F ixed F ield A lternating G radient Synchrotrons

1. 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 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 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 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. 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. 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 been both studied and employed for cancer treatment over many years, in laboratories all over the world. Energy deposition from electrons, photons and carbon ions. The fact that ions and protons deposit most of their energy at the end of their range makes them ideal for cancer therapy. 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. A comparison between proton and conventional radiotherapy from Loma Linda University Medical Centre clinical results, courtesy of IBA. Other possible commercial uses:  Scanning of trucks and containers using X-rays from intense electron beams or muon beams  ion implantation  radioactive isotope production  industrial irradiation  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. 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 non-scaling 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. Proton and Ion Cancer Therapy 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. 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 and perform a 3D scan of the tumour. Boron Neutron Capture Cancer Therapy Accelerator Driven Sub-critical Reactors 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. 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 U-233, 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. 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. Tests of BNCT have employed nuclear reactors, but these are impractical for large scale day-to-day treatment. An FFAG could provide the neutrons rather than a reactor. 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. 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. 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. What still needs to be done ? Physics research applications currently under study for FFAGs 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.  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. 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 non-scaling 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 current Neutrino Factory layout in the USA. 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 !