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FAIR builds future for ion and antiproton research

30 April 2007

Construction should begin later this year on the new Facility for Antiproton and Ion Research in Darmstadt, and the first experiments could start up in 2012.

Résumé

FAIR construit l’avenir de la recherche des ions et des antiprotons

La construction de FAIR (l’Installation de recherche sur les antiprotons et les ions) devrait commencer cette année à Darmstadt et les premières expériences pourraient débuter en 2012. Actuellement, 14 pays ont manifesté leur intention de participer au projet, qui nécessite un investissement d’environ un milliard d’euros. L’installation fournira une gamme de faisceaux de particules sans précédent. Elle s’appuiera sur deux synchrotrons supraconducteurs qui seront construits l’un sur l’autre dans le même tunnel et fourniront différents faisceaux d’ions lourds. Un dispositif adjacent d’anneaux de stockage, de cibles de production et de séparateurs fourniront des faisceaux d’antiprotons et des faisceaux radioactifs secondaires.

In 2001, GSI, together with a large international science community, presented the Conceptual Design Report (CDR) for a major new accelerator facility for beams of ions and antiprotons in Darmstadt (Henning et al. 2001). The following years saw the consolidation of the proposal for the project, which was named the Facility for Antiproton and Ion Research (FAIR). During that process high-level national and international science committees evaluated the project’s feasibility, scientific merit and discovery potential, as well as the estimated costs. About 2500 scientists and engineers from 45 countries contributed to this effort, which resulted last year in the FAIR Baseline Technical Report (BTR) (Gutbrod et al. 2006).

The International Steering Committee has accepted the BTR as the basis for international negotiations on funding for FAIR. The plan is to found a company, FAIR GmbH, as project owner for the construction and operation of the FAIR research facility under international ownership. Currently 14 countries (Austria, China, Finland, France, Germany, Greece, India, Italy, Poland, Romania, Russia, Spain, Sweden and the UK) have signed the Memorandum of Understanding for FAIR, indicating their intention to participate in the FAIR project; the European Union, Hungary and the US have observer status. The investment cost for the project will be about €1000 million, and about 2400 man-years will be required to execute the project. Negotiations at governmental level to secure the funding started in summer 2006. The aim is to complete this process in summer 2007 and begin construction in autumn. The construction plan foresees a staged completion of the facility in which the first experimental programmes commence as early as 2012 while the entire facility will be completed in 2015 (figure 1).

The research programme of FAIR can be grouped in the following specific fields:

• Nuclear structure and nuclear astrophysics, using beams of stable and short-lived (radioactive) nuclei far from stability.

• Hadron structure, in particular quantum chromodynamics (QCD) – the theory of the strong interaction – and the QCD vacuum, using primarily beams of antiprotons.

• The nuclear-matter phase diagram and quark–gluon plasma, using beams of high-energy heavy ions.

• Physics of very dense plasmas, using highly compressed heavy-ion beams in unique combination with a petawatt laser.

• Atomic physics, quantum electrodynamics (QED) and ultra-high electromagnetic fields, using beams of highly charged heavy ions and antimatter.

• Technical developments and applied research, using ion beams for materials science and biology.

The BTR lists 14 experimental proposals as elements of the core research programme. However, additional experiments as future options are already being considered and evaluated. In particular, experiments with polarized antiprotons could add an entirely new research field to the FAIR programme. One addition to the core research programme, as presented in 2001, is the Facility for Low-Energy Antiproton and Ion Research (FLAIR), which will exploit the high flux of antiprotons at FAIR. Here cooled beams of antiprotons with energies well below 100 keV can be captured efficiently in charged-particle traps or stopped in low-density gas.

The new SIS100/300 double synchrotron, with a circumference of about 1100 m and with magnetic rigidities of 100 and 300 Tm in the two rings, will meet experimental requirements concerning particle intensities and energies. This constitutes the central part of the FAIR accelerator facility (figure 2). The two synchrotrons will be built on top of each other in a subterranean tunnel. They will be equipped with rapidly cycling superconducting magnets to minimize both construction and operating costs.

For the highest intensities, the 100 Tm synchrotron will operate at a repetition rate of 1 Hz, i.e. with ramp rates for the bending magnets of up to 4 T/s. The goal of the SIS100 is to achieve intense pulsed (5 × 1011 ions per pulse) uranium beams (charge state q = 28+) at 1 GeV/u and intense (4 × 1013) pulsed proton beams at 29 GeV. A separate proton linac will be constructed as injector to the SIS18 synchrotron to supply the high-intensity proton beams required for antiproton production. It will be possible to compress both the heavy-ion and the proton beams to the very short bunch lengths required for the production and subsequent storage and efficient cooling of exotic nuclei (around 60 ns) and antiprotons (around 25 ns). These short, intense ion bunches are also needed for plasma-physics experiments.

The double-ring facility will provide continuous beams with high average intensities of up to 3 × 1011 ions per second at energies of 1 GeV/u for heavy ions, either directly from the SIS100 or by slow extraction from the 300 Tm ring. The SIS300 will provide high-energy ion beams of maximum energies around 45 GeV/u for Ne10+ beams and close to 35 GeV/u for fully stripped U92+ beams, respectively. The maximum intensities in this mode will be close to 1.5 × 1010 ions for each spill. These high-energy beams will be extracted over time periods of 10–100 s in quasi-continuous mode, which is the limit that the detectors used for nucleus–nucleus collision experiments can accept.

A complex system of storage rings adjacent to the SIS100/300 double-ring synchrotron, together with the production targets and separators for antiproton beams and radioactive secondary beams (the Super Fragment Separator), will provide an unprecedented variety of particle beams at FAIR. These rings will be equipped with beam-cooling facilities, internal targets and in-ring experiments.

The Collector Ring (CR) serves for stochastic cooling of radio-active and antiproton beams and will allow mass measurements of short-lived nuclei using the time-of-flight method when in isochronous operation mode. The Accumulator Ring (RESR) will accumulate antiproton beams after stochastic pre-cooling in the CR and also provide fast deceleration of radioactive secondary beams with a ramp rate of up to 1 T/s.

The New Experimental Storage Ring (NESR) will be dedicated to experiments with exotic ions and with antiproton beams. The NESR is to be equipped with stochastic cooling and electron cooling and additional instrumentation will include precision mass-spectrometry using the Schottky frequency spectroscopy method, internaltarget experiments with atoms and electrons, an electron–nucleus scattering facility, and collinear laser spectroscopy. Moreover, the NESR will serve to cool and decelerate stable and radioactive ions as well as antiprotons for low-energy experiments and trap experiments at the FLAIR facility.

The High-Energy Storage Ring (HESR) will be optimized for anti-proton beams at energies of 3 GeV up to a maximum of 14.5 GeV. The ring is to be equipped with electron cooling up to a beam energy of 8 GeV (5 MeV maximum electron energy) and for stochastic cooling up to 14.5 GeV. The experimental equipment includes an internal pellet target and the large in-ring detector PANDA, as well as an option for experiments with polarized antiproton beams.

The design of the FAIR facility has incorporated parallel operation of the different research programmes from the beginning. The proposed scheme of synchrotrons and storage rings, with their intrinsic cycle times for beam acceleration, accumulation, storage and cooling, respectively, has the potential to optimize parallel and highly synergetic operation. This means that for the different programmes the facility will operate more or less like a dedicated facility, without the reduction in luminosity that would occur with simple beam splitting or steering to different experiments.

The realization of the facility involves some technological challenges. For example, it will be necessary to control the dynamic vacuum pressure. The synchrotrons will need to operate close to the space-charge limits with small beam losses in the order of a few per cent; in this respect, the control of collective instabilities and the reduction of the ring impedances is a subject of the present R&D phase. Fast acceleration and compression of the intense heavy-ion beams requires compact RF systems. The SIS100 requires superconducting magnets with a maximum field of 2 T and with 4 T/s ramping rate, while the SIS300 will operate at 4.5 T with a ramp rate of 1 T/s in the dipole magnets – technology that will benefit other accelerators. Lastly, electron and stochastic cooling at medium and high energies will be essential for experiments with exotic ions and with antiprotons.

The past five years have seen substantial R&D effort dedicated to the various technological aspects. This has been funded by the German BMBF and by FAIR member states, as well as by the European Union. The work has made considerable progress and has demonstrated the feasibility of the proposed technical solutions. Now the next stage is underway and prototyping of components has started.

Further reading

W F Henning et al. (eds.) 2001 An International Accelerator Facility for Beams of Ions and Antiprotons, GSI Darmstadt, www.gsi.de/GSI-Future/cdr/.

H H Gutbrod et al. (eds.) 2006 FAIR Baseline Technical Report, www.gsi.de/fair/reports/btr.html.

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