Transcript Document

Fixed Field Alternating Gradient Synchrotrons
A new type of particle accelerator - with a wide variety of applications
Potential Applications and UK Activities
A wide variety of possible applications
FFAGs are a new type of accelerator with properties that lead to wide variety of possible
applications. In particular:
 they can be used to accelerate protons, electrons, muons and ions
 they can be rapidly cycled, much faster than a synchrotron
 they have a large acceptance for a particle beam, much bigger than a synchrotron
 they have the possibility of both large average and large peak beam currents
 they consist of a magnetic ring and do not require the same large magnets as
cyclotrons
 they do not have the same restrictions on energy as a cyclotron
 beam can be extracted at a number of energies
A number of FFAGs have already been constructed and more are now being developed for a variety of possible applications in medicine, industry and scientific research. In addition,
it is planned to build a model of entirely new type of FFAG which could bring substantial costs savings over those investigated so far.
Proton and Ion Cancer Therapy
Radiotherapy forms a major component in the
treatment of cancer, with 40-50% of patients
being treated in this way. Photons, in the form
of X- or gamma rays, are most commonly used
but have the problem that much of the energy
is deposited in healthy tissue surrounding the
tumour, rather than in the tumour itself.
Ideally, proton and ion therapy require very small, intense and mono-energetic beams. The
energy is particularly important, as this controls the depth at which the main energy
deposition takes place. In general, the protons used for this therapy are accelerated using
cyclotrons, which can only give a single proton energy. To produce the correct energy, this
must be degraded using absorbers and this can produce an undesirable spread.
Protons and light ions, on the other hand,
deposit most of the energy at one place which
depends on the energy of the proton or ion. In
addition, beams of these particles can be
steered and focused, making them ideal for
radiotherapy. As a result, proton and ion
therapy, in particular with carbon ions, have
Energy deposition from electrons, photons and carbon ions.
been both studied and employed for cancer
The fact that ions and protons deposit most of their energy at
treatment over many years, in laboratories all
the end of their range makes them ideal for cancer therapy.
over the world.
Both have proved very successful, protons particularly in the treatment of tumours for which
conventional radiotherapy presents an unacceptable risk, for example cancer of the eye, the
brain and the prostate. Carbon ion therapy is proving beneficial in the treatment of certain
cancers which are resistant to conventional radiotherapy with photons, for example in the liver,
pancreas and parotid gland.
Accelerator Driven Sub-critical Reactors
Accelerator Driven Systems address two main, but related, issues to do with nuclear power generation. The first is to
drive sub-critical nuclear reactors based on thorium-232 (Th-232). There has been interest in using thorium for
many years as it is 3 times more abundant in the Earth's crust than uranium and in principle all of it can be used in a
reactor, compared to 0.7% of natural uranium. It works by absorbing a neutron to become Th-233 which decays to U233, which fissions. The problem is there are insufficient neutrons generated to sustain the reaction. In ADS, a high
intensity proton accelerator is used to generate the neutrons required to sustain the reaction by spallation. It has a
big advantage over conventional reactors, in addition to burning thorium: if the accelerator is turned off, the
reactor stops without the need to employ moderators to absorb neutrons.
FFAGs, on the other hand, can
produce particle beams with a
variety of energies. A prototype
under test in Japan is designed for
three, but more may be possible.
This will reduce, if not eliminate,
the need for absorbers.
Furthermore, FFAGs produce very
intense particle bunches, so in
principle it will be possible to
select from these intense bunches
of exactly the right characteristics
A comparison between proton and conventional radiotherapy from and perform a 3D scan of the
Loma Linda University Medical Centre clinical results, courtesy of tumour.
IBA.
Boron Neutron Capture Cancer Therapy
BNCT is a possible method for treating one of the deadliest forms of cancer, a type of brain tumour
called a "glio-blastoma multiforme". This afflicts 12500 people in the USA each year, for example, and is
always fatal. In BNCT, a compound containing boron-10, a non-radioactive isotope, is introduced into the brain
and preferentially absorbed by the tumour. This is then exposed to intense neutron beam which causes the
boron-10 to fission, releasing an alpha particle and lithium nucleus. Both of these have a very short range and
hence destroy the malignant cells that the boron is in without damaging healthy cells.
BNCT has been investigated in a number of countries
with very positive results. Most studies have
employed reactors as the neutron source, which is not
practical for treating many patients on a day-to-day
basis. FFAGs provide a possible solution for producing
enough neutrons to treat patients in hospital and a
study of this has recently started in Japan.
The second issue is the transmutation of radioactive waste.
Along with safety, the disposal and storage of the waste is one
of main problems of nuclear power generation. In transmutation,
the long-lived waste is bombarded with neutrons which in
most cases causes fission and gives (in general) short-lived
products. This also generates energy and transmutation could
be combined with a sub-critical reactor.
Other possible commercial uses:
FFAGs are ideal for this application due to the high beam
intensity and rapid cycling. A five year project started at
Kyoto University Research Reactor Institute in 2002 to
develop an FFAG and a reactor to test the feasibility of this
form of energy generation and nuclear waste transmutation.
 Scanning of trucks and containers using X-rays from
intense electron beams or muon beams
 ion implantation
 radioactive isotope production
 industrial irradiation
A drawing of an ADS scheme using a linear
accelerator. There are a number of benefits to using
an FFAG for the proton acceleration instead.
Tests of BNCT
have employed
nuclear reactors,
but these are
impractical for
large scale dayto-day
treatment. An
FFAG could
provide the
neutrons rather
than a reactor.
What still needs to be done ?
Physics research applications currently under study for FFAGs
 high power proton drivers: FFAGs are being considered in relation to a number of future, high power proton drivers.
 eRHIC: a 10 GeV electron FFAG is being investigated as part of the project to create electron-ion collisions at the
Brookhaven Laboratory.
 ion acceleration: FFAG rings have been proposed to accelerate ions as a part of
the EURISOL ion beam facility.
 muon acceleration: the current layouts for a Neutrino Factory in Japan and the
USA employ FFAGs to accelerate the muons, while this form of acceleration is
also under study in Europe.
 muon FFAG: an FFAG will be constructed soon in Japan to make precise
measurements of the properties of muons.
The current Neutrino Factory layout in the USA.
What are we planning to do in the UK?
Physicists from the UK started working on scaling FFAGs about 2 years ago and have been investigating
the use of these machines for a variety of applications. More recently, we have become interested in nonscaling FFAGs and in particular the non-scaling FFAG model. It is now proposed to build this unique
machine at the Daresbury Laboratory in Cheshire, in collaboration with colleagues from Europe, Japan
and the US. Existing infrastructure at Daresbury will be used to provide the electron beam. Funding is
being sought from the European Commission Framework 6 Programme and elsewhere. Successful
operation of this machine will have a major impact in the world of accelerators. In addition, we will
continue to investigate the utility of both types of FFAGs for high power beam applications.
There are two types of FFAG envisaged. All those built or under construction so far are
so-called "scaling" FFAGs in which the orbits of particles around the machine are the same,
except they scale with energy. The problem with this is the magnets required tend to be
large and complex, and hence quite expensive.
The second type is a "non-scaling" FFAG, in
which the orbit shapes change as a function
of energy. This allows the apertures of the
magnets to be up to 10 times smaller than
for a scaling machine, making the FFAG
much more compact. In addition, the nonscaling magnets are less complex. Taken
together, these could make a non-scaling
machine considerably cheaper than a scaling
machine for the same performance.
A magnet for the prototype 150 MeV
scaling FFAG built at KEK. The
magnets for a non-scaling FFAG
could have a 10 times smaller
aperture, making them smaller and
cheaper.
The orbit shape in scaling FFAG cells is the same at each energy, but varies with non-scaling machines. This allows
the apertures of the magnets to be much smaller in the latter, reducing the cost for the same performance.
The non-scaling nature of the second type of FFAG introduces a number of problems,
however. In particular, there are a number of features which are entirely novel to
this type of machine and never before tested in an accelerator. As a result, it is
planned to build a small electron non-scaling FFAG, the first of this type ever built,
to check that none of these features will stop the machine working.
We are seeking collaborators to work with us on the development of this novel form of accelerator for any of the
potential applications !