
source. The UK has a diverse programme of
Neutrino Factory RD under the UKNF
Collaboration. Research activities focus on
design and computer modelling for the various
subsystems, several of which use techniques never
used before in accelerators. Development
projects such as MICE, EMMA and FETS will
demonstrate in reality the key technologies
required for a neutrino factory.
Web Links UK Neutrino Factory website (links to
all related projects) http//hepunx.rl.ac.uk/uknf/
International Scoping Study of a Neutrino
Factory and Super-Beam Facility http//www.hep.ph.
ic.ac.uk/iss/ Muon1 a public distributed
computing project to optimise the neutrino
factory http//stephenbrooks.org/muon1/