Project of a Next-generation ISOL Facility for Exotic Beams at LNL
In the framework of the European program to define a second generation Radioactive Ion Beam facility, LNL are proposing the construction in the next five-seven years of a specialized national facility for RIB originated by fission fragments produced by secondary neutrons. It consists on a two-accelerator ISOL-type facility to provide intense neutron-rich radioactive ion beams of highest quality, in the range of masses between 80 and 160. The conceptual design is based on a high intensity 50 MeV (100 kW) proton linac as driver and on the availability of the heavy-ion accelerator ALPI as post accelerator. The estimated neutron yield is 2 x 10 n/s at 0, high enough to satisfy the demand for an advanced RIB facility. An intense R\&D program on different items is actually in progress in collaboration with other Laboratories and University groups and is moving in a European context.
A 100 MeV Superconducting Proton Linac: Beam Dynamics Issues
Proton linacs with beam intensities between 10 and 120 mA in CW are under study in various laboratories, for applications that go from fundamental physics to energy production and nuclear waste transmutation. The majority of the projects consider, for energy above 100 MeV, the use of a superconducting linac, which is particularly convenient for "moderate" currents (10-50 mA). For the low energy part the situation is unclear, and the advantages of a superconducting structure have not been generally recognized yet. In this paper we consider a possible architecture for a 100 MeV linac based on independently phased resonators, and we give a first analysis of the beam dynamics issues, and the resulting cavity specifications. The flexibility of such a linac, for the use with different charge over mass ratios and beam currents, will be underlined.
Superconducting Re-Entrant Cavities for Heavy Ion Linacs
Superconducting niobium cavities of reentrant shape have been built and tested at Stanford. The cavities have a 35cm diameter, 10cm length, and 2cm accelerating gap. They resonate at 430 MHz. A large number of tests show that the performance of the cavities is reproducible: field strengths in excess of 12 MV/m were consistently achieved at Q values in the range 2 × 109 to greater than 1010. The highest field obtained was 17 MV/m. To obtain these performance levels, our studies show that it is necessary to use special fabrication procedures, chemical treatment, and of perhaps greater importance, ultra high vacuum firing to temperatures of 1600 to 1800°C. The geometry of the accelerating gap of the cavities in relation to the resonant frequency, make the cavities suitable for accelerating heavy ions with energies upward of 1 MeV/nucleon. A sequence of cavities could thus be used to boost the energy of particles obtained from existing tandem Van de Graaff accelerators. Compared with a superconducting helix structure, the reentrant niobium cavities have a much greater mechanical stiffness, much larger surface area for cooling, comparable or better accelerating voltage gradients, and provide a single rather than a "double" accelerating gap per resonator. The latter feature makes it possible to build an accelerator as a sequence of independently controlled accelerating gaps. The phase and amplitude of each gap can be adjusted to provide essentially any velocity profile for the purpose of particle acceleration.