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JANNuS-Saclay triple beam facility

Latest addition : 9 July.

JANNuS-Saclay offers the rare possibility to simultaneously deliver three concurrent ion beams on a single target allowing for a wide range of irradiation and implantation conditions for well-controlled modelling-oriented experiments.

Introduction

Ion beams are employed to understand neutron-induced effects in nuclear materials for decades as they can produce nuclear recoil damage and implant a large variety of elements mimicking helium and hydrogen from nuclear reactions, transmutation products, fission products and gasses [G.S. Was, and R.S. Averback, Radiation Damage Using Ion Beams, Comprehensive Nuclear Materials 1 (2012) 195]. Among the most stringent reasons for using electrostatic ion accelerators are the scarcity of neutrons sources and the ease of use: a high damage level either as implanted ions and/or as dpa is obtained over a very short time –typically a few hours– and the irradiated sample has no residual radioactivity. Ion beams allow also to perform well controlled experiments in terms of energy, dose, flux, temperature… with little variation during the irradiation. This is of great value in an analytical approach.

At CEA Paris-Saclay, a triple beam facility has been installed for simultaneous ballistic damage, gas implantation and/or electronic excitation. Samples can be irradiated in the wide temperature range from liquid nitrogen to 850K. Evolution in the ion-irradiated material microstructure and changes in the service properties (mechanical, thermal…) are then characterized by on line Raman spectrometry or post mortem. Simulation can greatly help in validating the transposition of material laws derived from ion irradiations –formation and evolution of defect loops and of cavities, segregation, amorphization– to in-reactor conditions.

Together with JANNuS-Orsay at CSNSM, it forms since 2005 the multi-ion beam irradiation platform JANNuS for Joint Accelerators for Nanosciences and Nuclear Simulation.

Ion sources and accelerators

The JANNuS-Saclay facility comprises three electrostatic accelerators (respectively named Épiméthée, Japet and Pandore) connected to a triple beam chamber for single-, dual- and triple beam irradiations. Two other chambers are linked to Épiméthée and Pandore for single beam irradiation and/or Ion Beam Analysis. The layout is divided into six linked rooms, separated by suitable concrete walls for radioprotection safety.


Artistic view of the JANNuS-Saclay facility

Irradiation chambers and on-line controls/measurements

On line Raman Spectroscopy

Raman spectroscopy is an efficient technique for studying the evolution of the microstructure of materials under irradiation. It allows to determine the phases present before and formed after irradiation, to outline the stress induced by irradiation, to evidence phase transition under irradiation and to monitor the damage build-up.

For that purpose, a confocal Raman spectrometer has been installed at JANNuS-Saclay in 2013, which allows characterizing a variety of materials of nuclear interest. The Raman spectrometer is a Renishaw Invia Reflex device equipped with a Leica DM2500 microscope with 5 objectives (x5, x20, x50, x50L and x100). A 100 mW, frequency-doubled Nd:YAG (532 nm) laser is used as the excitation source. Complementary He:Ne (633 nm) laser is available for ex situ characterization. In March 2014, the spectrometer has been coupled to the triple beam chamber. The main objective of the on line Raman spectrometry is to monitor in real time the evolution of the damage induced by single-, dual- or triple beam irradiations. For in situ measurements, a dedicated device has been connected to the Raman spectrometer and to the triple beam chamber.


Photo and schematic of the on line Raman system implemented in the triple beam chamber

Off line characterization by IBA

An experimental vacuum chamber is connected to Pandore for conventional ion beam analysis methods as Rutherford backscattering spectrometry (RBS), elastic recoil detection analysis (ERDA) and direct observation of nuclear reaction (NRA) can be applied using protons, deuterons, helium ions as incident beams. Ion beam analyses induced by medium and high energy heavy ions, mainly RBS and ERDA, were also implemented in the single beam chamber connected to Epiméthée.

References

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