International partners are being sought for the AUSTRON, a proposal for a pulsed high-flux neutron spallation source which could provide an international research centre in central Europe. Austria has offered to put up a third of the costs.
In 1996 the Austrian Government declared its intention to aim for a large-scale international research facility,
and the AUSTRON proposal was submitted by the Ministry of Science and Research to the European Science Foundation (ESF) for assessment.
In November 1997 the ESF panel recommended the AUSTRON project as a potential candidate for a medium- to large-scale international research facility based on a pulsed high-flux neutron spallation source. It was suggested that some aspects of the regional impact and specific issues regarding the instrumentation should be added. The Ministry requested a project group to gather the extra information and to prepare a project proposal for international presentation.
Based on a decision of the Austrian Government dated 20 August 1998, Austria is offering to contribute one-third of the total cost of the AUSTRON, and international partners are now invited to participate. Although the AUSTRON offers obviously attractive and unique possibilities for research with neutrons, extensive political negotiations with potential transnational partners will be needed to conclude such co-financing agreements. The partners may contribute to the project both in cash or in kind. Political as well as financial decisions need to be taken within the next few months.
Around 1000 users of neutron facilities have been identified within the Central European Region (the catchment area of AUSTRON) according to a report by the European Neutron Scattering Association. And the number is growing, particularly in the eastern countries.
In contrast, the number of neutron sources in Europe (today more than 20) will have dropped to less than six by 2015. The proposed AUSTRON project for a pulsed neutron spallation source is a great opportunity for the neutron scattering community in Europe to counteract this developing “neutron gap”.
Accelerator
The AUSTRON is based on an accelerator design using state-of-the-art technologies to allow for a relatively short construction period and a favourable ratio of cost to scientific and technological potential. The proposal is for a 0.5 MW neutron source which can be operated with 10 Hz repetition rate. To generate a proton beam with 1.6 GeV energy per particle and an average beam current of 0.311 mA, the accelerator chain comprises an H-ion source, a radiofrequency quadrupole and a drift tube linac, providing a final ion energy of 130 MeV, from which the ions enter a rapid-cycling synchrotron via a stripper foil which removes their electrons to enable the acceleration of a high-intensity proton beam to a final energy of 1.6 GeV. Using a dual-frequency magnetic cycle, losses should be kept to about 0.5%, occurring at lowest energies during trapping only.
The operation frequency of the acceleration process has been determined to be 50 Hz. In principle, all neutron scattering instruments could be operated at this repetition rate. Since, however, there is strong emphasis on cold neutron instrumentation, a preference for a lower operation frequency was expressed for these instruments.
This can be achieved by adding an additional storage ring which works as a bunch accumulator for the proton bunches leaving the rapid-cycling synchroton (RCS). With such an installation, stacking of up to four proton bunches is feasible. Extracting these bunches together with the bunch which has just reached its final energy in the RCS gives a 10 Hz source with 1.6 GeV protons (some 2×1014 protons in total), which deposit 50 kJ per pulse on the spallation target.
The average thermal neutron flux is expected to be 7×1012 neutrons cm-2 s-1 with a peak flux of some 3.5×1016. This configuration will make AUSTRON truly unique among present neutron sources. The effective flux for certain classes of neutron instruments will be increased by a factor of 15-20 compared to present standards.
With more than an order of magnitude higher performance, the exploration of completely new fields of research can be envisaged. Furthermore, the 10 Hz option takes the increasing demand for cold neutron scattering into account and no flux penalty will be experienced by those instruments usually operated at higher frequencies.
Concerning AUSTRON’s relation to the proposed European Spallation Source (ESS ), these facilities will belong to two different generations of neutron sources which will be separated by a decade in time and an order of magnitude in beam power.
For the target design, a flat target geometry is proposed. The target material under consideration is solid tungsten/5%-rhenium with its excellent thermal and mechanical properties. The target block will be 10 cm high, 30 cm wide and 60 cm long. Due to the edge-cooling concept, cooling channels are only installed within 2 cm of the top and bottom surfaces.
Calculations of the temperature distribution in the target, based on a 0.5 MW version of AUSTRON running at 50 Hz, yield a maximum of 1200-1300 °C. Edge-cooling is possible under these conditions and an improved cooling system has been designed. Material properties such as ductility, thermal conductivity or self-healing after irradiation damage look favourable for this temperature range. From the present point of view, a 50 Hz, 0.5 MW solid W5%Re target is feasible. Operation with 10 Hz/0.5 MW leads to a marginal temperature increase of less than 10 °C.
The suggestion has also been made to operate the target at even higher temperatures, above 2000 °C, and to cool by radiation cooling only, which would help to avoid thermally induced stress inside the target block. The final decision on the target design will take place in the design phase immediately after approval of the project.
