Y. Kadi

Beam cooling with ionization losses

Abstract This novel type of Ionization Cooling is an effective method in order to enhance the (strong) interaction probability of slow (few MeV/A) ions stored in a small ring. The many traversals through a thin target strongly improve the nuclear reaction rate with respect to a single-pass collision, in a steady configuration in which ionization losses of a target “foil” (typically few hundred μg/cm 2 thick) are continuously recovered by an RF-cavity. With a flat foil, betatron oscillations are “cooled”, but the momentum spread diverges exponentially, since faster (slower) particles ionize less (more) than the average. In order to “cool” the beam also longitudinally, a chromaticity has to be introduced with a wedge-shaped “foil”. Therefore, in equilibrium conditions, multiple scattering and straggling are both balanced by phase-space compression. Classic Ionization Cooling [A.A. Kolomensky, Atomnaya Energiya 19 (1965) 534; Yu.M. Ado, V.I. Balbekov, Atomnaya Energiya 31(1) (1971) 40–44; A.N. Skrinsky, V.V. Parkhomchuk, Sov. J. Nucl. Phys. 12 (1981) 3; E.A. Perevendentsev, A.N. Skrinsky, in: Proceedings of the 12th International Conference on High Energy Acceleration, 1983, p. 485] is designed to cool the direct beam until it has been compressed and extracted for further use. In practice, this limits its applicability to non-interacting muon beams. Instead, in this new method, applicable to strongly interacting collisions, the circulating beam is not extracted. Ionization cooling provides “in situ” storage of the beam until it is converted by a nuclear interaction with the target. Simple reactions—for instance 7 Li + D → 8 Li + p —are more favourably produced in the “mirror” kinematical frame, namely with a heavier ion colliding against a gas-jet D 2 target. Kinematics is generally very favourable, with angles in a narrow angular cone (around ∼10° for the mentioned reaction) and with a relatively concentrated outgoing energy spectrum which allows an efficient collection of 8 Li as a neutral gas in a tiny volume, a technology perfected by ISOLDE at high temperatures. The method should be capable of producing a “table top” storage ring with an accumulation rate in excess of 10 14 8 Li radioactive ion/s. It has however a much more general applicability to many other nuclear reactions.

A Realistic Plutonium Elimination Scheme With Fast Energy Amplifiers and Thorium-Plutonium Fuel

In a previous report [1] we have presented the conceptual design of a subcritical device designed for energy amplification (production). The present note further explores the possibilities of the Energy Amplifier (EA) in the field of the incineration of unwanted actinide “waste” from Nuclear Power Reactors (PWR) and from the disassembly of Military Weapons.

Results from the commissioning of the n_TOF spallation neutron source at CERN

Abstract The new neutron time-of-flight facility (n_TOF) has been built at CERN and is now operational. The facility is intended for the measurement of neutron induced cross-sections of relevance to Accelerator Driven Systems (ADS) and to fundamental physics. Neutrons are produced by spallation of the 20 GeV /c proton beam, delivered by the Proton Synchrotron (PS), on a massive target of pure lead. A measuring station is placed at ≈185 m from the neutron producing target, allowing high-resolution measurements. The facility was successfully commissioned with two campaigns of measurements, in November 2000 and April 2001. The main interest was concentrated in the physical parameters of the installation (neutron fluence and resolution function), along with the target behavior and various safety-related aspects. These measurements confirmed the expectations from Monte Carlo simulations of the facility, thus allowing to initiate the foreseen physics program.

Neutron driven nuclear transmutation by adiabatic resonance crossing

The use of accelerator driven system (ADS) like for instance the Energy Amplifier concept (EA) proposed by C. Rubbia and his group might be one of the solutions to solve the energy problem and in particular to answer the question: what could we do with the nuclear waste produced by the present nuclear reactors? We present in this paper the EA concept, which is illustrated by two experiments performed at the CERN-PS facility. One of them is the TARC (Transmutation by Adiabatic Resonance crossing) experiment which is designed to demonstrate the high efficiency offered by the EA to destroy the long-lived fission fragments.

Neutron capture cross section of unstable 63Ni: implications for stellar nucleosynthesis.

The 63Ni(n,γ) cross section has been measured for the first time at the neutron time-of-flight facility n_TOF at CERN from thermal neutron energies up to 200 keV. In total, capture kernels of 12 (new) resonances were determined. Maxwellian averaged cross sections were calculated for thermal energies from   kT=5-100  keV with uncertainties around 20%. Stellar model calculations for a 25M⊙ star show that the new data have a significant effect on the s-process production of 63Cu, 64Ni, and 64Zn in massive stars, allowing stronger constraints on the Cu yields from explosive nucleosynthesis in the subsequent supernova.

New neutron detector based on micromegas technology for ADS projects

A new neutron detector based on Micromegas technology has been developed for the measurement of the simulated neutron spectrum in the ADS project. After the presentation of simulated neutron spectra obtained in the interaction of 140MeV protons with the spallation target inside the TRIGA core, a full description of the new detector configuration is given. The advantage of this detector compared to conventional neutron flux detectors and the results obtained with the first prototype at the CELINA 14MeV neutron source facility at CEA-Cadarache are presented. The future developments of operational Piccolo-Micromegas for fast neutron reactors are also described.

GEANT4 simulation of the neutron background of the C6D6 set-up for capture studies at n_TOF

The neutron sensitivity of the C6D6 detector setup used at n TOF for capture measurements has been studied by means of detailed GEANT4 simulations. A realistic software replica of the entire n TOF experimental hall, including the neutron beam line, sample, detector supports and the walls of the experimental area has been implemented in the simulations. The simulations have been analyzed in the same manner as experimental data, in particular by applying the Pulse Height Weighting Technique. The simulations have been validated against a measurement of the neutron background performed with a nat C sample, showing an excellent agreement above 1 keV. At lower energies, an additional component in the measured nat C yield has been discovered, which prevents the use of nat C data for neutron background estimates at neutron energies below a few hundred eV. The origin and time structure of the neutron background have been derived from the simulations. Examples of the neutron background for two di erent samples are demonstrating the important role of accurate simulations of the neutron background in capture cross section measurements.

The HIE-ISOLDE Project

The HIE-ISOLDE project is a major upgrade of the existing ISOLDE radioactive ion-beam facility at CERN. The present energy of 3 MeV/u for post-accelerated radionuclides will be boosted to up to 10 MeV/u which will allow experiments to address all exotic nuclides produced at ISOLDE using, e.g., Coulomb excitation and nucleon transfer reactions. A R&D program on the superconducting linear accelerator is ongoing, including cavity manufacturing with prototype and sputtering tests. Besides the energy upgrade, the beam quality has already been improved and the beam intensity will be increased in the future with the upgrade of the CERN injector chain. An overview of the HIE-ISOLDE project and the present status is given.

EURISOL High Power Targets

Modern Nuclear Physics requires access to higher yields of rare isotopes, that relies on further development of the In-flight and Isotope Separation On-Line (ISOL) production methods. The limits of the In-Flight method will be applied via the next generation facilities FAIR in Germany, RIKEN in Japan, and RIBF in the United States. The ISOL method will be explored at facilities including ISAC-TRIUMF in Canada, SPIRAL-2 in France, SPES in Italy, ISOLDE at CERN, and eventually at the very ambitious multi-MW EURISOL facility [1]. ISOL and in-flight facilities are complementary entities. While in-flight facilities excel in the production of very short lived radioisotopes independently of their chemical nature, ISOL facilities provide high Radioisotope Ion Beam (RIB) intensities and excellent beam quality for 70 elements. Both production schemes are opening vast and rich fields of nuclear physics research.

Monte Carlo Simulation of the Neutron Time-of-Flight Facility at CERN

The neutron Time of Flight (n_TOF) facility at CERN is a source of neutrons produced by spallation of 20GeV/c protons onto a solid lead target. The out- standing characteristics of this facility (very high intensity, 200 m flight path, wide spectral function) make it an extremely useful tool that provides the neces- sary data for the design and understanding of Accelerator Driven Systems [1-3]. The proton beam is delivered by the CERN-PS [4] which is capable of providing one to four bunches with an intensity of 71012 protons per bunch, within a 14.4 s supercycle, at a momentum of 20 GeV/c.